Pigments and flavour compounds

PIGMENTS AND FLAVOUR COMPOUNDS

Chlorophyll :

Chlorophyll is the green pigment of leafy vegetables and other green coloured vegetables

Carotenoids:

Carotenoids are the yellow, orange, red fat soluble pigments distributed in nature. They are divided into three groups viz. carotenes present in carrot, green leafy vegetables and other fruits, lycopenes present in tomatoes and xanthophylls present in yellow fruits.

Pigments that contain the phenolic group include anthocyanin, anthoxanthin, leucoanthoxanthin, catechin, quinones and betalins. The first four groups are collectively known as 'Flavanoids'

Anthocyanin :

They are a group of reddish water-soluble pigments occurring in many fruits and vegetables. Cherries, red apples, pomegranates have their colour appeal due to anthocyanins.

Anthoxanthins :

They are colourless white to yellow pigments that give colour to cauliflower, onions, spinach or other leafy vegetables. In green leafy vegetables the colour is masked by chlorophyll.

Leucoanthoxanthins :

They are colourless and contribute to the puckeriness or astringency of some foods, such as apple and olives. They also play an important role in the enzymatic browning of fruits.

Catechins :

They are pigments that are involved in enzymatic browning.

Betalins :

They are the red water soluble pigments found in beetroot and berries.

Quinone :

The yellow            pigment      juglone is  a     quinone   present        in

walnut.

Mangiferin :

This is the yellow pigment belonging to the xanthone group. It is found in mangoes.

Tannins :

They are complex mixtures of polymeric polyphenols. The appearance of tannins ranges from colourless to yellow or brown. Tannins contribute to the astringency of foods and also to enzymatic browning.

Flavour Compounds :

The flavour of fruits and vegetables are extremely important to their acceptance in the diet.

The overall flavour impression is the result of the tastes perceived by the taste buds in the mouth and the aromatic compounds detected by the epithelium in the olfactory organ in the nose.

In fruits and vegetables, this means that sugars, acids, salts and bitter quinine-like compounds are tasted while the food is chewed in the mouth.

Sweetness may result from the presence of glucose, galactose, fructose, ribose, arabinose and xylose.

All fruits and vegetables contain a small amount of salt, which is detected in the overall taste impressions contributing to flavour.

The natural flavours of vegetables are due to mixtures of aldehydes, alcohol, ketones, organic acids and sulphur compounds. Some fruits and vegetables have an astringent taste attributed to phenolic compounds or tannins.

Two types of vegetables viz., vegetables belonging to the Allium and Cruciferae families have strong flavours resulting from the presence of various sulphur containing compounds. Allium is the genus that includes onions and garlic. Members of the family cruciferae, which include broccoli, cabbage, turnips and cauliflower also contain prominent sulphur compounds. They are described as strong flavoured vegetables.

Vegetables of the onion family are usually strong flavoured in the raw state and tend to lose some of the strong flavours when cooked in water.

Onions contain sulphur compounds that are acted upon by enzymes in the tissues when the vegetable is peeled or cut to eventually produce the volatile sulphur compounds that irritate the eyes and give biting and burning sensations on the tongue.

Vegetables of the cabbage family (cauliflower, cabbage, knolkhol) are relatively mild when raw but develop strong flavours when overcooked or improperly cooked.

An amino acid s-methyl l-cysteine sulphoxide is also present in raw cabbage and appears to be a precursor of cooked cabbage flavour.