Isolation, identification and application of Aspergillus oryzae BL18 with high protease activity as starter culture in doubanjiang (broad bean paste) fermentation

This study aimed to obtain an Aspergillus oryzae strain with high protease activity and to evaluate its potential to apply as starter culture in bean-based fermented foods (BBFFs) production using doubanjiang fermentation as research model. A. oryzae BL18 with higher protease activity than the commonly used starter A. oryzae 3.042 was obtained through two rounds of screening. Moreover, this strain was also proved to be safe to apply in BBFFs fermentation due to the lack of the ability to produce aflatoxin B1 through genomic and experimental analysis. A. oryzae BL18 was optimal to grow under 0–12% salinity, 25–40 °C and pH4-6. During koji-making, A. oryzae BL18 had stronger ability to produce spores (4.19 × 108 spores/g dry weight) and to secrete protease (4654.35 U/g) than A. oryzae 3.042 (2.89 × 108 spores/g dry weight and 3604.40 U/g). Significantly higher concentrations of umami amino acids and volatile flavor compounds were found in doubanjiang fermentation inoculated by A. oryzae BL18 while better sensory characteristics were observed. Therefore, A. oryzae BL18 might be a promising starter to apply in fermentation of doubanjiang or other BBFFs.