Foeniculum vulgare (PROSEA)
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Introduction |
Foeniculum vulgare Miller
- Protologue: Gard. Dict., ed. 8 no. 1 (1768).
- Family: Umbelliferae
- Chromosome number: 2n = 22
Synonyms
- Anethum foeniculum L. (1753),
- Foeniculum capillaceum Gilib. (1782),
- F. officinale Allioni (1785).
Vernacular names
- Fennel (En).
- Fenouil, aneth doux (Fr)
- Indonesia: adas (general), adas londo (Javanese), hades (Sundanese)
- Malaysia: adas pedas
- Philippines: anis, haras (Tagalog)
- Laos: phak s'i:
- Thailand: thian-klaep, phakchi-duanha (northern), yira (Central)
- Vietnam= tiểu hồi hương
Origin and geographic distribution
Fennel most probably originated from southern Europe and the Mediterranean. It is cultivated throughout the world and has naturalized in many places. It is grown throughout South-East Asia and is subspontaneous on several mountains in East Java; for example, it is common on Mt. Tengger.
Uses
Fennel has been used for flavouring since antiquity; young leaves as well as fruits (referred to in the spice trade as "seeds”) are used for this purpose. The leaves are eaten raw or more commonly cooked. The leaves are also used as a pot-herb, especially in fish sauces and garnishing. Ground fennel fruit is often a constituent of curry powder. In Java, fennel is eaten as lalab and used to season pickles. Stem pieces are chewed for their pleasant taste. Several sweet and common or bitter fennel cultivars are applied in the food industry to flavour, for instance, beverages, candies, baked goods, meat and meat products, gravies and processed vegetables. The swollen basal parts of the petioles ("bulbs") of cv. group Florence Fennel are cooked as a vegetable like celery, mainly in Italian cooking.
All plant parts contain essential oil, which is used for flavouring and in detergents, cosmetics such as soaps, creams, lotions and luxury perfumes. Sweet-fennel oil is extensively applied in food products, including alcoholic and non-alcoholic beverages, desserts, candies baked goods, meat and meat products, condiments and relishes. The maximum permitted level in food products is about 0.3%. Bitter and sweet-fennel oils are applied in perfumery, with maximum permitted levels of 0.4%. Bitter-fennel oil is used to a limited extent and mainly in cosmetics. Anethole obtained from sweet fennel is applied as a flavouring agent and in the pharmaceutical and perfume industries but anethole from cheaper sources is usually available. The fruit residue after essential-oil distillation may be fed to cattle. In the United States the regulatory status "generally recognized as safe" has been accorded to common or bitter fennel (GRAS 2481), sweet fennel (GRAS 2482) and sweet-fennel oil (GRAS 2483).
The medicinal use of fennel also dates from ancient times. It was mentioned by Hippocrates and Dioscorides as a diuretic and emmenagogue, and has been used as a main ingredient in the Arab and Ayurvedic medicinal systems. The fruits are widely known as a stimulant, stomachic, expectorant and carminative, and are official in many pharmacopoeias. The roots are traditionally applied as a diuretic and purgative. In Indonesia, the fruit is traditionally used in combination with the bark of Alyxia species, to give an agreeable flavour to medicines, but the combination is also believed to be useful in the treatment of sprue. In India, the leaves are considered diuretic, fruit juice is administered to improve the eye-sight, and hot infusions of the fruits are applied to increase milk secretion and to stimulate sweating. In Chinese herbal medicine, fennel is used against gastro-enteritis, hernia, indigestion and abdominal pain, to resolve phlegm and to stimulate milk production. In modern western medicine, fennel and fennel oil are administered as a carminative or flavouring agent in certain laxatives. In Germany, the fruits are used in phytomedicine against dyspeptic disorders, as a gastro-intestinal antispasmodic, as an expectorant and in syrups against children's coughs.
Production and international trade
Few trade statistics are available for fennel alone but it is one of the most important aromatic spices in the category "spice seeds" in the international market. It is estimated that in the period 1976-1980, annual world imports of spice seeds as a whole averaged about 50 000 t. India, China and Egypt are the main suppliers of fennel. In 1988 the United States imported 1750 t fennel fruits, valued at US$ 1.8 million. The annual value averaged US$ 3.4 million over the period 1990-1994. India alone produces annually 20 000 t fennel fruits, of which 2000 t are exported. The main producer of Florence fennel is Italy, with an area of 18 000 ha and an annual production of 400 000 t "bulbs".
