Isolation of Multi Stress Tolerant Yeast for Ethanol Production at Elevated Temperature

Abstract

In recent decades, bioethanol and biofuels have emerged as alternatives to fossil fuels globally. Utilizing dairy waste (whey) as substrate is lucrative option for utilizing it and producing ethanol. Therefore, in deliberating the cost-effectiveness of ethanol fermentation there is a requirement of a microorganism strain that can convert substrate (lactose) into ethanol at higher temperatures. The study aims to isolate multi-stress tolerant lactose fermenting yeast strain for economical production of ethanol. Out of 215 samples of lactose fermenting yeast 9 strains were selected for ethanol production. Taxonomical identification and multi-stress tolerance (thermal, sugar, ethanol) of the 9 strains were conducted. After optimizing ethanol production at different temperatures (37℃, 40℃, 42℃, 45℃), significant ethanol production (8% v/v) could be observed at 37℃ in 40 h from 15% w/v lactose (YPL medium) while at 40℃ and 42℃ the productivity of ethanol slightly decreased, i.e., 7.5% v/v after 30 h with 0.5% residual lactose and at 45℃, only 3.5% v/v ethanol has been produced with approximately 7.5% w/v residual lactose. Thus, the isolated Kluyveromyces sp. 6C17 strain showed notable stress tolerance, making it promising for economical bioethanol production using lactose containing substrates at high temperature.