PHYSIOLOGICAL, BIOCHEMICAL AND GENETIC REGULATION OF CARBOHYDRATE METABOLISM IN CEREAL TISSUES
Location: Cereal Crops Research
Title: Comparisons of amylolytic enzyme activities and ß-amylases with differing Bmy1 intron III alleles to sugar production during congress mashing with North American barley cultivars
Submitted to: Journal of American Society of Brewing Chemists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 21, 2012
Publication Date: December 11, 2012
Citation: Duke, S.H., Vinje, M.A., Henson, C.A. 2012. Comparisons of amylolytic enzyme activities and ß-amylases with differing Bmy1 intron III alleles to sugar production during congress mashing with North American barley cultivars. Journal of American Society of Brewing Chemists. 70:230-248.
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 of are desirable. Activities of Beta-Amylase are considered by many to be the key contributor to the diastatic power value. However results of correlations of this enzyme’s activities with diastatic power in many different genotypes from many different growing environments and during many different mashing processes vary from very strong to very weak associations. None of these studies focused on initial activities. The work done here focuses on initial rates of activities during early stages of industrial processing (i.e.mashing), which is when the majority of fermentable sugars are produced. Additionally, this work examined the potential utility of a genetic marker developed internationally as an indirect measure of the contribution of beta-amylase to diastatic power. The results support two hypotheses: (1) that beta-amylase activities correlate better than other starch degrading enzyme activities early in mashing and (2) the beta-amylase genetic marker previously utilized does not predict sugar production during mashing of North American genotypes. The impact of this research is that it aids North American barley breeders in selecting for high diastatic power by simply measuring beta-amylase activity early in mashing and without the time consuming sequencing of the beta-amylase gene.
This study was conducted to determine the relationships between patterns of activity development of malt amylolytic enzymes (a-amylase, ß-amylase, and limit dextrinase) and sugar production in two- and six-row North American cultivars during the course of Congress mashing and to test two hypotheses: 1) that rates of increase in and maximal activity of ß-amylase in the initial phases of mashing would correlate better than the other amylolytic enzymes with sugar production and 2) that ß-amylase intron III allelic variation would have little to no association on sugar production during mashing. Malts of twelve barley cultivars were mashed in a micro-masher and aliquots removed for amylolytic enzyme activity and sugar assays at 6 time points during the 115 min mashing regime. Peak activities of ß-amylase were positively and significantly correlated with wort total sugars (r=0.704, P=0.011), glucose (r=0.654, P=0.021), and maltose (r=0.780, P=0.003) and negatively and significantly correlated with maltotetraose (r=-0.830, P=0.001) and maltopentaose (r=-0.767, P=0.004) at the time of peak activity. In contrast, with the same comparisons, there were no significant correlations with wort total sugars for a-amylase and limit dextrinase and only a-amylase significantly correlated with some individual sugars (glucose, r=0.611, P=0.035; maltotriose, r=0.594, P=0.042; maltotetraose, r=-0.772, P=0.003; maltopentaose, r=-0.728, P=0.007). Correlations of rates of change ß-amylase activity from 5 min to maximal activity versus total sugars and individual sugars revealed positive and significant correlations with wort total sugars (r=0.794, P=0.002), maltose (r=0.851, P=0.0004), and maltotriose (r=0.605, P=0.038) and significantly negatively correlated with maltotetraose (r=-0.663, P=0.019) and maltopentaose (r=-0.677, P=0.016). In contrast, with the same comparisons, there were no significant correlations with wort total sugars or individual sugars versus a-amylase or limit dextrinase. Least significant difference (LSD) analysis revealed that there was no consistent pattern in total wort sugars and the most and least abundant wort sugars and maltodextrins produced during mashing amongst cultivars with Bmy1.a or Bmy1.b intron III alleles. Cultivars producing the highest levels of total wort sugars early in mashing, when the bulk of total sugars are produced or at the end of mashing as determined by LSD analysis had both the Bmy1.a (1st 30 min, Legacy, Tradition; end of mashing, Legacy, Pinnacle, Tradition) and Bmy1.b (1st 30 min, Harrington; end of mashing, Harrington, Merit) intron III alleles. This study supports both of the proposed hypotheses.