The estimated world production of essential oil from bitter fennel is about 28 t, that of sweet fennel about 255 t. In 1993 the total value of the essential oils was estimated at US$ 700 000 and US$ 7.7 million respectively.
Properties
Sweet-fennel fruits smell strongly of anise, and have a penetrating and sweet taste, whereas those of bitter or common fennel have a pungent odour and taste like camphor. Fennel "seed” contains per 100 g edible portion: water 8.8 g, protein 15.8 g, fat 14.9 g, carbohydrates 36.6 g, fibre 15.7 g, ash 8.2 g (Ca 1.2 g, Fe 19 mg, Mg 385 mg, P 487 mg, K 1.7 g, Na 88 mg, Zn 4 mg), vitamin A 135 IU, niacin 6 mg, thiamine 0.41 mg and riboflavin 0.35 mg. The energy value is about 1440 kJ/100 g. The lipid fraction contains 9.9 g total mono-unsaturated and 1.7 g total poly-unsaturated fatty acids. The fixed oil is mainly composed of petroselinic acid 60-75%, oleic acid and linoleic acid. The fruits also contain flavonoids and stigmasterol.
The essential oil is present in secretory channels in most parts of the plant, but in mature fennel about 95% of the oil is located in the fruit. The essential oil yield after hydrodistillation of the fruits is 1.9-3.1%. The oil obtained from sweet fennel possesses a finer odour and flavour than that from bitter fennel. The major compound of sweet-fennel oil is (E)-anethole (up to 70-80%), which is responsible for the anise fragrance and sweet taste. The (E)-anethole content of bitter-fennel oil is only half that of sweet fennel, whereas the fenchone content is higher. Fenchone is considered a character-impact constituent of bitter-fennel oil.
The concentration of major compounds of the essential oil varies with plant part and development stage. In bitter fennel populations from different origins it was found that the anethole and fenchone concentrations were higher in the waxy and ripe fruits than in the stems and leaves, whereas the α-pinene concentration showed an opposite trend. Furthermore, the anethole and fenchone concentrations increased from the bud stage until fruit ripening, whereas the α-pinene and limonene concentrations decreased. The estragole concentration varied only slightly. The composition of essential oil from the roots is very different from that from the rest of the plant, with terpinolene, myristicin and apiole being the main compounds.
The residue after essential-oil distillation from fennel fruits contains 14-22% protein and 12-18.5% fat.
The ground spice and the essential oil have antioxidant properties, whereas the essential oil has antifungal and antibacterial activity. The essential oil also possesses antiviral activity against potato virus X (PVX), tobacco mosaic virus (TMV) and tobacco ringspot virus (TRSV), and shows spasmolytic effects on smooth muscle of experimental animals. Monographs on the physiological properties of sweet-fennel oil and bitter-fennel oil have been published by the Research Institute for Fragrance Materials (RIFM).
With respect to individual compounds, anethole is effective against Staphylococcus aureus, Escherichia coli, Candida albicans and Corynebacterium sp. and has stimulant and carminative properties. Furthermore, it is allergenic and weakly insecticidal. Long-term studies have shown that anethole is not carcinogenic. The oestrogenic activity (e.g. increasing milk secretion and promoting menstruation) of fennel is probably due to polymers of anethole, such as dianethole and photanetholes. Estragole is a hepatic carcinogen in mice. In experiments with rats, limonene limited mammary tumour growth.
The 1000-seed weight is 4-8 g.
Composition
Sweet-fennel oil (from Italy) (Source: Piccaglia & Marotti, 1993)
- 87.1% (E)-anethole
- 4.7% limonene
- 3.5% (Z)-anethole
- 2.1% fenchone
- 0.4% 1,8-cineole
- 0.3% α-pinene
- 0.2% myrcene
- 0.1% para-cymene
- trace camphor
- trace camphene
- trace linalool
- trace menthol
- trace menthone
- trace (E)-β-ocimene
- trace (Z)-β-ocimene
- trace α-phellandrene
- trace β-pinene
- trace sabinene
- trace terpinen-4-ol
- 98.4% total
Bitter-fennel oil (from Italy) (Source: Piccaglia & Marotti, 1993)
- 81.9% (E)-anethole
- 10.2% fenchone
- 4.9% limonene
- 1.7% (Z)-anethole
- 0.4% α-pinene
- 0.2% camphor
- 0.2% myrcene
- 0.1% menthol
- 0.1% para-cymene
- 0.1% sabinene
- 0.1% (Z)-β-ocimene
- trace camphene
- trace 1,8-cineole
- trace linalool
- trace menthone
- trace (E)-β-ocimene
- trace α-phellandrene
- trace β-pinene
- trace terpinen-4-ol
- 99.8% total
Adulterations and substitutes
Commercial spice samples are sometimes adulterated with sand, stem tissue, fruit residues left after distillation, immature or mouldy fruits or with other umbelliferous fruits. Fennel fruits and those of anise (Pimpinella anisum L.) are often confused and substituted for each other.
