Reverse reaction of Aspergillus niger APC-9319 alpha-galactosidase in a supersaturated substrate solution: Production of alpha-linked galactooligosaccharide (alpha-GOS)

The a-galactosidase that effectively catalyzes a reverse reaction of galactose, Aspergillus niger APC-9319 alpha-galactosidase, was screened from Industrial enzyme preparations for food processing containing alpha-galactosidase activity. Reverse reaction of A. niger APC-9319 alpha-galactosidase was performed using a supersaturated solution (90% galactose [w/v]). A. niger APC-9319 alpha-galactosidase was not inhibited even in high substrate concentration, and effectively catalyzed the reverse reaction. The yield of the reaction product, alpha-linked galactooligosaccharide (alpha-GOS), increased greatly as the initial concentration of galactose increased to 90% (w/v), and was more than 50%. Furthermore, the half life of enzyme activity was about three times as long as that using 60% galactose (w/v). alpha-GOS (1.4g) was prepared from galactose (3.0g) by reverse reaction of A. niger APC-9319 a-galactosidase. The alpha-GOS contained 58% alpha-galactobiose (alpha-Gal2), 28% alpha-galactotriose, and 14% oligosaccharides larger than alpha-galactotriose. The main component of positional isomers in alpha-Call was alpha-1,6Gal2.