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).