The expression profiles of acid-stable α-amylase and acid-labile α-amylase of Aspergillus luchuensis mut. Kawachii effect on the microstructure of koji and alcohol fermentation

Abstract

We investigated the contribution of the complex expressions of two α-amylases, namely acid-stable α-amylase (AS-amylase) and acid-labile α-amylase (AL-amylase), from Aspergillus kawachii to the microstructure of koji and the brewing. AL-amylase was found to be the primary contributor to the decomposition of starch in the early stage of koji making. From the middle stage, both α-amylases decomposed the starch in a coordinated manner, and at the final stage, acid-stable α-amylase and glucoamylase decomposed the starch granules. Characterization of koji prepared by the single disruptions of AS-amylase or AL-amylase genes, double disruption of both α-amylase genes, and triple disruption of two α-amylase and glucoamylase genes in A. kawachii cells indicated that both α-amylases can work in a synergistic manner to decompose starches during koji making. AL-amylase was found, for the first time, to play an important role in starch decomposition in koji. The speed of alcohol fermentation and ester contents of the fermented mash were higher the mash prepared the control strain, followed by single, double, and triple disruptants. These results indicate that the microstructure of koji plays a role in promoting alcohol fermentation and flavor development.