Determination of ethanol tolerance in yeast cultures isolated from indigenous starter murcha and the effects of uv mutation on ethanol tolerance

Abstract

Microorganisms improved through various methods of strain improvement have been used in industrial production of various organic compounds efficiently for consumption or use in food production. The use of yeast in food grade alcohol production from sugar may be the most known of these processes. In recent years, the research has shifted from the optimization of the reaction parameters to the improvement of the microorganism used. Strain improvement, usually done by gene manipulation are more precise but also tend to be cost-prohibitive. A simpler method to bring about improvement is by mutation of the microorganism. The primary objective of the investigation was the isolation and identification of fermentative yeast from an indigenous starter culture followed by improvement of the alcohol tolerance through UV mutation. The study took place in the laboratory of National College, Khusibu from March 2022 to July 2022. In the present study, 21 isolates were obtained from murcha samples of which 8 were found to be fermentative yeasts. These isolates were subjected to identification, and tolerance tests to sugar and alcohol followed by mutation of best-performing isolates. Isolates Y1 and Y11 were identified as having the best tolerance to sugar and alcohol and were subsequently exposed to UV radiation for mutation. The growth as observed through UV spectrophotometry at 600nm increased for isolate Y10 from 0.89 to 1.55, 0.54 to 0.97, 0.23 to 0.43 at 0%, 5%, 10% respectively, and an increase from 0.73 to 1.1.59, 0.57 to 0.89, 0.23 to 0.6 at 0%, 5%, 10% respectively for isolate Y11. Isolates Y10 and Y11 also grew at 12.5% of ethanol after mutation but they were not able to before UV treatment. The isolates Y10 and Y11 were identified as Saccharomyces spp. The mutated isolates were found to have increased tolerance to ethanol in terms of ethanol percentage while all mutated isolates were found to have more growth in the media than the unmutated isolates after UV irradiation.

Keywords: Yeast, Murcha, Indigenous Starter, Sugar Tolerance, Alcohol Tolerance, Mutation