Anethole-rich oil is also obtained from anise and star anise (Illicium verum Hook.f.). The cultivation of fennel as a source of anethole was developed in Europe to reduce the dependence on anethole obtained from star anise in Asian countries. Anethole can also be produced chemically, either by hemisynthesis from estragole (e.g. extracted from Pinus oil) or by complete synthesis. However, in some countries the use of synthetic anethole for food products is prohibited by law.
Description
- Robust, perennial, glabrous, glaucous, aromatic herb, up to 2 m tall. Stem erect, terete, longitudinally striate, profusely branched at all heights, internodes hollow when older.
- Leaves alternate, decompound, sheathed, lower leaves largest; leaf sheath forming an open cylinder, at base embracing the stem, 2-15 cm long, margins white scarious, sheath much larger and fleshier in Florence fennel; rest of petiole subterete, 0-10 cm longer than the sheathing part, longitudinally striate; blade triangular in outline, up to 30 cm × 50 cm, 2-6-pinnately divided into fililorm, acute, blue-green lobes 1-14 cm long; primary pinnae odd-numbered 3-19.
- Inflorescence a terminal, compound umbel, up to 20 cm in diameter but usually smaller; peduncle (1-)5-16(-24) cm long; primary rays 5-30(-70) per umbel, 0.5-12 cm long, unequal in length, the shortest ones in the centre; secondary rays (pedicels) (2-)10-30(-45) per umbellet, up to 1 cm long, unequal in length; involucre and involucels absent.
- Calyx vestigial at the top of the ovary; petals 5, distinct, subovate in outline, up to 1.5 mm × 1 mm, with strongly inflexed, notched apex, yellow, with a thin membranous outgrowth on the ventral side of the midrib; stamens 5, about 1.5 mm long; pistil with inferior, bilocular ovary, 2 styles, each with a stylopodium at base and a stigma at top.
- Fruit an ovoid-cylindrical, usually slightly curved schizocarp, 3-8.5 mm × 2-2.5 mm, light green to yellow-brown, splitting at maturity into 2 mericarps each with 5 prominent ridges and oil-vittae between the ridges.
- Seed with testa adnate to the pericarp.
- Seedling with epigeal germination.
Growth and development
Seeds normally germinate within 2-3 weeks after sowing. Initial development is slow, with a period of 2-2.5 months from sowing to stem emergence. Flowering occurs 3-4 months after sowing, and the time from sowing to first fruit harvest is 5-7 months. Fruit yield of the second year is generally higher than that of the year of sowing. Fennel is mainly cross-pollinated, and fruit ripening is uneven. Florence fennel is generally grown as an annual.
Other botanical information
The taxonomy of Foeniculum is not yet well established. Generally only one species (F. vulgare) is distinguished, which is often subdivided into 2 subspecies: subsp. piperitum (Ucria) Coutinho (wild taxa) and subsp. vulgare (cultivated taxa). The group of cultivated taxa can best be classified into cultivar groups and cultivars. Several cv. groups can be distinguished:
- cv. group Bitter Fennel or Common Fennel (other names: F. vulgare Miller var. vulgare; cultivars have fruits with a bitter aftertaste;
- cv. group Florence Fennel (other names: F. azoricum Miller, F. vulgare Miller var. azoricum (Miller) Thellung, finocchio; cultivars with swollen basal part of the petiole which is eaten cooked as a vegetable;
- cv. group Sweet Fennel (other names: F. dulce Miller, F. vulgare Miller var. dulce (Miller) Battand. & Trabut, Roman fennel; cultivars with sweet-tasting fruits.
Other cv. groups and cultivars have been distinguished on the basis of the composition of their essential oil.
Fennel is often confused with dill (Anethum graveolens L.), which is closely related and easily crosses with fennel. Fennel and dill can be distinguished by their odour (fennel smells like liquorice, dill smells bitter and slightly pungent) and their ripe fruits (fennel has wingless fruits, dill fruits have a wide wing). Fennel plants without fruits may be recognized by their finely dotted stems, the longer and broader leaf-sheaths and the usually shorter secondary rays in the umbel.
