Fermentation of grain sorghum starch by co-cultivation of schwanniomyces occidentalis and saccharomyces cerevisiae

Abstract The amylases of a Schwanniomyces occidentalis mutant hydrolysed grain sorghum starch completely. Heat pretreatment to effect gelatinization was essential for total starch hydrolysis. Ethanol fermentations were conducted by using a stationary-phase culture of S. occidentalis in conjunction with Sacchromyces cerevisiae to ferment the sugars liberated from the grain sorghum starch by the amylases of S. occidentalis. Increasing the grain sorghum concentration from 8 to 28% (m/v) did not affect the final ethanol yield of 0·45 g ethanol/g glucose equivalents, although the fermentation rate decreased considerably at the higher slurry concentration, requiring 8 days for completion of the fermentation. A 28% grain orghum slurry yielded 12·5% (w/v) ethanol, indicating that nearly 390 l of ethanol could be produced per tonne grain sorghum, with about 430 kg residual biomass containing 43% crude protein.

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