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Ethanol is considered as one of the most suitable substitutes for the petroleum, since it offers attractive functional features at an economical cost. Glucoamylase producing yeasts were isolated and characterized. Based on the morphological character, carbon fermentations, assimilation of carbon and nitrate, growth on vitamine-free medicine, and urease activity, five isolates of Saccharomyces diastaticus, two isolates of Saccharomycopsis fibuligera, and two of Schwanniomyces occidentalis, and each isolate of Ambrosiozyma monospora and Lipomyces kononenkoae were identified. Among 12 isolates, one of the S. diastaticus, E3 showed the highest activity of glucoamylase and identified as Saccharomyces diastaticus. The hydrolysis of starch by the E3 strain showed the release of considerable amount of reducing sugar, along with the reduction in iodine staining capacity. The product of action of glucoamylase, glucose was determined by thin-layer chromatography. The enzyme activity was found to be stable in broad pH range of 5.0∼7.0 with optimal activity at pH 5.0∼6.0. The enzyme showed optimal activity at 50℃∼60℃. Soluble starch and glucose were better carbon sources for the enzyme production than xylose and glycerol Na^+ and Mg^(2+) increased the glucoamylase activity, however Hg^(2+) and Ag^(2+) inhibited the activity. Soluble starch was the best substrate for the enzyme activity.
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