Gelatinization temperature of rice starch and its determination.

Abstract

The gelatinization temp. (GI) of rice starch has traditionally been defined in rice quality research as the temp. at which nearly all the starch granules in a sample lose their birefringence. This value ranges roughly from 55 degree to 79 degree C in rice var. Various changes undergone by a rice flour slurry upon gelatinization (starch granule alteration, increase in viscosity, increase in light transmittance, solubilization of amylose, swelling and degradation of rice kernels) have all been utilized in methods for measuring the GT of rice. Gelatinization can be achieved in each case with either heat or alkali. With either of these treatments the parameter measured can be either the temp. or the alkali concn. required to produce a given change, or the extent of change observed under a given treatment. Of these methods, those based on alkali degradation and water uptake of rice kernels, light transmittance of a heated or alkali-treated slurry, and solubilization of amylose from rice flour by dilute alkali are the most convenient for routine use. [All these methods can only be calibrated against the BEPT method - see Halick et al., Cereal Chemistry (1960) 37 670-672.]