Comparisons of Barley Malt Amylolytic Enzyme Thermostabilities to Wort Osmolyte Concentrations, Malt Extract, ASBC Measures of Malt Quality, and Initial Enzyme Activities

Abstract

The hypothesis that wort osmolyte concentration (OC) would correlate much better than malt extract (ME) with barley amylolytic enzyme thermostabilities of malts produced over several days of germination was tested. Seeds of four two-row and four six-row North American barley cultivars were malted in a micromalter and sampled every 24 hr throughout 6 days of germination. α- and β-amylases and limit dextrinase were assayed before and after mashing at 70°C for 30 min to determine thermostabilities. Wort OC, ME, and ASBC measures of malt quality were determined for each day of germination. For all cultivars combined, over all days of germination, wort β-amylase thermostabilities correlated negatively and highly significantly with both wort OC and ME, although more strongly with OC (r = −0.62, P < 0.0001; r = −0.46, P < 0.001, respectively). Correlations of limit dextrinase thermostabilities with wort OC were also much stronger than with ME (r = −0.87, P < 0.0001; r = −0.68, P < 0.0001, respectively). α-Amylase thermostability was either unaffected by or increased after mashing at 70°C. These data suggest that β-amylase and limit dextrinase thermostabilities become more limiting to starch degradation as reflected by OC than as reflected by ME as germination proceeds. β-Amylase intron III allelic variation had no effect on OC or ME in these North American barley cultivars. For all cultivars combined over 6 days of germination, the correlations for β-amylase and limit dextrinase thermostabilities versus the initial activities of α- and β-amylase and limit dextrinase were significant and negative ([β-amylase thermostabilities versus initial activities of α-amylases: r = −0.63, P < 0.0001, β-amylases: r = −0.68, P < 0.0001, and limit dextrinases: r = −0.54, P < 0.0001] and [dextrinase thermostabilities versus initial activities of α-amylase: r = −0.63, P < 0.0001, β-amylase: r = −0.68, P < 0.0001, and limit dextrinase: r = −0.54, P < 0.0001]). These data suggest that selection for high initial activity of any of these amylolytic enzymes would also select for high thermostability of β-amylase and limit dextrinase.