PHYSIOLOGICAL, BIOCHEMICAL AND GENETIC REGULATION OF CARBOHYDRATE METABOLISM IN CEREAL TISSUES
Location: Cereal Crops Research
Title: A comparison of barley malt osmolyte concentrations and standard malt quality measurements as indicators of barley malt amylolytic enzyme activities
Submitted to: Journal of American Society of Brewing Chemists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 2, 2009
Publication Date: April 5, 2010
Citation: Duke, S.H., Henson, C.A. 2010. A Comparison of Barley Malt Osmolyte Concentrations and Standard Malt Quality Measurements as Indicators of Barley Malt Amylolytic Enzyme Activities. Journal of American Society of Brewing Chemists. 67(4):206-216.
Interpretive Summary: Barley seeds that have the desired attributes to be rated as a malting barley command a premium in the marketplace. Although more than a dozen characteristics are assessed to determine the market grade of barley, the most important attribute necessary for a malt to receive this rating is based on its ability to convert starch, the primary storage compound in the seed, to simple sugars that can be fermented by brewers’ yeast. This ability is entirely dependent upon the activity of four enzymes. However, only one of these enzymes is specifically quantified as part of the specifications for rating barley malt. This is in part due to historical reasons but also due to the fact that specific measurement of the four individual enzymes is beyond the technical capabilities of many, if not most, maltsters and brewers. This is especially true for the nation’s expanding craft and microbrewing business community. The work conducted here compared the ability of a new test to predict these enzyme activities with the abilities of the six most characteristics most commonly measured by the malting and brewing industry. This work demonstrated the value of measuring osmolyte concentration by proving that this test of malt quality better predicts the activity of several of these important enzymes than do the standard, more laborious malt quality measurements that have been used for over a century. The impact of this rapid, simple, inexpensive new test will be that it can provide a versatile quality screening tool for broad use in the marketplace.
This study was conducted to test the hypothesis that barley malt osmolyte concentrations (OC) would correlate better with malt a-amylase, ß-amylase, and limit dextrinase activities than do the standard malt quality measurements (malt extract [ME], diastatic power [DP], ASBC a-amylase activity, soluble/total protein [S/T], and ß-glucan concentration). Seeds of four two-row and four six-row elite North American barley cultivars were steeped and germinated in a micromalter for 6 days. At intervals of 24 hr throughout germination, green malt was removed and kilned and then assayed for individual amylolytic activities, standard measures of malt quality, and OC. Over all days of germination, for all cultivars combined, malt OC correlated well with a-amylase, ß-amylase, and limit dextrinase activities (r=0.891, P<0.0001; r=0.659, P<0.0001; r=0.889, P<0.0001, respectively). With all cultivars combined most standard measures of malt quality did not correlate as well with malt amylolytic enzyme activities as did OC (low to high correlations with a-amylase activities [S/T, r=0.676, P<0.0001 to ß-glucan concentrations, r=-0.840, P<0.0001], ß-amylase activities [S/T, r=0.385, P=0.0068 to ß-glucan concentrations, r=-0.597, P<0.0001], and limit dextrinase activities [S/T, r=0.636, P<0.0001 to ß-glucan concentrations, r=-0.847, P<0.0001]). Two expected exceptions were a-amylase activity as measured by the ASBC method, which correlated better with Megazyme a-amylase activity than did OC, and DP, which correlated better with ß-amylase activity than did OC. In general, combined two-row cultivar malt OC and standard malt quality measurements correlated better with individual amylolytic enzyme activities than those measurements of combined six-row cultivars and, in general, OC correlated better with amylolytic enzyme activities than standard malt quality measurements of combined two- or six-row cultivars. With individual cultivars no malt quality measurement correlated consistently better with amylolytic enzyme activities although OC correlated consistently well. Overall, with populations of cultivars malt OC was usually a consistent and better indicator of individual malt amylolytic enzyme activities than standard measures of malt quality, supporting the tested hypothesis.