Breeding of Aspergillus oryzae mutants with low levels of xylanolytic enzymes from soy sauce Koji mold and their utilization for the production Usukuchi soy sauce

摘要

Xylose is considered to be the main sugar component in the amino-carbonyl reaction (browining reaction) which occurs during the soy sauce fermentation process, and even after packaging in bottles. Xylose in the soy sauce mash is released from soybeans and wheat by the xylanolytic enzymes of the Koji mold, either Aspergillus oryzae or A. sojae. Several mutants difective in the formation of a clear zone on agar plates containing xylan were isolated from A. oryzae HL-15. The activities of the endo-xylanase and #beta#-xylosidase of the shoyu-Koji produced by the LX-02 strain, which had the lowest enzyme activities among the mutants isolated, were about 41 percent and 19 percent, respectively, of the enzymes in the parental strain. A small-scale soy sauce mash with the LX-02 strain produced less than 60 percent of the xylose concentration produced by the HL-15 strain during the aging period (30 deg C for 77 days). As a result, the absorbance at 530 nm, which represents the intensity of the brown color, of the raw soy sauce obtained from the LX-02 soy sauce mash was less than 90 percent of that of the HL-15 soy sauce. Moreover, there was a 9 percent reduction in the oxidative browning of the LX-02 usukuchi soy sauce compared to that of HL-15.