EFFECT OF MILLING ON MINERAL AND TRACE-ELEMENT COMPOSITION OF RAW AND PARBOILED RICE

The effect of milling on the mineral and trace element composition of raw and parboiled grain samples of 16 varieties of rice was investigated. Varietal, locational and seasonal differences in the nutrient composition of brown rice were noted. The mean values for different nutrients per 100 g brown rice were total ash 1.37 g, phosphorus 349 mg, magnesium 157 mg, calcium 18 mg and iron 2.16 mg and in μg per g samples, zinc 14.3, manganese 11.0, copper 2.39, molybdenum 0.775 and chromium 0.088. Parboiling per se had no effect on the composition of brown rice. The degree of milling and the initial concentration of the nutrient in the grain determined the magnitude of loss on milling both in raw and parboiled grain. Percent losses of different nutrients on 5 and 10% milling of raw rice respectively were total ash 40, 62; iron 51, 67; magnesium 40, 64; calcium 36, 57; iron 54, 64; copper 26, 45; manganese 48, 56; molybdenum 24, 34; chromium 57, 69; and zinc only 2.8, 4.6. Zinc in rice grain was uniformly distributed and a major portion of other nutrients was concentrated in the outermost 2.5% surface layers of the grain. Parboiling appeared to have altered the distribution of some nutrients in rice grain except for zinc, magnesium and copper. Milling losses for other nutrients were therefore significantly lower in parboiled than in raw rice. Copyright © 1979 John Wiley & Sons, Ltd