Direct alcoholic fermentation of starchy biomass using amylolytic yeast strains in batch and immobilized cell systems

Abstract

Direct alcoholic fermentation of dextrin or soluble starch with selected amylolytic yeasts was studied in both batch and immobilized cell systems. In batch fermentations, Saccharomyces diastaticus was capable of fermenting high dextrin concentrations much more efficiently than Schwanniomyces castellii. From 200 g·l−1 of dextrin S. diastaticus produced 77 g·l−1 of ethanol (75% conversion efficiency). The conversion efficiency decreased to 59% but a higher final ethanol concentration of 120 g·l−1 was obtained with a medium containing 400 g·l−1 of dextrin. With a mixed culture of S. diastaticus and Schw. castellii 136 g·l−1 of ethanol was produced from 400 g·l−1 of dextrin (67% conversion efficiency). S. diastaticus cells attached well to polyurethane foam cubes and a S. diastaticus immobilized cell reactor produced 69 g·l−1 of ethanol from 200 g·l−1 of dextrin, corresponding to an ethanol productivity of 7.6g·l−1·h−1. The effluent from a two-stage immobilized cell reactor with S. diastaticus and Endomycopsis fibuligera contained 70 g·l−1 and 80 g·l−1 of ethanol using initial dextrin concentrations of 200 and 250 g·l−1 respectively. The corresponding values for ethanol productivity were 12.7 and 9.6 g·l−1·h−1. The productivity of the immobilized cell systems was higher than for the batch systems, but much lower than for glucose fermentation.