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​Malt Pasting Properties and Starch Molecular Structural Changes During Mashing

Barley malts differing in pasting properties were mashed to investigate how different malt pasting properties correlated with wort fermentable sugar (WFS) production and malt starch molecular structural changes during mashing. The whole-starch molecular size distribution before and after mashing and that of the individual chains following debranching were obtained using size-exclusion chromatography, where the individual chains were fitted with models to identify parameters for statistical treatment. Results showed that a larger than average size of branched amylopectin (R_h,Ap) significantly positively correlated with the pasting characteristics and, concomitantly, had a lower WFS content. With larger malt (R_h,Ap), less malt starch was solubilized during mashing, while the hydrolysis of starch molecules was also inhibited. Results also showed that for intermediate molecular sizes of branched amylose, the amount of malt amylose with short chain lengths and/or intermediate chains of malt amylopectin positively correlated with the final viscosity of malt determined using rapid visco analysis. An increased gelatinization temperature not only resulted in a lower content of WFS, but also a lower content of wort-soluble starches with larger molecules. Smaller malt starch molecules with shorter starch chains were preferentially hydrolyzed by malt β-​amylase. This study provides important information that indicates malt starch molecular structures affect the pasting properties of malt flour and, thereby, significantly determine the mashing efficiency of barley malts.

Keywords: amylopectin ion, amylose, barley, Hordeum vulgare, malt, starch molecular structure​