Abstract: Mucor spp.plays very important role in formation of a unique flavor of sufu in the brewing process.Fundamentally,improving sufu flavor namely the enhancing fresh flavor and reducing of bitterness can be achieved by solving the issues of high production of proteases and the formation of exopeptidase.This study aimed to obain the mutant strain of Mucor spp.with high production of proteases and the formation of exopeptidase by compound mutation,which can overcome the disadvantage of single mutation having no obvious repeated effect.Results showed that compared with primitive strain,under the mutagenesis conditions of radiation dose of Co60 8×104 roentgen and UV mutation time 60 s,the production capacity of amino acid of the mutant strain is increased by 22%.Under the fermentation conditions of culture temperature 28 ℃,time 48 h,initial pH 7.2 and inoculation amount 10%,the production capacity of amino acid of the mutant strain is increased by 30%,and the activity of exopeptidase is the highest.Because of the limitations of sufu product characteristics,the optimal salt and alcohol concentra-tions for fermentation are set at 6 % and 4 %.After fermentation,the products flavor of sufu is improved significantly,with delicious fresh flavor and little bitterness.

Key words: sufu, Mucor spp., compound mutation, fermentation condition