Properties of Starches from the Outer Layer and Central Core of the Rice Endosperm

Abstract

The outer layer and central core of four varieties of milled rice grain (92% milling degree) were separated by the wet-milling method, and starch granules were prepared by the alkali method. Differences were found in the physicochemical properties between the outer layer and central core starches. In our four varieties, the size of the outer layer starch granules was smaller as compared with the central core starch. The outer layer starch contained less amylose and protein, and more starch lipids in three non-waxy rice varieties. The outer layer starch showed a higherpeak gelatinization temperature and a smaller gelatinization heat in differential scanning calorimetry and a higher pasting temperature on mini-amylography. It also released more amylopectin into boiling water. SDS-PAGE showed that protein extracted from the outer layer starch had a thinner color at certain bands although not the main band with a molecular weight of 60, 000. These results suggested that the outer layer and central core starches differed in their chemical components as well as granule structure, and one reason for the difference is considered to be due to the physiological gradient in the rice endosperm.