Production of Cellulose- and Xylan-Degrading Enzymes by a Koji Mold, Aspergillus oryzae, and Their Contribution to the Maceration of Rice Endosperm Cell Wall.

Abstract

The production of cellulose- (CEL), xylan- (XYL), and pectin-degrading enzymes (PEC) by a koji mold, Aspergillus oryzae, was studied, and their contributions to the maceration of the rice endosperm cell wall were investigated with regard to the utilization of available rice in the sake mash. The sake koji mold showed higher CEL and XYL productivities, whereas the miso and soy sauce koji molds showed higher PEC productivity. Statistical analyses indicated that CEL and XYL contribute predominantly and synergistically to the maceration of the rice endosperm cell wall. A. oryzae produced at least three kinds of CEL (Cel-1, 2, 3) and two kinds of XYL (Xyl-1, 2) when cultured in a wheat bran medium. In the solid-state culture, the production of Cel-3 and Xyl-2 was markedly stimulated by decreasing the moisture content of the solid substrate, although the production levels of Cel-1 and Xyl-1 were almost the same. These data suggest that the production of Cel-3 and Xyl-2 is strongly influenced by culture conditions, and that water activity is one of the dominant factors in the regulation of their production.