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Title: Comparisons of modern United States and Canadian malting barley cultivars with those from pre-Prohibition: II. Amylolytic enzyme activities and thermostabilities

item Henson, Cynthia
item DUKE, STANLEY - University Of Wisconsin
item Bockelman, Harold

Submitted to: Journal of the American Society of Brewing Chemists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2017
Publication Date: 1/17/2018
Citation: Henson, C.A., Duke, S.H., Bockelman, H.E. 2018. Comparisons of modern United States and Canadian malting barley cultivars with those from pre-Prohibition: II. Amylolytic enzyme activities and thermostabilities. Journal of American Society of Brewing Chemists. 76(1):38-49.

Interpretive Summary: Sustained increased interests over the past decade in the use of locally grown crops in local production of small batch, craft malt beverages combined with increased interests in the use of ‘heirloom’ varieties resulted in a series of studies to compare a broad spectrum of malt quality traits of pre-Prohibition malting barley cultivars with those of modern malting barley cultivars. This report, the second in a series, compares the activities and thermostabilities of four enzymes that convert starch in malt to fermentable sugars during mashing. Mashing is the process of extracting malt to make the nutrient solution that supports fermentation by brewers’ yeasts. The results show that modern cultivars have more activity of two of these four starch degrading enzymes than pre-Prohibition cultivars and have the same amount of the other two enzymes. Interestingly, all four of these enzymes in the heirloom cultivars were more resistant to the high temperatures used in the mashing process than were the enzymes in the modern cultivars. The impact of this work is the identification of several heirloom malting barley cultivars with the potential to provide the enzymatic activity and thermostability during mashing that is needed to produce sufficient fermentable sugars to be useful in a modern brewery. These heirloom cultivars (Silver King, Hanna, Manchuria) may be of interest to those craft brewers looking for heirloom cultivars for use in certain market applications.

Technical Abstract: United States and Canadian pre-Prohibition and modern elite malting barley cultivars were evaluated for activities of alpha-amylase, beta-amylase, alpha-glucosidase and limit dextrinase over the course of Congress mashing to determine the changes in activities and thermostabilities since the end of Prohibition. A comparison of mean activities and thermostabilities of the two populations showed that modern cultivars were significantly higher in alpha-amylase activities than pre-Prohibition cultivars at all stages of mashing. However, the pre-Prohibition alpha-amylases were more thermostable as 88% of their initial activity was retained at the end of mashing compared to 62% in the modern cultivars. The population means showed that modern cultivars were also higher in limit dextrinase for the first 60 min of mashing and, again, the limit dextrinases in the pre-Prohibition cultivars were more thermostable. There were no significant differences in either beta-amylase or alpha-glucosidase activities between the two population means at any time point during mashing although the pre-prohibition cultivar mean thermostabilities for both these enzymes were greater than in the pre-Prohibition cultivars than the modern cultivars. A comparison of the individual cultivar activities showed that the four or five cultivars with the highest activities of alpha-amylase were modern cultivars, identified Charles has having the most thermally activated and thermostable (116%) alpha-amylase among the modern cultivars and Tradition as having the least thermostable (21%) alpha-amylase of the modern cultivars. Among the pre-Prohibition cultivars, the most thermostable alpha-amylases were in Oderbrucker (132%) and Manchuria (127%). The cultivars with the highest beta-amylase activities at 30 and 45 min of mashing were Hanna and Manchuria and no cultivar had beta-amylase activity beyond 45 min of mashing. At the end of mashing, the cultivars with the highest three alpha-glucosidase activities and thermostabilities were Silver King, Hannchen and Oderbrucker with 88%, 52% and 53% thermostability, respectively. The modern cultivars with the highest activity and thermostabilities of alpha-glucosidase at the end of mashing were Tradition (47%) and Metcalfe (39%). The highest activities and thermostabilities of limit dextrinase at the end of mashing were in Manchuria (57%) and Hannchen (60%). The modern cultivars with greatest limit dextrinase thermostabilities were Tradition (44%) and Metcalfe (26%).