Cereal Chem 68:221-227   |  VIEW ARTICLE

Total and Acid-Soluble Beta-Glucan Content of Hulless Barley and Its Relationship to Acid- Extract Viscosity.

R. S. Bhatty, A. W. MacGregor, and B. G. Rossnagel. Copyright 1991 by the American Association of Cereal Chemists, Inc. 

The relationship between total and acid-soluble beta-glucan and acid extract viscosity (AEV) was investigated in 13 genotypes of barley (12 hulless and one hulled low beta-glucan mutant for comparison). The range in AEV was 3.0-145.5 cS; in total beta-glucan, 3.9-5.4%. AEV was correlated (+0.83, P less than 0.01) with total beta-glucan percentage but with none of the other components of barley measured, such as starch, protein, pentosans, or their constituent sugars (arabinose and xylose). The acid-soluble fraction of barley contained 1.0-2.7% beta-glucan, 0.8-2.7% starch, 1.6-2.2% nitrogen, and 0.2-0.6% pentosans (determined by gas chromatography), representing an average of 44.7, 2.4, 81.8, and 14.8%, respectively, of their concentrations in the grain. Thus, besides beta-glucan, the major components of the acid-soluble fraction were nitrogen and pentosans. The correlations between AEV and soluble beta-glucan, starch, and pentosans were +0.71, P less than 0.01), +0.90, P less than 0.01), and +0.61, P less than 0.05), respectively. The positive correlation between AEV and soluble starch seemed coincidental, as the latter contributed very little to AEV; viscosities of acid extracts of three genotypes of barley containing 0.9-2.7% starch were completely abolished in 15 min on addition of beta-glucanase to the extracts. Earlier addition of protease and alpha-amylase to an acid extract of one genotype of barley did not lower viscosity significantly, but the viscosity was lowered by the addition of xylanase, a pentosan-hydrolyzing enzyme. The present data confirm that soluble beta-glucan is largely, and pentosans are to a minor extent, responsible for AEV in spite of AEV's large variability in genotypes of hulless barley.