Research On Mechanism Of Fermentation, Improvement Of Quaility And Mode Identification Of Sufu

Sufu, a kind of Chinese traditional fermented soybean food, is rich of nutrition. It has some disadvantages in competition at modern market due to its traditional processing methods. This paper is aimed to improve the traditional sufu production and develop a new kind of sufu by enzymatic treatment. The changes by proteolysis and texture profiles during grey sufu fermentation, the protease generated by the starter culture Actinomucor elegans (AS 3.227) and the lactobacillus separated from grey sufu and their contributtions to its flavor were firstly investigated. The physical and chemical properties and mode identification of 27 kinds of typical sufu were studied.Results of changes by proteolysis and texture profiles of sufu showed that the changes of texture, resulting mainly from the breakage of gel structure, mainly occurred duiring the initial 3 weeks of ripening. No granule proteins were found in ripened grey sufu. The contents of total water soluble protein and amino nitrogen reached to 35.36 g/100g and 2.40 g/100g (dry base). The hardness, firmness, stickness and adhesiveness were 96.7g, 479.2 J, 56.2g and 48.4J, respectively. The total content of free amino acid reached to 9.86 g/100g (dry base), in which Leucine, Alanine, Isoleucine, valine and Phenylalanine were dominant free amino acids and the rate was 76.30%. Methanethiol and disulfide dimethyl were main volatile components and no sulfureted hydrogen was detected under the experimental conditions. It was suggested that the combination of the changes of texture with the disappearance of granule protein and the content of amino nitrogen being 2.40 g/100g (dry base) could be index for ending proteolysis duiring the production of new sufu.There were two kinds of protease systems generated by Actinomucor elegans, intracellular and extracellular protease system. The intracellular protease system could be released by crashing the mycelial and the extracellular loosely clung outside of the mycelial . Both could be extracted well by 0.3 mol/L NaCl and showed similar molecular weights, precipitation curve by (NH4)2SO4 and hydrolysates, which implied that both the intracellular and extracellular proteases could be prepared simultaneously and they could be used for sufu ripening and the production of NSE. The optimum experimental conditions obtained by uniform design for production of protease were: the culture medium were 3.7% powder of soybean cake, 0.2% sucrose, 0.04% MgSO4 , 0.4% KH2PO4 and 0.1% CaCl2; the fermentation condition were 32 h, 4% inoculation, initial pH 9.0 and 90 mL culture medium per 500 mL conical flask. The protease preparation was comparatively stable under neutral condition, 40 ℃, 4% NaCl and 2% ethanaol content, which could be used as the condition for new sufu production.Three lactobacillus strains were separated from grey sufu, all of which could improve the flavor of grey sufu. Two of them were identified as Lactobacillus plantarum and Atopobium parvulus, respectively. The third strain (2#) showed similar colony, shape, morphological, physiological and biochemical properties with Pediococcus, however, 98% similarity with Salinicoccus roseus by 16S rRNA analysis. After the strain 2# was added to produce grey sufu, the content of free amino acid,sensory property and texture of sufu changed, which suggested the strain 2# was a potential non-starter lactobacillus that could improve the flavor of sufu and the new enzymatically treated sufuResults of physical and chemical properties and mode identification of sufu suggested that the six physical and chemical index could be replaced by three principal components. The models were F1=-0.801X1+0.845X2+0.553X3+0.815X4, F2=-0.923X6, F3=0.935X5. Total acid, amino nitrogen and water soluble solid were related to proteolysis and they had a high relative coefficiency. There was a close relationship between moisture content and concentration of Nad. The typical 27 types of Chinese sufu were classified into two groups, in which the center scores were 3.471 and -1.215, respectively. 96.3% of original cases w...