3. Results and discussions
3.1. Physical properties of koji
As shown in Fig. 1a, the initial pH of koji was 6.32, then the pH decreased to 6.12 after 24 h of
fermentation. However, it increased to 6.97 at the end of fermentation period. Similar results have also been
reported for A. oryzae in soybean koji by Liang et al. [4]. The increasing of pH of fermented matter was due
to the microbial metabolic activities especially various extracellular proteins production [4].
Moisture in substrates brings a suitable water activity and swells substrates for mold growth [12]. The
results showed that the initial moisture content of koji was 40% then increased to 45% at 12 h cultivation.
However, it decreased to 22% after 72 h of fermentation (Fig. 1a). The high moisture content at the beginning
of fermentation period resulted in decreasing the porosity of substrates and reduction of heat transfer.
Consequently, low enzymes activities at the beginning of cultivation period (Fig. 1b) might be caused by the
increasing of temperature (data not shown) [13].