Studies on the Regulation of Acid Value of Fatty Matter in Rice Bran. IV.

Abstract

Studies were made, under the optimum constant temperature of 37.5°C determined in Report No.3, on the effects of the hydrolytic action of the fatty matters in rice bran due to lipase by such physical factors as packing degree (apparent specific gravity) of rice bran, water content, irradiation of ultraviolet ray, freezing treatment, and size of rice bran particles.As a result, it was found that the greater the packing degree (apparent specific gravity) of rice bran the faster the hydrolytic velocity of the fatty matters by lipase, and that the lipase action is accelerated when the water content is approximately 20%. The hydrolysis velocity decreases when the water content is less than 20% or more than 20%. Irradiation of ultraviolet ray of a carbon arc lamp and sunlight upon rice bran had no effect on the lipase action. The hydrolytic velocity was the fastest when distilled water and various kinds of buffer solutions were added to rice bran, mixed by stirring and given a freezing treatment. Next fastest hydrolytic velocity was observed when the aforementioned aqueous solutions were added after giving a freezing treatment to raw rice bran. The hydrolytic velocity was the slowest when a freezing treatment was not given. It was also found that lipase action ceases at a temperature ranging from -16 to -18°C. In regard to particle size of rice bran, the smaller the particle size the faster the hydrolytic velocity by lipase. The hydrolytic velocity of pulverized rice bran is faster than that of unpulverized rice bran. It was found that the following index law exists between the residual percentage of rice bran sieving (R) and the acid value (x) of its fatty matters : R=100e-bxnin which b and n represent constants.