Five rye lines exhibiting a wide range of extract viscosities, along with commercial cultivars of rye and wheat, were compared with respect to their physical and chemical properties. Rye wholemeals contained significantly higher concentrations of total and soluble dietary fiber (TDF and SDF, respectively), total and water-extractable arabinoxylan (TAX and WEAX, respectively), 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 chromatography (GPC) of water extracts of rye wholemeals revealed the presence of a high molecular weight fraction (HMWF), which was found in higher concentration 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 wholemeals. Treatment of a rye wholemeal extract with xylanase, followed by GPC, indicated that the HMWF consisted primarily of WEAX. Successive treatment of a rye wholemeal extract with alpha-amylase, lichenase, protease, and xylanase confirmed that the viscosity of the extract was primarily related to its content of WEAX. WEAX was isolated from high, intermediate, and low extract viscosity ryes. Structural differences were observed among the three arabinoxylans using H NMR and high-pressure size exclusion chromatography with triple detection. The WEAX from high extract viscosity rye was a higher molecular weight macromolecule exhibiting a higher intrinsic viscosity, a larger radius of gyration, a larger hydrodynamic radius, and a lower degree of branching compared to WEAX from low and intermediate extract viscosity ryes.
Five rye lines exhibiting a wide range of extract viscosities were evaluated for the rheological and baking properties of their flours, individually and in blends with hard red spring wheat flour. Commercial cultivars of rye and triticale were included in the study as controls. Extract viscosities of rye flours were higher than those of corresponding wholemeals, indicating shifting of water-extractable arabinoxylan into flour during roller milling. Falling numbers of the rye flours correlated positively with their extract viscosities in the presence (r = 0.73, p < 0.05) or absence (r = 0.65, p < 0.05) of an enzyme inhibitor. Farinograms revealed the weakness of rye and triticale flours compared to wheat flour. Extract viscosities of rye flours were negatively correlated (r = -0.65, p < 0.05) with mixing tolerance index and positively correlated (r = 0.64, p < 0.05) with dough stability, suggesting a positive impact of extract viscosity on dough strength. Extract viscosity was negatively correlated (r = -0.74, p < 0.05) with loaf volume and specific volume (r = -0.73, p < 0.05) and positively correlated (r = 0.73, p < 0.05) with loaf weight of rye/wheat bread. Overall, the results indicated that 30% of flour from high or low extract viscosity rye could be incorporated into rye/wheat breads without seriously compromising bread quality. Inclusion of rye, particularly high extract viscosity rye, in chick diets seriously impeded growth performance and feed efficiency. Part of the arabinoxylan survived bread-making and exerted an effect on chicks, although substantially lower digesta viscosities were observed in chicks fed rye bread diets than in those fed rye wholemeals.
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