Effects of Liquid Nitrogen Deep Freezing Treatment on Rice Starch Properties

Rice is the most important food crop in Thailand but has low value as commercial uses of rice are limited. Changes in rice starch after deep freezing with liquid nitrogen are studied. Results show that deep freezing affects the physicochemical properties of rice starch depending on amylose and moisture contents. Deep freezing cause alterations in particle size, swelling power, and acid hydrolysis. Pasting properties analyzed by a rapid visco analyzer (RVA) indicate that after freezing, samples are more stable to shear than native rice. Thermal properties determine by differential scanning calorimetry show that gelatinization enthalpy is lower in deep frozen samples. Scanning electron microscopy shows that starch granules are affected by deep freezing, while the sample surface exhibits merging between granules that contain large amounts of water.