Enhonced Production of Bioethano from Highly efficient Salt and Ethanol tolerant Yeast Isolated from Murcha

Abstract

Ethanol is one of the oldest product known to human that is obtained through traditional biotechnology which has been known for long time. It can be made from large variety of natural lignocellulosic renewable materials such as agricultural crops, industrial and domestic wastes etc. Microorganisms used for ethanol production must have high tolerance for ethanol, must grow vigorously and produce large quantity of ethanol. Among many other organisms, yeast is still the primary choice for the fermentation. As yeasts are ubiquitous they can be isolated from variety of substrate from the environment. Total 19 yeasts were isolated from 8 samples of Murcha collected from Bhaktapur and Lubhu. Murcha is an amylolytic starter used for the production of alcoholic drink. The 8 isolates were selected on the basis of high ethanol production as compared to others. The yeasts were identified based on the morphological and physiological characterization. The isolated yeasts were found to be Saccharomyces cerevisae, Zygosaccharomyces bailii, Pichia canadensis, Zygosaccharomyces rouxii, Saccharomycopsis fibuligera, S. exiguus and Pichia pijperi. Among them two were Saccharomyces cerevisiae and these were selected on the basis of high ethanol production. The viability count for salt tolerance found to be maximum at 14%. As the salt concentration was increased viability decreased gradually. However growth was seen up to 20% salt concentration. Likewise ethanol tolerance was seen up to 20% but the growth was very less. At substrate concentration of 15% highest ethanol of 6.52 mg/ml was produced by S2Y4 and for 20% highest ethanol produced by S2Y8 was 7.7 mg/ml. The temperature of 24oC and 28oC was found to be optimum, maximum ethanol produced at 28oC was 7.2 mg/ml by S2Y1 and at 24oC maximum ethanol produced was 7.4 mg/ml by S2Y8. Similarly, pH of 4.5 to 6 was found to be effective for higher concentration of ethanol production. At pH 4.5 S2Y8 produced 7.9mg/ml, at pH 5 S1Y3 produced 8.2mg/ml, and at pH 6 S2Y4 produced 7.4 mg/ml ethanol. Among the nitrogen sources used ammonium phosphate and urea was found to be effective for ethanol production. 6.9 mg/ml ethanol was produced by S2Y8 using ammonium phosphate whereas S1Y5 produced 8.7mg/ml ethanol using urea. These conditions were considered as optimum for ethanol production. However the optimizing parameters were species specific.