Optimization of Protease and Amylase Activities Derived from Soy Sauce Koji

Author(s): Nguyen Xuan Hoang, Ching-Hua Ting, Cheng-Kuang Hsu

The present study was aimed to determine the optimal fermentation conditions for the koji production and to evaluate the influences of temperature, pH, and brine concentration on the enzyme activity and stability of protease and amylase. The experiments were conducted by inoculating the different ratios of soybean to wheat with the spores of Aspergillus oryzae. The ratios of soybean to wheat were 2:1 and 1:1 in Chinese-type (BA1) and Japanese-type (BA2), respectively. The optimum time of koji-making for both BA1 and BA2 was found at 60 h fermentation. No remarkable difference of enzymatic characteristic was observed between BA1 and BA2, with the exception that BA1 exhibited the higher activities of both protease and amylase than those in BA2. The protease released from A. oryzae was most active and stable in the pH range 7.0-7.7 (neutral protease). The optimum temperature for protease activity was 52-55°C, and the enzyme was stable at around 40°C. Oppositely, the acidic region, pH 5, was preferred to amylase activity and stability. The amylase, which was most active at 60°C and stable at around 48°C, was more tolerant to heat and salt as compared to the protease.