EXTRACTION AND PARTIAL CHARACTERIZATION OF BETA-GLUCAN FROM THE ENDOSPERMS OF 2 BARLEY CULTIVARS

(1 --> 2\1 --> 4)-linked-beta-glucan was extracted from dehusked flour of two barley cultivars, Waxiro and Cameo, by sequential treatment with water at 40 degrees C (S40), water at 90 degrees C with heat-resistant alpha-amylase (S90) and 1 M NaOH at room temperature (SA). The flours had similar beta-glucan contents, 5.1% for Waxiro and 4.7% for Cameo, and the sequential extraction released all the beta-glucan. The distribution of beta-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 beta-glucan for cultivar Cameo, whereas, for Waxiro, S40, S90 and SA contained 15, 55 and 35% of the beta-glucan, respectively. In both cultivars, polysaccharide (beta-glucan and arabinoxylan) and protein accounted for about 85% of each of the three fractions, but only S40 had a high beta-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 patter ns. Waxiro S40 beta-glucan had a higher weight-average molecular weight (M(w): 150k) and intrinsic viscosity ([eta] : 168 ml/g) than beta-glucan from Cameo S40 (M(w) = 80k; [eta] = 108 ml/g). The proportions of beta(1 --> 4)- (71%) and beta(1 --> 3)-linked (29%) residues were similar for beta-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 beta-glucan, and that the proportion of these units was different in Waxiro S40 and Cameo beta-glucan.