Analysis Of The Microorganism Separated From The Natural Fermented Bean Curd Of Yiyang City In Hunan Province And The Impact Of Salt Concentration On The Ripening Process Of Fermented Bean Curd

This paper used naturally-fermented sufu which a food factory of Yiyang city inHunan province provided as raw materials, analyzed the dominant microorganism in sufu,artificially inoculated fermentation was token, studied microbial changes and somebiochemical and physical changes during the preparation of the enzyme-ripening sufu,under different salt content. At last, studied the characteristics of mucor racemosusf.racemosus alkaline enzyme, results are as follows:（1） Carried on isolation and identification of dominant from sufu, determinated kindsof proteases and the optimum growth temperature. The results indicated that mucor M₁andM₅which were isolated from fugu were determinated as mucor racemosus fracemosus andmucor rouxianus.The optimal cultural temperature of M₁was30℃,culture duration72h.Under this optimal conditions, the neutral protease was2453.314u/g,the alkalineprotease was2808.765u/g, acid protease was383.330u/g.（2） Sufu is a Chinese soybean cheese obtained by solid-state fungal fermentation oftofu followed by ripening in dressing mixture.The aim of this study was to quantifymicroflora changes during the sufu process, which is carried out under non-sterileconditions.From tofu to pehtze （tofu overgrown with fungus） stages, total counts ofmesophilic aerobic bacteria（TMAB）, bacterial endospores（spores）, Bacillus cereus, lacticacid bacteria （LAB）, Enterobacteriaceae and fungi increased. All of them decreased afterthe salting of pehtze. TMAB and spores in sufu with8%and11%salt content decreased toaround106cfu/g during the ripening. B. cereusremained at around103cfu/g. LAB in sufuwith8%and11%salt content decreased gradually to <102cfu/g, but increased to109cfu/gin sufu with5%salt. Enterobacteriaceae and fungi decreased to non-detectable level after20and30days of maturation.（3） Sufu was prepared by ripening the salted tofu in the mash of mucor racemosusfracemosus, under different salt content. It was found that protease, a-amylase, lipaseactivities and crude protein, viscosity observed in the sufu reduced most pronouncedlyduring ripening period. Meanwhile, the content of Soluble protein、amino nitrogen totalacid were increased. Salt content of5%of the fermented sufu, soluble protein, amino acidnitrogen increased significantly higher than the salt solubility of8%,11%, which reflectsthe advantages of low salt fermented bean curd, but the total acid in the ripeningprocesshigh levels of and reach1.18g/100g in after-ripening20d, while the total estercontent lower, resulting in poor quality of fermented sufu. （4）The enzyme characters of alkaline enzyme from mucor racemosus f.racemosusisolated from sufu were studied.The results show that the maximum mucor racemosusf.racemosus alkaline enzyme activity reaction temperature were55℃,the optimum pHwas10.5,the thermal stability is relatively stable in the40-45℃,when the temperatureexceeds50℃the thermal stability quickly declined,salt concentration of mucor racemosusf.racemosus alkaline enzyme activity is very significant. With the the salt increase in theconcentration of enzyme activity decreased,when the salt concentration of21%,therelative enzymatic activities of only26.91%of the reference solution,Mn²⁺to the proteaseactivation, the relative enzyme activity as the control of171.843%;of Fe²⁺for theirperformance strongly inhibited the relative activity to almost zero.