Food Science and Processing

FOOD SCIENCE AND PROCESSING 3 (2+1)

Lesson 8 : Rice

Composition

It is influenced by genetic and environmental factors. The germ, the pericarp and aleurone layers which are richer than endosperm in nutrients like protein, minerals and vitamins are separated from the grain during milling alongwith the husk.

1. Carbohydrate: The major carbohydrate of rice is starch which is 72- 75 per cent.
   
   The amylase content of starch varies according to the grain type. The longer grain and superior types containing upto 17.5 per cent amylase while some coarse type are completely devoid it. Rice also contains free sugars like glucose, sucrose, dexrine, fructose and raffinose.


2. Protein: The protein content of rice is 7 per cent.Oryzenin is the principal protein of rice. The proteins of polished rice have a lower biological value but a higher digestibility than those of rice bran and rice polishing. Parboiling has no effect on the biological value or digestability of the proteins. Rice is deficient in lysine and threonine.


3. Minerals: Most of the minerals present in the rice are located in the pericarp and germ. Polished rice is poor in calcium and Iron. Coloured types of rice contain more iron than the white rice. The phosphorus content is high, about 4 per cent of which is present as phytic acid.


4. Enzymes: Rice contains amylases, proteases, lipases, oxidases, peroxidises and phenolases. On storage the amylse, lipase, peroxidise activites decrease.In fresh rice α amylase is responsible for its sticky consistency after cooking.


5. Pigments: Coloured rice contains anthocyanins and carotenoids.