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Extraction of β-Glucan from Oats for Soluble Dietary Fiber Quality Analysis

¹U.S. Department of Agriculture, Agricultural Research Service, Hard Red Spring and Durum Wheat Quality Laboratory, Harris Hall, North Dakota State University, Dept. 7640, P.O. Box 6050, Fargo, ND 58108-6050. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. ²Corresponding author. Phone: (701) 239-1413. Fax: (701) 239-1377. E-mail: douglas.doehlert@ndsu.edu ³Department of Plant Sciences, North Dakota State University, Dept. 7650, P.O. Box 6050, Fargo, ND 58108-6050.

Extraction protocols for β-glucan from oat flour were tested to determine optimal conditions for β-glucan quality testing, which included extractability and molecular weight. We found mass yields of β-glucan were constant at all temperatures, pH values, and flour-to-water ratios, as long as sufficient time and enough repeat extractions were performed and no hydrolytic enzymes were present. Extracts contained about 30–60% β-glucan, with lower proportions associated with higher extraction temperatures in which more starch and protein were extracted. All commercial starch hydrolytic enzymes tested, even those that are considered homogenous, degraded β-glucan apparent molecular weight as evaluated by size-exclusion chromatography. Higher concentration β-glucan solutions could be prepared by controlling the flour-to-water ratio in extractions. Eight grams of flour per 50 mL of water generated the highest native β-glucan concentrations. Routine extractions contained 2 g of enzyme-inactivated flour in 50 mL of water with 5mM sodium azide (as an antimicrobial), which were stirred overnight, centrifuged, and the supernatant boiled for 10 min. The polymer extracted had a molecular weight of about 2 million and was stable at room temperature for at least a month.