Isolation, fractionation, and structural characteristics of alkali-extractable β-glucan from rye whole meal

The main nonstarch polysaccharide of rye is arabinoxylan (AX), but rye contains significant levels of (1 -> 3)(1 -> 4)-beta-D-glucan, which unlike oat and barley beta-glucan, is not readily extracted by water, possibly because of entrapment within a matrix of AX cross-linked by phenolics. This study continues objectives to improve understanding of factors controlling the physicochemical behavior of the cereal beta-glucans. Rye beta-glucan was extracted by 1.0N NaOH and increasing concentrations of ammonium sulfate were used to separate the beta-glucan from AX and prepare a series of eight narrow molecular weight (MW) distribution fractions. Composition and structural characteristics of the isolated beta-glucan and the eight fractions were determined. High-performance size-exclusion chromatography (HPSEC) with both specific calcofluor binding and a triple detection (light scattering, viscometry, and refractive index) system was used for MW determination. Lichenase digestion followed by high-performance anion exchange chromatography of released oligosaccharides, was used for structural evaluation. The overall structure of all fractions was similar to that of barley P-glucan.