Engineering Chemistry

Lesson 24. Food Flavors and Colors

24.2   Flavors

Flavor is the sensation produced by a material taken in the mouth, perceived principally by the senses of taste and smell, and also by the general pain, tactile and tmperature receptors in the mouth. Flavor denotes the sum of the characteristics of the material which produces that sensation. Flavor is one of the three main sensory properties which help in deciding slection, acceptance and ingestion of food (the other two being appearance which includes colour, size shape, etc and kinesthetics which includes texture and consistency).

Flavor is composed of taste and odor. Other qualities like texture or temperature contribute to overall sensation of flavor. The main taetes are Salty (sodium chloride), Sweetness (sugar), Sourness (all acids like citric, tartaric etc), Bitterness (quinine), Umami (glutamic acid). The important odors are Camphoraceous (camphor), Pungent (formic acid), Etheral (chloroform), Floral (terpineol), Pepperminty (menthone), Musky (Androsan-3oc-ol), Putrid (skatole).

24.3   Flavor Compounds

Volatile compounds in food like aliphatic esters, aldehydes or ketones are responsible for aroma of foods. The important groups of flavoring compounds are as follows:

24.3.1 Flavonoids

They are responsible for flavor of fruits like orange, lemon. The peel of these fruits contain flavanone glycosides like Hesperidin (tasteless) and naringenin (bitter).

24.3.2 Terpenoids

They are omnipresent in plant foods. They contribute to flavor of citrus fruits and are major components of citrus oils. The major constituent  of the essential oils is Limonene (about 90%).

24.2.3 Sulphur Compounds

Some volatile sulphur-containing compounds possess distinctive odours which contribute to aroma of many foods, e.g. the aroma of onion, garlic, cabbage, cauliflower, broccoli, etc.  The compounds belong to class thioglucosides, isothiocyanates etc.

24.3.4 Other volatile flavor compounds

Foods can be classified into four groups in terms of volatile flavour. They are:

(1) Foods whose aroma is due to a single compound only. E.g., banana (isopentyl acetate), lemon (citral), almonds (benzaldehyde), etc.

(2) Foods whose aroma is due to mixture of small number of compounds, one of which is rhe major component. E.g., the major flavour imparting component of apple is 2-methyl butyrate and it contains four other components.

(3) Foods whose aroma can be reproduced with the help of a large number of compounds e.g., pinepple, walnut etc.

(4) Foods whose aroma cannot be reproduced by complex mixture of compounds e.g., strawberries, chocolate, etc.

The volatile compounds can be classified into following groups:

Carbonyl compounds: Acetaldehyde (butter), hexanal (apples), benzaldehyde (almonds, cherries), geranial (lemon), 2-3butanedione (butter, celery), etc

Acids: Acetic acid (vinegar), 2-methylbutyric acid (cranberries), etc

Esters: pentyl valerate (apple), methyl salicylate (grapes), pentyl acetate (banana), octyl acetate (orange), ethyl butyrate (strawberry), butyl acetate (strawberry), etc

Hydroxyl compounds: cis-3-hexen-1-ol (tomato, raspberry), 1-octen-3-ol (mushroom), phenol (some cheeses), eugenol (cloves), etc.

24.4   Types of flavors

The flavours can be broadly classified into three types

24.4.1 Developed flavor

Flavor compounds are formed during food processing and may originate from fractionation (manufacture of perfumes) and decomposition and other reactions of food components.

24.4.2 Processed flavor

Heating changes the flavor of many compounds, e.g., coffee, beans, peanuts, etc.

24.4.3 Added flavor

These are added to foods and are of two types

Essential oils or oleoresins or other extracts of aromatic plants, e.g., peppermint oil

Synthetic substances that may or may not occur in nature, e.g., benzaldehyde (almond), acetylmethylcarbinol (butter), citral (orange), eugenol (clove) limenone (lemon), vanillin (vanilla), etc.

24.5   Flavor Enhancement

24.5.1 Monosodium glutamate

It is prepared from wheat gluten, beet sugar waste and soy protein. It is also used in the form of protein hydrolysate derived from proteins. Wheat gluten, casein and soy flour are good sources of glutamic acid and are used to prepare protein hydrolysates.

