Studies on rye (Secale cereale L.) lines exhibiting a range of extract viscosities. 1. Composition, molecular weight distribution of water extracts, and biochemical characteristics of purified water-extractable arabinoxylan

Five rye lines exhibiting a wide range of extract viscosities, along with c ommercial cultivars of rye and wheat, were compared with respect to their p hysical and chemical properties. Rye wholemeals contained significantly hig her concentrations of total and soluble dietary fiber (TDF and SDF, respect ively), total and water-extractable arabinoxylan (TAX and WEAX, respectivel y), and beta -glucan than did wheat. Significant positive correlations were obtained between rye wholemeal extract viscosity and;SDF content (r = 0.90 , p < 0.05) and WEAX content (r = 0.89, p < 0.05). Gel permeation chromatog raphy (GPC) of water extracts of rye wholemeals revealed the presence of a high molecular weight fraction (HMWF), which was found in higher concentrat ion in the ryes than in wheat. A significant positive correlation (r = 0.84 , p < 0.05) was observed between HMWF content (expressed as a proportion of the total carbohydrate in water extracts) and extract viscosity of rye who lemeals. Treatment of a rye wholemeal extract with xylanase, followed by GP C, indicated that the HMWF consisted primarily of WEAX. Successive treatmen t of a rye wholemeal extract with a-amylase, lichenase, protease, and xylan ase confirmed that the viscosity of the extract was primarily related to it s content of WEAX. WEAX was isolated from high, intermediate, and low extra ct viscosity ryes. Structural differences were observed among the three ara binoxylans using H NMR and high-pressure size exclusion chromatography with triple detection. The WEAX from high extract viscosity rye was a higher mo lecular weight macromolecule exhibiting a higher intrinsic viscosity, a lar ger radius of gyration, a larger hydrodynamic radius, and a lower degree of branching compared to WEAX from low and intermediate extract viscosity rye s.