Bio-conversion of lactose to ethanol by Kluyveromyces lactis yeast as a stage of cheese whey utilization

Growing accumulation of lactose-containing waste resulting from the growth of cheese production in Russia and throughout the world has increased interest in the search for new effective biotechnologies for their processing, including through the bioconversion of lactose into ethanol. The work used cheese whey with an initial lactose content of 40 g/L and a pH of 4.84, three industrial strains of Kluyveromyces lactis Y-2035, Y-2037, Y-2040, and the reference strain Saccharomyces cerevisae Y-187. We carried out yeast cultivation in a FA-2 fermenter (Prointech, Russia) for 48 hours in cheese whey with the addition of nutrient solutions and zinc ions, at a temperature of 34 °C, stirring, and aeration. As indicators of the dynamics and efficiency of the biotechnological process we choose pH, the number of yeast cells, the concentration of protein, lactose and ethanol in the culture medium for periodical control using commercial kits. After that, we calculated the growth rate, percentage and average rate of lactose utilization, average rate of ethanol formation, and fermentation efficiency. As a result, it was shown that the K. lactis Y-2035, K. lactis Y-2037 and K. lactis Y-2040 can utilize from 76.3 to 86.0 % lactose, while from 17.7 to 21.0 g/l of ethanol is formed in the medium. The fermentation efficiency varies in K. lactis strains from 75.6 to 89.7 % versus 5.6 % in the reference strain S. Cerevisiae Y-187. Among those studied the K. lactis Y-2037 strain has the maximum capacity for lactose utilization and ethanol formation. It is proposed to use technology for processing lactose-containing dairy industry waste by converting lactose into ethanol with yeast cultures K. lactis for obtaining promising raw materials, reducing pollution, as well as for the internal production of bioethanol, and to recommend the K. lactis Y-2037 strain for this purpose.