The flavour of glutamate is unique and has no resemblance to flavour of other compounds. Glutamate causes a tingling feeling and persistency of tatse sensation. It provides a feeling of satisfaction. Presence of salt is required to produce glutamate effect. Monosodium glutamate improves the flavour of many food products and is widely used in processed foods like meat and poultry products, soups, vegetables and seafood.

24.5.2 Maltol

Maltol has the ability to enhance sweetness produced by sugars. Maltol is formed during roasting of malt, coffee, cacao and grains. It is also formed in the crust of bread during baking process and in dairy products that have been heated as a product of decomposition of casein-lactose system. Maltol has anti-oxidant properties. It increases storage life of coffee and roasted cereal products. Maltol is used as a flavour enhancer in chocolate, candies, ice cream, baked products, instant coffee and tea, liqueurs and flavourings.

 24.6   Food Colors

Color plays a major role in deciding acceptance of food. It also serves as a criteria for quality of food. The characteristic color of raw food is due to natural pigments present in plant and animal materials. Sometimes artificial coloring matter is added to improve the color of processed foods. The natural pigments occuring in food products can be classified into following groups:

24.6.1 Chlorophylls

They are green pigments involved in photosynthesis in plants and some microorganisms. There are number of chlorophylls such as chlorophylls a,b,c and d, bacteriophylls a and b, and chlorobium chlorophylls. In food, only chlorophyll a and b, found in higher plants are important. Chlorophylls are complex molecules containing four pyrrole rings with a central Magnesium atom. In presence of an acid, the central magnesium of the chlorophylls is replaced by hydrogen. As a result the colour changes from gteen to dull brown.

24.6.2 Myoglobin and Haemoglobin

Myoglobin imparts red colour to fresh muscle. Haemoglobin imparts red colour to the blood. Both are complex proteins consisting of protein part called globin and non-protein part called haem. Haem is a porphyrin consisting of four pyrrole rings, at the centre of which is Iron atom in Fe²⁺ state. Myoglobin and haemoglobin complex with and transport Oxygen required for metabolic activity of the animal.

24.6.3 Anthocyanins

These pigments are responsible forr red, purple and blue colour of fruits, vegetables and flowers. These are water soluble pigments. Anthocyanins are polyphenols and are found linked with sugar molecules like glucose, rhamnose, galactose, xylose and arabinose.

24.6.4 Flavanoids

These pigments impart yellow colour and are present in all plants. They have structures similar to that of anthocyanins.

24.6.5 Tannins

They are complex mixtures of polymeric polyphenols. They impart colour ranging from colourless to yellow or brown. They contribute to astringency and enzymatic browning of foods.

24.6.6 Betalains

They are group of pigments found in red beet, cactus fruits, pokeberries and flowers like bougainvillia. The pigments are red and yellow in colour.

24.6.7 Quinones and Xanthones

They are found in cell sap of flowering plants, fungi, bacteria and algae. Their colour ranges from pale yellow to black.

24.6.8 Carotenoids

These are a group of lipid soluble hydrocarbons. They are the principal colouring matter of carrot roots. They are widely distributed in plant world and found in green leaves, yellow and red fruits and many roots. Carotenes obtained from natural extracts of annatto, saffron, paprika, tomatoes, etc are used as food colourants.

24.6.9 Synthetic colours

A number of synthetic colourants are used in food materials. They may functions as colour stabilizers, colour fixatives, colour retention agents, etc. Even though colours have no role in nutritive valus of foods, they are frequently added to restore the natural colour which is lost during processing.

The synthetic colours are generally manufactured from coal tar. They are generally more suitable in terms of colouring power, uniformity, stability and cost. They are used in carbonated breverages, gelatin dessert, candies, bakery products etc. Many coaltar compounds are carcinogenic and many countries have totally banned or restricted the use of these compounds.

Food colours also include inorganic materials like iron oxide to give redness and titanium dioxide to intensify whiteness.

Some synthetic colours used are

Red: Ponceau 4R, carmoisine, erythrosine

Yellow: Tartrazine, Sunset yellow FCF

Blue: Indigo carmine, Brilliant blue FCF

Green: Fast green FCF

References & Further Reading:

1. N. Shakuntala Manay & M. Shadaksharaswamy (2001), “Foods: Facts and Principles”. New Age International Publishers, pp. 92-115.