关键词: 米根霉, 耐高温, L-乳酸, 乳酸脱氢酶, 乙醇脱氢酶

Abstract: The optimum temperature for Rhizopus oryzae fermentation is 32℃,but it is difficult to separate lactic acid and easy to be contaminated by other bacteria at this low temperature. A Rhizopus orzae mutant,mut-5,which was resistant to high temperature of 38 ℃ and still has stable genetic character after continuous 7 passages,was screened out by 60Co-γ irradiation at 400 Gy that gave a perfect positive mutation rate. Compared with the parent strain,the L-lactic acid concentration in broth fermented by the mut-5 for 72h increases by 24.15 %,and the ethanol concentration decreases by 9.27 %. The specific activity of lactate dehydrogenase(LDH) of the mut-5 up to 39.41 %,while the specific activity of alcohol dehydrogenase(ADH) falls down. In addition,the mut-5 has a higher reducing sugar consumption rate and biomass accumulation than the parent strain.

Key words: Rhizopus oryzae, heat-resistant, L-lactic acid, lactate dehydrogenase, alcohol dehydrogenase