Ethanol production from raw starch by a recombinant yeast having saccharification and fermentation activities

Abstract

In order to develop a method for converting raw starch into ethanol efficiently, direct fermentation of ozonized raw starch using a recombinant yeast was investigated. Ozonolysis was carried out as a pretreatment to convert raw starch into ethanol rapidly and efficiently, and then the effect of the ozone degradation conditions on the degree of polymerization and the amount of amylose in a raw starch was determined. Since the degree of polymerization was low and the amount of amylose was high, raw starch treated with an ozone concentration of 40 gm À3 and an ozonation time of 30 min was the material chosen for alcohol fermentation. Though the recombinant yeast could not convert the untreated raw starch, it converted the soluble starch and the ozonized raw starch at a comparatively high yield into ethanol. About 56% of the ozonized raw starch decomposed, and the ethanol concentration obtained from the ozonized raw starch was markedly greater than that obtained from untreated raw starch. The dynamic behavior of cell growth, substrate degradation, and ethanol production was examined in a continuous culture under various dilution rates, and the optimal dilution rate, ie 0.15 h À1, was determined for maximizing the ethanol productivity (amount of ethanol produced per unit time).

Genetic Modifications of Saccharomyces cerevisiae for Ethanol Production from Starch Fermentation: A Review

“…Genetically modified flocculent strains produced higher ethanol levels compared to non-flocculent counterparts (4.61 kg.l -1 and 5.1 g.l -1 , respectively) in a 90 h fermentation period. However, the general accepted concept is that S. cerevisiae should express a high amount of α-amylase under aerobic conditions for effective starch fermentation [56,58]. As a different strategy, apart from genetically engineered S. cerevisiae that expresses recombinant α-amylase, ethanol production rate sometimes increased by addition of exogenous glucoamylase enzyme [53,59].…”