PHYSIOLOGICAL, BIOCHEMICAL AND GENETIC REGULATION OF CARBOHYDRATE METABOLISM IN CEREAL TISSUES
Location: Cereal Crops Research
Title: A Comparison of Barley Malt Amylolytic Enzyme Activities and Malt Sugar Concentrations
Submitted to: Journal of American Society of Brewing Chemists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 2, 2009
Publication Date: April 5, 2009
Citation: Duke, S.H., Henson, C.A. 2009. A Comparison of Barley Malt Amylolytic Enzyme Activities and Malt Sugar Concentrations. Journal of American Society of Brewing Chemists. 67:99-111.
Interpretive Summary: The conversion of starch to fermentable sugars during mashing is critical as these sugars are fermented into alcohol by brewers’ yeast. The enzymes necessary to convert starch to fermentable sugars are well known, but are not individually and independently measured during malting and mashing with the exception of alpha-amylase. It is standard practice to measure the collective action of these enzymes in a single assay, termed diastatic power, which cannot be apportioned among the individual enzymes and is generally accepted to be largely a measure of beta-amylase activity. The value of adding a specific measure of beta-amylase activity to the standard set of malting quality parameters is a topic of interest to the malting and brewing industries. This work demonstrates that the enzyme activity that correlates best the production of fermentable sugars is alpha-amylase. Hence, the addition of an assay specific for beta-amylase is unlikely to increase the ability of maltsters and brewers to predict the production of fermentable sugars.
This study was conducted to test the hypothesis that barley malt alpha-amylase activity would correlate better with malt sugar concentrations than the activities of beta-amylase, or limit dextrinase. Seeds of four two-row and four six-row North American elite barley cultivars were steeped and germinated in a micromalter for 6 days. At 24h intervals throughout germination, green malt was removed and kilned. Malts were assayed for individual amylolytic activities and malt sugars were extracted and assayed. Increases in malt alpha- and beta-amylase and limit dextrinase activities were greatest between day 1 and day 2 of germination. Over all days of germination, for all cultivars combined, malt alpha-amylase activities correlated much better with total malt sugar concentrations (r=0.830, P<0.0001) than beta-amylase activities (r=0.665, P<0.0001), and somewhat better than malt limit dextrinase activities (r=0.785, P<0.0001). Correlations of individual sugar concentrations (glucose, maltose, sucrose, fructose, and the maltodextrins maltotriose through maltoheptaose) for all cultivars combined over all days of germination were greater with alpha-amylase activities than with beta-amylase or limit dextrinase activities (e.g. glucose and maltose r values, respectively: alpha-amylase, r=0.872, P<0.0001, r=0.763, P<0.0001; beta-amylase, r=0.587, P<0.0001, r=0.679, P<0.0001; and limit dextrinase, r=0.806, P<0.0001, r=0.733, P<0.0001). Over all days of germination, individual cultivar malt alpha-amylase activities correlated better with total sugar concentrations (low to high r values, r=0.738, P<0.0001 [Harrington] to r=0.925, P<0.0001 [Legacy]) thanbetabeta-amylase activities (low to high r values, r=0.446, P=0.064 [Harrington] to r=0.891, P<0.0001 [Legacy]) or limit dextrinase activities (low to high r values, r=0.577, P=0.012 [Harrington] to r=0.867, P<0.0001 [Lacey]). Correlations of individual malt sugar concentrations for individual cultivars over all days of germination, for the most part, were greater with alpha-amylase activities than with beta-amylase or limit dextrinase activities (e. g. low to high r values for glucose: alpha-amylase, r=0.791, P<0.0001 [Garnet] to r=0.901, P<0.0001 [B1202]; beta-amylase, r=0.619. P=0.0008 [B1202] to r=0.849, P<0.0001 [Garnet]; limit dextrinase, r=0.763, P=0.0002 [Harrington] to r=0.890, P<0.0001 [Merit]). Overall, malt alpha-amylase activity correlated better with sugar production during malting and a short period of mashing than other malt amylolytic enzymes, supporting the tested hypothesis.