A Comparison of Barley Malt Amylolytic Enzyme Thermostabilities and Wort Sugars Produced during Mashing

Abstract

This study was conducted primarily to determine the relationship between barley amylolytic enzyme thermolability of malts produced over several days of germination and wort sugar concentrations produced during mashing. Seeds of 4 two-row and 4 six-row North American elite barley cultivars were steeped and germinated in a micromalter. At 24 hour intervals throughout 6 days of germination, green malt was removed and kilned. Malts were assayed for activities of α- and β-amylase and limit dextrinase before and after mashing at 70°C for 30 min to determine thermostabilities. Wort sugars were assayed after mashing. α-Amylase thermostability was either unaffected or higher after the 70°C mashing indicating that it is not thermolabile for 30 min at 70°C. In contrast, malt β-amylase and limit dextrinase thermostabilities greatly decreased between days 1 and 2, indicating a strong developmental influence on this parameter. For all cultivars combined, over all days of germination, malt β-amylase and limit dextrinase thermostabilities correlated negatively and highly significantly with total wort sugars (r = −0.656, P < 0.0001; r = −0.767, P < 0.0001, respectively) and with fermentable wort sugars. Six-row cultivar β-amylase and limit dextrinase thermostabilities correlated slightly better than two-row cultivar thermostabilities with total and individual sugar concentrations (e.g., total sugars: two-row β-amylase and limit dextrinase, r = −0.645, P < 0.0001, r = −0.770, P < 0.0001, respectively; six-row β-amylase and limit dextrinase, r = −0.686, P < 0.0001, r = −0.808, P < 0.0001, respectively). In contrast, the non-fermentable maltodextins, maltotetraose through maltoheptaose, correlated positively and highly significantly with β-amylase and limit dextrinase thermostabilities. These data suggest that β-amylase and limit dextrinase thermostabilities become more limiting to starch degradation as germination proceeds. Also, these data are in direct contrast to correlations of initial activities of these enzymes and wort sugars produced by malts over 6 days of germination. β-Amylase intron III allelic variation had no effect on thermostability or activity on the day of optimal malt modification (day 5) or any other day where LSD analysis was significant, indicating that, as in past studies, North American barley germplasm, β-amylase thermostability, and activity are not influenced by intron III allelic variation.