Screening of protease-producing strains from traditional fermented soybean paste

The 389 fungal strains were isolated from 254 home-made soybean paste samples collected in the Northeast of China. Using skim milk plate screening, 31 strains with protease activity were obtained, including 12 strains of Aspergillus sp., five strains of Penicillium sp., four strains of Mucor sp., three strains of Fusarium sp., one strain of Scopulariopsis sp., three strains of Cladosporium sp., one strain of Absidia sp., and two strains of Monascus sp. Through secondary screening of fermentation, the protease activity of crude enzyme fluid was determined by Folin-reagent method.Two Aspergillus oryzae strains with high protease activity were screened.