Ecology
Fennel prefers sunny locations in fairly mild climates. In India, it is grown as a cold-weather crop in the north and does not perform well in the south, except at higher elevations. In Java, it is found at altitudes from 500 m upwards. The tops are injured by long cold spells and fennel is therefore cultivated as an annual in temperate regions. Fennel is found under conditions of 500-2000(-4000) mm mean annual rainfall and 6-12(-24) °C mean annual temperatures. Moisture stress causes the basal stalk to split. In Tasmania it has been shown experimentally that fennel (cv. C25) is a long-day plant, with umbel initiation and stem elongation occurring at photoperiods longer than 13.5 h per day.
Fennel thrives in non-acid, well-drained loams and tolerates a soil pH between 6.3 and 8.3. It is salt-sensitive.
Propagation and planting
Fennel is normally propagated by seed, though vegetative multiplication by root or crown division is also possible. Seed germinates well between 15-20(-25) °C, with better germination in dark than in light, and it retains its viability for 2-3 years. Propagation through in vitro culture is also possible. Callus may be produced from explants (hypocotyl, stem or petiole) in MS medium at 25 °C. From callus, plants may be regenerated through embryogenesis or organogenesis, or cell suspension cultures may be formed.
Seeds are usually sown in drills, 35-120 cm apart. Within the row seedlings are thinned to 15-50 cm when 8-10 cm tall. The sowing depth is 1-3 cm. Seed may also be sown first in a seedbed and seedlings transplanted when 7.5-10 cm tall. Transplants are often used in Florence fennel cultivation in northern temperate zones to assure a mature crop within a short growing season. The seed rate is either 3-5 kg/ha when using seedbeds and transplanting or 10-15 kg/ha for direct sowing. The seedbed should be roofed or covered with straw until the seeds germinate, about 2-3 weeks after sowing. Seedlings are ready for transplanting about 2-2.5 months later, when they are 10 cm tall.
In Indonesia, fennel is usually planted in home gardens.
In vitro production of active compounds
The use of cell cultures has no importance for the production of fennel essential oil or anethole. In callus cultures and cell suspensions of fennel, hardly any or no aromatic compounds were found. In tissue colonies derived from plantlet apices very small amounts of anethole were produced.
Husbandry
Fennel should be kept free from weeds, especially during the initial growth period. A fennel crop may develop a large vegetative mass (40-60 t/ha) for which ample nutrient supply is required. However, too much nitrogen should be avoided, as this may result in disproportionately high vegetative mass and poor fruit development. In India, 20-30 t farmyard manure per ha is usually applied at planting and 45 kg/ha N as top dressing. In various parts of India it has been experimentally shown that 80-100 kg/ha N and 40 kg/ha P is optimal.
Fennel is usually grown as an irrigated crop in India. Under European conditions, irrigation stimulated both crop growth and the essential oil content of the fruits. Under dry summer conditions in Tasmania, total biomass yield was increased most by irrigation during the stem elongation phase, whereas umbel dry weight and umbel oil yield were increased most by irrigation at late flowering. The anethole content of the umbel oil was not affected by irrigation.
Florence fennel may be earthed up when the shoot base starts to swell, to encourage blanching.
Diseases and pests
In India the most important disease is powdery mildew caused by Leveillula taurica, characterized by white, powdery patches on the plant and shrivelling and shedding of fruits. Fennel is also susceptible to fungal diseases caused by Cercospora and Sclerotinia spp. Aphids are the most important insect pest.
Harvesting
Tender shoots and leaves for culinary purposes should be gathered before flower-bud formation. Fruits are harvested when they are sufficiently hard and waxy in appearance, which is usually 5-7 months after sowing. Not all umbels on a plant mature at the same time. Umbels are ready for harvesting when they turn brown. If harvested late, fruits are liable to shatter; if harvested early they are immature and of lesser quality. Selective harvesting of fully mature umbels is desirable but labour-intensive. To reduce labour costs, entire plant tops can be cut when the fruits on the side branches are nearing the waxy stage. When harvesting the crop several times in a season, the best fruits and best oil quality are usually obtained from the first harvest.
Florence fennel is harvested after enlargement of the "bulbs”. The top of the foliage is removed just before flowering, followed later on by the remainder of the plant, after which the roots are cut away. Bulbs with some foliage are cleaned of soil and debris, washed and stored.
