A Comparison of Barley Malt Osmolyte Concentrations and Standard Malt Quality Measurements as Indicators of Barley Malt Amylolytic Enzyme Activities

This study was conducted to test the hypothesis that barley malt osmolyle concentration (OC) would correlate better with malt alpha-amylase, beta-amylase, and limit dextrinase activities than do the standard malt quality measurements (malt extract, diastatic power [DP], alpha-amylase activity as measured by the ASBC method, soluble/total protein [S/F], and beta-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, kilned, and 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 alpha-amylase, beta-amylase, and limit dextrinase activities (r = 0.891, 0.659, and 0.889, respectively; P < 0.0001). 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 alpha-amylase activity [S/T: r = 0.676, P < 0.0001; beta-glucan concentration: r = -0.840. P < 0.0001]; beta-amylase activity [S/T: r = 0.385, P = 0.0068; beta-glucan concentration: r = -0.597, P < 0.0001]; and limit dextrinase activity [S/T: r = 0.636 P < 0.0001; beta-glucan concentration: r = -0.847, P < 0.0001]). Two expected exceptions were alpha-amylase activity as measured by the ASBC method, which correlated better with alpha-amylase activity as measured by the Megazyme method than did OC, and DP, which correlated better with beta-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 did 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 were standard measures of malt quality, supporting the tested hypothesis.