Soymilk oligosaccharide hydrolysis by Aspergillus oryzae α-galactosidase immobilized in calcium alginate

α-Galactosidase was immobilized in calcium alginate in the presence of glutaraldehyde. The optimum pH of the soluble enzyme was 4.8, whereas that of the immobilized enzyme was 4.5. The optimum temperature of the soluble enzyme was 50 °C and that of the immobilized enzyme was increased to 57 °C. The immobilized enzyme retained its activity for a longer period. The immobilized enzyme exhibited higher Km and lower Vmax compared to the soluble enzyme. Immobilized α-galactosidase was used in batch, repeated batch and in continuous mode. After 12 h, soluble and immobilized enzyme resulted in 93 and 81% reduction in raffinose family oligosaccharide content in soymilk. Immobilized calcium alginate beads were used for repeated hydrolysis at 50 °C and showed good operational stability. The performance of immobilized α-galactosidase was also tested in a fluidized bed reactor at different flow rates and 90% reduction of raffinose family oligosaccharides in soymilk was obtained at 40 ml h−1 flow rate.