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

Abstract

The α-galactosidase that effectively catalyzes a reverse reaction of galactose, Aspergillus niger APC-9319 α-galactosidase, was screened from industrial enzyme preparations for food processing containing α-galactosidase activity. Reverse reaction of A. niger APC-9319 α-galactosidase was performed using a supersaturated solution (90% galactose [w/v]). A. niger APC-9319 α-galactosidase was not inhibited even in high substrate concentration, and effectively catalyzed the reverse reaction. The yield of the reaction product, α-linked galactooligosaccharide (α-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). α-GOS (1.4 g) was prepared from galactose (3.0 g) by reverse reaction of A. niger APC-9319 α-galactosidase. The α-GOS contained 58% α-galactobiose (α-Gal2), 28% α-galactotriose, and 14% oligosaccharides larger than α- galactotriose. The main component of positional isomers in α-Gal2 was α-1,6Gal2.