PROSEA, Introduction to Spices

Definition of spices

Definitions of spices abound in the literature. According to the International Organization for Standardization (ISO), the term "spices and condiments” refers to "vegetable products or mixture thereof, without any extraneous matter, that are used for flavouring, seasoning and imparting aroma to foods” (ISO 676). The term is applicable to the "product either in the whole form or in the ground form”. The ISO lists a total of 109 spices. The United States Food and Drug Administration (FDA), in the Code of Federal Regulations on food labelling, defines spices as "any aromatic vegetable substance in the whole, broken or ground form (except for those substances which have been traditionally regarded as foods, such as onions, garlic, celery); whose significant function in food is seasoning rather than nutrition; that is true to name; and from which no portion of any volatile oil or other flavouring principle has been removed” (Farrel, 1985). On the other hand, the American Spice Trade Association (ASTA) defines spices broadly as "the products of dried plants, essentially used for seasoning food”. This specification appears to emphasize the fact that for the most part spice products are traded internationally in the dried form. However, spices can also be used fresh, particularly in areas of production. The International Trade Centre UNCTAD/GATT (1982) market report on spices defined this commodity "as various strongly flavoured or aromatic substances of vegetable origin obtained from tropical or other plants, commonly used as condiments or employed for other purposes on account of their fragrance and preservative qualities”. This definition includes the utilization of spices other than for the flavouring of food.

It is common in the literature to encounter the term "herbs and spices”, as if inseparable twins, but suggesting a clear distinction between the two. In the food industry, the herbs are considered as "soft-stemmed plants, the whole herbaceous tops of which are gathered and may be used either fresh or dried in the seasoning of food”. Most temperate flavouring plants fall in this category. On the other hand, the term "spices” covers "all other dried aromatic vegetable products used in food seasoning, usually of tropical or subtropical origin”. In contrast to the herbs, spices refer generally to only parts of the plant such as barks, rhizomes, flower buds, fruits, seeds and other parts of fruits (aril).

The distinction between spices and herbs presents some difficulty when applied to some members of each category. Bay-laurel, although of Mediterranean origin, is botanically a tree but is often classified as a culinary herb. So is rosemary which eventually develops a woody stem. Ginger and turmeric are herbaceous perennials but on account of their rhizomes fall under the term spices. Anise, caraway, coriander, cumin, dill and fennel are known in the international trade as sources of spice seeds, not herb seeds. Thus, the distinction is rather imprecise.

In this volume the term "spice” is used in a wide sense, covering all aromatic plants and their parts, fresh or dried, whole or ground, used to impart flavour, fragrance and sometimes colour to foods and drinks.

Choice of species

The spices form a large and diverse commodity group. In addition to the classifications based on taxonomic families, properties and plant parts used, many subgroups have been proposed, such as tropical spices, spice seeds, herbs, aromatic vegetables, tree spices, leafy spices, pungent spices, phenolic spices, aromatic barks, and coloured spices, but the combination of chemistry, morphology and agronomy has so far not led to a comprehensive, satisfactory classification (Prakash, 1990).

In this volume, 61 important spices are described in 50 papers (Chapter 2).

Summary data are presented on 65 minor species (Chapter 3). About 150 plant resources with another primary use but also used as a spice, are listed in Chapter 4, with a reference to the Prosea volume where they are or will be treated in more detail.

The selection of species for this volume primarily reflects the commodity grouping adopted for the Prosea handbook (Jansen et al., 1991), which somewhat arbitrarily subdivides the aromatic plants into "spices” (Prosea 13) and "essential-oil plants” (Prosea 19). The "spices” are those species in which the direct use of the whole or ground, fresh or dried plant parts preponderates over the use of the essential oils. The "essential-oil plants” are those species in which the extraction and use of essential oils is more important than the direct use of the plants. "Spices” are predominantly used in the flavour industry, whereas "essential-oil plants” are applied in the fragrance industry as well.

The selection of species is further influenced by diffuse boundaries with some other commodity groups, especially "vegetables”, "edible fruits and nuts” and "medicinal and poisonous plants”. Mauritius papeda (Citrus hystrix DC.) and tamarind (Tamarindus indica L.) are dealt with in Prosea 2: "Edible fruits and nuts”. Saffron (Crocus sativus L.) is described in Prosea 3: "Dye and tannin-producing plants”. Garlic (Allium sativum L.), onion (A. cepa L.), chives (A. schoenoprasum L.), celery (Apium graveolens L.), and capsicum pepper (Capsicum L.) are detailed in Prosea 8: "Vegetables”. Calamus (Acorus calamus L.), poppy (Papaver somniferum L.) and mint (Mentha L.) are described in Prosea 12: "Medicinal and poisonous plants”. Sesame (Sesamum L.) appears in Prosea 14: "Vegetable oils and fats”.

In view of the above-mentioned choices, it may seem inconsistent that Citrus amblycarpa (Hassk.) Ochse (similar in use to C. hystrix, described in Prosea 2) and Capsicum pubescens Ruiz & Pavón (Capsicum annuum L. and C. frutescens L., capsicum pepper, are described in Prosea 8) are included in this volume under Minor spices, but this was done to make good earlier omissions. Citrus amblycarpa was overlooked during the compilation of Prosea 2. As for Capsicum pubescens, it was only recently realized (Grubben & Anggoro H.P., 1996) that a sizeable production of this South American capsicum pepper exists around the West Javanese city of Lembang.

It was decided to pay some attention in this volume to natural sweeteners and flavour enhancers, as they do not fit well into the Prosea commodity grouping. They are briefly described in general terms in section 1.10.

Origin and geographic distribution

It is estimated that in the course of time and on a worldwide scale, 400-500 plant species have been used as a spice. For South-East Asia the number is close to 275 species. Among the 126 "primary use” spices described in this volume, about half of the species is mainly cultivated, and about half is still mainly collected from the wild.

Most of the important tropical spices (cardamom, cinnamon, clove, ginger, nutmeg, pepper and turmeric) have their origin in the Orient. The only major spices native to the American tropics are pimento and vanilla (capsicum pepper being considered a vegetable).

Up to the 16th Century, the spice trade was centred on India, Sri Lanka, China and Indonesia. Subsequent introduction into other parts of the world has led to diversification of production areas, so that nowadays Zanzibar and Madagascar are important producers of clove, Guatemala produces first-quality cardamom, Grenada the finest nutmeg and mace, and Brazil good-quality pepper.

The spices originating from the American tropics have also been introduced into other regions, and the best quality vanilla is grown in the Indian Ocean Islands of Madagascar and Réunion, in the Pacific Island of Tonga, and in Indonesia.

The Mediterranean area (southern Europe, northern Africa, Middle East) is the home of most of the temperate species (coriander, cumin, dill, fennel, fenugreek, laurel, mustard, oregano, rosemary, sage, sweet basil and thyme). The cold temperate regions have produced only a few such as caraway, horseradish and tarragon.

Most culinary herbs have become widely distributed, although in these crops too certain provenances (local selections and/or specific ecological conditions) are known for their top-of-the-line or special-purpose qualities (Indian dill, Dalmatian sage). Some culinary herbs introduced into South-East Asia have succeeded in becoming part of local cuisine, others occupy small niches at higher elevations, satisfying the demand of a foreign clientele (international hotels) or catering to a local clientele acquiring a taste for foreign cuisine (international fast-food chains).

The increased interest in exotic cuisine through contacts with migrant communities and international travel helps the introduction of new crops. Vietnamese refugees in the United States not only brought along their traditional spices such as Eryngium foetidum L. and Perilla frutescens (L.) Britton, but also generated a local market and initiated local production.

Historical aspects

No commodity has played a more pivotal role in the development of modern civilization than the spices (Parry, 1969; Rosengarten, 1973). In a period when Europe had no knowledge of sugar, tea, coffee, chocolate, potatoes or tobacco, Oriental spices already supplied flavour and pungency to bland foods and drinks, and fragrancy to mask a multitude of unpleasant odours. So indispensable were spices, both politically and economically, as well as culturally, that monarchs sent expeditions in search of them, merchants risked life and fortune to trade in them, wars were fought over them, populations were enslaved, the globe was explored, and revolutionary changes were brought about by the ruthless competition.

The earliest cultivation and trading of aromatic herbs probably took place in Mesopotamia, the cradle of civilization and agriculture. Initially, selected herbs would be planted near habitations for family use, but with the development of an agrarian society, some farmers specialize in the production of these aromatic plants. As contacts between communities, countries and people grew, spices were among the first products exchanged and traded. During the reign of Charlemagne in the 9th Century, the cultivation and use of Mediterranean aromatic herbs greatly expanded in Europe.

Transport over long distances was greatly facilitated by the discovery that aromatic plants retained most of their flavour after drying. To ancient people, spices were so necessary in food, medicine and religious rituals, that they were in short supply and merchants went far in search of aromatics. Camel trains travelled across Asia, but also sea communication between Asiatic countries intensified. Arabia prospered as the great monopolistic carrier of goods between East and West.

Since the beginning of our era 2000 years ago, trade between eastern Mediterranean ports increased in importance. In the early centuries merchants thrived in Alexandria, and later during the Middle Ages in Venice, which controlled the flow of spices from the east through the Mediterranean into Europe.

Gradually the spice merchants in western European countries organized themselves in guilds, which sought direct access to the eastern lands of spices, to free themselves from the monopoly of Mediterranean traders. Portugal, Spain, the Netherlands and England all established sea routes to India and the Far East, and the English and the Dutch in particular founded powerful trading companies. The Dutch East India Company was long successful in securing its monopoly in the Spice Islands by aggressive policies. This ultimately led to the smuggling of spice plants out of those islands into areas beyond the control of the Dutch, marking the beginning of the era of free commerce. The spice trade became highly competitive, comparable to the food industry in general.

The Second World War had a devastating effect upon spice production and trade. Strict rationing of spices became necessary, and this had two important effects. First of all it led to many eastern spices being introduced and tried out in the western hemisphere after the war. Secondly, it gave a strong impetus to the manufacture of artificial and imitation spices.

Advances in organic chemistry have resulted in 5000 or so aroma chemicals. The synthetics strongly outnumber the naturals. The synthetic compounds have allowed cheap fragrance materials to be produced, which greatly extended their use into everyday products such as soaps, detergents and air fresheners. However, the total eclipse of natural materials predicted for the end of the 20th Century has not happened because of changes in life-style: increased concern for the environment and health has renewed interest in natural aroma products and other natural food additives.

Main product forms and uses

Main product forms

The principal way in which spices are used is directly, in the form of a fresh or dried, whole or ground, vegetable product. The aromatic principles of spices are mainly situated in their essential oils, which can be isolated from the spice by hydrodistillation, steam distillation, hydrodiffusion, expression or solvent extraction. Essential-oil contents of spices vary from as low as 0.1% to as high as 18%. Spice oils have a number of advantages over ground spices in processed foods: no debris and bacterial or fungal contamination, concentrated flavour, better control over flavour strength, usually colourless, less bulky, stable in storage. However, distilled oils can be regarded as artefacts. In many cases, the spice oil does not fully reproduce the natural taste and odour of the spice. For instance, the characteristic bite of pepper and ginger is absent, the characteristic yellow colour of turmeric is lost.

Another product of modern spice processing are oleoresins. Oleoresins consist of non-volatile compounds and volatile essential oils, and they contain the flavour constituents in concentrated form. Oleoresins are obtained by extraction with solvents and subsequent removal of the solvent. Spices contain on average 10% oleoresin (variation 3-30%). Oleoresins can be used as direct substitute for the dried spices. Ginger, pepper and turmeric oleoresins are of greater value than their essential oils because of the taste and colour compounds. However, some argue that even oleoresins often fail to reproduce the natural flavour (Greenhalgh, 1982).

Uses

Spices, spice oils and spice oleoresins are important products of the flavour and fragrance industry: they are indispensable in the food and beverage manufacturing industry, the perfumery and cosmetic industry and the pharmaceutical industry.

Spices are first and foremost indispensable in the culinary art. They give taste, smell and sometimes colour to our dishes through their addition to the foods and beverages before, during or after their preparation. It is the spices that make food dishes into original creations, into artistic experiences related to the history, the culture and the geography of a country (e.g. curry powder in India, houng-liu (five-spice powder) in Chinese/Vietnamese cuisine, pizza herbs in Italy, the "fines herbes” in French cuisine).

Curry powder has many recipes. It usually contains capsicum pepper, coriander, cumin, pepper and turmeric, but other components may be black cumin, cardamom, caraway, cinnamon, fenugreek, ginger, mace, mustard, nutmeg and poppy. Houng-liu (five-spice powder) contains Chinese cassia, clove, fennel, pepper and star anise; it combines well with pork, chicken and duck. Countries or regions are not only associated with particular spiced dishes or drinks but also by other aromatic products (e.g. kretek or clove-cigarettes in Indonesia).

The food manufacturing industry depends on spices to flavour the great variety of products. Spices proper are still most important, but the use of spice oils and spice oleoresins is increasing.

Oleoresins are finding wide application in the canning and frozen-food industries, and in the baking and processed meat industries. The beverage industry is making wide use of spices proper and their essential oils for a great variety of liquors and cordials.

