Morphological characters and protease properties of two strains of Aspergillus oryzae

Comparative studies on the differences of colony morphologies, hyphae morphologies and protease properties of mature koji between Aspergillus oryzae No.1 and No.2 had been conducted. The results showed that there was a big difference in morphological characters of two strains of A. oryzae. A. oryzae No.1 had larger colonies and its germination and sporulation were faster than that of No.2, its koji was little yellow with shorter hyphae and more pores comparing with A. oryzae No.2. The No.2 had small colonies, the spore germination time and spore producing time was later than the No.1, and it had longer and stronger hyphae, its koji had slant green color, and mature koji was partial white, and the enzyme production capacity was stronger. The results of studies on the properties of protease showed that the protease properties of mature koji between A. oryzae No. 1 and No. 2 were different: the optimum reaction temperatures were 45℃ and 50℃, and the optimum pH value were 6.0 and 9.0, respectively. In addition, the salt tolerances of proteinase were similar in the mature koji of two strains of A. oryzae. With the increase of salt concentration, the protease activity both decreased gradually. In 20% sodium chloride conditions, their protease activity both reduced to 20%-30% of the salt free conditions.