Dill Production - Compounds influencing flavour

Dill

Introduction

Dill (Anethum graveloens Linn.) is an annual aromatic branched herb known for culinary use since ancient times. It is a native of south-east Europe and is cultivated commercially in most parts of Europe, particularly The Netherlands, Hungary, Germany, Romania, South Russia, Bulgaria and on a lesser scale in France, Sweden, Belgium, Poland, Greece, Spain, UK, Turkey and the United States of America. A variant called east Indian dill or Sowa (Anethum graveloens var sowa Roxb. ex, Flem.) occurs in India and is cultivated for its foliage as a cold weather crop throughout the Indian sub-continent, Malaysian archipelago and Japan. The earliest reference to use of dill seed in medicine goes back to Charak Samhita 0 BC , an ancient renowned medical treatise on Indian medicinal plants.

Dill foliage, fruits and their volatile oil are used extensively for culinary and medicinal purposes. The fresh aromatic leaves are used in flavouring of soups, sausages, curries, gravies, salad, marinades and pickles; the leafy stems and tops are used in flavouring vinegar, pickled cucumber and fermented cabbages, whereas the seed is used for flavouring meat. In Malaysia and Indonesia, the leaves are steamed with rice whereas fruits are used in flavouring native confectionery. Balkan countries use dill in flavouring yogurt, sour cream and wine. In Sweden, bread is flavoured with dill seed. Dill fruit faintly resembles caraway in odour but has a less sharp taste. It is a popular condiment in Asian countries and is used in seasoning several types of processed meat. The leaf oil has largely replaced the use of the fresh herb in the food industry in Europe.

The International Trade Centre (Anon. 9 ) has brought out a material survey of four west European countries (France, UK, The Netherlands and Germany) estimating an overall demand of freeze-dry herb to be less than 0 tonnes per annum. France produces a small quantity and imports it from Egypt, Israel, The Netherlands and Morocco. The Netherlands and Germany are larger producers and import a part of their demand from Hungary. The USA is said to import between 0 and 0 kg of herb oil annually, largely from Hungary. India exports 0 to 0 tonnes of seed annually to west Asian countries

and a small quantity of dill seed oil to western Europe. Varshney ) has reported world production of dill weed oil as 0 tonnes and that of dill seed oil as 0 tonnes; the seed oil is produced mainly in India, Russia and Poland.

Dill is characterized by long dissected leaves and compound radiating umbels. It grows to between 1 and 1.2 m in height under cultivation. Dill is an annual glabrous, long-day plant with long fusiform (1015 cm) tap root with few secondary rootlets. The stem is erect, dull-green, glaucous, cylindrical, fistular with longitudinal light-green streaks, up to 1.5 cm thick around the base. It is subdichotomously branched, usually above the basal few nodes. Leaves are decompound, tripinnati-partite with ultimate segment 515 ( 20) mm long and

mm wide. Flowers are small, bisexual, more in outer unbellules (3040) than inner ones (1520), and opens centripetally. The fruit is oblong, slightly plano-convex in shape, dorsally compressed, 34 mm long and 1.53.0 mm broad, glabrous, with three prominent longitudinal ridges, developed into thin broad wings, 0.250.5 mm wide. Dill flowers in JuneAugust and fruiting takes place in AugustOctober in Europe, while it is February March and MarchApril respectively in India.

In the Sowa plant, the fruits are longer, ( 5) 5 ( ) mm in dimension, with three longitudinal ridges on the dorsal side more pronounced than the (European) dill. The carpophore holds two mericarps more firmly and consequently these remain joined together in the fruit for a longer time. The vittae has irregular marginal walls in contrast to straight walls in the dill. It has a number of local races like Vizak Sowa, Variyali Sowa and Ghoda Sowa distinguished by the oil composition of their fruits (Shah and Quadri, ; Randhawa and Kaur,

Production

Dill is grown as an irrigated annual crop both in temperate and tropical regions up to

0 m (m.s.l . The crop remains in the field for 5 to 0 days. In India, sowing is staggered at a fortnights interval (Octmid-December) to obtain fresh foliage crop, marketed throughout the winter season. A large number of varieties are known in cultivation (Randhawa and Kaur, . Dill prefers light sandy to loamy well drained fertile soils, slightly acidic to neutral in reaction; the pH extends to 5 in sub-tropical parts of India. It prefers warm sunny weather, particularly cool moist climate favours vegetative growth and warm, drier and sunny conditions are needed for luxuriant flowering and fruiting to ensure a high crop yield.

