Exploring the variation in α-amylase activity and thermostability in green malt of diverse barley (Hordeum vulgare L.) germplasm

Abstract

This study investigated the activity and thermostability of α-amylase in green malt across a diverse panel of 54 barley genotypes, comprising 20 mutants, 19 hulled, 4 hulless, and 11 wild types, using starch as a substrate. The primary objective was to assess the variability in α-amylase activity among these genotypes and identify those with superior enzymatic activity and thermostability. Given that α-amylase is the most thermostable enzyme among the diastatic power enzymes yet exhibits significant activity reduction above 72.5 °C, a threshold frequently exceeded in industrial kilning and mashing. This research is therefore crucial for identifying genotypes that could enhance starch hydrolysis efficiency during mashing, a process critically dependent on sufficient enzymatic activity. We reported α-amylase activity and thermostability across a temperature range of 37 to 85 °C. The findings indicated that optimal temperature for α-amylase activity in barley malting lies between 65 and 75 °C. Interestingly, wild barley genotypes demonstrated the highest mean α-amylase activity, while hulless varieties exhibited the lowest. These results were validated by a significant negative correlation between α-amylase activity and the content of starch. Among the 54 genotypes, 11 displayed high α-amylase activity at 65 °C. Furthermore, one mutant (BL2105) and one wild genotype (WS230) exhibited high activity and thermostability at 75 °C, and another wild genotype (WS236) retained 30% of its original activity after heat treatment at 85 °C. These genotypes with enhanced α-amylase activity and thermostability could be strategically exploited in breeding programs to develop superior malt varieties. Such advancements could significantly enhance both malt quality and efficiency in beer production industry.