Comparisons of Amylolytic Enzyme Activities and β-Amylases with Differing Bmy1 Intron III Alleles to Osmolyte Concentration and Malt Extract during Congress Mashing with North American Barley Cultivars

Abstract

This study was conducted to determine the relationships between patterns of activity of malt amylolytic enzymes (α-amylase, β-amylase, and limit dextrinase) and the patterns of osmolyte concentration (OC) and malt extract (ME) production in two- and six-row North American barley cultivars over the course of Congress mashing and to test three hypotheses: 1) that maximal activity of and rates of increase in β-amylase activity during the initial phases of mashing would correlate better than the other amylolytic enzymes with OC and ME production, 2) that positive rates of change of OC would continue for a longer period than ME during mashing regardless of cultivar β-amylase intron III allelic variation, and 3) that β-amylase intron III allelic variation would have no significant association with the magnitude or OC and ME production during mashing. Malts of 12 barley cultivars were mashed in a micromasher and assayed for amylolytic enzyme activities and OC and ME levels at six time points during the 115-min Congress mashing regime. Maximal β-amylase activity correlated positively and significantly with OC (r = 0.701, P = 0.011) and better than with ME (r = 0.419, P = 0.175). Maximal α-amylase activity correlated positively and significantly with OC (r = 0.582, P = 0.047) but not as well as did β-amylase, nor did it significantly correlate with ME. Maximal limit dextrinase activity did not correlate significantly with either OC or ME. Rates of increase of β-amylase activity correlated well with rates of increase of OC (r = 0.656, P = 0.0205) but not with ME (r = 0.269. P = 0.398) during the initial phase of mashing (5 to 30 min). Rates of increase of α-amylase and limit dextrinase activities did not correlate significantly with OC or ME over this period. Rates of increase for wort OC and ME for each cultivar were greatest over the period from 5 to 30 min of mashing. Between 55 and 75 min, rates of increase of wort ME plummeted to near nil and remained significantly the same (P < 0.0001) for the remainder of mashing. In contrast, rates of increase in wort OC for each cultivar were still positive between 55 and 75 min, albeit at a lower level than earlier in mashing. For most cultivars, rates of increase in OC, although decreasing, remained positive until the end of mashing. β-Amylase intron III allelic variation had no apparent association with this pattern of OC change. The OC data indicate continued degradation of storage compounds for a significantly longer duration than increases in ME after the mass of material in wort had stabilized. Throughout mashing, cultivars with either the β-amylase Bmy1.a or Bmy1.b intron III alleles were not significantly different for the highest OC or ME. OC measurements resulted in more significant differences between cultivars than ME measurements. Also, OC did not consistently rank cultivars in the same pattern as ME during mashing, indicating that the intrinsic differences in the two methods yield slightly differing results. These data support all three hypotheses.