S. H. DUKE (1), C. A. Henson (2), M. A. Vinje (3); (1) Department of Agronomy, University of Wisconsin, Madison, WI, U.S.A.; (2) USDA, ARS, Cereal Crops Research Unit, and Department of Agronomy, University of Wisconsin, Madison, WI, U.S.A.; (3) USDA, ARS, Cereal Crops Research Unit, Madison, WI, U.S.A.

Poster

This study was primarily conducted to test the hypothesis that wort osmolyte concentration (OC) would correlate much better than malt extract (ME) with barley amylolytic enzyme thermostabilities of malts produced over several days of germination. This hypothesis was largely based on the results of a previous study indicating higher thermostability for beta-amylase and limit dextrinase in malts produced early in seed germination. Seeds of 4 two-row and 4 six-row North American elite barley cultivars were steeped and germinated in a micromalter. At 24 hr intervals throughout 6 days of germination, green malt was removed and kilned. Malts were assayed for alpha- and beta-amylase and limit dextrinase before and after mashing at 70°C for 30 min to determine thermostabilities. Wort OC, ME, and ASBC measures of malt quality were determined for all days of germination. For all cultivars combined over all days of germination, wort beta-amylase thermostabilities correlated much better with wort OC (r = –0.616, P < 0.0001) than with wort ME (r = –0.464, P = 0.0009). Correlations of limit dextrinase thermostabilities were also much better with wort OC than with ME (r = –0.874, P < 0.0001; r = –0.680, P < 0.0001, respectively). Two- and six-row cultivar beta-amylase thermostabilities correlated much better with OC than with ME (two-row: OC, r = –0.577, P = 0.0031; ME, r = –0.403, P = 0.0510; six-row: OC, r = –0.647, P = 0.0006; ME, r = –0.498, P = 0.0133). Two- and six-row cultivar limit dextrinase thermostabilities also correlated much better with wort OC than with ME (two-row: OC, r = –0.914, P < 0.0001; ME, r = –0.719, P < 0.0001; six-row: OC, r = –0.865, P < 0.0001; ME, r = –0.630, P = 0.0010). These data strongly support the tested hypothesis. Alpha-amylase thermostability was either unaffected or higher after mashing at 70°C. These data suggest that malt beta-amylase and limit dextrinase thermostabilities are a greater limitation to starch degradation as germination proceeds. This is reflected by OC much better than by ME. In general, wort OC values increased in malts produced until day 5 of germination, whereas ME only increased until 4 day of germination. This difference in the pattern of OC and ME development may have contributed to the better correlations of OC with thermostabilities. Beta-amylase intron III allelic variation had no affect on thermostability or activity on the day of optimal malt modification (day 5) or any other day where LSD analysis was significant, indicating that, as in our past studies, in North American barley germplasm beta-amylase thermostability and activity are not influenced by intron III allelic variation. For all cultivars combined, beta-amylase thermostabilities correlated negatively and highly significantly over all days of germination with initial alpha-amylase (r = –0.628, P < 0.0001), beta-amylase (r = –0.682, P < 0.0001), and limit dextrinase (r = –0.541, P < 0.0001) activities. Also, for all cultivars combined, limit dextrinase thermostabilities correlated negatively and highly significantly over all days of germination with initial alpha-amylase (r = –0.857, P < 0.0001), beta-amylase (r = –0.720, P 0.0001), and limit dextrinase activities (r = –0.910, P < 0.0001) activities. These data reflect the greater thermostabilities of beta-amylase and limit dextrinase from malts produced early in germination.

Stanley H. Duke received his Ph.D. degree in botany in the areas of plant physiology and biochemistry at the University of Minnesota, Minneapolis-St. Paul, in 1975. As a graduate student he received an NSF fellowship. He subsequently served as a post-doctoral fellow at the University of Wisconsin-Madison (UW-Madison) until he became an assistant professor of agronomy at UW-Madison in 1978. Stanley served as associate chair of the Department of Agronomy, UW-Madison, from 1989 to 1993 and served as chair from 1993 to 2004. Over the period from graduate student to departmental chair his research primarily focused on nitrogen and starch metabolism. His research in malting and mashing began after his service as chair, although he had an interest in malting and brewing for many years. He has served on the editorial boards of Plant Physiology (1987–1992) and ASBC Journal (2009–present).