Effect of fruit pulp supplementation on rapid and enhanced ethanol production in very high gravity (VHG) fermentation

Background: The energy crisis and climate change necessitate studying and discovering of new processes involved in the production of alternative and renewable energy sources. Very high gravity (VHG) fermentation is one such process improvement aimed at increasing both the rate of fermentation and ethanol concentration. The technology involves preparation and fermentation of media containing 300 g or more of dissolved solids per liter to get a high amount of ethanol. Findings: Saccharomyces cerevisiae was inoculated to the very high gravity medium containing 30% to 40% w/v glucose with and without supplementation of three selected fruit pulps (mango, banana, and sapota). The fermentation experiments were carried out in batch mode. The effect of supplementation of 4% fruit pulp/puree on the metabolic behavior and viability of yeast was studied. Significant increase in ethanol yields up to 83.1% and dramatic decrease in glycerol up to 35% and trehalose production up to 100% were observed in the presence of fruit pulp. The fermentation rate was increased, and time to produce maximum ethanol was decreased from 5 to 3 days with increased viable cell count. The physical and chemical factors of fruit pulps may aid in reducing the osmotic stress of high gravity fermentation as well as enhanced ethanol yield. Conclusions: It was found that fruit pulp supplementation not only reduced fermentation time but also enhanced ethanol production by better utilization of sugar. Production of high ethanol concentration by the supplementation of cheap materials in VHG sugar fermentation will eliminate the expensive steps in the conventional process and save time.