NUTRITIVE VALUE OF RICE | GRAINS | GERMS | BRAN | POLISHING

The chemical composition of the rice grain varies considerably depending upon the genetic factor of plant variety and upon such environmental influences as location and season in which grown, degree of milling and conditions of storage. According to Ihekoronye and Ngoddy (1985), a sample of milled rice grain will contain about 80% starch, 8% protein, 0.5% ash, and 11% water.

            The starch is a mixture of amylose and amylopectin. The proportion of these two starches has much to do with the cooking and eating qualities of rice. The higher the proportion of amylose, the drier and more separated the grains after cooking. True glutinous rice, on the other hand, are essentially 100% amylopectin.

            The protein content of polished rice is somewhat lower than that of wheat, maize and sorghum. Lysine, the most important limiting amino acid, constitutes about 4% of the protein of rice twice the level in wheat flour or dehulled maize. Nevertheless, rice protein does not contain enough lysine, threonine, or methionine. Consequently, for proper nutrition, supplementary foods such as grain legumes, meat, and fish should be part of the diet of those who consume large amounts of rice.

            The lipids of rice are concentrated in the bran, germ and polish fractions. In the tropics however, oil recovery from rice for food use is hardly practiced. Like other cereals, rice is lacking in vitamins A, D. and C, it does contain small amount of thiamine, riboflavin and niacin. The levels of these vitamins are considerably higher in brown rice than in polished rice, because the B- complex vitamins are concentrated largely in the bran and germ, which are removed by milling.

            Home-pounding, which is still the common way rural people in the tropics dehull their rice, leaves the grain higher in the B- complex vitamins than milled rice because bran and germ are not completely removed. Polished rice that is parboiled also tends to provide larger amounts of these vitamins than are available in the non parboiled grain (Table 2.2).           

 Table 2.2: Vitamin and Mineral content of rice grains, rice germ, rice bran, and rice polishing

Component	Whole Rice	Milled Rice	Parboiled Rice	Rice Bran	Polished Rice	Rice Germ
Vitamins (micrograms per gram of dry material)
Thiamine (B1)	3.90	0.55	2.30	24.00	22.00	65.00
Riboflavin (B2)	0.66	0.30	0.60	2.00	2.20	5.00
Pyridoxine	6.20	0.37	1.00	25.00	20.00	16.00
Pantothenic acid	15.20	7.66	13.70	27.70	33.30	30.00
Nicotinic acid	41.00	10.00	30.00	336.00	330.00	33.00
Inositol	1194.00	125.00	250.00	4627.00	4536.00	3725.00
Choline	1124.00	452.00	982.00	1700.00	1020.00	3000.00
Biotin	0.12	0.06	0.10	0.60	0.57	0.58
Minerals (percent dry matter)
Calcium	0.04	0.027	0.061	0.13	0.09	0.275
Phosphorus	0.27	0.09	0.130	1. 48	2.44	2.100
Iron	0.0027	00.011	0.0015	0.019	0.012	0.013

 

Source: Ihekoronye and Ngoddy (1985).