Enhancing the Enzymatic Hydrolysis of Germinated Brown Rice by Ultrasonic Pretreatment
Rice is a raw material in the beer and sake industries. Brown rice contains a variety of enzymes such as amylase. Effective use of the endogenous amylase may lead to reducing requirement for external enzyme preparations and improving of rice saccharification efficiency. In the present study, the amylase in brown rice was activated by a germination process, and then the germinated brown rice was hydrolyzed using the endogenous amylase after ultrasonic pretreat-ment. The effect of ultrasonic pretreatment on reducing-sugar yield was investigated, and the mechanism for the changes of amylase activity was discussed. The experimental results showed that the optimal Ca2+ concentration in the reaction liquid was lowered, and the reducing-sugar yield was remarkably increased by ultrasonic pretreatment under proper conditions. When the reaction liquid was pretreated under the optimal condition of an ultrasonic intensity at 0.19 W/cm2, an ultrasonic frequency at 45 kHz and a treatment time at 5min, a reducing-sugar yield increased to 37.5%, which was 3.5 times as high as that without ultrasonic pretreatment. Endogenous amylases of germinated brown rice transferred to the reaction liquid during the ultrasonic pretreatment, which resulted in the elevation of amylase activity in the reaction liquid. This is the main reason for the improvement of reducing-sugar yield in the enzymatic hydrolysis of germinated brown rice.
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