Purification, Growth Characteristic Of Soy Brewing Yeasts And Their Preliminary Application

In this paper, yeasts' purification, their growth curve cultured in malt wort or adding salt malt wort, reducing sugar consumption and yield of ethanol in yeasts' growth, effect of addition level of salt and calcium ion, pH and culture temperature on yield of ethanol in growth of yeasts and preliminary application in production were studied.At first, purification of four kinds of yeasts was implemented by streak plate isolation method. Four pure colonies were obtained by streak plate isolation, respectively. The results were confirmed by observation with microscope and the forms of yeasts were pictured. The pure yeasts for later study were prepared by inoculating the tube slant.The growth curves of four kinds of yeasts determined at malt wort and adding salt wort showed: four kinds of yeasts all took on three phase of their growth evidently, namely lag phase, log phase and stationary phase. The salt added into culture medium had significant effect on yeasts' growth, especially CanV yeast. Compared to malt wort, the growth curves of yeasts cultured in adding malt wort moved right and the three phases of growth had differently lengthened. Moreover, the total count during stationary phase all declined and the most was that of CanV yeast's.The determined content of reducing sugar and ethanol in the fermentation process of yeasts showed: the declined content of reducing sugar and increased content of ethanol were related to different growth phase of yeasts. They changed slowly during lag phase and rapidly during log phase and stationary phase. During decline phase, they changed slowly too because of autolyzation of yeasts and inhibition to yeasts' growth as a result of ethanol. After 54 hours, the contents of reducing sugar in T yeast, S yeast, CanV yeast and Saccharomyces rouxii culture medium were 1.512 mg/mL, 2.12 mg/mL, 1.125 mg/mL and 1.72 mg/mL, respectively and the ethanol contents in T yeast, S yeast, CanV yeast and Saccharomyces rouxii culture medium were 1.512%(w/w), 2.120%(w/w), 1.125% and 1.720%, respectively.The effect of salt concentration of culture medium, temperature, pH and addition level of calcium ion on yield of ethanol was studied. The results showed: the optimum culturing condition of T yeast were salt concentration 7%(w/w), temperature 28 ℃, pH 5 and calcium ion concentration 10^-3mol/L;the optimum culturing condition of S yeast were salt concentration 7%(w/w), temperature 25 ℃, pH 5 and calcium ion concentration 10^-4mol/L;the optimum culturing condition of CanV yeast were salt concentration 6%(w/w), temperature 32 ℃, pH 6 and calciumion concentration 10'4mol/L;the optimum culturing condition of Saccharomyces rouxii were salt concentration 8%(w/w), temperature 32 °C, pH 5 and calcium ion concentration 10³mol/L.With the application of above optimum conditions, the soy sauce production at laboratory was studied. The results showed: the ethanol content in soy sauce increased significantly, 2 to 6 times larger than that of natural curing soy sauce. They had significant effect on flavour and colour of product. Furthermore, some ethanol content is helpful to preserve of soy sauce.