Yield
Fruit yields range from 0.5-2 t/ha, but yields are low in the first year. European fruit yields are 0.4 t/ha in the first, 1-2 t/ha in the second, and 0.6-1.5 t/ha in the third year. Average fruit yields in India are 0.5-0.7 t/ha, reaching up to 1.5 t/ha with adequate management.
Handling after harvest
The harvested material should be dried carefully in the shade, since sun-drying will lead to loss of essential oil. After drying, fruits are separated from the stems and cleaned. For essential-oil production, fruits are then crushed and immediately distilled to prevent loss of oil by evaporation.
Genetic resources
Many countries have some fennel germplasm in their collections. In Europe some larger collections are available in Russia (St. Petersburg, N.I. Vavilov Research Institute of Plant Industry with 128 accessions), Germany (Braunschweig, Institute of Crop Science with 72 accessions) and in France (Brion, Unité Experimentale d'Angers, Groupe d'Etude et de Contrôle des Variétés et des Semences (GEVES) with 52 accessions). As fennel is cultivated and naturalized throughout the world, there is no danger of genetic erosion.
Breeding
As cross-fertilization is predominant in fennel, most cultivars are highly heterozygous and heterogeneous. High seed-yielding cultivars have been obtained in Europe and India, as well as cultivars tolerant of aphids. Present selection work on sweet and bitter fennel is mainly aimed at increased fruit yield and fruits with high anethole content. Other objectives include resistance to parasites, reduced stem size and precocity. In Europe, a range of commercial cultivars of Florence fennel is available.
Prospects
Because fennel prefers mild climates and needs long days for flowering, the prospects for the crop as a source of fruits and essential oil in South-East Asia are limited. It is likely that its present role as locally used condiment for the vegetative parts, vegetable and medicine will remain, but an increase in use and cultivation is not to be expected.
Literature
- Bernáth, J., Németh, E., Kattaa, A. & Héthelyi, E., 1996. Morphological and chemical evaluation of fennel (Foeniculum vulgare Mill.) populations of different origin. Journal of Essential Oil Research 8(3): 247-253.
- Boelens, M.H., 1991. Spices and condiments II. In: Maarse, H. (Editor): Volatile compounds in foods and beverages. Marcel Dekker, New York, United States. pp. 449-482.
- Buntain, M. & Chung, B., 1994. Effects of irrigation and nitrogen on the yield components of fennel (Foeniculum vulgare Mill.). Australian Journal of Experimental Agriculture 34(6): 845-849.
- Földesi, D. & Hornok, L., 1992. Fennel (Foeniculum vulgare Mill.). In: Hornok, L. (Editor): Cultivation and processing of medicinal plants. John Wiley & Sons, Chichester, United Kingdom. pp. 162-166.
- Hunault, G., Desmarest, P. & du Manoir, J., 1989. Foeniculum vulgare Miller: cell culture, regeneration and the production of anethole. In: Bajaj, Y.P.S. (Editor): Biotechnology in agriculture and forestry. Vol. 7. Medicinal and aromatic plants 2. Springer Verlag, Berlin, Germany. pp. 185-212.
- Husain, A., 1994. Essential oil plants and their cultivation. Central Institute of Medicinal and Aromatic Plants, Lucknow, India. pp. 240-245.
- Leung, A.Y. & Foster, S., 1996. Encyclopedia of common natural ingredients used in food, drugs and cosmetics. 2nd edition. John Wiley & Sons, New York, United States. pp. 240-243.
- Peterson, L.E., Clark, R.J. & Menary, R.C., 1993. Umbel initiation and stem elongation in fennel (Foeniculum vulgare) initiated by photoperiod. Journal of Essential Oil Research 5: 37-43.
Sources of illustrations
Jansen, P.C.M., 1981. Spices, condiments and medicinal plants in Ethiopia, their taxonomy and agricultural significance. Centre for Agricultural Publishing and Documentation (Pudoc), Wageningen, the Netherlands. Fig. 2, p. 23 (flowering branch, flower at male flowering stage, flower at female flowering stage, fruit, cross-section of fruit); Hegi, G., 1906--1931. Illustrierte Flora von Mitteleuropa. Lehmanns Verlag, München, Germany. Vol. 5 (1926). Fig. 2486, p. 1289 ("bulb" of Florence fennel). Redrawn and adapted by P. Verheij-Hayes.
Authors
- Purwaningsih, Harmida & M. Brink