The perfumery and cosmetic industries use the oils of many spices in the blending with chemical substances for perfumes and cosmetics, including personal care products such as soaps and toothpastes. Spice oils are also popular in fringe medicine applications (e.g. aromatherapy).

In traditional medicine, aromatic plants are important in driving out diseases. However, modern developments have largely destroyed the ancient beliefs in the medicinal value of spices. Modern pharmacopoeias are cautious in attributing medicinal effects to spices. Spices impart a pleasant taste to disagreeable medicines and may aid the effect of the chief ingredient. The principal use for spices in medicine lie in their adjuvant and alleviative qualities, e.g. analgesic, anthelminthic,

aphrodisiac, carminative, expectorant, purgative, stomachic, tonic.

Some definitely have antibiotic (bactericidal, mycocidal) properties. This has increased interest in the commercial exploitation of aromatic plants for food preservation and crop protection.

Economic aspects

The production and marketing of spices and their derivatives are characterized by the great complexity of the global network; the species involved are numerous, while the economic significance of most individual species is limited.

The fact that more than 70% of natural and synthetic flavours and fragrances are consumed by 15% of the world population, suggests there is considerable potential for growth (Verlet, 1993).

Spices

Spices in fresh form are traded in large quantities within the countries of production. In organization and structure such trade is similar to the fresh-vegetable trade.

Most spices enter international trade in the crude dried form. Further processing beyond drying is increasingly undertaken in the producing countries, but final refinement is almost invariably done in the country of consumption for quality reasons (retention of aroma, avoiding adulteration).

The annual world import of spices increased in both quantity and value from 1970 to 1995. It rose from an average of 220 000 t during the period 1970-1975 to 500 000 t during the years 1993-1995, and in value from US$ 300 million to US$ 1.75 billion. The future growth rate in terms of volume is estimated to be between 3% and 4% annually.

Pepper is the most important spice in world trade, cornering over 30% of the total quantity imported in 1991-1993 (Table 1). This is followed by capsicum pepper with a 22% share while the spice seeds rank third (mustard is not included in these statistics). Perennial tropical spices dominate the world import scene.

The three largest importing countries of spices during the years 1992-1996 belong to the group of highly industrialized ones (Table 2), with the United States topping the list, and Japan ranking second. Almost half of the list of leading importers are European countries. The developing countries are meagerly represented. In South-East Asia Singapore and Malaysia are important importers.

On the other hand, the developing countries form the bulk of spice exporters, with Indonesia as the leading one (Table 2). Singapore, which ranks second, does not produce spices but serves as entrepôt for this commodity. Most of the European countries and the United States are important re-exporters of spices too. A majority of the countries listed as leading exporters are in Asia. South-East Asia contributes considerably to world exports.

World production and import statistics specific for the culinary herbs of traditional Western usage are often not available or difficult to obtain. The most recent available data for this commodity can be derived from the market study published by the International Trade Centre UNCTAD/GATT in 1991 on the most traded culinary herbs in Western Europe. Table 3 shows an overall annual market size of 17*100 t in 1989-1990 for the most popular culinary herbs in the region. Parsley has the largest market size, about 20% of the total volume. Herbs contributing 10% or more include mint, oregano, sage and thyme. Except for the Netherlands, where local production figures were not available, the supply into the market was predominantly through import (65%-75%) and the rest from domestic production. The origin of imported dried herbs is not very diversified, being mainly countries in the Mediterranean region (e.g. Morocco, Greece, Egypt, Turkey) and eastern Europe (in particular Hungary and Poland).

Essential oils

World production of essential oils (excluding ==Citrus== oils) in the mid-eighties was estimated at about 45 000 t with a value of US$ 700 million. The most recent comprehensive review of essential-oil production and marketing (Lawrence, 1993) estimated the production and value of the 20 most important essential oils at 56 000 t with a value of US$ 350 million. Only two "spice” oils figure among these 20 most important essential oils, i.e. clove leaf oil (1915 t, US$ 7.7 million) and coriander oil (710 t, US$ 49.7 million), the latter being by far the most expensive one.

About 65% of the world production of essential oils is derived from perennial woody plants (some cultivated, some wild); this adversely affects the elasticity of the supply. The remaining 35% is derived from herbs, mostly cultivated.

In terms of value, developing countries account for about 55% of the annual world production, with the main producers (together accounting for 35-40%) being China, Brazil, Indonesia and India. All four countries have large populations and thus large domestic markets. This has led to reliable production and marketing infrastructure, policies favouring local production, scientific and technical training, and a strong economic position for some products (large share of the world market).

Oleoresins

Spice oleoresin consumption in the world was estimated to be about 1000 t in 1977 (Lewis et al., 1982), and is now several thousand t. About 50% of the world's oleoresin production is pepper oleoresin (Richard, 1991). Major producers are India, Indonesia and Malaysia. Another important oleoresin (several hundred t) is derived from capsicum pepper.

Characteristics of the spice sector per country

Based on market visits and interviews with sector specialists, an attempt has been made to indicate the importance of all major "primary use” spices described in this volume (Table 4). The situation of the sector in some South-East Asian countries is sketched below.

Indonesia

Spices are very important in the economy of Indonesia, although less now than before the Second World War. The main spices commercially cultivated are candlenut tree, galanga, round cardamom, Indonesian cassia, turmeric, nutmeg, pepper, clove, vanilla and ginger, large amounts of which are used in the traditional medicine ("jamu”) industries. They also account for most of the spice exports, although in some cases, such as clove, local production does not always meet domestic demand, leading to imports. National statistics on the spices are not readily available and are often conflicting and confusing. The data available are presented in the individual species entries in this volume.

A number of Indonesia's spices originate from India and China and have been brought in over the past 1000 years by migrating people. In the last 400 years about 20 species have been introduced from tropical America, the Mediterranean area and other parts of Europe and Africa. The Mediterranean species introduced by the Europeans when they colonized South-East Asia include anise, dill, fennel, parsley, rosemary and thyme; these are grown on a small scale only. Some herbs such as parsley and rosemary were initially introduced without much success, but renewed interest is being shown in them because of the increasing popularity of European dishes. Indonesia imports small amounts of processed spices, mainly from European countries.

In recent decades Indonesia has begun to develop the technology for widening the prospects for the use of spices in the country, particularly by more local industries. The establishment of the Research Institute for Spice and Medicinal Crops (RISMC) testifies to the importance accorded to the commodity.

The Philippines

From 1991-1996 the Philippines imported an annual average of 1400 t of spices, reaching almost 2000 t in 1996. The value of the imports increased from US$ 1 million in 1991 to US$ 3.4 million in 1996, with an annual average of US$ 2 million. On the other hand, over the same six-year period, export of spices amounted to an annual average of only 150 t valued at US$ 0.2 million. Clearly, the Philippines is a net importer of spices.

Pepper constitutes 50% of the total quantity and total value of spices imported in 1996 (Table 5). Individual spices imported in amounts of 30 t or more and valued at over US$ 50 000 include pimento, anise, laurel, vanilla, saffron, nutmeg and ginger. The bulk of the imports of coriander, fennel, pepper, nutmeg and mace comes from Singapore; pimento from Spain; caraway, ginger, thyme, turmeric and vanilla from the United States; clove and saffron from Hong Kong and laurel from Turkey.

In 1996, the small export of spices from the Philippines included ginger, pepper, saffron and vanilla (Table 5). Except for pepper, the values given represent re-exports. Pepper, saffron and vanilla are mainly exported or re-exported to the United States, ginger to the United Kingdom.

Compared with neighbouring countries in South-East Asia, Filipino cuisine is basically bland. Only the Bicol Region, in the far south of the island of Luzon, is known for its spicy hot dishes. Two of the most popular spices used in almost all Filipino households are pepper and ginger; recently, lemongrass has become a popular stuffing for roasted chicken and pork with a proliferation, particularly in Metro Manila, of small food outlets supplying this type of delicacy. Fresh herbs such as coriander, dill, mint, sweet basil and tarragon are produced in small quantities in the province of Cavite, but their market is limited to first-class hotels and speciality-food establishments.

Spice production in the Philippines is dominated by pepper, the current area of production being about 2000 ha located in the provinces of Batangas, Negros Occidental and Basilan. Production of vanilla has been recently initiated in Negros Oriental. Ginger used to be a major spice crop, but areas of production have dwindled because of problems with diseases and product quality. There is renewed interest in the production of ginger but sourcing large quantities of appropriate planting material is a major stumbling block. The feasibility of producing locally some of the imported spices, e.g. turmeric and the spice seeds, at least to satisfy the import demand, should be looked into.

Thailand

Table 6 presents a summary of the Thai spice imports and exports in 1997.

The detail in which the properties of spices have been studied varies, and there are therefore varying gaps in knowledge. There is still much to be learned about the relationship between chemical composition and organoleptic properties, changes in composition during the development of the spicy parts of the plant and during storage, and the differences in composition within a species produced by environment and geographical location (Purseglove et al., 1981).

Because most spices are consumed in minute quantities, their nutritional contribution is usually minor, but their physiological effects may be pronounced. Monographs on the physiological properties of many fragrance raw materials have been published by the Research Institute for Fragrance Materials (RIFM), United States, many of them in the journal Food and Chemical Toxicology. They give numerous biological data, such as metabolism in mammals, toxicity, carcinogenicity, sensitization and pharmacology. The existence of such monographs for the spices dealt with in this volume is indicated in the individual papers.

Description of flavours and fragrances

The ability of spices to impart a distinct flavour to otherwise bland and less exciting meals distinguishes them from food crops. Taste and smell are the two discriminatory chemical or organoleptic senses through which humans obtain information about the chemical composition of the environment. Whereas the sense "taste” recognizes only 5 conditions (bitter, salty, sour, sweet, umami), the sense of smell recognizes an immense number of odours and odour compounds. The sense of smell is crucial in the study of flavours and fragrances. It is unique among the senses because it is subjective and lacks objective standards. Smells are often described in terms of sensations related to other odours or to experiences of the other senses. The memory of these odours and associated experiences is personal and an odour that is repulsive to some may be attractive to others.

Systems of characterization of odours can be developed by two different methods. A qualitative description of an odour or odour pattern can be obtained either by a "reference procedure”, i.e. by direct comparison with the odour of a series of known chemicals, or by a "semantic procedure”, i.e. in a verbal descriptive way. A standardized vocabulary to describe odours is used, in which each term is precisely defined. Several systems have been developed (Harper et al., 1968; Müller & Lamparsky, 1994; Ohloff, 1990).

The terms "flavour” or "sensory properties” pertain to "an overall integrated perception of all contributing senses (smell, taste, sight, feeling and sound) at the time of food consumption” (Lindsay, 1985). Perception of flavour is a combined effort of the specialized cells of the olfactory epithelium of the nasal cavity, the taste buds on the tongue and back of the oral cavity, and the non-specific or trigeminal neural receptors detecting sensations such as cooling, burning, pungent or biting effects, in contrast to a true or basic taste, i.e. bitter, salty, sour, sweet and umami (Kulka, 1967).

The objective evaluation of flavour in spices has long been a matter of keen interest among food chemists. Correlation of the more or less subjective sensory data with objective flavour chemical profile is more the current practice. Subjective sensory analysis by human beings is being replaced by less subjective instrumental methods (the so-called "iron nose”) (Maarse & van der Heij, 1994; Taylor & Mottram, 1996). Recent developments in more objective sensory analysis are the gas chromatography-olfactometry techniques, which involve sniffing at gas chromatography columns.

Biological and ecological aspects

Many organic products are formed during plant growth. Some (primary metabolites) are necessary for plant development, energy and food reserves, others (secondary metabolites) are not fully understood by-products of the complex physiological processes (Deans & Waterman, 1993). Among the latter are the essential oils.

Essential oils are formed, stored and released by a variety of epidermal or mesophyl structures: oil cells, secretory glands, secretory ducts or canals, glandular hairs or trichomes.

Oil production is usually separate or a side-path from basic metabolic processes, but it must be presumed that it results in the plant having some selective advantage over a non-producing plant.

Essential oils somehow seem to be involved in "fitness for life”:

• attracting insects for pollination (if odour is pleasant);

• attracting animals for seed dispersal (if odour is pleasant);

• protecting against herbivores (if odour is offensive or irritating);

• protecting against pathogens by antibiotic activity;

• reducing competition by allelopathic action;

• influencing nutrient recycling by regulating decomposition of litter;

• acting as solvent for other bioactive lipophilic compounds.

There is certainly increased interest in the commercial exploitation of aromatic plants in food preservation (antimicrobial and antioxidant properties) and crop protection (broad-spectrum activity, no accumulation in the environment, low toxicity to mammals). Antioxidants are added to processed foods to restrict oxidation, particularly of unsaturated lipids, which causes deterioration. The consumer push to replace synthetic antioxidants by naturals has led the search for essential oils that contain phenolic compounds as major constituents (e.g. rosemary, sage, thyme), because the flavour of phenolic oils is acceptable and their antimicrobial activity strong.

In view of heavy losses of food to insect pests, especially in the tropics, effective insecticides or anti-feedants based on cheap essential oils or plant parts containing essential oil would contribute significantly to the alleviation of food shortages.

