3.3. Growth of A. oryzae S. during koji fermentation
The growth of A. oryzae S. during koji fermentation was observed by a scanning electron microscope. As
shown in Fig. 2, A. oryzae S. grew continuously during cultivation period. The growth of mold also showed
the contrasting relation with the moisture content (Fig. 1a). The decrease of moisture content in koji is due to
the utilization of water in substrate by mold to generate mycelia [12].
Furthermore, the increasing of enzyme activity was also related to the growth of A. oryzae S. (Fig. 1b).
Sanchez and Pilosof (2000) have indicated that development of conidia and protease production of A. niger
are correlated during the fermentation period [14]. Additionally, the results showed that neither high content
of enzyme activity nor spore forming of mold was observed at the beginning of cultivation (24 h). However,
we found the formation of spores and the highest enzyme activities at 48 h of cultivation. The reason was
reported that the asexual cycle or spore forming is related to the secondary metabolite production, such as
enzyme and organic acid [3].
Fig. 2. Scanning electron micrographs of mycelium propagation on soybean koji fermentation. at 0 h (a), 24 h (b), 48 h (c) and 72 h (d