Food Science and Processing

FOOD SCIENCE AND PROCESSING 3 (2+1)

Lesson 14 : Vegetables

Water-Soluble pigments

These pigments are not membrane-bound molecules but are dissolved in the cell sap of epidermal cells of these parts. Flavonoids are classified into anthocyanins and anthoxanthins. Anthocyanins are highly water-soluble pigments that range in colour from red to purple. The anthoxanthins are colourless or white. Anthocyanins and anthoxanthins are important cyaniding based compounds.

1. Anthocyanins: Anthocyanins have cyaniding with attached sugar. Cherries, red apples, various berries blue and red grapes, pomegranates, and currants archive their colour appeal because of predominance of anthocyanins. The red colour in the skin of radishes and sweet potatoes and the leaves of red cabbage is due to anthocyanins too. Anthocyanin pigment in purple brinjal is water insoluble.



2. Betalins: Anthocyanin pigments are absent in some families and are replaced by highly different compounds, betacyanins and betaxanthins. These two pigments together are known as betalins. High ratio of betacyanin to betaxanthin lead to violet, medium to red and low to orange tuber colours. A some what yellow pigment is contributed by the betaxanthins.


3. Anthoxanthins: These are colourless or pale yellow pigments closely related to anthocyanins depending on the pH, Anthoxanthins give colour to cauliflower, onion and spinach or other leafy vegetables.


4. Organic acids: Vegetables contain a number of organic acids, metabolic products of the cells. Formic, succinic, citric, acetic, malic, fumaric, tartaric, and benzoic acids are present in fruits and vegetables. The concentration of acid is lower in vegetables than in fruits. Tomatoes and vegetables with the concentration of acid have a pH Ranging from 4 to 4.6. Foods like lemon, mango green, tamarind (tartaric acid), gooseberries, raw citrus fruits and grapes have low PH. Most of the vegetables have pH 5.0 to 5.6. Potatoes and peas have PH 6.1 to 6.3, more neutral in taste.


5. Polyphenols and tannins: These include anthocyanins, flavones, flavonols and tannins. They are responsible for the astringent taste of some vegetables and for the astringent taste of some vegetables and for the discolouration of some vegetables after cutting, cooking or processing.