Turmeric - Post-harvest processing and Quality specifications

Turmeric

1 Introduction

Turmeric of commerce is the dried rhizome of the plant Curcuma domestica Val. syn. C. longa L. Turmeric is used in curry powder, chicken bouillon, sauces, gravies, dry seasonings, backing mixes, processed cheese pickles, relishes, breading soups, beverages, and confec- tions (Peter, 1999) in addition to its use in medicine, religious functions and as biopesticide. The genus Curcuma originated in the Indo-Malayan region (Purseglove, 1968). Considerable species diversity of Curcuma occurs in this region. However, about 40 species of the genus including C. longa are indigenous to India indicating the Indian origin (Velayudhan et al., 1999). The antiquity of turmeric dates back to the Assyrians of

600 BC. Ethnobotanical evidence indicates that the use of turmeric has been in India since very ancient days. It is believed that the crop spread out from India to distant Asian countries under the influence of the Hindu religion. According to Marco Polo (1280) the spread of turmeric to China took place in AD 700 (Ridley, 1912). Burkill (1966) believed that the crop spread to West Africa in the thirteenth and to East Africa in the seventeenth centuries, respectively. It was introduced to Jamaica in 1783 (Velayudhan et al., 1999). Though turmeric is now grown in India, Pakistan, Malaysia, Myanmar, Vietnam, Thailand, Philippines, Japan, China, Korea, Sri Lanka, Nepal, South Pacific Islands, East and West Africa, Malagasi, Caribbean islands, and Central America, India is the major producer and exporter of turmeric at present.

The genus Curcuma belongs to the family Zingiberaceae and contains 49 genera and

1400 species. In addition to Curcuma longa, C. zedoaria Rosc. and C. xanthorrhiza Roxb. are also minor sources of curcumin colour. Velayudhan et al. (1999) recognized six taxonomic varieties within C. longa based on numerical taxonomic analysis, namely C. longa var. typica, C. longa var. atypica, C. longa var. camphora, C. longa var. spiralifolia, C. longa var. musacifolia and C. longa var. platifolia. Most of the C. longa found in India belong to C. longa var. typica or atypica.

Turmeric is an erect perennial herb, grown as an annual crop. The above ground morphology of the plant is mainly represented by an erect pseudostem bearing leaves and inflorescence. There may be 23 pseudostems (tillers) per plant. The height of the

pseudostem varies from 90100 cm depending on the variety. Leaf number ranges from 7

12. In fact, it is the leaf sheath which forms the pseudostem. The leaf sheath is usually green in colour. Lamina may be lanceolate or elliptic in shape, thin with acuminate tip. The colour of lamina is usually green above and pale green below, with a length of about 3040 cm and width 812 cm. Inflorescence is a cylindrical, fleshy, central spike of 1015 cm length, arising through the pseudostem. Flowers are subtended by bracts in the spike. The bracts are adnate for less than half of their length and are elliptic, lanceolate and acute. The upper bracts are white in colour while the lower bracts are green. One to four flowers are borne in the axil of the bract, opening once at a time. About 30 flowers are produced in a spike

(Nazeem and Rema Menon, 1994). The calyx is short, usually toothed and split nearly halfway down on one side. The corolla is tubular, thin and whitish with a yellow tip. Usually the upper most and lower most bracts will be sterile. Seed set is observed in turmeric and seeds are viable. Seeds are produced in capsules and there will be from one to numerous sunken capsules in an inflorescence depending on the flowers fertilized.

At the base of the pseudostem, below the ground, rhizomes are formed consisting of mother rhizome(s), primary, secondary and even tertiary fingers, the whole forming a compact clump. Rhizomes grow symbodically and are of orange brown, pale yellow or reddish yellow colour.

C. longa is considered to be a triploid with a somatic chromosome number of 63 (2n =

3x = 63).

2 Production India is the major producer and exporter of turmeric in the world. In India turmeric is grown over 1.34 ha with an annual production of 5.43 lakh tonnes. India exported 23 000 t of turmeric during 199697 to 67 countries (Peter, 1999). Turmeric is exported as turmeric dry, turmeric fresh, turmeric powder, turmeric oleoresin and turmeric oil. The major turmeric importing countries from India are Iran, Japan, South Africa, Singapore, Sri Lanka, USA, UAE, Malaysia, Germany and Bangladesh. Export of turmeric by item from India during 199496 is given in Table 1.

