Arabinoxylan distribution and functionality in selected mill streams and effect on flour blending

Daniel D. Ramseyer

Arabinoxylans (AX) are an important constituent in wheat flour that affects end-product attributes. It is of interest to determine the distribution and functionality of AX in flour mill streams in order to better formulate flour blends. Thirty-one genetically pure grain lots representing six wheat classes were milled on a Miag Multomat pilot mill. Ten flour streams were collected and analyzed for total arabinoxylan (TAX), water-unextractable arabinoxylan (WUAX) and water-extractable arabinoxylan (WEAX) content as well as oxidative cross-linking potential. A two-way ANOVA indicated that mill streams were the greater source of variation compared to grain lots for all response variables. TAX and WUAX were highly correlated with ash at r= 0.94 and r= 0.94, respectively. However, there were unexplained sample groupings in the 5th middlings. This indicates that, at times, arabinoxylan content and ash are largely independent phenomena. The correlation for WEAX and ash decreased in magnitude at r= 0.60. The oxidative cross-linking potential of mill streams was determined with Bostwick viscosity measurements. Flour slurries were made with either water alone (to measure the endogenous oxidative cross-linking) or with added hydrogen peroxide-peroxidase (to measure the enhanced oxidative cross-linking). Mill streams with high oxidative cross-linking potential were those with the largest differences between water and peroxide-peroxidase viscosity; these included: 1st Break, 1st and 2nd Middlings, and 1st Midds Re-dust. Conversely, mill streams 3rd Break and 4th and 5th Middlings were the least likely to form oxidative cross-links. The ability to form oxidative cross-links is dependent on the availability of ferulic acid and tyrosine residues. Therefore, the arabinoxylan and protein polymers in mill streams that have a high oxidative cross-linking potential have a structure that is more conducive to form oxidative cross-links. Straight grade and patent flour blends were also tested for oxidative cross-linking potential. Patent flour was more likely to form oxidative cross-links and produced larger cookie diameters and Japanese sponge cake volumes than straight grade flour. Indeed, the functionality of flour blends is related to which mill streams were selected for the formulation.

Arabinoxylan distribution and functionality in selected mill streams and effect on flour blending

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