Improved ethanol production by cheese whey-based simultaneous saccharifying fermentation using 　Kluyveromyces marxianus KD-15 released from catabolite repression

Abstract

　To examine a method for producing Japanese spirits (shochu) from cheese whey-based fermentation broth, we evaluated the ethanol production by simultaneous saccharifying fermentation using Kluyveromyces marxianus KD-15 released from catabolite repression. The rice koji obtained by growing Aspergillus luchuensis or A. oryzae was mixed in combination with each yeast strain of K. marxianus NBRC1963 (wild strain), K. marxianus KD-15 and Saccharomyces cerevisiae NBRC10515. The pH, α-amylase and glucose forming activities as well as the glucose, lactose and ethanol contents in cheese whey-based fermentation broth were determined for 21 days. The results showed that the production of ethanol by K. marxianus KD-15 in combination with either koji was significantly higher than that by other yeast strains and the level in combination with rice koji obtained by A. luchuensis was approximately 30% higher compared with others. The α-amylase and glucose forming activities tended to decrease during fermentation. Nevertheless, the total amounts of lactose consumption in the fermentation broth using K. marxianus KD-15 were the highest even in combination with either koji, indicating that the improved ethanol production by K. marxianus KD-15 could be caused by its higher consumption ability of lactose derived from cheese-whey, but not of starch-derived glucose. These results show that K. marxianus KD-15 has high abilities of both cheese whey utilization and ethanol production even in the presence of mixture components including starch-degraded products, and is efficient for producing cheese whey-based Japanese spirits (shochu).