A Comparison of Barley Malt Amylolytic Enzyme Activities as Indicators of Malt Sugar Concentrations

Abstract

This study was conducted to test the hypothesis that barley malt α-amylase activity correlates better with malt sugar concentrations than the activities of β-amylase or limit dextrinase. Seeds of four two-row and four six-row North American elite barley cultivars were steeped and germinated in a micromalter for 6 days. At 24-hr intervals throughout germination, green malt was removed and kilned. Malts were assayed for individual amylolytic activities, and malt sugars were extracted and assayed. Increases in malt α- and β-amylase and limit dextrinase activities were greatest between days 1 and 2 of germination. Over all days of germination for all cultivars combined malt α-amylase activities correlated much better with total malt sugar concentrations (r = 0.830, P < 0.0001) than with β-amylase activities (r = 0.665, P < 0.0001) and somewhat better than with malt limit dextrinase activities (r = 0.785, P < 0.0001). Correlations of individual sugar concentrations (glucose, maltose, sucrose, fructose, and the maltodextrins maltotriose through maltoheptaose) for all cultivars combined over all days of germination were greater with α-amylase activities than with β-amylase or limit dextrinase activities (e.g., for glucose and maltose, respectively: r = 0.872 and 0.763 and P < 0.0001 for α-amylase; r = 0.587 and 0.679 and P < 0.0001 for β-amylase; and r = 0.806 and 0.733 and P < 0.0001 for limit dextrinase). Over all days of germination individual cultivar malt α-amylase activities correlated better with total sugar concentrations than with β-amylase or limit dextrinase activities. Correlations of individual malt sugar concentrations for individual cultivars over all days of germination, for the most part, were greater with α-amylase activities than with β-amylase or limit dextrinase activities. Overall, malt α-amylase activity correlated better with sugar production during malting and a short period of extraction than with other malt amylolytic enzymes, supporting the tested hypothesis.