To date, there is little in vivo evidence of major pharmaceutical activity of essential oils or their components. Medical use is therefore mainly restricted to health care products (non-specific bactericides, decongestants, carminatives).

Physical aspects

Spices and derivatives offered for trade must meet certain quality standards. Spices proper are usually described physically (physico-chemically) in terms of purity (extraneous matter content), moisture content, total ash, acid-insoluble ash, and volatile-oil content. An overview of standard values established for the spices covered in this volume is given in the Table on standard physical properties of some dried spices (see p. 311).

The physical parameters most commonly used to characterize essential oils are relative density, refractive index, optical rotation, and miscibility with ethanol and water.

Relative density is the ratio of a substance's mass to its volume. Refractive index refers to the property of transparent materials to deflect light by a specific degree when it enters such materials at an oblique angle from another material with a different density. Optical rotation refers to the fact that molecules with an asymmetrical structure rotate the plane of polarization of polarized light. Pure, optically active compounds deflect the plane of polarized light by a characteristic angle. Optical isomers, which are identical molecules but each other's mirror images, rotate the plane of polarization in opposite directions. Optical rotation provides a measure of the relative concentration of isomers of optically active compounds. In synthetic asymmetrical compounds, optical isomers are almost always present in equal amounts, resulting in an optical rotation of 0°. The optical rotation of essential oils and of individual compounds of the oils is often highly characteristic of the oil and even of its origin. Miscibility of essential oils refers to the solubility of an essential oil in a solvent. It is usually measured with aqueous ethanol as the solvent. The amount of essential oil soluble in a given amount of alcohol of a given concentration is recorded. An oil may be fully soluble in pure ethanol, but only slightly soluble in a mixture of ethanol and water. An overview of standard values established for the spice oils covered in this volume is given in the Table on standard physical properties of some spice oils (see p. 317).

Chemical aspects

In most spices it is the essential oils that are responsible for the flavouring properties. Essential oils are complex mixtures of hundreds of chemical compounds, most of which are still unknown. The organoleptic quality of the oil can be due to one or a few so-called character-impact components, e.g. anethole in anise, eugenol in clove, cinnamaldehyde (cinnamic aldehyde) in cinnamon, cuminaldehyde (cumic aldehyde) in cumin and d-carvone in caraway. For an indication of the complexity of the oils, see Composition of spice-oil samples (p. 281).

Although most spices are odoriferous, it is not only the lower molecular volatile compounds that are important for the organoleptic quality, but also the less volatile or non-volatile higher molecular compounds. The latter constituents comprise principles that give a bitter, hot or pungent taste to the spices, or they consist of pigments psychologically influencing the perception of flavour through appearance.

Most of the chemical compounds can be grouped into a few major classes, but some components are difficult to classify. In the overview of important and characteristic constituents given below the compounds are classified into 4 major groups: aliphatic compounds, terpenoids (or isoprenoids), benzenoids, and miscellaneous compounds (Bauer et al., 1997; Lewis et al., 1982; Oyen & Nguyen Xuan Dung, 1999; Waterman, 1993; Zutshi, 1982).

Aliphatic compounds

Aliphatic compounds are acyclic organic compounds with a straight or branched carbon chain. These compounds can be saturated or unsaturated, the latter meaning that they possess one or more double or triple bonds between two carbon atoms. Aliphatic compounds can, for instance, be derived from fats or amino acids.

The leaves of plants can produce a series of volatile aliphatic compounds, as for instance (Z)-3-hexenol (leaf alcohol) and (E)-2-hexenal (leaf aldehyde), by enzymatic lipoxidation of linoleic acid. The alcohol has the characteristic odour of freshly cut grass, whereas the aldehyde has a sharp herbal-green odour somewhat reminiscent of bitter almond. Aliphatic aldehydes such as octanal and decanal are organoleptically important constituents of sweet-orange oil. The oil isolated from coriander leaves contains a series of higher saturated and unsaturated aliphatic aldehydes, which give the oil its characteristic odour. Many essential oils contain 3-methylbutyl derivatives, such as the alcohol, aldehyde and acetate derived from the amino acid leucine by reaction with a sugar. Aliphatic esters are important flavour and fragrance compounds occurring widely in nature.

Terpenoids (terpenes and terpene derivatives)

Isoprene is one of the basic compounds in animal and plant biochemistry from which terpenoids, carotenoids, steroids and also rubber are formed. Isoprene is formed from acetyl-CoA via mevalonic acid and dimethylallyl pyrophosphate. The terpenoids in spices are built up of 2 isoprene units (monoterpenoids), 3 isoprene units (sesquiterpenoids), or occasionally 4 (diterpenoids).

The terpene hydrocarbons contribute little to the organoleptic quality of essential oils. Monoterpene hydrocarbons conform to the molecular formula C10H16 and may be acyclic (e.g. myrcene and ocimene), monocyclic (e.g. limonene and p-menthatriene), bicyclic (e.g. α-pinene and β-pinene), and even tricyclic (e.g. cyclofenchene and tricyclene). The quantitatively most important monoterpene hydrocarbons are limonene and the pinenes. The dominant monoterpene hydrocarbon in all citrus oils is d- or (+)-(R)-limonene; for instance, it is present in amounts of over 95% in cold-pressed sweet-orange oil. Limonene most probably forms during growth and ripening of the fruit via mevalonate, geranyl- and (-)-(R)-linalyl pyrophosphate. Limonene is also an important constituent of caraway oil.

1,3,8-p-Menthatriene makes up to 65% of the oil from parsley leaves. The p-menthane skeleton in monoterpene hydrocarbons can be converted to p-cymene by oxidation. p-Cymene is an important benzenoid in essential oils and can be converted into thymol and carvacrol. Monoterpene hydrocarbons in general have harsh, turpentine-like odours.

The quantitatively most important sesquiterpene hydrocarbon (C15H24) occurring in spice oils is caryophyllene; for instance, it is present in clove leaf oil in amounts of up to 20%. Caryophyllene can easily be oxidized to caryophyllene oxide.

Oxygen-containing monoterpene derivatives are important for the organoleptic quality of spice oils. The aliphatic monoterpene alcohol d- or (S)-(+)-linalool (coriandrol) occurs in coriander fruit oil and gives this oil its fresh floral odour. Its enantiomer (optical antipod) l- or (R)-(-)-linalool (licareol) is responsible for the characteristic odour of lavender oil. The monocyclic terpene alcohols α-terpineol and terpinen-4-ol are essential for the odour properties of several herb oils. The monocyclic terpene ketone d- or (S)-(+)-carvone is responsible for the organoleptic quality of caraway oil, which finds application in liqueurs because of its fresh taste. l- or (R)-(-)-Carvone has a different odour and is a character-impact compound of spearmint oil, which is used in toothpaste for its minty note. The bicyclic ketone fenchone is responsible for the camphoraceous odour aspect of bitter-fennel oil. Although present in rather low concentration in rosemary oil, the bicyclic ketone verbenone gives this oil a characteristic odour. α-Thujone and β-thujone are important for the organoleptic quality of oil of ==Salvia officinalis== L. Dill ether (3,6-dimethyl-2,3,3a,4,5,7a-hexahydrobenzofuran) is responsible for the characteristic odour of dill oil.

Benzenoids (benzene derivatives)

Many compounds with tasty and spicy odours are found amongst the benzenoids, which is why the chemistry of the benzene derivatives is called aromatic chemistry. All compounds contain the characteristic benzene nucleus to which one or more functional groups are connected, such as allyl, propenyl, hydroxy, methoxy, methylenedioxy and aldehyde. The benzenoid spice constituents can be divided into two groups, i.e. the para-menthanoids such as cuminaldehyde (cumic aldehyde), carvacrol and thymol, and the phenylpropanoids such as cinnamaldehyde (cinnamic aldehyde), methylchavicol, anethole, eugenol, myristicin and apiol.

Cuminaldehyde is the character-impact odour compound in cumin. Carvacrol and thymol are responsible for the organoleptic quality of thyme oils and oil of oregano. Cinnamic aldehyde is olfactively characteristic of cinnamon, whereas its 2-methoxy derivative gives cassia oil its characteristic aromatic odour. Methylchavicol is organoleptically important in chervil. Anethole gives the sweet anisic note to anise oil and other umbelliferous oils, e.g. dill and sweet fennel. Eugenol is indispensable for the flavouring properties of clove oils and of some other spice oils. Myristicin is a character-impact compound in oil of nutmeg. Apiol is an organoleptically important constituent of parsley.

Benzenoid aldehydes are important constituents of spice oils, e.g. benzaldehyde in bitter-almond oil, vanillin in vanilla spice, heliotropin in some exotic flowers. These aromatic aldehydes have tasty, sweet aromatic flavours.

Miscellaneous compounds

Nitrogen and sulphur compounds play an important role in the organoleptic quality of spices. Several nitrogen compounds impart characteristic sensory properties, even when they are present in concentrations of less than 0.1%, e.g. alkylmethoxypyrazines which occur in green capsicum pepper and in green leaves.

Examples of bitter, hot or pungent compounds are: gingerol, shogaol, paradol, piperine, chavicine, isopiperine, isochavicine, capsaicin, dihydrocapsaicin, nordihydrocapsaicin, homocapsaicin, homodihydrocapsaicin, piperyline, piperettine, piperanine, piperoleine A, piperoleine B, zingerone.

Several natural chemical compounds from spices providing a pungent taste sensation are nitrogen derivatives of 2-methoxyphenols. Capsicum pepper, for example, contains a group of substances called capsaicinoids, which are vanillyl-amides of saturated or unsaturated, monocarboxylic acids with straight chains of varying length (C8-C11). The group includes capsaicin and dihydrocapsaicin. In pepper the pungent principle is mainly piperine, an amide derived from piperic acid and piperidine (hexahydropyridin). The "trans” or "entgegen” (E) geometry of the unsaturated part is responsible for the strong, biting effect; isomerization of these double bonds upon exposure to light and storage leads to loss of pungency. The pungency in fresh ginger has been atributed to the phenylketones called gingerols, with 6-gingerol as the most active compound. Gingerols vary in the length of the terminal part of the aliphatic chain (Govindarajan, 1977; Lindsay, 1985). Other examples of methoxyphenol derivatives are eugenol (found in clove) and isoeugenol (found in nutmeg and various other essential oils) (Kulka, 1967). These two not only contribute to the taste sensation but also impart characteristic aroma because of their volatile nature. Sweet aromatic odoriferous substances, like vanillin, for instance, can have a bitter taste.

Sulphur compounds can be very characteristic, such as di-alkyl disulphides and alkenyl isothiocyanates, which are character-impact constituents of garlic, onion, horseradish and mustard. The character-impact compound in black mustard and horseradish is allyl isothiocyanate, in white mustard it is 4-hydroxybenzyl isothiocyanate (Parry, 1969; Pruthi, 1980).

Bitterness as a basic taste in flavour is sometimes disagreeable, but in subtle blend with sweet or sweet and sour condiments it can enhance the basic appeal of a given food. A bitter tonality is appreciated in drinks such as coffee, beer, campari or bitter lemon.

Alkaloids and glycosides are chemical families associated with bitterness and so are other compounds, e.g. coumarins (Kulka, 1967). Coumarins provide a substantial contribution to the organoleptic properties of cinnamon (Purseglove et al., 1981).

Many spices contain pigments, which are mostly carotenoids, often derived from β-carotene. Examples of pigments are: α-crocin, α-crocetin, β-crocetin, γ-crocetin, curcumin, demethoxycurcumin, bis-demethoxycurcumin (Richard, 1991). Turmeric and paprika are appreciated not only for their characteristic organoleptic quality but also for their ability to give colour to food preparations. The colour of turmeric is attributed to the major pigment curcumin, which is used to colour a variety of savoury products, particularly curry powders and mustard pickles. It exhibits an unusually intense yellow colour in acidic products. Paprika powder, on the other hand, is a red-orange colouring material extracted from sweet capsicum pepper (==Capsicum annuum== L.), with capsanthin and capsorubin (red pigments) and β-carotene (yellow-orange pigment) as the major chromaphores (Henry, 1979; Lauro, 1991). Capsicum pepper oleoresin is an economically important natural colourant in foods and drinks, especially for cooked meat products. The green pigment (chlorophyll) from fragrant pandan is traditionally extracted in the Philippines to colour sweet cakes and other food preparations. Perilla leaves, which contain high concentrations of anthocyanins, are extensively used to give an appetizing red colour to various Japanese and Korean dishes.

Taxonomy

The heterogeneity of the commodity group spices is well illustrated by the fact that the 126 species described belong to approximately 35 families: spices occur throughout the plant kingdom. Nevertheless, some families figure prominently with respect to number of spice species as well as economic importance:

• Labiatae: basil, marjoram, oregano, perilla, rosemary, sage, summer savory, thyme

• Lauraceae: cassia, cinnamon, laurel

• Myrtaceae: clove, pimento, salam

• Piperaceae: pepper, cubeb, Indian long pepper, Javanese long pepper

• Umbelliferae: anise, caraway, chervil, coriander, cumin, dill, fennel, parsley, sawtooth coriander, surage

• Zingiberaceae: cardamom, Chinese keys, etlingera, galanga, ginger, turmeric

The proper naming of plants is important, because it enables repeatability and use of scientific methods. Taxonomy provides such a naming service and is therefore an important biological science. Many taxonomical problems are still unsolved. Few major genera of economically important spice families have been revised in their entity within the last 50 years. The taxonomy of genera such as ==Cinnamomum== Schaeffer, ==Piper== L. and ==Thymus== L. is still poorly known, and the lack of linkage of data to well-defined taxa makes part of the information useless.

