Effect of Novel Engineered Aspergillus oryzae on Soybean Meal Fermentation and Optimization of Cultivation Conditions

The filamentous fungus Aspergillus oryzae is an important strain in fermentation industry. In this study, to test the possibilities of improving polypeptides production, the soybean meal fermentation products were used to investigate the efficiencies of four different novel recombinant engineered A. oryzae strains A. oryzae subC, A. oryzae asp, A. oryzae Ap and A. oryzae pep. Gel filtration was employed to separate the products produced by the four engineered strains and wild-type A. oryzae and the antioxidant activities of each component of the products were compared. The results showed that the proportion of small-molecule peptides produced by A. oryzae pep fermentation was higher, mainly in the range of 1000-2000 Da, when compared with that yielded by wild-type A. oryzae fermentation. The antioxidant activities of the different components of the fermentation products produced by various engineered strains, especially component I of A. oryzae pep, showed varying degrees of improvement on DPPH and ·OH free radical scavenging activities, reaching 73.1%±0.9% and 81.4%±1.2%, respectively. To further enhance the fermentation performance of A. oryzae pep, response surface methodology was used to optimize the fermentation conditions. The results indicated that the polypeptide conversion rate reached 40.4% following fermentation with 8% inoculum for 108 h at 31°C. These findings are significant for the development of A. oryzae strains and high-value utilization of soybean meal resources.