Fermentation alcohol from grain sorghum starch

Abstract

Grain sorghum is an attractive agricultural feedstock for ethanol production because of its high starch content and the fact that it is more drought-resistant than other cereal crops such as maize. The popular bird-proof grain sorghum variety was investigated. This was subjected to a chemical pretreatment to remove the polyphenolic compounds prior to starch hydrolysis and subsequent fermentation. Starch hydrolysis was accomplished with a commercial α-amylase for liquefaction and amyloglucosidase for saccharification. Depending on the saccharification conditions, the hydrolysate contained 65 to 128 g litre⁻¹ glucose with corresponding maltose concentrations of 50 to 20 g litre⁻¹. Several yeast strains were evaluated for their ability to ferment maltose. The total saccharification plus fermentation time could be shortened substantially by inoculating after a brief saccharification period. The addition of ammonium chloride to the hydrolysate improved the fermentation rate. From a 30% grain sorghum slurry an ethanol concentration of over 12% (v/v) was obtained, which was 84% of the theoretical maximum. The data indicated that about 380 litres of ethanol could be produced per ton grain sorghum.