By Sweta Rai, Sabbu Sangeeta and Santoshi Rawat*
Flavour is a sensory phenomenon which is a combination of the sensations of taste, odour or aroma, heat and cold, and texture or “mouthfeel”. The appearance of food is important, but it is the flavor that ultimately determines its quality and acceptability. Natural flavouring materials such as spices, essential oils and fruit juices have been used for long in food preparations but as their supply has not kept up with the demand, with a consequent rise in their cost, natural flavouring agents have been largely substituted by synthetic ones. Thousands of these synthetic compounds are now being used as food additives. There are four basic tastes: salty, sweet, sour and bitter.
Salty: Sodium chloride is the only salt that has a pure salty taste. Besides imparting flavor to food, it is also an essential nutrient. Other salts have different tastes, e.g., some iodides and bromides are bitter while some salts of lead and beryllium are sweet.
Sugar: Sugar is used more to impart sweetness than flavor to food. Fructose present in honey is the sweetest sugar followed by sucrose and glucose, whereas lactose in milk is slightly sweet and gives less flavour. Natural sweet compounds are generally polyhydroxy compounds with a straight-chain structure, such as sugars and the hexahydroxy cyclic alcohols, mannitol and sorbitol. Diverse compounds, such as saccharin, some peptides and cylcamates are also sweet.
Sourness: Sourness of food is due to the presence of organic acids of which citric, tartaric and malic are the most common. Acetic acid produced by fermentation of alcohol is common in processed fruits. Ascorbic acid is abundantly present in fruits and vegetables. Oxalic acid found in spinach and phosphoric acid and its salts are often used in the food industry. Remarkably, the hydrogen ion is mainly responsible for sour taste. Except for oxalic acid, all other acids are weak acids and the degree of sourness is not proportionately related to the hydrogen ion concentration.
Bitterness: It may be due to alkaloids, glycosides, other classes of organic compounds as well as inorganic salts. Naringin the bitter principle of grapefruit is a glycoside of rutinose and is not toxic, while amygdalin, a glycoside present in bitter almonds contains gentiobiose and cyanide group, and it toxic. Mustard and horseradish contain the alkaloid sinigrin, which is harmful and gives an off flavour. Quinine, strychnine, nicotine, etc., are bitter alkaloids. Caffeine, a constituent of coffee and tea, is bitter. Phenolic compounds like tannin and some flavonoids combine bitterness with astringency.
The flavor of any food depends upon minute quantities of 100 or more chemicals that are present in food. These flavoring components are present in concentrations ranging from a few ppm to 0.1 percent.
Classification of flavours:
- Natural Flavours: Herbs, Spices, Aromatic seeds, Fruits, Vegetables
- Processed flavours: Fermented, Baked, Toasted, Roasted, Cara-melized
- Added flavours: These are two types:
- Natural extracted flavours:
Essential oils: Clove oils
Extract: Yeast and Beef
b Synthetic Flavours:
Fruits flavours (blend of esters): Banana, peach,
pineapple and vanillin
Savoury flavours: Chicken, Onion and Smoked
Some plant produce flavours:
- Herbs: Basil. Parsley, celery, thyme, mint, etc.
- Fruits: Orange, lemon, apple, banana, strawberry, Pineapple, etc.
- Spices: Cardamon, clove, turmeric, peppercorns, etc.
- Vegetables: Mushrooms, corn, peas, onion, garlic, cabbage, turnips, etc.
- Aromatic seeds: Aniseed, cumin, fennel, dill, caraway, etc.
The aroma of onion, garlic, cabbage, etc. is mainly due to sulphur – containing compounds. These vegetables should not be overcooked. Other flavouring components in vegetables are methanol, acetone, propanal, etc.
The substances mainly responsible for the aroma of food products are volatile compounds. These may be aliphatic esters, aldehydes, or ketones and are present in fruit and other natural foods in very low concentration: many thousands of natural flavouring compounds are known and in any one food there may be hundreds of these present. Some of the important groups of flavouring compounds are as under:
- Flavonoids: Flavonoids are responsible for the flavor of many fruits, e.g., orange, lemon and grapefruit peels contain a number of flavanone glycosides. Among these, hesperidin (orange and lemon) and naringenin (grapefruit) are the most common. Hesperidin is quite tasteless, whereas naringenin has an extremely bitter taste.