Classic taxonomy is primarily intended for wild taxa, and closely related wild types are often classified as subspecies or varieties (formal classification under the International Code of Botanical Nomenclature). For cultivated plants, the most recent approach is to distinguish cultivars and to group these in cultivar groups (the informal "open” classification guided by the International Code of Cultivated Plants). The taxonomy of cultivated plants is developing: as yet there is no worldwide accepted system for naming and classification, but proposals are being discussed. Where workable cultivar group classifications seem possible, as for instance in dill, parsley and tarragon, these are being promoted in this volume.

In spices, the number of chemotypes can be considerable because composition is influenced by environment as well as genetic factors and development stage. In a number of cases, however, strong and simple genetic control has been evidenced, as in sweet basil and perilla. Plant morphology does not necessarily correlate with a plant's essential-oil composition.

Morphology

Plant parts used as spice comprise anything from roots (horseradish) to rhizomes (ginger, turmeric), bark (cassia, cinnamon), leaves (chervil, coriander, laurel, oregano, parsley, rosemary, sage, sweet basil, tarragon, thyme), flower buds (clove), fruits (anise, caraway, cassia, coriander, cumin, dill, fennel, pepper, pimento, star anise, vanilla), seeds (black mustard, fenugreek, nutmeg, white mustard), and aril (mace).

In a number of spice crops more than one plant part is used as a flavouring agent. Aside from the bark, Chinese cassia yields cassia buds (dried unripe fruits). In coriander, the fruit is internationally traded, while fresh leaves are popular for flavouring a number of South-East Asian dishes. Commercial marjoram and oregano are a mixture of both dried leaves and floral parts. Apart from the rhizomes the young shoots of turmeric and galanga are used domestically as a spicy vegetable, while in perilla the leaves, spikes, seeds and sprouts are used as flavouring in Japanese, Korean and Vietnamese dishes.

Considerable anatomical modification can be observed in cells or tissues yielding the specific flavour characteristic of a given spice. Aromatic compounds are formed or stored in special organs in plants. The variability of these organs reflects the varied taxonomy of spice plants; only a few examples of the many structures found can be given here (Hardman, 1973; Parry, 1969).

Oil glands may be simple or compound hairs on the leaves, as in several Labiatae, where the gland consists of a multicellular hair with the oil concentrated in the enlarged apical cell or in the space between the cell-wall and the outer cuticle.

In the Rutaceae and Myrtaceae the essential oil is concentrated in large subepidermal glands arising from a specialized mother cell. The mother cell divides into daughter cells that separate from one another and disintegrate to leave a central cavity. The cells surrounding the cavity produce essential oil and the cavity enlarges by the breakdown of the walls of the surrounding cells. Examples are the floral buds of clove as well as the outer mesocarp of the fruit of pimento.

Another form encountered is a secretion-containing cell whose contents differentiate it from the adjacent cells. It is easily recognized by its larger size or cuticularized lining. Examples of this type include the essential-oil cells in the seed-coat of cardamom, in the bark of cassia and cinnamon, and in the mesophyll tissue of laurel leaf, but also the oleoresin cells in the mesocarp of the pepper fruit, in the mesocarp of the carpel and cortex of the peduncle of star anise, and the aril mesophyll, perisperm, embryo and radicle of nutmeg seed.

Umbelliferous spices such as coriander, dill and fennel form long secretory ducts in the fruit wall, called vittae. These vittae, which arise schizogenously and contain oleoresins, serve as a discriminating character for Umbelliferae.

The variation in the plant organ utilized and in the position of cellular structures responsible for the flavouring properties of the spice in the specific plant organ, necessitates a diversity of management practices in crop establishment, cultivation, harvesting and primary processing. A different approach is needed, for example, when the product is to be the fresh leaves rather than the fruits, e.g. in coriander. In chervil, where the leaves are important as a culinary herb, inflorescences need to be removed to encourage denser foliage. The lesser pungency of white pepper compared with black pepper has been attributed to the mesocarp of the fruit (where oleoresins are embedded) being removed during processing. The degree of peeling the ginger rhizome before drying affects its quality: removal of the cork layer can desirably lower the fibre level and pungency. If peeling is done without proper care, however, the volatile-oil content can also be reduced due to the removal of oleoresin cells in the cortex (Purseglove et al., 1981).

Growth and development

Knowledge of crop growth and development and insight into the eco-physiology should help the grower to manipulate the crop and its environment to achieve the optimum yield of the desired plant part. Many spices do not pass through their complete life-cycle in cultivation because they are grown for their vegetative parts, or young, immature generative parts. Information on the growth and development of spice crops is rather limited except for some of the economically most important ones. The sequence of germination, vegetative growth, and generative development (flower initiation, flowering, pollination, fruiting) has been highlighted in the species treatments as far as known.

Three major classes of growth habit can be distinguished: annuals, biennials and perennials. In areas with cold winters, annual or biennial crops dominate the agricultural scene, but as one moves from higher latitudes towards the equator, woody perennials become more important, and this also applies to spices.

The annual spices are herbaceous in character and include for the most part the so-called "spice seeds” (botanically fruits) of commerce, e.g. anise, coriander, cumin and dill. Biennial spices are exemplified by caraway (although annual types exist) and parsley, which remain vegetative during the first year of growth and initiate flowering in the second year.

The vast majority of spices are perennials. Among these are the small, evergreen understorey trees (e.g. clove, pimento, star anise) that take several years to come into bearing. The first flowering of the tree spices often occurs 5-8 years after the planting of seedling material, but usually much earlier for material propagated vegetatively. Full bearing, however, is attained at the advanced age of 15-20 years; productive life can range from a low of 30-40 years to a high of 70-80 years and even up to 100 years.

Much shorter is the productive life for the perennial herbs, e.g. fennel, horseradish, oregano, sage, tarragon and thyme, and the shrub rosemary. They need to be re-established after 3-5 years. Pepper and vanilla are climbing spices which commence flowering 3 years from planting and attain full bearing at the age of 7-8 years. Some biennial and perennial herbs like parsley and the rhizomatous ginger and turmeric are cultivated as annuals.

There is considerable variation in the flowering and fruiting behaviour of spices. Only a few studies have been conducted on the induction or promotion of flowering through exogenous application of plant growth regulators (gibberellic acid on chervil, coriander, fennel and parsley). The same is true for modification of sex expression using plant growth regulators. Indolebutyric acid (IBA), malic acid and 3-chloro-2,2-dimethylpropionic acid reduce the ratio of male to female flowers in andromonoecious coriander. Surprisingly, no such studies have been reported for nutmeg and pimento, which both exhibit dioecy and the problem of sex identification at an early stage. In terms of fruit development, parthenocarpic pods have been successfully induced in vanilla using either 2,4-dichlorophenoxyacetic acid (2,4-D), 2-methoxy-3,6-dichlorobenzoic acid (dicamba) or a mixture of indoleacetic acid (IAA) and indolebutyric acid (IBA) (Gregory et al., 1967). For one reason or another, this treatment, however, has not been adopted to replace the laborious hand pollination still being done in commercial plantations. Nevertheless, these studies reveal the possible application of chemical substances in the control of flowering and fruiting (Halevy, 1989).

The core area covered by Prosea lies between 20°N and 10°S. It consists mainly of tropical lowlands, but also has large areas at medium to high altitude. The choice of crops and cropping systems is mainly determined by interactions of ecological factors (climate, soil) and management variables. However, many spice crops, the herbs in particular, are part of horticulture, an intensive form of agriculture, usually on small acreages, in which restrictions imposed by adverse climatic factors and poor soils can often be overcome by intensive management practices.

On the other hand, a particular area's climate and soil can greatly influence the taste of spices. This has been experimentally proven in many cases, e.g. irradiance in thyme, photoperiod in sweet basil.

Climatic factors

The climates of South-East Asia are of the monsoon type. Monsoons are seasonal winds blowing moist air from the sea to the heated land mass bringing heavy rains during the hot season, and blowing air from the land to the sea during the cool season. In Indonesia and Malaysia, situated close to the equator, the dry south-east trade wind from Australia causes a dry spell from May to October. This wind turns to the north above the equatorial zone and takes up much moisture above the ocean. It is known as the south-west monsoon in Thailand and neighbouring countries and causes the rainy season from May to October ("summer”). The inverse happens from December to February when the north-east monsoon causes the dry season ("winter”) in Thailand but brings rain as the west monsoon in Indonesia.

In the lowlands near the equator the average daily temperatures are generally about 27°C the year round, the differences between a hot and a cool season becoming more pronounced northwards. In northern Vietnam the average temperature from November to April is only 16°C. In these areas the summers, from May to October, are very hot and subject to typhoons.

In mountainous areas the temperature drops by about 1°C per 160 m increase of elevation, and the difference between day and night temperature broadens. The occurrence of micro-climates is quite common. The distinction between highland and lowland cultivars, or, at the higher latitudes of northern Thailand, Philippines and Vietnam, between "summer” (hot season) and "winter” (cool season) cultivars is well known, e.g. in coriander.

There are spices which require a period of low temperature exposure (vernalization) for flower initiation, e.g. parsley.

The variation in daylength is a less important climatic factor in the area close to the equator, but is of increasing importance further north. At 10°N (southern part of the Philippines, Thailand and Vietnam) the daylength varies from about 11.30 h to 12.40 h, and at 20°N (northern part of the Philippines, Thailand and Vietnam) from about 10.50 h to 13.20 h. The distinction between a "summer” and a "winter” becomes tangible above 10°N, by variations in the photoperiod and in the total daily radiation. Some crops are very sensitive to daylength, examples being the long-day plants fennel and oregano, or the short-day plant perilla. These daylength effects will be dealt with in the species treatments.

Soil factors

The predominant soil types in South-East Asia are andosol and latosol (both of the sandy loam type) and alluvial clays. Light soils have the advantage of easy tillage, adequate drainage and aeration, provided that the organic matter content is sufficiently high. Clay soils have the advantage of a better water-holding capacity and higher natural fertility. Some spices such as horseradish prefer a heavy soil, whereas others such as Ceylon cinnamon, Mariana caper-bush and perilla prefer a light soil.

The lack of chemical fertility is not perceived as the most serious limiting factor, because amendments with manure and/or inorganic fertilizer are relatively easy. However, in most cases appropriate fertilizer recommendations are not available, and farmers must rely on their own experience.

The pH of the soil influences the availability of nutrients and also the soil structure. If the soil is very acid the choice of the crop will be limited to fewer species. Crops on acid soils often suffer from Mg, Ca or P deficiencies, or from Mn and Al toxicity. Liming with basic slag (or preferably with dolomite) is useful at a rate of about 2 t/ha per crop until a level of pH 6-6.5 has been reached. On acid soils, it is recommended not to use too much of acidifying fertilizers such as ammonium sulphate or urea.

The pH tolerance of many spices is well-documented (Barker, 1989; Duke & Hurst, 1975). Four major groupings can be observed in terms of sensitivity to acid soil conditions: very sensitive (where growth is already hampered at pH lower than 6.3, e.g. cumin); sensitive (where growth is hampered at pH lower than 5.3, e.g. perilla); moderately sensitive (where growth is hampered at pH lower than 4.5, e.g. laurel), and less sensitive (where growth is only hampered at pH lower than 4.3, e.g. sweet basil).

Crops such as laurel and rosemary exhibit a wide range of pH tolerance (almost 4 pH units), but most spices have a much smaller range.

A high soil salinity (electrical conductivity > 3.0 mmho/cm) is a serious restriction for crop growth; however, a crop like Mariana caper-bush is reasonably salt-tolerant, whereas Ceylon cinnamon and fennel are very sensitive.

Crops with shallow root systems, such as clove and nutmeg, are much more susceptible to drought than deep-rooting species such as rosemary. Most spices are sensitive to waterlogging.

The type of soil has been shown to have a pronounced effect on the quality of the spice product. In Ceylon cinnamon, for example, the best bark is obtained from trees cultivated around Negombo (Sri Lanka) where the soil is fine white quartz sand. In areas where the soil is lateritic and gravelly, the bark produced is thicker and coarser (Purseglove et al., 1981).

The expected increase in demand for spices can be satisfied by larger acreages or by intensifying the existing production of spices in short supply. Cultivation offers a number of advantages over collection from the wild: crops give higher yields, with more consistent properties. Cultivation facilitates selection and improvement of planting stock, weeding, crop protection, mechanization, harvesting, transportation and correct processing, all of which help to maintain and improve the aroma. These advantages become more important when quality specifications become more stringent.

