Protein: The content of protein in grain is 7% ~ 15%. Due to the lack of lysine, the contents of threonine, tryptophan, phenylalanine and methionine are low, and the nutritional value is not high.
Carbohydrate: The carbohydrate content of cereals is above 70%, and the most carbohydrate content is starch, accounting for about 90%, mainly concentrated in endosperm. There are two kinds of cereal starch, amylose and amylopectin, which have similar nutritional value except for different viscosities. Besides starch, cereals also contain about 10% dextrin, pentosan, glucose, fructose and dietary fiber.
Fat: The fat content of cereals is low, with 1% ~ 2% for rice and wheat, and 4% for corn and millet. Mainly concentrated in aleurone layer and germ, it is easy to be converted into by-products during grain processing. Rice bran can extract rice bran oil, oryzanol and sitosterol which are closely related to human health. Germ oil extracted from corn and wheat germ is 80% unsaturated fatty acid, of which linoleic acid accounts for 60%, which has the functions of lowering serum cholesterol and preventing atherosclerosis.
Minerals: cereals contain 65,438+0.5% ~ 3% minerals, mainly in chaff and aleurone layer, mainly phosphorus and calcium. Cereals contain less iron, with iron 1.5 ~ 3 mg per 100 grams of cereals, and zinc, magnesium, copper and molybdenum also have certain contents. Because it mostly exists in the form of phytate, its digestion and absorption are poor, so the nutritional value of cereal minerals is low.
Vitamins: Cereals are an important source of B vitamins, such as thiamine (vitamin B 1), riboflavin (vitamin B2), nicotinic acid, pantothenic acid and pyridoxine, among which thiamine and nicotinic acid are more, and riboflavin is relatively less. Vitamins are mainly distributed in aleurone layer and germ. The higher the precision of grain processing, the less germ and aleurone layer are retained, and the more vitamins are lost.
Corn and millet contain a small amount of carotene. Nicotinic acid in corn is mainly bound and must be processed and converted into free state before it can be used. Wheat germ contains more vitamin E, which is a good raw material for extracting vitamin E. The contents of vitamin A, vitamin D and vitamin C in cereal raw materials are very low, almost none.