Qualitative Zymographic Studies of Major Proteinases from Malted Sorghum (Sorghum bicolor L.) and Effects of Cultivar

Abstract

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.

Influence of High Protein Digestibility Sorghums on Free Amino Nitrogen (FAN) Production during Malting and Mashing

“…This indicates that despite the higher lysine content and digestibility of these HPDS, the proportion of nitrogen as protein, as opposed to amino acids and peptides, was the same as in the NPDS. As expected, there was a very large increase in FAN, on average 65 mg/100 g sorghum in all the sorghums with malting, which was as a result of the action of the endogenous proteolytic enzymes 6,11,14 . The malts of the HPDS contained substantially higher levels of FAN than those of the NPDS, on average 32 mg FAN /100 g (51%) more.…”