Production systems

Collection from the wild

A number of spices are still harvested from the wild. Spices obtained from the wild are intended mainly for local use, e.g. wild cinnamon in Sri Lanka and wild "Papua” nutmeg (from ==Myristica argentea== Warb.) in Indonesia (Purseglove et al., 1981; Rugayah et al., 1989). In the Mediterranean countries the culinary herbs rosemary, sage and thyme are handpicked from the wild and subsequently traded in the international market. It is generally believed that herbs collected from their natural habitat have more flavour than those cultivated commercially. This point, however, is still a matter of controversy. Although some culinary herbs are still collected from the wild since their cultivation has proved uneconomic, e.g. rosemary, harvesting from wild-growing plants may be insufficient to meet the growing demand for the raw material. In the major markets of Western Europe, wild thyme actually accounts for less than 10% of the total import of thyme (International Trade Centre UNCTAD/GATT, 1991).

Harvesting from the wild seems conceptually attractive for a commodity with a relatively small trade volume, particularly if it involves non-destructive harvesting of aerial parts that quickly regrow. However, the problems include the difficulty of collecting material scattered over large areas, unpredictable supply of raw material for processing, and variability in quality related to the origin. Persistent and unregulated collection may also soon lead to the rapid erosion of important genetic resources. In the long run, spices are better cultivated than gathered from the wild.

Production on smallholdings

Smallholdings are generally single-family enterprises (e.g. for clove in Zanzibar), established by cooperatives (e.g. pepper in Indonesia) or formed on a communal basis (e.g. ginger in China) (Purseglove et al., 1981). In India, Indonesia, Malaysia (Sarawak), the Philippines, Madagascar and Brazil, smallholdings devoted to pepper have a mean size of about 1 ha (de Waard, 1980). Smallholdings are often characterized by insufficient cultural and manurial care, resulting inevitably in low yields, e.g. 250 kg/ha of dry pepper for small farms as opposed to 900-1000 kg/ha in large-scale production in India (Paulose, 1973).

Production in plantations

Most tree spices and herbaceous perennial spices are managed as plantation crops. Over 70% of nutmeg production in Grenada, for example, comes from large farms and only 30% is derived from peasant holdings (Cruickshank, 1973). A substantial part of cardamom in Sri Lanka is produced on holdings of 20 ha or more (Wijesekera & Jayawardena, 1973). Large holdings are almost always established by private enterprises that are able to invest more capital to undertake intensive cropping for high yields. In most cases, processing is carried out in the company's own integrated processing unit, thus with better quality control and more added value. In the Philippines, pepper from smallholders' farms is simply sun-dried, usually on concrete floors. In contrast, a private company in the southern region of the country, producing pepper from 20 ha, is fully equipped with artificial driers, blanching apparatus, conveyor belts and mechanized sorters and graders.

Production in market gardens

Herbaceous spices grown as annuals such as coriander, dill, parsley and sweet basil, are often grown in market gardens. They generally follow the techniques and trading and selling schemes appropriate for vegetables. Cultivation is labour-intensive and the product is intended mainly for the local fresh market. Mulching with e.g. rice straw, sawdust, rice hulls is often practised and net enclosures are constructed over raised plots to protect the crop from insect attack. Spices in market gardens have a high rate of production turnover and provide farmers with an opportunity of getting quick cash returns.

A high premium is paid for culinary herbs which are produced organically, making use of farm manure and compost and avoiding pesticides. Such farms are presently very trendy in the Philippines.

Protected cultivation in soilless media

The use of soilless media for spice production under protective cover is fairly recent and has mainly been applied on annual culinary herbs. Successful hydroponic culture of dill, perilla, sweet basil and thyme has been reported (Barker, 1995; Kim, 1995; Udagawa, 1995) while the use of commercial growing media such as peat-like mix have also been tried for rosemary and sweet basil (Adler et al., 1989; Boyle et al., 1991). Nutrient solutions used in these investigations were based on the one developed by Hoagland and Arnon (Hoagland & Arnon, 1950). This nutrient solution is seldom used commercially, however, because of the difficulty of preparing it. Instead, water-soluble, concentrated fertilizers, e.g. 20-10-20 or 20-20-20, supplemented with Ca, Mg and micronutrients are commonly used (Barker, 1995).

Spice production in soilless media under protective cover, particularly the hydroponic system, offers possibilities of overcoming constraints associated with field production: balanced application of nutrients and better control of light and temperature conditions. The system, however, demands a higher level of technical skill, requires a bigger initial capital input, and has considerable operational expenses for maintenance compared with traditional field culture. Such requirements have limited the use of hydroponics to developed, industrialized countries. Despite these constraints, this type of production has great potential for maximizing not only yield but also the level of secondary metabolites associated with the flavour of a particular spice because of the highly controlled growing conditions.

In vitro production

The production of natural flavours through in vitro culture has been explored in recent years. Its application may pave the way for eliminating some constraints associated with spice production from whole plants: wide fluctuation in supply and availability of raw material, difficulties of transport from remote areas, and problems of political nature in the countries of origin (Whitaker & Hashimoto, 1986). Batch culture of natural flavours is also viewed as a possible means towards overcoming toxicological objections to synthetic flavour and colour additives (Collins & Watts, 1983).

However, the exciting promise of large-scale production of spice flavours and other related secondary metabolites using cell cultures remains unfulfilled. The limited body of tissue culture work on the production of food flavours indicates that production has been hampered by the absence of specialized and highly differentiated cells in the cultures. For example, the essential-oil components carvone and limonene in dill cell culture are lost beyond the seventh generation, despite various modifications in chemical and environmental factors (Everitt & Lockwood, 1995). Neither could these components be detected even in the embryoids and embryogenic callus of caraway (Furmanowa et al., 1991).

There are, however, instances where some of the flavour principles have been detected even in undifferentiated cells. In coriander, geraniol has been detected in root callus culture, but not the other flavour components such as linalool, borneol, α- and β-pinene and p-cymene (Sardesai & Tipnis, 1969). In callus culture of oregano, minute amounts of essential oil were found using microsteam distillation apparatus with microcapillary collector (Svoboda et al., 1995). Gas chromatography (GC) analysis revealed the presence of carvacrol in the volatile oil. Small amounts of thymol and β-elemene, but not γ-terpinene and p-cymene, were detected in the volatile oil from thyme callus tissue. Other metabolites, e.g. geranylacetone, chamigrene and nerolidol, were found to exist in the callus culture but not in the intact plant (Tamura et al., 1993).

It is worth noting that the enzyme systems involved in the biosynthesis of important secondary metabolites have been detected even in cultures of undifferentiated cells. These reports point not only to the potential of biotransformation in the production of flavours or other chemicals for industrial purposes, but also to the utility of cell culture in the elucidation of basic metabolic schemes involved in the biosynthesis of secondary metabolites.

The accumulation and isolation of chemical products via cell culture from spices other than those distinctly associated with flavour have also been reported: condensed tannins from ==Cinnamomum cassia== (Yasaki & Okuda, 1993); caffeic acid and rosmarinic acid from rosemary and sage (Whitaker & Hashimoto, 1986).

Planting material

Spices are generally propagated by seeds, which normally germinate in a span of 2-3 weeks, but sometimes up to 6 weeks from sowing, e.g. cardamom and nutmeg (Ilyas, 1978; Rosengarten, 1973; Samarawira, 1972). Some spice seeds require pre-sowing treatment to enhance germination. Seed viability may pose a problem in some of these spices. Seeds of the tree spices cassia, cinnamon, clove, pimento and nutmeg are recalcitrant in nature, losing their viability upon drying to a low moisture content and subsequent storage at low temperatures. Thus, freshly harvested seeds are used for sowing. On the other hand, when dried to a certain moisture content and kept under proper conditions, some seeds can maintain their viability for several years: sage and thyme seeds can be stored in airtight, polythene bags for 6 years or more. Seed of anise, chervil, coriander and sweet basil is also viable for long periods (Halva & Craker, 1996).

The flavouring herbs within the Umbelliferae, e.g. anise, caraway, coriander, dill and parsley are commercially propagated only by seed. These plants do not transplant well and are thus sown directly into the field. Seeds used for sowing must be obtained from fully ripe fruits collected from vigorous, high-yielding and disease-free mother plants of the desired type.

Some spices are difficult to propagate from seed. French tarragon (tetraploid) and turmeric are sexually sterile and therefore do not produce viable seeds (Nambiar et al., 1982; Rousi, 1969). Fertile seeds are rarely obtained in ginger, while horseradish fruit pods frequently fail to mature or to contain viable seeds (Rosengarten, 1973). In some cases, the seeds are small, e.g. oregano, and thus are difficult to handle. The use of seeds may also result in considerable delay in production. From seed or tissue culture it may require 4-5 years to harvest the first crop for vanilla, as opposed to only 2-3 years when cuttings 1 m long are used (Davis, 1987).

Vegetative means of propagation have been successfully employed for various spices. Since the new plant is genetically identical to the original stock plant, asexual propagation can ensure the continuation of unique genotypes that may have a special type of oil, disease resistance and other useful traits. These are accomplished through the use of cuttings, air layering and grafting. Cuttings are excised from vegetative portions of the plant, such as stems and their modified structures (rhizomes, corms and bulbs), leaves or roots. The most significant type is the stem cutting. The basic protocol is to excise stem portions bearing 2 or more nodes from a healthy, well-established plant, and to treat the basal cut end with plant growth regulators, e.g. indolebutyric acid (IBA), naphthaleneacetic acid (NAA) or a combination of both, to enhance the rooting response and shorten the period to root initiation. Vanilla, pepper and most members of the Labiatae such as marjoram, sage, sweet basil and thyme are easily propagated by stem cuttings. Root cuttings are employed for a few spices like horseradish, marjoram and oregano. Sets obtained by dividing old rootstocks are also employed in cinnamon and cassia. Unlike stem cuttings, it can be very laborious to get root cuttings in sufficient quantities, unless they can be obtained by trimming roots from nursery plants as they are dug out. Planting material for cardamom, ginger and turmeric is obtained using their specialized stem structure, the rhizome. Propagation is carried out by cutting the rhizomes into sections, ensuring that each piece has at least one lateral bud or "eye”. Cardamom can also be propagated from seed.

Vegetative propagation has advantages for nutmeg and pimento, which are normally both propagated by seed. Both crops exhibit dioecy and it is rather difficult to distinguish between male and female trees until they come into bearing at 5-6 years or even later. Although other techniques have been tried, marcotting or air layering appears to be the most effective means of producing new nutmeg plants. The method gives 60-70% success. In pimento, approach grafting has been reported to produce as much as 95% success. Layering is a common technique employed for spice crops such as cassia, cinnamon and pepper.

Division of the crown is an important method of propagation for some herbaceous perennials because of its simplicity and reliability. Many of these spices must be divided every 2 or 3 years to prevent plants from becoming overcrowded. Plants are essentially dug out and cut into sections. Crops that can be propagated by division are oregano and tarragon.

Tissue culture techniques have also been used in the production of planting material. This technique offers a method of mass propagating disease-free plants in a short period of time. It also provides the opportunity to select plants with desirable features through somaclonal variation which is otherwise difficult to obtain by traditional plant breeding. The explants used for tissue culture of spices include rhizome buds, hypocotyls, nodal stem segments, petioles, leaf segments, shoot tips, seeds and young ovaries, generally cultured in Murashige and Skoog's basal medium with various concentrations of auxins and cytokinins. Some of the spices that have been successfully micropropagated are caraway (Furmanowa et al., 1991), clove (Mathew & Hariharan, 1990), horseradish (Meyer & Milbrath, 1977), ginger (Hosoki & Sagawa, 1977), vanilla (Kononowicz & Janick, 1984), turmeric (Nadgauda et al., 1978), parsley (Vasil & Hildebrandt, 1966), fennel (Maheshwari & Gupta, 1965), dill (Sehgal, 1968), cinnamon (Yasaki & Okuda, 1993), cardamom (Bajaj et al., 1993), oregano (Kumari & Saradhi, 1992) and tarragon (Mackay & Kitto, 1988).

As with seeds, planting material produced through whatever type of asexual technique should be derived from well-established, vigorous and disease-free mother plants.

Husbandry

Crop husbandry measures in spices differ little from those of other annual and perennial crops. For most species, the aim is to maximize or optimize yield and to harvest before deterioration in quality and quantity. Best quality and greatest quantity do not always occur at the same moment.

In experiments on temperate culinary herbs, it has been shown that nitrogen application influences crop oil yield predominantly through its influence on biomass production. The effects on oil content and oil quality are much smaller or negligible. It is therefore especially important to monitor the nitrate content in crops produced for direct human consumption. In the case of limitation of biomass production through water stress, there are complex relationships between N application, quantity and timing of irrigation, crop yield and crop quality (Hay, 1993).

Weeds can become a problem in spice production, and their detrimental effects are keenly prominent during the establishment phase. Weeds not only compete with the major crop for nutrients, water and light but can also serve as hosts for a variety of diseases and insects attacking spices. The inadvertent inclusion of weeds in the raw material during harvesting can decrease the quality and market value of the herb product, especially in the case of savoury herbs. In the spice-producing countries in the tropics, weed control is generally and simply accomplished by hand; mechanized weeding is more favoured in the industrialized economies, where it is normally employed on large farms specializing in the production of culinary herbs. Few herbicides have been registered for use in spices. Herbicide use is avoided in organic systems of cultivation. Currently, mulching appears to be the least expensive and environment-friendly technique for reducing if not totally eliminating weeds.

