Screening and application of high yield protease fungus from traditional fermented Pixian broad bean paste

Abstract:

[Background] Aspergillus oryzae can degrade proteins into nutrients such as peptones, peptides and various amino acids by the action of proteases. An important indicator of broad bean paste, amino nitrogen content is directly affected by protease. Therefore, Aspergillus oryzae plays a key role in the fermentation of broad bean paste. However, we still do not have an appropriative strain for the fermentation of broad bean paste. Thus, the study about high-yield protease fungus special for broad bean paste is meaningful for the development of the entire industry. [Objective] To screen appropriative fungi for broad bean paste and study the effect of fermented broad bean paste compared with Aspergillus oryzae 3.042. [Methods] We screened high yield protease fungi from koji produced by spontaneous fermentation. Then we use these screened fungi as starter to ferment broad bean paste. Then we detected the growth rates of the fungi and the concentration of protease through the koji process. In addition, we also detected the broad bean paste’s amino acid nitrogen and volatile flavor substances in order to analyze the flavor enhancement. [Results] Seventeen strains of high-yield protease were screened. Strain PCSM002 had the fastest growth rate, strain PCSM001 and PCSM002 showed the strongest protease production ability. Protease reached 1 450.25 and 1 703.25 U/g respectively after cultivated 72 h in bran medium. Amino nitrogen content of the fermentation broth with PCSM001 and PCSM002 reached 0.86 μg/kg after 24 days’ fermentation. Broad bean paste fermented by the two strains had rich aroma and perfection in taste. Both strains had been preserved in the Guangdong Provincial Collection of Microbial Strain, and the preserved numbers are GDMCC 60198 and GDMCC 60199 respectively. [Conclusion] The two high-producing protease molds screened in this experiment are expected to be used as the starter of broad bean paste, and provide special fermentation strain for the broad bean paste industry.