- Terpenoids: Terpenoids are ubiquitous in plant foods. They are the major components of citrus oils and contribute to the flavor of citrus fruits. Limonene, a monoterpene hydrocarbon, possessing a lemon-like odour constitutes approximately 90 percent of most citrus oils. Naturally occurring oxygenated terpenes (mainly alcohols, aldehydes and ketones) provide the characteristics flavor of individual citrus species, e.g., neral and geranial of lemons and nootkatone (bicyclic sesquiter-pene) of grapefruit.
In the presence of air or dissolved oxygen terpenes undergo struct-ural changes and hydration, hence citrus juice concentrates prepared by low-temperature vacuum evaporation are superior in flavor than those processed at high temperatures. Juices of certain varieties of orange and grapefruit become bitter when kept at room temperature for some time, due to the formation of the bitter limonin from its nonbitter precursor (limonin monolactone) by the action of the organic acids present in the juice. This can be prevented by removing the precursor by exposing the fruits to ethylene before juice extraction, or by the addition of a specific enzyme to the juice to degrade limonin.
- Sulphur compounds: Certain volatile sulphur – containing compounds possess powerful and distinctive odours which contribute to both the pleasant and unpleasant aroma of many foods, e.g., vegetables belonging to the genus Allium (onion, garlic) and Brassica (cabbage, cauliflower, Brussels sprouts, broccoli).
Vegetables of the Brassica family contain the sulphur compounds S–methylcysteine sulphoxide and thioglucosides. On cooking the vegetables, the former is converted into dimethyl sulphide which is partly responsible for odour. However, the predominant odour is that of the isothiocyanates formed from thioglucosides by enzymatic hydrolysis. This occurs only after rupturing of the cells when enzymes convert the thioglucosides into the unstable thiohydroxamic-o-sulphate which too is unstable and undergoes spontaneous degradation to isothiocyanate.
The sulphur volatiles responsible for the odour of onion and garlic are not present as such in the intact vegetable tissue, but are formed rapidly when the tissue is ruptured by cutting or chewing, by the action of an enzyme on a precursor. The precursors and the enzyme are present in different cells of the tissue and come into contact only when the cells are ruptured. The precursors are cysteine sulphoxide derivatives which on enzymatic decomposi-tion are converted into flavor compounds. The latter then un-dergo nonenzymatic degrada-tion to more volatile compounds such as sulphides, disulphides and trisulphides.
The characteristic odour of garlic is due to allicin, which is formed from the odourless alliin (S-2 propenyl cysteine sulpoxide) by the action of the enzyme allinase. Allicin then undergoes nonenzymatic decomposition to disulphide and thiosulphinate. The disulphide further decom-poses into a complex mixture of monosulphide and trisulphide.
The production of the volatile constituent of onion takes place similarly. Here the precursor S-1- propenyl cysteine sulphoxide is enzymatically cleaved to give propenyl sulphenic acid which is unstable and undergoes re-arrangement to thiopropanal S-oxide, the lachrymatory factor in onion.
- Other volatile components: A number of other important volatile components contribute to the aroma of foods. In terms of aroma, food can be classified into four groups, namely:
(i) Those in which aroma is mainly due to one compound, e.g., banana (isopentyl ace-tate), orange (citral), almond (benzaldehyde);
(ii) Those in which aroma is due to a mixture of a few compounds, of which one is the major component, e.g., apple (2-methyl butyrate and four minor components);
(iii) Those in which aroma can be reproduced faithfully by the use of a large number of compounds, such as pineapple, walnut; and
(iv) Those in which aroma cannot be reasonably reproduced by a mixture of specific com-pounds, e.g., strawberries, chocolate.
These volatile compounds can be classified into the following important groups:
- Carbonyl compounds: Acetal-dehyde contributes to the odour of butter, hexanal to that of apples, benzaldehyde is responsible for the aroma of almonds, cherries and peaches and geranial for that of lemon. Amongst ketones, 2, 3—butanedione contributes to the aroma of butter, celery and some other foods. Acetophenone is responsible for the flavor of many foods.
- Acids: Some acids have powerful odours. Acetic acid gives its characteristic odour to vinegar, and 2-methylbutyric acid to cranberries.
iii. Esters: The aroma of fruits is also due to esters, e.g., pentyl valerate (apple), methyl salicylate (grape), pentyl ace-tate (banana), octyl acctate (orange), ethyl butyrate strawberry), bulyl acetate (ras-pberry and strawberry).