The seed is sown directly during the spring season (FebruaryMarch) in temperate climate and October in tropical conditions. Seed rate is 5 to 0 kg per hectare depending on the method of sowing, viz. drilling in rows or broadcast; usually it is sown in rows, 1.5 to 0 cm deep at 0 to 0 cm apart and spacing at 5 0 cm is found to produce high seed yield in India (Gupta, . Germination commences after a week in tropical regions and may take two weeks in warm temperate conditions. Pre-emergence application of herbicide like Prometryne %) at 0 kg per hectare is recommended

(Timoshenko, . The plants are thinned when 7 to 0 cm tall at 5 to 20 cm apart in the rows. The crop remains 40 to 7 days in vegetative stage (after germination) and flowering/fruiting continues for the next 5 to 0 days. Powdery mildew (Erysiphae spp.) sometimes attack the crop at flowering, occasionally causing severe damage for which spraying of Bordeaux mixture three to four times at weekly intervals is recommended. Similarly, aphids (Myzus spp) suck flowering axils causing loss in growth vigour and weekly spraying of Melathione ) in water controls the infestation.

The crop responds favourably to use of inorganic fertilizers depending on the nutrient status of the soil. Atanasov et al. ) observed that application of 0 kg per hectare each of N, P O and K O produced maximum herbage yield and most economic oil yield in Bulgaria. In India where soils are rich in potash, 0 kg of N and 5 kg of P O₅ per hectare produced maximum seed yield (Gupta, . Usually, five to eight light irrigations are given to the seed crop. Two rounds of weeding cum hoeing given between

and 0 days and 0 and 0 days suffice to control weeds; later growth of the crop covers the field and smothers weeds.

The herb oil is a colourless to brownish-yellow mobile liquid. The fresh herb at vegetative stage contains % of oil, which progressively increases with growth and is

9% at flowering, rises to % at milky-wax seed ripening and 4% in the herb when the seed is nearing maturity. For herb oil, the crop is harvested when it is between maximum flowering to beginning of fruit formation stage as oil content in the leaves is high and the oil has a lower amount of oxygenated compounds. In Germany and The Netherlands, the entire over-ground crop is harvested at blooming stage (with no seeds) whereas milky-wax to mid-ripe fruiting stage is preferred for obtaining herb oil

(dill weed oil) in Hungary and USA. As a matter of fact, the relative quantity of fruits present in the harvested material and their state of ripening determine the oil content and flavour of the oil produced on distillation. On average 5 to 0 tonnes of fresh herb per hectare is produced when the crop is harvested at maximum flowering stage, which on distillation give 8 to 0 kg of herb oil, containing up to % carvone. Harvesting at later stages increased oil yield and its carvone content progressively.

In the seed crop, the terminal umbels are hand-picked when the fruit begins to turn yellowish-brown in colour; these come to maturity 0 days early. The rest of the crop is cut from the base later when tertiary umbels begin to turn brownish; delay may cause seed shattering leading to crop loss. The harvested crop is transported to the threshing floor where it is dried in a thin layer for one or two days before carrying out light threshing to separate the fruits. It is found that the milky-waxy fruit maturity stage contains maximum seed oil (Zlatev, 7 ; the carvone and dihydrocarvone contents accumulated rapidly in the later part of fruit maturity. The seed yield ranges from 0 to

0 kg per hectare and shade dried seed contains % oil; the seed yield in east Indian dill (Sowa) is higher 1 tonne per hectare

The wilted dried plants show a decrease in carvone content over the fresh herb at every stage of growth until flowering, but this trend is reversed in fruiting herb as wilted, dried and stored material showed an increase in carvone content in the oil. As a matter of fact, the dried herb produces oil emitting poor intensity of odour. The mature stored seeds yield a higher quantity of carvone because some of the terpines in the seed are lost during storage; this could be protected by storing seed in gunny bags, lined with polythene in a dry cool place.

