3.2. Enzyme production
The changes of neutral protease, alkaline protease and amylase production during soybean koji
fermentation were investigated (Fig. 1b). Neutral and alkaline protease activities of koji increased rapidly
after 24 h of fermentation. At 48 h of fermentation, soybean koji showed the highest neutral protease activity
at 84.38 unit/g of dry weight. However, alkaline protease activity was slightly increased and the activity was
lower than neutral protease. The highest alkaline protease activity was shown at the end of fermentation
period at 41.35 unit/g of dry weight. Amylase activity showed the highest activity (200 unit/g of dry weight)
at 72 h of fermentation. These results were similar to the previous study that extracellular proteins from A. 60 Chuenjit Chancharoonpong et al. / APCBEE Procedia 2 ( 2012 ) 57 – 61
oryzae on soybean koji were deduced by the intensity of time dependence during 48 h by digesting nutrients
from substrates [4]