Degradation of raffinose oligosaccharides in soymilk by immobilized alpha-galactosidase of Aspergillus oryzae

Alpha-galactosidase was immobilized in a mixture of k-carrageenan and locust bean gum. The properties of the free and immobilized enzyme were then determined. The optimum pH for both the soluble and immobilized enzyme was 4.8. The optimum temperature for the soluble enzymes was 50 degrees C, whereas that for the immobilized enzyme was 55 degrees C. The immobilized enzyme was used in batch, repeated batch, and continuous modes to degrade the raffinose-family sugars present in soymilk. Two hours of incubation with the free and immobilized alpha-galactosidases resulted in an 80% and 68% reduction in the raffinose oligosaccharides in the soymilk, respectively. In the repeated batch, a 73% reduction was obtained in the fourth cycle. A fluidized bed reactor was also designed to treat soymilk continuously and the performance of the immobilized alpha-galactosidase tested at different flow rates, resulting in a 90% reduction of raffinose-family oligosaccharides in the soymilk at a flow rate 40 ml/h. Therefore, the present study demonstrated that immobilized alpha-galactosidase in a continuous mode is efficient for reducing the oligosaccharides present in soymilk, which may be of considerable interest for industrial application.