Physicochemical and structural characteristics of water-extractable arabinoxylan from rye lines varying in extract viscosity and its relationship to end-use characteristics
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Five rye (Secale cereale L.) lines ranging in extract viscosity (EV) from 5 to 95 cp were evaluated with respect to their physiochemical characteristics and those of their constituent water-extractable arabinoxylans (WEAXs). A significant positive correlation was observed between the EVs of rye wholemeals and their soluble dietary fibre and WEAX contents. Gel permeation chromatography of rye wholemeal water extracts revealed the presence of different proportions of a high molecular weight fraction (HAM), which correlated positively with their EVs. Treatment of a water extract of rye with xylanase followed by gel permeation chromatography indicated that the FDAW consisted primarily of arabinoxylan. Successive treatment of a water extract of rye with α-amylase, lichenase, protease and xylanase confirmed that the viscosity of the extract was primarily related to its content of arabinoxylan. Microscopic examination revealed that kernels of high EV rye had somewhat larger aleurone cells and thicker endosperm cell walls than did kernels of low EV rye. Extract viscosities of rye flours were higher than those of corresponding wholemeals, indicating concentration of WEAX in flour. Failing numbers of flours in the presence or absence of enzyme inhibitor correlated positively with their EVs. Farinography and breadmaking tests revealed that EV of rye flours and rye/wheat flour blends was positively correlated with dough stability and negatively correlated with loaf volume. Inclusion of rye, particularly high EV rye, in chick diets seriously impeded growth performance and feed efficiency. Substantially lower digesta viscosities were observed in chicks fed bread diets than in those fed wholemeals. Water-extractable arabinoxylan was isolated from high, intermediate and low EV ryes. Structural analysis using H-NMR indicated that the WEAX from high EV rye was a less branched macromolecule having a lower degree of di-substituted Xylp residues and a higher degree of un-substituted Xylp residues as compared to WEAXs from intermediate and low EV ryes. Size exclusion HPLC/triple detection revealed that the WEAX from high EV rye had a higher molecular weight, a larger radius of gyration, a larger hydrodynamic radius and a higher intrinsic viscosity compared to the WEAXs from intermediate and low EV ryes.