There are about 60 turmeric cultivars (land varieties) available in the country. Some of the important local cultivars are Duggirala, Tekurpet, Sugandham Amalapuram,

Lakadong, Alleppey, Rajapuri, Mydukur, Wynad local, etc. Cultivars like

Alleppey, Wynad local, Lakadong, Edapalayam, Thodupuzha, etc., are rich in curcumin content (>7%). In addition to these land varieties, there are about 17 improved varieties in India. The important improved turmeric varieties are Prabha, Prathibha

(Fig. 1), Sudarsana, Suguna, Co-1, Sugandham, BSR 1, etc. (Sasikumar et al.,

1996). Maturity of these varieties is 79 months. The yield (fresh) of the improved varieties is 2040 t/ha.

Table 1 Export of turmeric from India during 199496

Item 199495 Quantity (t) 199596 Quantity (t)

Turmeric dry 16,727.9 19,189.5

Turmeric fresh bulk 5964.1 800.9

Turmeric powder 6093.7 7385.9

Turmeric oil 0.3 0.1

Turmeric oleoresin 159.0 149.1

1 Prathibha

3 Post-harvest processing

Harvested turmeric is washed well to remove the adhering soil; roots removed, the fingers and mothers are separated. Mother and finger rhizomes are boiled separately for about

4060 minutes under slightly alkaline condition (100 g of sodium bicarbonate or sodium carbonate in 100 l of water) in copper, galvanized iron or earthen vessels and sun dried on bamboo mat or clean drying floor for 1015 days so as to bring down the moisture content to 10%.

Another method of curing is by taking cleaned mother and finger rhizomes (approx.

50 kg) separately in perforated trough of convenient size made of GI or MS sheet with extended parallel handle. The trough containing the fingers are immersed in water using a paddle. The alkaline solution is then poured into the pan so as to immerse the rhizome, which are then boiled until they become soft and dried. The dry recovery of cured turmeric varies between 1530% depending on variety, location and cultural practices.

Dried turmeric is subjected to polishing either manually or mechanically in power operated drums (Purseglove et al., 1981). A weight loss of about 58% is expected due to full polishing. Polished rhizomes are made attractive by artificially colouring them with turmeric powder. During polishing itself turmeric is added to the drum either as powder or as emulsion.

Rama Rao et al. (1975) described an indigenous method of storing turmeric. The cured product is stored in suitable pits dug on a raised site. The bottom and sides of the pits are lined thickly with dried grass or similar material. After filling up the pits with the cured turmeric they are covered with mat or grass and finally with earth. The produce can be stored for one year like this. At Sangli, India, farmers usually store turmeric like this in pits dug in the field. Dealers usually store the cured turmeric in fresh jute bags or in sound, clean, dry, heat-sealed polythene bags in dry, cool, warehouses (Purseglove et al.,

1981). After harvest, fresh turmeric is kept in gunny bags or baskets or heaped open in well-ventilated sheds.

Turmeric is available as whole, ground, oleoresin and oil. Turmeric is used mainly as fine ground turmeric in cooking in the West while those in the growing countries buy turmeric mostly in whole or split form. Importing countries in the West buy ground turmeric, turmeric oleoresin and oil.

3.1 Ground turmeric

A sophisticated grinding process is not needed for ground turmeric, since there would not be much loss of quality while grinding turmeric. Usually clean, dry, stone-hard fingers are powdered through the use of hammer mills followed by disc-type attrition mills to obtain 6080 mesh powder. Accessory equipment for pre-cleaning includes an aspiration system (which removes the light extraneous matter), destoners and magnetic separators for fine iron contamination, vacuum fumigators, and the noise reducing fixtures, dust collection systems, mechanical or closed circuit pneumatic conveying system, blending and automatic packaging system, now employed by most big spice grinders for optimizing the output and for assuring hygienic and flavour quality. The smaller spice manufacturers in the West and Asia use simple cleaning and grinding equipment and partly mechanized packaging systems (Govindarajan, 1980).

