Water-soluble protein molecular weight distribution and effects on wheat malt quality during malting

Abstract

The content and the molecular weight distribution of wheat water-soluble proteins during malting were determined. Also, the relationships between wheat malt characteristics and water-soluble protein molecular weight distributions were studied. The water-soluble protein content was found to increase during malting and the increment was most significant on the first and second days. The molecular weight distribution of the wheat water-soluble protein was analysed by high-pressure size exclusion chromatography (HPSEC) and sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS-PAGE) methods. The HPSEC method showed that the content of all six molecular weight fractions (>24.4, 9.8–24.4, 3.9–9.8, 2.5–3.9, 0.4–2.5 and 24.4, 9.8–24.4 and 3.9–9.8 kDa fractions showed a declining trend during steeping but an increase during the first 2 days of germination. The content of the 9.8–24.4 kDa fraction increased during the process of kilning. Wheat had a high percentage of the >24.4 and 9.8–24.4 kDa fractions, while wheat malt had a high percentage of the 2.5–3.9 and 0.4–2.5 kDa fractions. The molecular weight fractions of the water-soluble protein had negative correlations with wheat malt viscosity and positive correlations with wheat malt extract. The SDS-PAGE analysis showed that the band of the 60 kDa water-soluble protein faded, while the bands of the 56, 44 and 12–15 kDa water-soluble proteins became darker during malting. Copyright © 2014 The Institute of Brewing & Distilling