ISOLATION AND SCREENING OF YEAST STRAINS FOR BIOETHANOL PRODUCTION USING SUGAR MOLASSES AND LIGNOCELLULOSE BIOMASS

Abstract

Ethanol is a highly useful hydrocarbon which is used extensively in major industrial and manufacturing processes. It is also used as fuel. Ethanol is mainly sourced from the fermentation of carbon-based feedstock by microorganisms such as yeasts, which can be found almost everywhere in the environment. In view of the anticipated shortage of the traditional supplies of fossil fuels, there is a great interest in the production of ethanol as an alternative biofuel in recent years. The main objective of this research work was to isolate and characterize stress tolerant and high potential ethanol producing yeast strains from various fruit juice. The potential yeast isolates capable of producing ethanol were isolated from rotten fruit juice samples of sugarcane, sweet lemon, grapes and guava and grown in YEPD medium. Six yeasts isolate S1, S2, Gr, M1, M2, and Gu were characterized based on morphological and physicochemical characters. Based on the morphological appearance of vegetative cells under microscope, colony character and physicochemical characters, the isolates were identified as yeast isolates. Selected yeast strains were checked for alcoholic fermentation using sugarcane molasses and organic kitchen wastes media. The fermentation of molasses was optimized with respect to pH, temperature and ethanol concentration. The results revealed the optimum condition was found as a 30°C, pH 6.0 and 5% ethanol for fermentation. Stress tolerance tests showed that the strains S1, S2 and Gr were found highly thermo-, pH- and ethanol-tolerant. Pycnometer and refractometer were used for estimating percentage of ethanol. Under optimized conditions, S1, Gu, Gr, S2, M1, and M2 produced 85% ,57%, 87%,47%, 60% and 70% of ethanol by using molasses. Kitchen- wastes resulted 53%, 25%, 43%, 42%, 59% and 37% ethanol production after 48 hours of fermentation by using yeast isolates S1, Gu, Gr, S2, M1, and M2. It was concluded that indigenous yeast isolates could be used for high production of bioethanol, spirit and industrial alcohol.