Influence of hydrothermal processing on physico–chemical qualities of red–pigmented and non–pigmented rice varieties

Four red–pigmented and one non–pigmented paddy rice varieties were subjected to shelling and milling properties and some of their physico–chemical qualities in pre and post hydrothermally processed form have been studied. Alkali score for rice indicated that these varieties were of high Gelatinization Temperature (GT) nature. (EMC) Equilibrium moisture content of raw husked/milled rice was less compared to their respective hydrothermally processed forms. Total amylose Equivalent (AE) was 28–30% in husked rice and 29–31% in milled rice. Hydrothermal processing reduced AE as well as soluble amylose equivalent to different extents. Amylography studies indicated that GT of husked rice of pigmented variety were high (77–81° C). Peak Viscosity (PV) was high for husked rice of IR–64 (1075 BU) compared to that of pigmented varieties (395 to 600 BU). In milled rice of all varieties GT decreased by 4–7° C compared to their respective husked rice, whereas PV increased by 340 to 720 BU in pigmented rice whereas 355 BU in IR–64. By hydrothermal processing, GT increased by 5 to 10° C in both forms of rice. PV decreased by 500 BU in non–pigmented rice and 75–445 BU in pigmented rice varieties. Pigmented rice showed negative break down (BD) inferring that they showed the property of cross linked starch which was not observed in IR-64. Proximate composition in all the raw and parboiled rice varieties indicated that, under given set of conditions, degree of milling in hydrothermally processed rice was always less compared to raw rice.

Author : YS Savitha and Vasudeva Singh*