Structure and properties of water-soluble arabinoxylans from flours of Canada Western Red Spring (CWRS) wheats
Rattan, Onkar S.
Ten flours from eight different varieties of the Canadian Western Red Spring (CWRS) wheat class (Neepawa, Katepwa, Roblin, Columbus, Benito, Laura, Lancer, and Selkirk) were used to isolate arabinoxylans (AX), the mian constituent of water-soluble pentosans. Preliminary technological tests on the flours of these varieties have shown that the water-soluble pentosan content was significantly correlated to the ash content and starch damage (r = 0.79 and r= 0.68, p<_ 0.05, respectively). Chemical analysis has shown that the amount of bound phenolics (ferulic acid) varied among the AX of various flours; the highest amounts were detected in the varieties Neepawa and Roblin while the lowest amount was found for the preparation of Columbus. A small variation in the ratio of xylose/arabinose was found among the Ax, while gel filtation on Sepharose CL-2B has indicated substantial differences in the molecular size among these polymers. These results were consistent with the intrinsic viscosity values which ranged between 3.69-5.48 dl/g. Oxidative gelation (H202/peroxidase system) studies (as probed by dynamic rheometry) have shown that a certain minimum amount of oxidant was needed for effective gel network formation. Furthermore, the high molecular weight (HMW) AX samples (e.g. Katepwa B) formed rigid gels at lower concentrations than their low molecular weight (LMW) counterparts (e.g. Columbus). In addition to the molecular size, the ferulic acid content was found to play a role in determining the rigidity of the gel network. Purified AX also exhibited substantial surface activity as evidenced by the low surface tension values of their solutions. Fortification studies using two arabinoxylan preparations (a high, HMW and a low molecular weight, LMW, sample) and flours of diverse breadmaking quality (a composite sample 2CW of CWRS class and HY368 of the Canadian Prairie Spring Wheat class) indicated that these polymers increased the water absorption and the dough development time. Significant correlations were found between farinography absorption and amount of AX added (r =0.90-0.99, p <_ 0.05 for HMW- and LMW- supplemented flours of 2CW and HY368) Both HMW and LMW arabinoxylans, when added at different levels, were found to effect the loaf volume of breads baked from the two flours. The HMW arabinoxylan increased the loaf volume up to a level of fortification of 0.5% (w/w) for both flours. The LMW arabinoxylan increased the volume up to a fortification level of 0.7% in the case of 2CW flour. In contrast, for the HY368 flour there was a continuous increase in loaf volume with added LMW arabinoxylan up to a level of 1.1% (w/w)...