Application of a mixed koji-making system by Aspergillus oryzae and Aspergillus niger in soy sauce production

The neutral protease activity,acid protease activity,glucoamylase activity and the number of spores in separate koji-making and mixed koji-making by Aspergillus oryzae and Aspergillus niger were measured in this paper.The feasibility of multi-strains for soy sauce koji was discussed.The effects of using AS3.042 and AS3.350 as fermented culture on koji-making were investigated.The results showed that separate koji-making was better than mixed koji-making in all respects.The optimal koji-making conditions were obtained as follows: fermentation temperature 33℃,fermentation time 42h for A.oryzae and 48h for A.niger,and the ratio of A.oryzae to A.niger 2∶1.Under these conditions,total protease activity of koji was 2748U/g,which was similar to the value of the control.The acid protease and glucoamylase activity were 712U/g and 1090U/g,respectively,which was increase by 55.8% and 25.4% compared to that of koji-making by A.oryzae,respectively.