Abstract:A strain of yeast producing a high ethanol yield was isolated from soybean molasses, and its fermentation characteristics were studied. The strain P14, with an ethanol yield of up to 9.07% (V/V), was isolated from soybean molasses by enrichment and isolation of strains, preliminary screening using a 2,3,5-triphenyl tetrazolium chloride (TTC) assay, and determination of ethanol tolerance and fermentation capacity. Strain P14 was identified as Saccharomyces cerevisiae on the basis of morphological characteristics, colony morphology, physiological and biochemical tests, and sequence analysis of the D1/D2 region of 26S rDNA. The effects of the concentration of soybean molasses, and addition of a nitrogen source and mineral salts on ethanol fermentation by Saccharomyces cerevisiae P14, as well as the utilization of oligosaccharides in soybean molasses by Saccharomyces cerevisiae P14 were studied. The results showed that soybean molasses concentration, and addition of a nitrogen source and mineral salts significantly influenced ethanol fermentation. The following conditions were determined to be optimal: 40% soybean molasses concentration, 1.2 g/L of peptone, and 0.4 g/L of added MgSO4. After fermentation for 72 h in this medium, 90.10% of glucose, 91.23% of sucrose, 92.56% of raffinose, and 96.97% of stachyose in molasses had been utilized by the yeast. Therefore, the Saccharomyces cerevisiae strain P14 identified from soybean molasses has a relatively strong capacity to produce ethanol by fermentation, using soy oligosaccharides present in soybean molasses.