The essential oil of herb as well as seed crop is obtained through hydrodistillation or steam distillation and complete exhaustion of the produce takes 0 and 5 hours respectively for herb crop and 8 to 0 hours for seed crop; the seed are crushed into powder to facilitate easy extraction of the oil. During the first one or two hours, the distilled oil has high d-carvone content and the broad ratio between carvone and limoanene is ) : ; because carvone is more easily soluble in water and being higher boiling fraction, it is distilled easily. This trend declines at a later stage. The wilted

(herb) material should be distilled within 2 hours.

Chemical composition Lawrence ) analysed dill herb using IR as a method of characterization of individual constituents by preperative GC and column chromatographic fractions. He reported the oil to contain -pinene , -pinene % , myrcene , -phellandrene

% , limonene % , -phellandrene % , p-cymene , terpinolene

% , -p-dimenthylstyrene , epoxy-p-menthlene , cis-p-mentha-2,8- dien-lol , transdihydrocarvone , cis-dihydrocarvone , carvone

% , di-hydrocarveol % , cis-carvyl acetate % , trans-carveol % , cis- carvyl acetate , trans-carveol , dihydrolimonene-10-ol , dihydrolimenon e10-yhexanoate % , p-mentha-l, 3-dien-10-yl-hexanoate %) and p-mentha-1(7), 2-dien-10-yl butyrate %) besides a host of other compounds in traces.

Lawrence ) has reproduced chemical composition of seed oil obtained through solvent extraction by Kodam at Leiden University (doctorate dissertation). It was found to contain limonene , d-p, dimethylstyrene , transhydrocarvone (0.4%), cis-dihydrocarvone , neodihydrocarveol , carvone , dihydrocarveol

% , isodihydrocarveol , trananethole % , trancarveol %) and cis- carveol ) besides many other compounds in traces. An interesting feature of growing dill is that after successive generations, the European dill develops higher oxygenated compounds in the oil, which includes a small quantity of dillapiole. It was found to contain up to % of dillapiole (Baslas et al., ) when grown under tropical climate. Gupta ) explained this as being due to more sunlight hours combined with solar intensity in the tropics.

Compounds influencing flavour

The principal constituents of the herb oil are phellandrene and limonene whereas ketone

(calc. as carvone) in the oil increases from % (vegetative stage) to % (maximum bloom) and rises to % at the milky-wax stage, when its herb character predominates. In trade, the oils containing % or less carvone have been found to be of finest flavour

(Guenther, . The herb oil has a powerful sweet-spicy, peppery and aromatic odour, reminiscent of spearmint oil with a sweet nutmeg-like undertone. The taste is warm and slightly burning, but pleasant and not pungent

For flavouring purposes, the herb oil with low ketones (carvone) is preferred. The typical flavour of the oil is due to -phellandrene (terpine) as the oil resembles the fresh herb in aroma. Haupalehti ) determined that -phellandrene, limonene, myrsticin and dill furan were the most significant contributors of dill herb aroma. Later, Blank et al.

) determined that the aroma of dill herb was directly related to concentration of five components namely dill-furan, -phellandrene, limonene, myrsticin and p-mentha dienbutyrate.

The seed oil is very mobile, light yellow to pale-yellow in colour, becoming dark on ageing; and its taste is less sharp than caraway oil. Its aroma is warm and spicy, slightly burning but pleasant and powerfully aromatic sweet. The oil contains large quantities of carvone 0 ) which is its principal flavour constituent. There is no difference in odour value between dill and Sowa seed oils. The aroma of dill seed oil was characterized by carvone but 4-vinyl-2-methoxyphenol (which gives it a spicy meat-like note), hydroxy-3-methyl-6(l-methylethyl) cyclohexenlone (responsible for dill like sweet note) and dill furan contribute to its characteristic flavour.

Functional properties and toxicity

The leaves are rich in minerals, mainly calcium, phosphorous and iron; they contain nine amino acids as well as flavanoids. However, both these oils have anti-bacterial property and are known to protect prepared food from contamination during storage

In traditional medicine dill fruit has carminative, aromatic stimulant, stomachic and diuretic properties. The emulsion of seed oil in water (dill water) is useful in relieving flatulence, colic pain, vomiting and is a household remedy to correct gastric disorders in children. The dill fruit contains petroselinic acid triglyceride, -sitosterol, glucoside, coumarins and flavanoids as well as large quantities of fats and proteins. It is also used in veterinary medicine.

