Submitted to: Journal of the American Society of Brewing Chemists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2013
Publication Date: 11/25/2013
Citation: Duke, S.H., Vinje, M.A., Henson, C.A. 2013. Comparisons of amylolytic enzyme activities and ß-amylases with differing Bmy1 intron III alleles to osmolyte concentration and malt extract during congress mashing with North American barley cultivars. Journal of American Society of Brewing Chemists. 71(4):193-207.
Interpretive Summary: The predication of the conversion of starch present in malted barley to fermentable sugars that can be used by yeast has been based primarily on one criterion, malt extract, for over 200 years and has more recently, in the past 100 years, been supplemented with a second criterion, which is diastatic power. While the use of these measures has undoubtedly resulted in improved quality of malting barleys grown around the world, more specific and/or discriminating methods are desirable. The work done here focuses on optimizing the application of a new tool to increase the ability to detect quality differences in the liquid stocks produced by malts of different barley cultivars used in North America to support fermentation. Additionally, this work examined the of a genetic marker developed internationally as an indirect measure of malt quality to determine its utility in North American barley breeding programs using molecular markers. The results demonstrate: 1) that maximal activity of and rates of increase in ß-amylase activity during the initial phases of mashing correlated better than the other amylolytic enzymes with OC rather than with ME production, 2) that positive rates of change of OC continued for a longer period than ME during mashing regardless of cultivar ß-amylase intron III allelic variation and 3) that ß-amylase intron III allelic variation had no significant association with the magnitude or OC and ME production during mashing. The impact of this research is that it aids North American barley breeders in selecting for high malting potential by reducing the need for and cost of a lengthy extraction at multiple temperatures followed by more expensive analyses as this work demonstrates the success of simply measuring OC after a brief isothermal extraction. Additionally, it eliminates the need for North American barley breeders to expend resources on an ineffective genetic marker in germplasm of North American parentage.
Technical Abstract: This study was conducted to determine the relationships between patterns of activity of malt amylolytic enzymes (a-amylase, ß-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 ß-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 ß-amylase intron III allelic variation and 3) that ß-amylase intron III allelic variation would have no significant association with the magnitude or OC and ME production during mashing. Malts of twelve barley cultivars were mashed in a micro-masher and assayed for amylolytic enzyme activities and OC and ME levels at 6 time points during the 115 min Congress mashing regime. Maximal ß-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 a-amylase activity correlated positively and significantly with OC (r=0.582, P=0.047) but not as well as did ß-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 ß-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 a-amylase and limit dextrinase activities did not correlate significantly with OC or ME over this period. These data support the first hypothesis. 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. ß-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. These data support the second hypothesis. Throughout mashing cultivars with either the ß-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 the third hypothesis.