Crop protection

Some spices such as Chinese keys, fragrant pandan, oregano, star anise and tarragon are not seriously affected by diseases and pests. Most spices, however, are damaged to such an extent that considerable production losses may result. For the majority of spices, damage caused by disease is far more significant than that attributed to pests. Fungal infection accounts for most of the diseases that have brought severe havoc to plantations and home gardens: foot rot in pepper, root or stem rot in vanilla and the witches' broom in Chinese cassia. The most common diseases of culinary herbs are leaf-spots or blights, grey moulds, downy and powdery mildews, rusts, vascular wilts and root rots (Schumann, 1989). Other diseases of importance for spices include those caused by viruses (in cardamom, horseradish and chervil), bacteria (in clove and ginger) and nematodes (in cinnamon, oxalis and pepper).

If unchecked, insect pest infestation can also reach serious proportions; nutmeg production was wiped out in Singapore and Pinang in the 1860s due to scolytid beetle (Purseglove et al., 1981). The more common insects attacking spices are chalcid fly, aphids, weevils, leaf-eating caterpillars, borers, thrips and scale insects. Rats, bats and birds can also afflict occasional damage, particularly on fruits and rhizomes. Spice products in storage are also not immune from attack by insect pests, e.g. biscuit beetle in coriander, coffee bean weevil in nutmeg.

By comparison with the major food crops there are only a few chemical pest control techniques available for spices. This has led to severe economic losses in the production of these crops. With regard to the collection of data for pesticide registration, the spices are generally considered as minor crops. The prohibitive cost of generating information to establish legal tolerance levels (pesticide level considered safe in food) and other pertinent data, coupled with the risk of limited sales, have discouraged pesticide manufacturers from registering many chemicals for specialty crops such as spices. Among the herbaceous spice crops where tolerance data (either as insecticide, fungicide or herbicide) have been established are anise, basil, chervil, dill, fennel, marjoram, parsley and rosemary (Frank et al., 1987). The use of herbicides and chemicals for disease and pest control in spices needs special care, as pesticide residues may affect the quality.

Chemical pesticides are generally expensive and often beyond the means of local farmers. This, together with the increasing interest in and demand for organically grown food, has prompted growers to focus on other means of control, particularly those involving appropriate cultural management techniques. Among those being employed include heat treatment of fruits (to eliminate seed-borne diseases), roguing or eradication of infected plants, crop rotation, pruning of infected branches, application of complete and balanced mineral nutrients (e.g. to control yellow disease in pepper), use of raised beds, choosing well-drained sites for cultivation, and grafting of susceptible cultivars onto resistant rootstocks. It is important to emphasize that planting material should be healthy and disease and pest-free to begin with and that proper sanitation should always be maintained in the farm.

For culinary herbs where production is relatively small scale, protected cultivation can be resorted to, as is done in the Philippines, where garden plots are enclosed in cages screened on all sides with very fine nylon nets to exclude insects; in some cases the cages are roofed with polythene film to protect from too much rain during the wet season when most fungal diseases are prevalent. Pesticides of plant origin are also being tested, but their effectivity and non-toxicity still warrant scientific validation. The technique of biological control, e.g. application of Bacillus thuringiensis, a bacterium used as insecticide, also deserves some investigation for spices (Halva & Craker, 1996).

Harvesting

Proper harvesting and handling are extremely important for highest organoleptic quality.

The first harvest depends on the plant's growth habit and the nature of the product: fruits and barks from perennial tree spices are first harvested several years from planting; in contrast, leaves, shoots or seeds from culinary herbs may be ready for harvesting a few months after establishment, while sprouted seeds, e.g. white mustard, can be obtained in only a few days after sowing.

To obtain the full flavour of the spice, harvesting should be done at the proper stage of maturity. Earlier or later than this stage could make a difference in quality and yield. Clove buds, for example, should be harvested when the buds become pink and are about 2 cm long; if gathered too early the cloves will be wrinkled, with lower eugenol content, while if picked too late the bud colour will change to deep red and bloom out (Guenther, 1948-1952). For most of the spice "seeds”, e.g. anise, caraway and coriander, late harvesting results in shattering of fruit clusters leading to a lower yield. Some spices are harvested before flowering occurs, e.g. summer savory and chervil, or when the first flowers have just developed, e.g. marjoram, oregano and sweet basil (Halva & Craker, 1996). Ginger and turmeric are harvested when the stalks begin to wither, about 9-10 months after planting.

The time of the day or the season of harvesting is also an important factor to consider. Spice seeds are preferably harvested early in the morning when dew is still fresh and when there is less danger of seed loss. Leaves from laurel and shoots from herbaceous spices are picked by hand early in the day when sunlight is not so intense that it leads to a rapid loss of volatile oil. Cinnamon and cassia bark is best cut during the rainy season, when the bark is easier to separate from the stem because of the increased flow of sap between wood and bark (Rosengarten, 1973).

Techniques of harvesting also vary depending upon the spice. Fruits of pepper and pimento and floral buds of clove are picked by hand, by pickers using ladders to collect those from the upper portion of the tree. For most herbaceous spices in small garden plots, harvesting is simply accomplished by hand or with the use of a knife, pruning shears or a sickle blade; a cereal combine harvester can be used for larger plots. Underground spices, e.g. horseradish and ginger, can be dug out by hand with the aid of tool bars or hoe, or with a mechanical digger when working on larger fields.

Handling after harvest

Damage to oil-filled glands and cells can be avoided, and loss of volatile oils kept to a minimum by careful handling.

Pretreatment

Spices undergo various pretreatment procedures before drying or other processing techniques. The roots and rhizomes of crops used as spices (e.g. horseradish, ginger, turmeric) are initially washed clean of adhering dirt. To enhance the rate of drying some spices are peeled or scraped (ginger, cinnamon bark), sliced (ginger, turmeric) or cut into pieces (quills, quillings, featherings and chips of cinnamon and cassia barks).

Blanching is a common pretreatment done on turmeric; in pepper it is said to hasten drying and provide uniform colour to the peppercorn. Chemical treatments are also employed for various ends: to retain the green colour of cardamom; to stabilize the carotenoids imparting the attractive red colour in capsicum pepper (suitable antioxidants are used for this); to improve the colour of ginger (using bleaching powder, sulphur dioxide or hydrogen peroxide). Vanilla is subjected to a series of curing or fermentation steps for the development of full flavour. In general, fermentation is used to hydrolyze the glucosides of characteristic flavour compounds.

Drying

Drying is considered to be the most important step in the primary processing of spices. The major objective of drying is conservation by reducing the moisture level of the raw material to a safe limit (e.g. 8-10%), to retain the original colour, and to prevent or minimize the action of spoilage organisms without great loss of the flavour characteristic to the spice product. Dried spices can be stored for a considerable period of time. Drying inhibits the activity of intrinsic enzymes and prevents other chemical reactions that can reduce the quality of spice during storage. Cost of storage and shipping is also minimized, since the weight of the dried material is only 10-25% of that of the fresh material.

Traditionally, and mainly for economic reasons, most spices are sun-dried. It is the cheapest method for bulk production and is employed when quality or appearance are not greatly affected by the action of direct sunlight. Sun-drying is done on concrete platforms, floors, grass or straw mats or simply by leaving the raw material to dry in the field. The spice product is often exposed to microbial contamination from the soil. Using raised platforms or racks not only circumvents this problem but also allows for a faster rate of drying because of the draugh of air circulating through the bottom and the sides. Sun-drying may take 2-14 days, depending upon the nature of the raw spice, the pretreatment applied, and the duration and intensity of sunlight.

Shade-drying is resorted to for some spices that tend to discolour or lose a considerable amount of essential oil under direct sunlight, e.g. cardamom, sage and most culinary herbs. Shade-drying permits the crop to be dried more slowly and uniformly.

Drying can also be accomplished by mechanical or artificial means, using natural convection dryers or forced-draugh dryers. It not only eliminates the disadvantages associated with sun-drying (e.g. microbial contamination, discolouration, dependence on the weather), but also provides controlled conditions of temperature, relative humidity and air flow, yielding a high-quality product. Temperature, the most critical factor in artificial drying, should not exceed 75°C, but varies depending upon the type of spice: just under 38°C for leafy and herbaceous spices, cooler for flowers, around 50°C for roots, and over 60°C for barks.

Grinding

Most spices are dried whole or as slices or chips, but not as powder. Grinding is done after drying. Grinding is basically a physical process of comminuting whole or pre-broken spices to a size suitable for a particular purpose. Some products like barks need to pass through a knife cutter or cracking machine before being ground. Various impact/disintegration mills (hammer mills, roller mills, attrition mills, limited mills, pulverizers) have been designed to yield products from coarsely broken uniform pieces to powders with a wide range of particle size. The suitability of these machines varies, depending on the fibre (e.g. high in ginger) or the fixed-oil content (high in nutmeg) of the spice products.

Grinding is generally performed in the consuming countries, to ensure adequate quality control.

Packaging and storage

Packaging aims to conserve the characteristic flavour and appearance of the spice product, protect it from disease and insect infestation, prevent oxidation and rehydration through absorption of moisture from the surroundings and minimize mechanical damage during handling and transport. Crude spices are generally packaged in burlap sacks, boxes, fibreboard drums or polypropylene feed sacks. Packaging is more critical for ground spices than whole spices. Ground spice has a greater surface area and is therefore more likely to lose essential oil; it will also lose or gain more moisture from the atmosphere and more easily oxidize. Three major types of packaging are recognized for ground spices and spice blends and mixtures. For bulk packaging: polythene-lined jute sacks, multi-walled paper sacks and fibreboard drums are preferred; for intermediate, catering or institutional packs: cardboard cartons lined with polythene, multi-walled paper sacks or traditional tinplate containers; for consumer packs: glass jars with plastic lids, acrylic or polythene drums, small tins or fibreboard drums with plastic lids (Hone & Milchard, 1993).

Spices should be stored in clean, dry and cool conditions, away from direct sunlight or heat and air. If stored for prolonged periods, the spice batches should be regularly inspected for insect infestation.

Freeze-drying is the best conservation procedure, but it requires special equipment. An excellent way to conserve spices is in vinegar (herbal vinegar/spice vinegar).

Processing of spices is mainly done by the flavour and fragrance industry, which is specialized in bringing together thousands of aromatic materials from all parts of the globe, refining and mixing them, and producing the range of flavours and fragrances that meets the requirements and demands of the user industries.

Grasse (France) was a famous perfumery centre. It developed in the 17th Century, and had its heyday between the two World Wars. The Second World War disturbed commercial activities, led to the loss of control of production through decolonization, breaking the Grasse monopoly.

Newcomers in the sector after the Second World War were huge multinational companies, also intensively involved in synthetic aroma chemistry, such as International Flavors and Fragrances, Quest, Givaudan, Haarmann & Reimer, Firmenich, Polak Frutal Works, Takasago, and Bush Boake Allen. Most companies are involved in food flavours as well as perfumery, because the technology is very similar. For the last 20 years, the natural flavour sector has expanded most, because of stricter legislation on food additives.

The user industries can be divided into "industries using flavours” (foods and beverages, semi-pharmaceuticals, toothpaste, tobacco), "industries using perfumes” (soaps, detergents, air fresheners, deodorants, haircare products, cosmetics, perfumes), and the health sector industries (specialized pharmaceuticals in phytotherapy and aromatherapy, animal care).

Techniques

The dried spice can be traded as it is or can undergo some extraction procedures to yield essential oils or oleoresins.

The isolates are further transformed by e.g. purification, decolourization, concentration, separation of single constituents for new formulations or as starting material for the synthesis of new compounds. The next step is the mixing of primary materials for specific requirements of the user industries (Lawrence, 1995).

Essential oils

Three distinct processes are used to produce essential oils: solvent extraction, expression and distillation. Solvent extraction is an industrial process in which highly purified, volatile media are used to extract aroma compounds from plant material, followed by the removal of the solvent by distillation.

Expression is used to obtain the essential oils from the peel of citrus fruits. It was originally a household industry using only simple tools, but it has been superseded by large-scale industrial processes.

Several forms of distillation are applied to produce essential oils, the most important being water distillation, steam distillation and hydrodiffusion. Water distillation or hydrodistillation is an old process for the production of essential oil and has undergone centuries of improvement. Small-scale traditional water distillation apparatus is still being operated alongside large industrial equipment, because in small fields on poorly accessible hilly land, it is more economical to operate small and simple portable stills than to move a bulky crop to a central still. Steam distillation is a similar process, but hot steam is forced through the plant material to extract the essential oil. Large-scale industrial systems, e.g. continuous distillation systems and the use of harvesting containers that can function as distillation vessels, have been developed alongside small, traditional systems. Hydrodiffusion is a recent process in which low-temperature, low-pressure steam is used to extract the essential oils.