- Hydroxy compounds: Amongst alcohols, cis-3-hexen-1-ol (tomato and raspberry), 1-octen-3-ol (mushroom) and geosmin (dry beans and beetroot) are important.
Among the phenols, phenol itself contributes to the aroma of some cheeses. Vinyl guaiacol is present in many foods, eugenol is an important component of oil of cloves but is also widely distributed and thymol is responsible for the odour of tangerine.
In the case of certain flavours the substances responsible for them are difficult or impossible to isolate from natural sources such as strawberry, cherry and beans. These natural flavours have, therefore, to be imitated as far as possible by mixing a number of flavouring agents, natural and / or synthetic. The success of such imitation is more a matter of art than of science and is judged by the consumer preference for the flavoured product. Both essential oils and synthetic flavouring agents must be used in accordance with good manufacturing practice the salient points of which are:
(i) The amount added shall not exceed that reasonably required to accomplish the intended effect.
(ii) Substances that may become part of the food as a result of manufacturing shall be kept as low as possible.
(iii) The substance shall be of a good grade. Moreover, a flavouring agent may not be added to a food for which there is a standard, unless the standard includes it.
The following chemicals are used as flavor additives:
- Monosodium glutamate (MSG): It is commonly known as Chinese salt or aji-no-moto. Worldwide used as flavor intensifier in soup, sauces, gravies, tastemakers and flourings, canned and frozen vegetables, meat, poultry and combination dishes. A level of 0.05-0.8% by weight in foods gives the best flavor enhancement and excessive use decreases the palatability of food. Under the PFA (Prevention of Food Adulteration) Act, MSG has been banned in foods meant for infants below 12 months of age, and should not exceed 1 percent weight in foods meant for adults.
- Nucleotides: Its flavor enhancers widely present in plant and animal cells. It is used in processed foods such as potato, chips, peanuts, dry and canned soups, sauces, ketchups, sausages, canned vegetables and meat. The quantity of nucleotide added is very low. They are 50 to 100 times stronger than MSG.
- Maltol: It is used as a flavor enhancer for sweet flavours. It is found in several plants and is formed when cocoa, coffee and malt are roasted and in bread. It is synthesized from soya bean protein fermentation and is used as a fragrant, caramel like flavor for addition to fruit-based products, ice cream, chocolates and candies. It imparts a ‘freshly baked’ flavor to bread and cake. It also used in cookies, beverages, instant pudding mix and soup mixes at levels ranging between 50-300ppm.
- Salt: Salt is used in food for its flavor, as a preservative and as a dietary constituent. The main role of salt in food is for salty taste, flavor intensification and as a digestive stimulant. It is used at 2 percent level.
- Sodium restricted flavouring: When salt is restricted on health grounds because of hypertension, oedema, kidney disorder, etc. the flavor of food can be improved by using herbs and spices such as pepper, dry mustard, paprika, lime juice, mint, celery, onion, ginger, garlic and bay leaf. Salt substitutes are salts which do not contain sodium but contain potassium or ammonium instead, such as potassium chloride and ammonium chloride.