Turmeric powder is packed in bulk in containers such as fibre hard drums, multi-wall bags and tin containers suitably lined or coated to prevent moisture absorption, loss of flavour and colour. For the retail trade the unit packages are in flexible packagings such as low and high density polyethylene, polyvinyl chloride, glassine or in glass packages. Storage studies conducted on turmeric powder using different packaging materials have shown that aluminium foil laminate or double pouch of glassine or low density polyethylene offered good protection for the stored product for about six months without

loss of quality and colour (Balasubramanian et al., 1979).

3.2 Turmeric oleoresin

Turmeric oleoresin is being used increasingly by the processed food industries in the West to impart colour and aroma. Oleoresin is a mixture of compounds, namely curcumin, volatile oil and other active ingredients, non-volatile fatty and resinous material extractable by solvents, used singly, in sequence or in combination. Turmeric oleoresin is orange-red in colour and consists of an upper oily layer and a lower crystalline layer (Krishnamurthy et al., 1976). For commercial use, it is usually mixed with a non-volatile edible solvent such as vegetable oil, propylene glycol or polyoxy ethylene sorbitan fatty acid esters in order to disperse the extracted material and to render it free flowing and soluble (Purseglove et al., 1981).

Turmeric oleoresin is obtained by solvent extraction of ground spice. Acetone is a good solvent for oleoresin extraction. Soxhlet apparatus or cold percolation is used for extraction. Curcumin, the principal colouring matter forms about one third of a good quality oleoresin. Yield of oleoresin varies from 715% depending on varieties. Govindarajan

(1980) has given the detailed steps for industrial extraction of turmeric oleoresin.

3.3 Turmeric oil

Turmeric contains 35% volatile oil, which is obtained by steam distillation of turmeric powder, for about 810 h. Turmeric oil is pale yellow in colour with peppery and aromatic odour. The oil contains about 60% turmeron, 25% zingiberene and small quantities of d- -phellandrene, d-sabinene, cineole and forneol.

3.4 Curry powder Turmeric powder is the major component (about 4050%) of curry powder. Curry powder is a spice mixture used for seasoning dishes containing vegetables, meat, fish, eggs or vegetable plus meat or fish (i.e. curry) in the orient. In the West also curry powder is used for seasoning dishes. India has been the principal exporter of curry powder to many countries like the UK, Australia, Fiji, etc.

Turmeric powder provides colour and background aroma to the curry powder. Govindarajan (1980) has given typical curry powder composition, quality standards, packaging details, etc.

4 Quality specifications Cured turmeric is sorted as fingers, round, split or non-specified and marketed under its varietal name, which is usually based on the place of production such as Alleppey,

Erode, Duggirala, Nizamabad, Rajapuri, Cuddappah, etc., from India. The Indian

Agmark, standards include separate gradings for different varieties. Special, good and fair are some of the grade specifications. Govindarajan (1980) has given the specification for turmeric (whole and ground).

1. Turmeric whole is the primary (bulbs, rounds) and secondary (fingers) rhizomes, harvested at full maturity, cured, dried to about 10% moisture level, polished and either coloured or not coloured.

2. The cured rhizomes, cleaned and dried, are ground to powder without any added matter.

3. Whole or powdered turmeric should have the characteristic fresh aroma and taste of turmeric and be free from foreign aroma such as mustiness. It must also be free from living insects, moulds; practically free from dead insects, insect fragments and rodent contamination visible to the naked eye or specified magnification.

4. Turmeric fingers should not be less than 15 mm in length, hard, smooth and the core colour should be lemon yellow or bright yellow with only admissible levels of small pieces and bulbs (Table 2).

5. Turmeric whole should not contain more than 2% by weight (lower limit for superior grade) extraneous matter. The admissible level of defective rhizome allowed in different varieties of turmeric is given in Table 2.

6. The limits for chemical characteristics specified for turmeric powder are presented in

Table 3.

American Spice Trade Association (ASTA) cleanliness specification effective from 21

May 1997 for turmeric allows only a maximum of three dead whole insects; 5 mg/1b mammalian or other excreta, 3% by wt. mould, 2.5% by wt. insect defiled or infested material and 0.5% by wt. extraneous foreign matter in turmeric (Sivadasan, 1998).