The type and duration of distillation depends on the nature and form of the plant material, the capacity of the distilling unit, the nature and volume of steam, and the volatility of the constituents. For clove buds, water distillation has been reported to provide the finest oils; steam distillation yields "strong oils” with higher levels of eugenol because eugenol acetate hydrolizes during the process. Sweet basil can be distilled in 1-2 hours (batches of up to 1000 kg), while it can take from 6-9 hours for the distillation of clove buds (batches up to 700 kg). In anise and coriander, crushing the seeds immediately prior to distillation has been shown to increase the yield of oil by 5% and 17% respectively, save up to 10-15% steam and reduce distillation time by as much as 25%.

Oleoresins

In some spices, the volatile components in the essential oils are only part of the flavour. For instance, the characteristic bite of pepper and ginger and the characteristic yellow colour of turmeric are absent from the essential oils obtained from these spices. The total organoleptic principle is best approached by oleoresins.

Spice oleoresins are obtained by extraction of the raw material with a volatile, organic solvent. The dried spice is generally crushed into a coarse powder and immediately extracted, using either a single-stage or a double-stage extraction method. In the single-stage technique, the oleoresin is extracted from the spice with the selected solvent, and then the solvent carefully evaporated. In the double-stage extraction, the spice is first steam-distilled to obtain the essential oil, then dried and extracted as in the single-stage process; the oleoresin is eventually mixed with the essential oil to yield a more standardized product. Solvents commonly employed in spice oleoresin extraction include acetone, chlorinated hydrocarbons (e.g. methylene chloride, trichloroethylene), and hexane. The choice of the solvent is determined not only by the nature of the spice but also by the food laws of the country utilizing the oleoresin, e.g. in the United States the use of chlorinated solvents is currently under review. The oleoresin may be used as it is or dissolved in an edible solvent, dispersed in an edible neutral base (fixed oil, salt, dextrose, flour, rusk) or encapsulated in arabic gum or gelatin.

Oleoresins can also be obtained by extraction of spices with supercritical (liquid) CO2. The process is similar to that used in the production of decaffeinated coffee and hop extracts. It has the advantage that the solvent is non-toxic, very easily removed, non-flammable. The solubility of various compounds can be regulated by manipulating temperature and pressure, making it possible to influence the ratio of volatile compounds to waxes in an oleoresin. CO2 extraction, however, is a capital-intensive, high-technology operation that is beyond the means of most spice-producing countries.

Oleoresins may be refined (for instance by removing the wax compounds) to adjust their taste or improve their solubility in water. This can be done by distillation or extraction with special solvents, e.g. CO2.

Quality standards

Quality standards have been defined for many spices, for both the whole and the ground forms, the essential oils and the oleoresins. Systems of quality standards have been developed to facilitate marketing and to guarantee the safety and quality of products. Such standards regulate not only the quality of individual products, but also methods of analysis and quality management systems. The most important systems of standards for spices and derivatives are those of the International Organization for Standardization (ISO), Geneva, Switzerland, the Essential Oil Association of the United States (EOA), and the International Fragrance Association (IFRA), Geneva, Switzerland.

The ISO issues 3 types of standards. The first type (ISO 9000) sets quality requirements for management and systems. The second type defines protocols and methods of analysis to be used in the establishment of particular parameters. For spices, ISO 927 deals with the determination of extraneous matter, ISO 928 with the determination of total ash, ISO 930 with the determination of acid-insoluble ash, ISO 939 with the determination of moisture content, and ISO 6571 with the determination of volatile-oil content. In the case of essential oils, ISO 279 deals with the determination of relative density, ISO 280 with the determination of the refractive index, ISO 592 with the determination of optical rotation, ISO 875 with the miscibility in ethanol, and ISO 11024 with general guidelines for chromatographic profiles.

The third type of standards defines the limits for several characteristics the dried spice or an essential oil must comply with. Traditionally, these have been physical determinations; for spices proper these are the maximum amount of extraneous matter, moisture content, total ash, acid-insoluble ash, and the minimum percentage of volatile oil; for essential oils these are relative density, refractive index, optical rotation, miscibility with aqueous ethanol, and chemical determinations of groups of components of major interest. Older ISO standards indicated acceptable ranges for alcohol, carbonyl, acid and ester number. The latest ISO standards incorporate a chromatographic profile and concentration ranges for the most characteristic components. However, the variety of methods and protocols of analysis that are used makes it difficult to compare published profiles with the standards. For tabulated overviews of ISO standards for physical characteristics of dried spices and essential oils from plants dealt with in this volume, see pp. 311-320. When no ISO standard was available, the information has been supplemented with data published in the Food Chemicals Codex (Committee on Food Chemicals Codex, 1996).

The Food and Drug Administration of the United States (FDA) and the Flavor and Extracts Manufacturers' Association (FEMA) deal specifically with the safety of products, including the spices and essential oils used in foods. Products it deems safe are issued with a "GRAS” or "generally recognized as safe” statement, which may specify restrictions in relation to their use in certain products. GRAS numbers are given in the individual species entries in this volume.

Adulterations and substitutes

Substitutes for a spice are materials that mimic its character; substitutes for natural essential oils are reconstituted compositions of aroma chemicals that mimic the character of the oil in question.

Spices and their essential oils are complex mixtures of hundreds of chemical compounds, most of which are present in minute amounts (a few parts per million or even less). Many of the minor chemical compounds that occur in nature are not commercially available. Moreover, those natural chemical compounds, which possess an asymmetrical carbon atom, are optically active, and their optical antipods, called enantiomers, may have different organoleptic qualities. No two natural products are chemically identical. Thus, substitutes for spices proper or reconstituted oils are generally approximations and often do not match the richness of their natural model.

Up to the 1930s, the aromatic scene was dominated by natural products. Developments in synthesis were relatively slow; the first step was to isolate natural compounds, e.g. cinnamaldehyde from cinnamon. One of the first nature-identical synthetic flavour compounds was vanillin, which appeared in 1876. It was by the end of the 1950s that synthetic citral, geraniol, nerol and linalool became viable alternatives for the reconstitution of natural essential oils (Verlet, 1993).

Industrialized countries are the most important producers of substitutes for natural aromatic materials. These substitutes can be isolated from other natural sources, e.g. isolation of eugenol from clove leaf oil. They may be produced by chemical modification of natural materials, e.g. methylchavicol and anethole from turpentine. They can be manufactured by chemical reactions with a natural chemical compound, e.g. condensations with citral. Other substitutes may also be produced completely synthetically, such as cinnamic aldehyde from toluene by oxidation via benzaldehyde and condensation with acetaldehyde. Thus the building blocks (chemical compounds) for reconstituted spice oils may be natural, nature-identical, or synthetic, not occurring in nature (for instance ethylvanillin as replacer for natural vanillin).

The identification of aromatic chemical compounds is nowadays facilitated by modern spectroscopic techniques: capillary gas chromatography (GC), mass spectroscopy (MS) and infrared spectroscopy (IS).

Substitution is a legitimate practice as long as it is properly declared. When not properly declared, substitution becomes adulteration.

Spices proper are sometimes adulterated with other dried or ground plant materials and with inorganic materials (sand, salts). Adulteration of natural essential oils takes place in a range of actions: standardization, reinforcement, liquidization, reconstitution, and commercialization.

Standardization involves improving the quality of a product to meet stipulated norms. The content of characteristic substances can be standardized by adding products that have been isolated from another natural source or produced synthetically. Common examples are the addition of eugenol from clove leaf oil to other spicy oils, or of synthetic cinnamaldehyde to cinnamon oil.

Reinforcement is an extension of standardization in which a natural or synthetic organoleptically characteristic compound is used to extend the original oil. When the odour quality of an essential oil can be improved there is always the temptation to add exaggerated amounts of the characteristic compounds to improve the quality and to make a product with "more olfactive value for money”.

Liquidization has the aim not to change the organoleptic quality of a product, but its appearance, in order to improve its applicability. Some oleoresins may be semi-solid or solid. If the liquid form is preferred, solvent or liquidizer can be added to the product. Various solvents are used for this purpose, such as propyleneglycol, triethyl citrate and benzoates.

Reconstitution is the compounding of a natural isolate using natural, nature-identical or synthetic chemical compounds to obtain a product that is similar to the original natural oil. Reconstituted essential oils are especially applied in functional perfumery. When a natural essential oil in a perfume composition is prohibitively expensive it may be replaced by a reconstituted oil.

Commercialization of a natural product involves expanding its volume and lowering its quality to make it more profitable. It may involve the use of reinforced, liquidized or reconstituted products. If properly declared, commercialization is an accepted practice. Some buyers cannot afford to pay the cost of a natural product and are willing to buy a commercialized product with similar, though inferior, organoleptic characteristics. However, a buyer has the right to know what he or she is buying.

Because of their food use the adulteration of spice oils for flavouring has more serious implications than adulteration in perfumery. Some examples of adulteration of spice oils are the addition of a chemical compound from a cheaper natural source, e.g. eugenol from clove leaf oil to pimento berry oil, or of 1,8-cineole from Eucalyptus globulus Labill. oil to rosemary and cardamom oil, and of camphor from Cinnamomum camphora (L.) J.S. Presl to rosemary oil. Other examples of adulteration of spice oils are the addition of (semi-)synthetic components, e.g. methylchavicol and anethole from turpentine, and synthetic cuminaldehyde and cinnamaldehyde.

Quality control

The quality of spices has long been evaluated using microscopic techniques that involve not only examination of cells or structures characteristic of the spice product but also the staining of certain chemical constituents (e.g. starch, lignin) it contains. The method provides initial clues about the identity of the spice; it also aids in the detection of adulteration. Preliminary tests are conducted prior to microscopic examination, such as taking note of the colour, odour and taste of the product. Although several micro-chemical analyses are subsequently performed, much information is yielded by microscopic examination of starch, epidermal trichomes, calcium oxalate, and lignin. For example, calcium oxalate crystals occur as rosettes in the ground form of clove, coriander and fennel, and as prisms in cardamom; they are lacking in ginger and nutmeg. Starch, on the other hand, is present in ground ginger, cardamom and nutmeg, but absent in clove, coriander and fennel (Trease & Evans, 1972). French tarragon (the methylchavicol type) is distinguished from Russian tarragon (the elemicin-sabinene type) by having no hairs or only hairs of the bifid type, whereas the latter has star-type trichomes in dried leaf fragments (ISO 7926). Application of the tools of microscopy to determine the quality of spice products, particularly the ground material, entails a considerable knowledge of plant anatomy. The identity of the spice in question can only be confirmed after all the diagnostic features observed are compared with samples of known authenticity (Parry, 1969).

Until a few decades ago, the chief means of verifying the density, purity and naturalness of essential oils was the human nose, supported by the measurement of a number of physical characteristics and a few chemical analyses. Rapid advances in methods of chromatographic and spectroscopic analysis have revolutionized our knowledge of essential oils. However, in many cases this knowledge is still inadequate, as the human sense of smell is even more sensitive.

Probably the oldest techniques to separate components from a mixture are the chemical ones. The extraction of essential oils with acidic or alkaline aqueous solutions allows respectively the basic complexes and the acids and phenols to be isolated. Carbonyl compounds can be isolated by transformation into water-soluble hydrazonium salts. Esterification of alcohols is another option. However, chemical separation methods have several drawbacks. They require relatively large amounts of product, they may cause formation of artefacts and they can only separate compounds on the basis of their chemical functionality.

Physical separation methods exploit differences in physical properties of the components of a mixture: density, vapour pressure and solubility. One commonly used method of separation is fractional distillation. Recent developments allow small quantities of product to be separated into large numbers of components. Distillation works best with components of low molecular weight and high vapour pressure. Heavy components require higher temperatures, which bring a risk of thermally-induced modification.

The commonest technique for separating compounds of a mixture when analysing essential oils is capillary gas chromatography (GC), resulting in a chromatogram from which components can be identified qualitatively and quantitatively.

Capillary gas chromatography is usually coupled with mass spectrometry (MS) and sometimes with infrared spectrometry (IS). The separated components of the mixture enter the spectrometer one by one, so that each of them can be analysed separately.

Gas-phase infrared spectrometry results in an absorption spectrum that is unique to the compound tested. The identity of the compound is established by comparison with spectra of reference compounds.

In the mass spectrometer the mass and electric charge of ions derived from the chemical compound are recorded and the identity of the original molecule can be established by comparing the information with reference data stored in a computer.

More detailed information on compounds is obtained by nuclear magnetic resonance spectroscopy (NMR), in which the resonance spectrum of the compound is recorded. All different H bonds are represented by specific peaks. To identify the compound tested, this pattern of peaks can be compared with reference data.

Advances in the chemistry of optical isomers have further enhanced the possibilities of identifying added compounds in essential oils. Most of the asymmetrical, optically active compounds in natural essential oils are represented by only a single isomer, or else both isomers are present in a proportion that may vary within a narrow range only. The addition of the compound obtained from another essential oil will often change this proportion and result in an enantiomeric excess concentration (E.E.C.). As chemically synthesized compounds are only rarely optically active, their presence can be accurately demonstrated. Enantiomers can be separated by gas chromatography on columns with optically active stationary phases.

