ARS | Publication request: A comparison of barley malt quality measurements and malt sugar concentrations

Submitted to: North American Barley Research Workshop Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: August 18, 2008
Publication Date: October 26, 2008
Citation: Duke, S.H., and Henson, C.A. 2008. A Comparison of Barley Malt Quality Measurements and Malt Sugar Concentrations. In: North American Barley Researchers Workshop Proceedings, October 26-29, 2008, Madison, Wisconsin. p. 29.

Technical Abstract: This study was conducted to test two hypotheses: (1) that malt osmolyte concentration (OC) values would be better correlated with malt sugar concentrations than malt extract (ME) values and (2) that malt alpha-amylase activity (alpha-AA) would be better correlated with malt sugar concentrations than diastatic power (DP). Seeds of four two-row and four six-row barley genotypes 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 ME, OC, DP, alpha-AA, and sugar concentrations. Sugars were extracted from milled malt in H2O at 70°C for 30 min. Except for cv. Harrington, total sugars increased throughout the entire 6 days of germination regime in two-row genotypes but either declined or plateaued after 4 days of germination in the six-row genotypes. Over all days of germination for all genotypes combined, OC correlated much better than ME with total sugar concentrations (OC, r=0.867, P<0.0001; ME, r=0.589, P<0.0001), strongly supporting the first hypothesis. When correlating individual sugar concentrations with ME and OC for all days of germination for all genotypes combined, OC also correlated much better than ME with glucose, maltose, sucrose, fructose, and the maltodextrins maltotriose through maltoheptaose [e.g. low to high r values for OC, r=0.642 (fructose) to r=0.924 and 0.928 (glucose and maltotetratose, respectively), P<0.0001; low to high r values for ME, r=0.282 (fructose) to r=0.723 (glucose), P=0.0524 to <0.0001], strongly supporting the first hypothesis. This may be explained by the observation that the level of magnitude for increases over six days in OC (48 and 58%, respectively for 2- and 6-row) for and total malt sugars (48 and 66%, respectively for 2- and 6-row) were similar, whereas the increases in ME (3.8 and 3.7%, respectively for 2- and 6-row) were not similar to that for total sugars. OC reflects the total number of hydrolytic cleavages of oligosaccharides, whereas ME only reflects hydrolytic gain (the insertion of H2O for each oligosaccharide cleavage). For all genotypes combined, alpha-AA correlated slightly better than DP with total sugar concentrations over all days of germination (alpha-AA, r=0.743, P<0.0001; DP, r=0.711, P<0.0001), supporting the second hypothesis. When correlating individual sugar concentrations with alpha-AA and DP for all days of germination for all genotypes combined, alpha-AA also correlated better than DP with most sugar concentrations [e.g. low to high r values for alpha-AA, r=0.517 (fructose) to r=0.900 (glucose), P= 0.0 002 to <0.0001; low to high r values for DP, r=0.412 (fructose) to r=0.792 (maltotetraose), P=0.0037 to <0.0001], supporting the second hypothesis. Overall, malt OC correlated better with malt sugar concentrations than ME, DP, or alpha-AA, indicating that OC best predicts starch hydrolysis during malting and a subsequent short mashing period.