- Popular herbs and spices:
|Basil||Small leaves with pungent flavor||Ajwain||Small round seeds with sharp pungent taste|
|Bay leaf||Dried aromatic leaf of the laurel tree||Allspice||Berries with flavor of cloves, nutmeg, and cinnamon|
|Aniseed||Seeds look like cumin and has delicately sweet liquorice aroma|
|Star anise||Pretty star-shaped fruit with aniseed flavor|
|Chervil||Looks like parsley with delicate stem and soft, almost wilting leaves; has faint flavor||Asafetida||Strong – flavoured dried resin with strong smell|
|Chive||Tender green shoots with mild onion and scallion flavor||Cardamom||Black large pods and green small pods with pleasing warm aroma|
|Coriander/cilantro||Looks like parsley; piquant taste and intense flavor with a fresh pungency||Chillies||Numerous varieties of dried ripened green chillies with varying degrees of pungency|
|Curry leaves||Long slender shiny dark green leaflets: strong warm spicy aroma curry flavor||Cinnamon||Delicate inner sweet and fragrant bark of small evergreen laurel-like trees|
|Dill||Fine feathery green stands with sweet aromatic flavor of caraway and lemon||Cloves||Dried unopened flower buds with a sweet pungent flavor and aroma|
|Fennel||Fine wispy leaves with mild aniseed and dill flavor||Coriander seeds||Yellowish brown round light seeds with pleasant flavor|
|Horseradish||Long tapering root with powerful smell and fiery taste||Cumin and caraway seeds||Caraway seeds are smaller new moon-shaped seeds resembling cumin; pungent, sharp, and astringent tasting seed|
|Kaffir lime leaf||Looks like bay leaf but fresh, green and smaller with aromatic lime flavor|
|Lemon grass||Pale green long sturdy leaves with distinct lemony flavor||Fennel seeds||Sweet aniseed-like flavor|
|Marjoram||Similar to oregano but slightly sweeter flavor and a sweet, almost perfumed aroma||Fenugreek seeds||Small aromatic curry flavoured hard beige-coloured seeds|
|Mint||Leaves of spearmint plant containing peppermint oil||Galangal||Galangal is simila to ginger|
|Oregano||Wild variety of marjoram with a stronger flavor; warm aroma and pleasant slightly musty flavor||Garlic||Bulb with characteristic flavor of diallyl disulphide and high medicinal value|
|Parsley||Refreshing flavor with grassy undertones||Kokum||Dried sour fruit rich in anthocyanin|
|Rosemary||Narrow spiky leaves with a fragrant evergreen smell||Ginger||Rhizome or root with sharp burning sensory stimulation, used fresh or dried.|
|Sage||Pale green leaves with earthy flavor||Mace and nutmeg||Mace is the outermost covering of the nutmeg fruit while nutmeg is the fruit; both have aromatic sweet and warm flavor|
|Tarragon||Slender leaves with intense sweet aniseed/vanilla flavor||Mango powder||Substitute for tamarind and lime|
|Thyme||Tiny greenish grey petals with pungent earthy flavor||Mustard seeds||Hot pungent taste, small round black, brown and yellow seeds|
|Wasabi||Root with delicate apple-green flesh; f flavor milder than horseradish||Pepper||Dried pungent small round berries, black, red, green and white in colour; also classified as condiment|
|Pomegranate seeds||Dried seeds of fruit with sharp sour taste used for sourness|
|Saffron||Stigmas of a crocus which are dried and used for distinctive flavor and bright yellow colour; very expensive spice.|
|Tamarind||Sour, fruity flavor, brown bean-like seed pod|
|Turmeric||Rhizome with bright yellow colour used in curry powder|
- Some flavours in food
|Foodstuff||Principal flavoring agent|
|Synethetic fruit flavours|
|Flavor||Chemical (mixtures of esters and alcohols)|
|Banana||Ethyl butyrate +amyl acetate|
|Peach||Benzaldehyde, benzyl alcohol|
|Strawberries||Methyl and ethyl acetates propionates and butyrates|
|Chicken soup||Monosodium glutamate|
|Mushrooms||Nucleotides, i.e., GMP Disodium 5-guanylate|
- Taste components in fruits and vegetables
|Sweet||Glucose, galactose, fructose, ribose, arabinose, and xylose|
|Sour||Organic acids such as citric, tartaric, oxalic, malic, isocitric, succinic acid, etc.|
|Salty||Small amount of salt|
Food flavours and food additives play a very important role in the industries to prevent the food from deterioration as well as human needs and desires is increasing. By using additives there are several benefits by which at least in the off-season we can get any foodstuffs and by adding the flavour we can get the desirable flavours in the food. As consumer’s demands will increase to the food worldwide as the benefit will be an increase in the industries which is directly proportional to the increase in the national economy. The ultimate benefits we are getting to prevent food from microbial and other deterioration, as well as the harmful losses, is happening to human health. Increasing concentration of any food additives is directly proportional to the diseases in humans that is why there is some food testing agencies are involved to fulfill the criteria to make the food standard by analysis of food nutrients and the presence of food additives.
* Sweta Rai and Sabbu Sangeeta are Asst. Professor Department of Food Science & Technology College of Agriculture, GB Pant University
Santoshi Rawat is Msc. Student in Food Science and Technology at G.B Pant University