However, the high prices paid for pure natural essential oils are encouraging the development of increasingly sophisticated reconstitution practices, so methods for detecting them have to keep pace. The adulteration of an essential oil with compounds chemically synthesized from carbon compounds derived from petroleum or coal can be detected by measuring the amount of radioactive carbon (14C) in the components of the oil. The atmosphere contains mainly 12C but also traces of 14C. The latter is produced by irradiation and subsequently decays slowly. Compounds synthesized by plants from atmospheric carbon dioxide contain 14C, whereas almost all the 14C in fossil material and in chemical compounds derived from it has decayed. Modern mass spectroscopy equipment is sufficiently accurate to measure the ratio of 14C/12C and makes a distinction between fossil and natural compounds possible.

Although this method has made it easier to detect adulteration with synthetics, it cannot reveal adulteration involving compounds derived from cheap natural linalool or pinenes. Refinements in the analysis of carbon isotopes exploit differences in the photosynthetic pathway used by different groups of plants. The C₄ pathway (typical of many tropical grasses) and C₃ pathway (typical of temperate grasses and most dicotyledons) of photosynthesis fix different proportions of ¹³C and ¹²C. C₄ plants are richer in 13C than C₃ plants. The measurement of nuclear magnetic resonance (NMR) has been refined to such extent that it can identify whether a compound originates from a C₃ or C₄ plant.

The newest way to characterize chemical compounds is a method based on deuterium nuclear magnetic resonance spectroscopy. A small proportion of hydrogen in nature occurs as ²H or deuterium. Nuclear magnetic resonance spectroscopy enables the magnetic resonance of individual bonds between atoms in a molecule to be studied. It appears that the ²H is unevenly distributed over the various bonds in a molecule. As the internal distribution varies with the origin of the molecule, this method can distinguish whether, for instance, anethole is prepared from star anise, estragole or turpentine.

The spice market is relatively small and comprises a large number of crops. The small size of the market for individual spices hampers the establishment of germplasm collections and breeding programmes.

Both direct selection and breeding work depend on the available genetic diversity. Very little systematic collection and evaluation of germplasm has been performed for tree spices, many of which have recalcitrant seeds, necessitating the establishment of living-tree collections. The genetic diversity of cultivated tree spices is narrowed by clonal propagation. Hence, the wild trees are essential as genetic resources. Breeding work in tree spices has received low priority. Even in "important” crops such as Ceylon cinnamon no breeding programmes are known to exist. For one thing this requires a long-term research commitment, the benefits of which will be available in the distant future. Fortunately, superior genotypes can in most cases be cloned; in this way, a selection can reach the grower within a reasonable number of years. An intimate knowledge of tree habit and phenology is needed before efficient breeding programmes can be designed. The same applies to breeding for disease and pest resistance: the relation between the life cycle of the pathogen and tree phenology has to be understood (Verhey & Coronel, 1991).

For a number of annual or short-lived perennial spice crops such as coriander, perilla and turmeric, germplasm collection and breeding work has received more attention. However, named, well-defined cultivars have only been developed in a limited number of species treated in this volume, and most of these originate from outside South-East Asia. Similarly, most germplasm collections are maintained outside the area. Institutes in India actively conduct breeding research on many of the aromatic plants highlighted here. Bilateral or regional cooperation between South-East Asian and Indian institutes would be beneficial.

Sweetening agents

Sources of sugar were dealt with in Prosea 9: "Plants yielding non-seed carbohydrates”. Sugar is the ideal sweetener, because it easily dissolves in water, its sweet taste has no unpleasant bitter or salt aftertaste, and it is rather cheap. It has considerable disadvantages, however. For instance, it is a major cause of dental decay and it contributes to obesity. Therefore, there has been a continuing search for sweetening agents that are low in energy value and even sweeter than ordinary sugar. There are some artificial sweeteners, such as saccharin (300-500 times sweeter than sucrose), cyclamate (30 times sweeter than sucrose), and aspartame (100-200 times sweeter than sucrose).

The following sweetening agents of plant origin are found in the following plants (Fox & Cameron, 1977; Rehm & Espig, 1991):

• miraculin, in the fruits of Synsepalum dulcificum (Schum. & Thonner) Baillon (syn. Richardella dulcifica (Schum. & Thonner) Baehni), which is able to make sour-tasting food taste sweet;

• monellin, in the fruits of Dioscoreophyllum cumminsii (Stapf) Diels, which is 3000 times sweeter than sugar;

• thaumatin, in the arillus of fruits of Thaumatococcus daniellii (Bennet) Benth., which is about 3 times sweeter than saccharin;

• stevioside, in the dried leaves of Stevia rebaudiana (Bertoni) Bertoni, being 200-300 times sweeter than sucrose.

In other cases, such as Perilla frutescens (L.) Britton, the plant contains substances that can be easily used for the synthesis of sweeteners (perillartine).

Since these sweetening agents are not carbohydrates, the plants producing them have not been treated in Prosea 9, but are dealt with in this volume.

Flavour enhancers

The most important flavour enhancer, common salt, is not of vegetable origin. Another important flavour enhancer is monosodium glutamate (umami taste) which is a white crystalline powder derived from vegetable protein. In Indonesia it is manufactured from sugar cane molasses (vetsin, ajino moto). Flavour enhancers may have little taste of their own, but they intensify the flavour of other products by making our taste buds temporarily more sensitive. Some "spices” act in the same way, the kemiri (==Aleurites moluccana== (L.) Willd.) being a nice example.

Uses

Worldwide, the popularity of spices as a basic food-flavouring ingredient has never waned through the years, quite the opposite: in more recent times, much interest has been focused on this special commodity. The interest has been attributed to a growing demand for natural and organic products, both food and non-food in nature, to complement an emerging lifestyle geared towards wholesome living. There is an increasing clamour to dispense with synthetic flavours and essences, artificial food colouring and too much salt in the daily diet, and spices nicely fulfill such a need.

The revived interest in spices has generally painted a more positive future scenario for this crop commodity. Particularly brighter prospects are envisioned for such spices as coriander, parsley, perilla, sage, sawtooth coriander, sweet basil and turmeric. For these and some other spices the greatest potential lies primarily in the development of products other than as flavouring materials per se.

Foremost among such products are the spices processed and manufactured into preparations aiding medicines in the treatment of various ailments through their adjuvant and alleviative qualities.

Essential oils and oleoresins from some spices can make excellent potent antioxidants while a number hold promise as natural biocides. The latter use is particularly significant in view of the ongoing global concern over the hazardous effects of synthetic pesticides on humans and the environment.

In recent years much attention has been devoted to the use of natural pigments as food colourants. The interest is related to the growing restrictions on the use of artificial colouring compounds. A number of spices could fill the need for these, with the extra benefit of imparting aroma, pungency and bitterness to foods and drinks.

Spices are also viable sources of industrial and other types of chemicals, e.g. peroxidase from horseradish, oestrogens from star anise, and diosgenin (a precursor of oral contraceptives and corticosteroids) from fenugreek.

Important as an added source of income to the spice producer is the prospective utilization of the biomass of some spices (e.g. torch ginger and candlenut tree) as a good source of pulp and paper. Others may well be suited for wood and timber production, e.g. cassia and cinnamon. Plant hobbyists and enthusiasts have started exploiting the potential of some spices as a viable component of the ornamental flower industry, e.g. dill, fragrant pandan, laurel, oxalis, rosemary, sweet basil, tarragon and torch ginger.

Marketing

Migration, intercontinental business and pleasure travel, together with the advent of modern satellite communication have all contributed as confluent factors in bringing countries of the world closer to one another, bridging distant cultures, particularly in regard to food habits and cuisines. Exotic oriental dishes are being introduced into the United States and Europe, and so are the vegetables and spices (including their production know-how) peculiar to the preparation of these cuisines. Several spices used in Vietnamese cooking, e.g. fragrant pandan, rau ram and sawtooth coriander have gained popularity in the Western world. In the Philippines savoury herbs such as dill, oregano and tarragon, commonly utilized in Western dishes, have also been introduced and have become established as a lucrative fresh-herb market niche catering to first-class hotels, restaurants and fast-food chains. Production ventures involving this group of spices are profitable; however, the market is rather limited, cultivation is labour-intensive and small-scale plantings can sufficiently satisfy the local requirement.

Production and marketing are generally well-established for some spices, e.g. caraway, cardamom, cinnamon, dill, laurel, mustard, nutmeg, pepper and pimento. In some instances, market growth parallels the increase in population, but current suppliers are expected to fill the need for any additional future increase in demand.

Many fresh culinary herbs in the traditional production areas in temperate and Mediterranean regions are only available for part of the year. This gives tropical countries plenty of opportunities to fill the gap.

Research

The brighter prospect envisioned for a number of spices can only be realized if it is coupled with diligent scientific research, particularly if the development of products other than flavouring agents is pursued. Preliminary indications of the effectivity of spices and spice products for their medicinal, pesticidal and other biological values should be subjected to further rigorous testing. If subsequently confirmed, there will be a need to conduct cost-benefit analyses for formulating such products and to assess realistically their market potential.

The chemical constituents of lesser studied spices, e.g. Chinese keys, galanga, Zingiber montanum (Koenig) Dietrich and Z. zerumbet (L.) J.E. Smith, need to be characterized and their biological activities examined for various applications, so that their potential can be fully exploited.

For some spices, research should focus on cultivation aspects. The development or improvement of agronomic practices and efficiency of harvesting and processing should be looked into for spices such as coriander, fragrant pandan, galanga, stevia, star anise and turmeric, to maximise production. Appropriate silvicultural techniques for camphor-wood production need to be worked out in detail for cinnamon and cassia, if silvicultural ventures are deemed viable in the long term.

Countries in South-East Asia cannot compete in the production of some spices for global trade, e.g. caraway, chervil, fenugreek, horseradish and summer savory, as these require temperate growing conditions. However, if intended as local import substitute or to satisfy foreign tourists or expatriates, then production trials can be performed and yield responses determined in the cooler, upland areas of South-East Asia.

Hydroponic culture may provide an efficient method for optimizing crop yield. Its use on a few culinary herbs has gained a considerable following in the United States, Japan and industrialized countries of Europe. The initial capital investment cost and the relatively sophisticated technical skills required in the management of such a system has precluded its use not only in South-East Asia but also in other developing regions. Recently a simple non-circulating hydroponic system has been developed for vegetables, showing promise for use in culinary herbs (Midmore, 1994). This method could be looked into, together with other soilless cultivation techniques.

Another interesting research topic for spices is the in vitro culture for secondary metabolite production. Few spices have been investigated in this regard and little success has been attained in laboratory trials so far. The production of bioactive chemicals is still experimental.

Breeding work should also be one of the research priorities on spices, with the primary goal of obtaining high quality and yield of the desired product. Resistance to diseases, pests and environmental stress should also be an important objective of crop improvement. In the case of spices whose flowering and/or seed-setting remain stumbling blocks to conventional breeding work, e.g. ginger, tarragon and turmeric, biotechnological and tissue culture approaches such as selection for somaclonal variants, protoplast fusion, and recombinant DNA technology may be worth resorting to. Not many crop physiological studies have been carried out on spices. This is unfortunate, since a number of interesting physiological phenomena need to be investigated: the mechanism of shade tolerance of pepper and vanilla, the nature of recalcitrant seeds in cinnamon, clove, laurel and pimento, the variation in the growth rhythm in clove, and the influence of daylength and temperature on the vegetative and reproductive stages of spices such as oregano, sage, stevia and tarragon.

Finally, the taxonomy of some spices and their relatives, e.g. Cinnamomum, Piper and Thymus, is poorly known and has often engendered considerable confusion in the literature. Application of modern chemotaxonomy may provide a tool to establish appropriate evolutionary linkages in this regard.

Despite the role played by spices during thousands of years to titivate the palate and olfactory nerves and to fulfill our gustatory desires, research on spices is wanting compared with other economically important crops. A more critical view of this commodity and serious consideration of several suggested avenues of research mentioned above is called for, in view of the growing importance of spices in the modern world.

Tables on standard physical properties of some dried spices

The data presented here have been issued by the International Standardization Organization (ISO). ISO standards are determined in accordance with standard procedures. The procedures used to determine the parameters in this table are stipulated in the following standards:

• ISO 927-1982: Determination of extraneous matter content.
• ISO 928-1980: Determination of total ash.
• ISO 930-1980: Determinatioin of acid-insoluble ash.
• ISO 939-1980: Determination of moisture content - Entrainment method.
• ISO 6571-1984: Determination of volatile oil content.

In the last column the number of the standard referring to the spice in question is given. If available, the ISO standard with the year of its publication is indicated. ISO/DIS refers to a standard that is currently under review.

Tables on standard physical properties of some spice oils

Most of the data presented here have been issued by the International Standardization Organization (ISO). ISO standards are determined in accordance with standard procedures. The procedures used to determine the parameters in this table are stipulated in the following standards:

• ISO 279-1981: Determination of relative density at 20 °C.
• ISO 280-1976: Determination of refractive index.
• ISO 592-1981: Determinatioin of optical rotation.
• ISO 875-1981: Determination of miscibility in ethanol.

In the last column the number of the standard referring to the essential oil in question is given. If available, the ISO standard with the year of its publication is indicated. ISO/DIS refers to a standard that is currently under review. If no ISO standard was available for an essential oil, the information was supplemented with data published in the Food Chemicals Codex (FCC) (Committee on Food Chemicals Codex, 1996).