EXTRACTION AND ENRICHMENT OF (1-]3),(1-]4)-BETA-D-GLUCAN FROM BARLEY AND OAT BRANS

Beta-glucan was extracted and purified from Tupper barley bran (6.6% beta-glucan), Azhul barley bran (13.4% beta-glucan), and commercial oat bran (6.9% beta-glucan) with solvent 1 and, in the case of Azhul barley bran, with two additional solvents (2 and 3). Solvent 1 was distilled water adjusted to pH 10 with 20% sodium carbonate, solvent 2 was distilled water adjusted to pH 7, and solvent 3 was 4% (w/v) sodium hydroxide. Solvent 1 extracted 61-64% of the total beta-glucan from the barley brans and 70% from oat bran; solvents 2 and 3 extracted 72 and 84%, respectively, from Azhul barley bran. The final yields, in percent beta-glucan recovered from barley brans, were solvent 1, 52-55%; solvent 2, 40%; solvent 3, 81%. The yield from oat bran with solvent 1 was 61%. The purified preparations contained 72-81% beta-glucan + pentosans from barley brans and 84% from oat bran, expressed on an ash-free basis. They also contained 0.2-0.5% total nitrogen, 0.4-1.2% starch, 1.1-10.9% pentosans, and 3.7-12.6% ash. Ether extract was not detected in any of the preparations. Enrichment index, calculated by percent yield X (percent beta-glucan + pentosan, ash-free basis)/100, was highest for solvent 3 (65), lowest for solvent 2 (33), and varied from 38 to 51 for solvent 1. Sodium hydroxide (solvent 3) appeared to be a better solvent for extraction and purification of beta-glucan from barley bran. Size-exclusion chromatography of the three beta-glucan preparations from Azhul barley bran suggested an apparent molecular weight of about 2 X 10(6). Molecular weights of the preparations were not correlated with their flow viscosity.