Ethanol tolerance, osmotolerance and sugar conversion efficiency were used to screen yeasts for potential ethanol production from sweet-stem sorghum juice. Of the ten strains of Saccharomyces sp. that produced ethanol from the sorghum juice or from yeast extract/phosphate/sucrose (YEPS) media, the best sugar conversion efficiencies were greater than 85% for the strains Vin7, SB9, N96 and GSL. Vin7 and SB9 had higher sugar conversion efficiencies for sweet-stem sorghum juice, while strains N96 and GSL gave higher conversions in YEPS.

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Cereal Chem. 86(5):575-581Proteolysis during cereal germination is vital both to seedling growth and the success of commercial malting and brewing. In this study, proteinases in proteolytic extracts from seeds and germinated grains of 11 Botswana sorghum cultivars were analyzed and partially characterized by one-dimensional electrophoresis on SDS-PAGE gels containing incorporated gelatin. Proteinase polymorphism was detected in both germinated and ungerminated sorghum grains. Fifteen distinct proteinase bands, with M r valuesof 27,000-100,000 were detected in sorghum malt extract, while ungerminated sorghum displayed a maximum of four bands (M r ≈ 78,000-100,000). Band numbers and identity varied markedly according to cultivar. More proteinase bands were detected at pH 4.6, than at pH 6.2 and 7.0, suggesting pH optima considerably below neutrality. Cysteineproteinases constituted a higher proportion (9 of 15) of the detected sorghum malt proteinases and were most detectable at pH 4.6. Multiple representatives were also detected for both serine-and metallo-proteinases, although these were more active at pH 6.2 and 7.0. 1-10 Phenanthroline inhibited malt metallo-proteinase more strongly than EDTA, suggesting that these enzymes were most probably zinc-dependent. Aspartyl-proteinases were not detected, probably because of the substrate employed. Results indicate that the sorghum proteinase system is complex.