The oil of east Indian dill (Sowa) has an additional component called dillapiole

C H O , molecular weight ) in high proportion ) and, compared to dill, has lower carvone content 5 . The dillapiole is toxic when taken in large doses. But being heavier than water with high boiling point (285sC), it is easily separated through fractional distillation. The oil free of dillapiole approaches physical constants of European dill (seed) oil (Shah et al , ) and being a cheaper source, is employed in production of gripe water. The dillapiole is a viscid colourless substance and is found to have a synergic action on pyrethrins (used in insecticides), making it more effective over synthetic synergics like piperonyl butaoxide.

Quality indices and standards

The presence of a minimum of 5 % 3,9,epoxy-p-menthene in dill herb oil is a good indicator of its purity. There is no commercial source of this compound available to enable reconstitution of the oil. Lawrence ) has opined that examination of the percentage ratio of, -phellandrene to limonene to -phellandrene is another test for quality determination; the acceptable ratio was found to be 5 3 in dill herb oil.

Dill herb oil is easily differentiated from caraway oil as carvone content in the latter ranges from % to , while in dill oil it is 2 to %. Further, the -pinene and -phellandrene in the caraway oil is very meagre (traces to 1 ) whereas these are between 1 to % and % respectively in dill herb oil.

The east Indian dill seed (Sowa) oil contains large quantity of dillapiole %) and the oil has three flavanoids, viz. quercetin, kaempterol and isorhamnetin, which produce distinct spots on TLC (Shah and Quadri, . The presence of high carvecrol is usually an indicator of an aged, partially oxydised, seed oil. The LD ₀ of dill seed oil is 0 mg per kg body weight (tested on mice)

According to the British Pharmaceutical Codex (Anon. , the dill fruits should contain not less than % (volume by weight) of volatile oil and not more than % of acid soluble ash. The commercial powdered dill should be ground fine enough to pass through a mesh of 4 screen. It should contain not less than % (w/w) and not more than % (w/w) of carvone.

The physical constants of dill are (Anon., 4

 specific gravity (25sC) 0 5 (temp. correction factor 0 6 per sC)

 optical rotation s to +82s

 refractive index (20sC ) 1.4830s1.490s

 carvone content 2 to 0 (by neutral sulphide method)

 soluble in two or more volumes of % alcohol (occasionally) with slight opalescence.

As a rule, organoleptic evaluation of the oil can easily identify variations introduced through addition or substitution of any flavour compounds in the oil. The specification of oil of east Indian dill seed (Sowa) is (Anon.

 specific gravity (27sC) 0

 optical rotation s to 65s

 refractive index (20sC) 4

 ester value before acetylation

 ester value after acelylation 0 to

 total ketone (calc. as carvones) min.

 soluble in 5 and more vols of % alcohol.

References

ANON. ) British Pharmaceutical Codex. The Pharmaceutical Press, London, pp.

ANON. ) Revised and New Standard of the Essential Oils Association of the USA. EOA: 8 (dill seed European)

ANON. ) Dry Culinary Herbs an overview of selected western European markets. International Trade Center (ITC), Geneva, p.

ANON. ) Oil of dill seed (Sowa) specification. Bureau of Indian standards (BIS) Manak Bhavan, New Delhi, IS:3 ,

ATANASOV, Z.H., ZLATEV, S, ZLATEV, M. and STOYANOV, M. ) The effect of mineral fertilization on the yield and essential oil content of dill. Restoniv dni Nauki, 3

3 (Hort. Abstr ) ,

BASLAS, R.K., GUPTA, R. and BASLAS, K.K. ) Chemical examination of essential oil from plants of genus Anethum (Umbelliferae): Oil of seed of Anethum graveolons.

(Pt I) Flavour Ind. 2 ,

BLANK, I. and GROSCH, W. ) Evaluation of potent odorants in dill seed and dill herb

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Prakashan, Ahemdabad, pp.

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