Effects Of Inoculation Of Mucor Racemosus On The Quality Of Yunnan Low-salt Sufu

Yunnan sufu is a kind of white fermented bean curd made from soybean through milling,blank making,bacteria cultivation and fermentation.It is deeply loved by consumers because of its fine texture and delicious taste.However,sufu is still produced by natural fermentation in Yunnan.The open production environment makes the quality of sufu unstable.And the high salt in sufu brings health risks to consumers,thus limiting consumption.In this paper,the sufu in Yunnan Mouding was taked as the research object and Mucor racemosus(M2)was used as the fermentation strain of sufu.The quality difference between inoculated fermented sufu and naturally fermented sufu was investigated.And low-salt sufu was prepared,the influence of low-salt fermentation on the quality of Yunnan sufu was explored.The main research contents and results are as followed:Firstly,the growth characteristics of M2 was analyzed.The results showed that the pH of the culture medium had a certain influence on the growth of M2,and the optimum pH was 7.Culture temperature had a great influence on M2 growth.The optimum growth temperature was 20?,and when the temperature exceeded 35?,the strain can hardly grow.The strain can reach its maximum growth after 3 d of culture.Subsequently,M2 was used to prepare inoculated fermented sufu.The quality difference between inoculated fermented sufu and natural fermented sufu was studied.The results showed that after 90 d of fermentation,both natural fermented and inoculated fermented sufu reached the maturity standard of sufu.With the extension of fermentation time,the degree of protein hydrolysis in sufu was increased,and the degree of natural fermented sufu was slightly higher than that of inoculated fermented sufu.Texture of sufu was analyzed by texture analyzer and scanning electron microscope.The results showed that the hardness and viscosity of inoculated fermented sufu were significantly higher than those of natural fermented sufu(P < 0.05),and the internal structure of natural fermented sufu was denser and more uniform than inoculated fermented sufu.The flavor compounds of sufu during fermentation were analyzed by GC-MS.The results showed that 50 volatile flavor compounds were detected,including 16 esters,13 alcohols,5 acids,5 aldehydes,4 alkenes,3 ketones and 4 heterocycles.And the sufu with different fermentation strains and different fermentation times could be effectively distinguished by the principal component analysis method.The sensory evaluation results showed that the texture and aroma of inoculated fermented sufu was slightly better than that of natural fermented sufu after 90 d of fermentation.After 180 d of fermentation,the aroma,taste,texture and taste of inoculated fermented sufu was slightly better than that of natural fermented sufu.The total number of bacterial colonies in natural fermented sufu was significantly higher than that in inoculated fermented sufu,while the number of fungal bacterial colonies was significantly lower than that in inoculated fermented sufu(P < 0.05).The content of pathogenic bacteria in the two kinds of sufu met the standard(The reference standard is GB 29921-2013: National standard for food safety-limit of pathogenic bacteria in foods).The content of biogenic amines in sufu was determined by HPLC,and the results showed that the content of biogenic amines in natural fermented sufu was significantly higher than that in inoculated fermented sufu(P < 0.05).Thirdly,low-salt sufu with different salt content(M2-100%?M2-70%?M2-40%)was prepared by reducing the salt addition of inoculated fermented sufu.The effect of salt content on the quality of inoculated fermented sufu was studied.The results showed that low-salt fermentation could accelerate the hydrolysis of protein.With the decrease of salt content,the hardness of sufu gradually decreases and the internal structure becomes more compact and uniform.A total of 45 volatile flavor compounds were detected in low-salt sufu,including 15 esters,12 alcohols,5 acids,4 aldehydes,4 alkenes,2 ketones and 3 heterocycles.The volatile flavor compounds in three kind of sufu with different salt contents were similar,but the content changes were different.After 90 d of fermentation,the contents of volatile flavor compounds in M2-100%,M2-70% and M2-40% had no significant difference(P ? 0.05),while after 180 d of fermentation,the contents of volatile flavor compounds in M2-70% were significantly higher than those in M2-100% and M2-40%.The sensory evaluation results of low-salt sufu showed that the preference ranking is M2-70%> M2-40%> M2-100%,and M2-70% had the highest scores in taste and texture,while M2-40% had the lowest scores in taste and texture.The content of microorganism and biogenic amine in low-salt sufu was within the safe range.Therefore,M2-70% could be recommended for the actual production of low-salt sufu.