Whole, dried or fresh turmeric is usually free from adulteration. However, turmeric powder is adulterated with foreign starch (tapioca, arrowroot, cereal floor), husks, coal tar colours, lead chromate, etc. Adulterated turmeric powder will have low curcumin content. Depending upon the adulterant used, the curcumin content of the samples vary from 0.372.07% (Balasubramanian et al., 1979). Gas chromatographic methods are available to detect volatile oil of other Curcuma sp. used for admixing the turmeric powder. Similarly, specific tests are now available to detect each of the above adulterants in ground turmeric (Govindarajan, 1980).

Table 2 Indian specification for turmeric grade

Grade Pieces Foreign Defectives Bulks Characteristics

(max. matter (max. (max.

wt. %.) (max. wt. %.) wt. %.)

wt. %.)

Fingers (general) Finger-like shape, breaks with a

Special 2.0 1.0 0.5 2.0 metallic twang; well set and

Good 3.0 1.5 1.0 3.0 close grained; perfectly dry, free

Fair 5.0 2.0 1.5 5.0 from weevil damage, over boiling, etc.

Fingers (Alleppey)

Good 5.0 1.0 3.0 4.0 As above

Fair 7.0 1.5 5.0 5.0

Fingers (Rajapuri)

Special 3.0 1.0 3.0 2.0 As above, admixture of other

Good 5.0 1.5 5.0 3.0 turmeric varieties are allowed at

Fair 7.0 2.0 7.0 5.0 a maximum of 2.5 and 10% in 3

grades, respectively.

Bulbs (rounds)

Special 1.0 1.0 Be well developed, smooth

Good 1.5 3.0 round and free from rootlets

Fair 2.0 5.0 The Rajapuri type has higher allowance of 3.0, 5.0 and 7.0% defectives in 3 grades, respectively.

Source: Govindarajan (1980).

5 Chemical structure Turmeric is valued mainly for its principal colouring pigment, curcumin, which imparts the yellow colour to turmeric, besides other nutritive constituents like potassium (Peter,

1999) (Table 4). The main colouring constituent of turmeric and other yellow Curcuma species is

curcumin, having a molecular formula of C₂₁H₂O O₆. In fact, besides curcumin there are a few other related pigments which imparts the yellow colour, all together called curcuminoids (Verghese, 1999). Curcumin [1,7-bis (4-hydroxy-3-methoxy-phenyl)-1,6- heptadiene-3,5-dione]; demethoxy curcumin [4-hydroxy-cinnamoyl (4-hydroxy-3- methoxycinnamoyl) methane and bis-demethoxy curcumin [bis-(4-hydroxy cinnamoyl methane] together make the colouring pigment in the turmeric rhizomes (see Fig. 2). The curcumin content in different turmeric varieties varies from 28%

(spectrophotometric estimation). However, Verghese (1999) reported the total colour in eight C. longa varieties ranging from only 2.33.9%, by HPLC analysis. Alleppey type recorded maximum colour. The distribution of the curcuminoids is also reported to vary with different samples (Table 5) (Verghese, 1999).

In the pure form curcuminoids separate as an orange yellow crystalline powder, insoluble in water, slightly soluble in ether, soluble in alcohol and in glacial acetic acid. Verghese (1999) is of the opinion that the melting point of curcumin is an unworthy

Table 3 Analytical specification for turmeric (whole and powder)

Sample Moisture Ash Starch Crude fibre Vol. oil Colour as Lead Chromate test max. Total Acid insol. max. max. max. curcumin max. ppm

(% wt.) max. max. (% wt) (% wt.) (% wt.) min.

(% wt.) (% wt.) (% wt.)

Whole BP 810 69 46 25 US 9 7 0.5 6 4 5 DDR 7 2.6 34

Powder India 10 7 1.5 60.0 1.5 Negative

WHO 10 7 1.5 3 Negative

Note: The chromate test is negative if there is no violet colour developed when dilute acid soluble ash from 2 g of sample (45 ml) is reacted with 1 ml of 0.2% alcoholic solution of diphenyl carbazide.

Source: Govindarajan (1980).

Table 4 Nutritional composition of turmeric

Constituent Quantity per 100 g

Water (g) 6.0

Food energy (Kcal) 390

Protein (g) 8.5

Fat (g) 8.9

Carbohydrate (g) 69.9

Ash (g) 6.8

Calcium (g) 0.2

Phosphorous (mg) 260

Sodium (mg) 30

Potassium (mg) 2000

Iron (g) 47.5

Thiamine (mg) 0.09

Riboflavin (mg) 0.19

Niacin (mg) 4.8

Ascorbic acid (mg) 50

Source: Peter (1999).

