This study investigated the effects of temperature and sodium chloride concentration on the proteolytic
and amylolytic activities of soy sauce koji. The optimal temperatures for both protease and amylase
were found in the range of 50-55 °C. The protease was not stable at 55 °C and retained only 20%
residual activity after incubation at 55 °C for 4 h. The protease was labile in sodium chloride solution,
whereas the amylase was quite stable. The residual protease activity in an 18% NaCl solution was
only 3%. The harvested koji was mixed with 1.5 volumes of water (v/w) and incubated at 45 °C for
48 h; the total nitrogen and amino nitrogen contents were 1.3 and 0.56%, respectively. The results
indicated that the hydrolysis of koji at the critical temperature of 45 °C could be employed as a rapid
fermentation method to reduce the time for soy sauce manufacturing. According to this study, the
combination of 5% sodium chloride and fermentation at 45 °C was considered as the best condition
for the prohydrolysis of koji for making soy sauce. In addition, the critical temperature of 45 °C was
very important when used in the preparation of protein hydrolysates for the flavoring industry and for
the preparation of biologically active peptides.