Extraction and physicochemical characterization of rye β-glucan and effects of barium on polysaccharide molecular weight

Use of saturated Ba(OH)(2) to extract rye beta-glucan led to a depolymerized product. Similar depolymerization of beta-glucan was observed when oat bran was extracted with this reagent. Isolated oat beta-glucan, detarium xyloglucan, guar galactomannan, and wheat and rye arabinoxylan were also depolymerized by treatment with the barium reagent. The degree of depolymerization was related to time of contact with, and concentration of the barium. Rye beta-glucan of two different molecular weights (MW) were isolated and characterized. The structure of rye beta-glucan, as evaluated from the ratio of (1 -> 3)-linked cellotriosyl to (1 -> 3)-linked cellotetraosyl primary structural units, most closely resembles barley beta-glucan. Analytical variability of this ratio is discussed. A freshly prepared solution (2%) of the higher MW sample showed shear thinning behavior typical of cereal beta-glucans. The lower MW sample at 2% was not shear thinning, but on further purification, after storage for seven days, a 6% solution had gelled as shown by the mechanical spectrum.