Extraction and Partial Characterisation of β-glucan from the Endosperms of two Barley Cultivars

Abstract

(1 → 2|1 → 4)-linked-β-glucan was extracted from dehusked flour of two barley cultivars, Waxiro and Cameo, by sequential treatment with water at 40°C (S40), water at 90°C with heat-resistant alpha -amylase (S90) and 1 M NaOH at room temperature (SA). The flours had similar β-glucan contents, 5·1% for Waxiro and 4·7% for Cameo, and the sequential extraction released all the β-glucan. The distribution of β-glucan in the different extracted fractions was different for the two cultivars. The S40, S90 and SA fractions each contained ca. 30% of the total β-glucan for cultivar Cameo, whereas, for Waxiro, S40, S90 and SA contained 15, 55 and 35% of the β-glucan, respectively. In both cultivars, polysaccharide (β-glucan and arabinoxylan) and protein accounted for about 85% of each of the three fractions, but only S40 had a high β-glucan content (53% for Waxiro and 65% for Cameo). The S90 and SA fractions from both cultivars had similar gel-permeation chromatography behaviour, whereas the S40 fractions gave different elution patterns. Waxiro S40 β-glucan had a higher weight-average molecular weight (Mw: 150k) and intrinsic viscosity ([η]: 168 ml/g) than β-glucan from Cameo S40 (Mw = 80k; [η] = 108 ml/g). The proportions of β(1 → 4)- (71%) and β(1 → 3)-linked (29%) residues were similar for β-glucan from both cultivars, as shown by methylation analysis. Licheninase degradation showed that blocks of cellotriosyl and cellotetraosyl units accounted for about 90% of the β-glucan, and that the proportion of these units was different in Waxiro S40 and Cameo β-glucan.