Fig. 2 Structures of (a) curcumin, (b) demethoxy curcumin and (c) bis-demethoxy curcumin.

Table 5 Concentration of curcuminoids in typical curcumin samples by HPLC analysis

Sample Curcumin Demethoxy bis-demethoxy Total

(%) curcumin (%) curcumin (%) (%)

1. Curcumin puriss (Fluka) 53.5 17.2 9.6 80.3

2. Curcumin crys. natural 80.8 7.1 1.0 89.9

(Koch-light)

3. Pure curcumin (Chr. Harsen) 64.9 11.3 6.4 82.6

4. Curcumin/(Syndiferuloyl 79.6 12.2 1.6 93.4

methane (ICN) (1)

5. Curcumin (ICN) 58.3 16.6 7.0 81.9

6. Curcumin (Biomol) 66.3 15.3 4.0 85.6

7. Synthite 1 71.0 23.2 2.8 97.0

8. Synthite 2 68.6 23.0 3.0 94.6

Source: Verghese (1999).

quality parameter and need not be mentioned in any specifications, as many different melting points are reported by many workers for curcuminoids!

Curcumin exhibits strong absorption between 419 and 430 nm in organic solvents and on this property revolves the spectrophotometric methods of the American Spice Trade Association (1968) and Essential Oil Association (EOA) (1965), though now the HPLC method is available (Tonnesen and Karlson, 1983). The EOA stresses the fact that

turmeric extracts are evaluated strictly in colour and this is best expressed in terms of colour value (cv), which is equivalent to ten times the specific extinction coefficient in ethanol at 422 nm (c.f. Verghese, 1999). Verghese (1999) further reported that the specific extinction coefficient in ethanol of curcumin at 420430 nm varies between

1528 and 1586, of demethoxy curcumin at 420430 nm between 1513 and 1580, and of bis-demethoxy curcumin at 419430 nm between 1565 and 1682. By repeated crystallization from ethanol, the dye yielded specific extinction coefficient 1596 at

425 nm in ethanol (c.f. Verghese 1999). Coupling this observation and the values already reported in the literature, specific extinction coefficient 1600 was recommended as a reasonable yardstick for assaying curcumin and this fits the HPLC data excellently

(Verghese, 1999). However, for most routine, quality control work, it is sufficient to measure the extinction

of an alcohol extract at the absorption maximum at 420455 nm, taking the precautions of using neutral alcohol and avoiding exposure to direct sunlight, and calculate the curcumin content by using the molecular absorption value (Govindarajan, 1980).

Turmeric oil has a major role in the aroma and flavour of turmeric though the oil as such is not used. Turmeric oil is comprised of oxygenated sesquiterpenes which are accompanied by smaller quantities of sesquiterpene hydrocarbons, monoterpene hydrocarbons and oxygenated monoterpenes (Purseglove et al., 1981). Among the various constituents of the oil, sesquiterpenes, ar-turmerone and turmerone comprise 50 per cent of the oil (see Fig. 3) (Purseglove et al., 1981).

6 Use in the food industry

Turmeric powder is used in mustard paste and curry powder as both colour and aroma are important in these products. Turmeric oleoresin is used mainly in the brine pickles

Fig. 3 (a) Turmerone, (b) ar-Turmerone.

(Eiserle, 1966; Cripps, 1967) and to some extent in mayonnaise and relish formulations; in non-alcoholic beverages such as orangeades and lemonades; gelatins; in breading of frozen fish sticks; potato croquettes; butter and cheese in the form of powder or granules for garnishing and even in ice creams (Perotti, 1975). In all these cases, its function is predominantly to colour the product and it merely replaces the synthetic colours such as tartrazine, formerly used (Govindarajan, 1980).

In Asian countries whole, dry or fresh turmeric, ground or turmeric powder with other spices like chillies, coriander, pepper, cumin, etc., are used for making vegetable and meat dishes and soup-like dishes. Turmeric powder mixed with seasame, coconut or groundnut oil is used for pickling mango, lime, gooseberry, garlic, etc. (Govindarajan, 1980).

The colours in the Food Regulation Act came into force in UK in 1996. Part III, Schedule 5 of this Regulation specifies the limits for curcumin in various food items