Oxidative Gelation of Solvent-Accessible Arabinoxylans is the Predominant Consequence of Extensive Chlorination of Soft Wheat Flour

Authors: Kweon, Meera; LOUISE, SLADE - FOOD POLYMER SCIENCE CONS; HARRY, LEVINE - FOOD POLYMER SCIENCE CONS

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2009
Publication Date: 7/30/2009
Citation: Kweon, M., Louise, S., Harry, L. 2009. Oxidative Gelation of Solvent-Accessible Arabinoxylans is the Predominant Consequence of Extensive Chlorination of Soft Wheat Flour. Cereal Chemistry. 86(4):421-424.

Interpretive Summary: Arabinoxylans and glutenins are two of the critical network-forming biopolymers of wheat flours, functionally related to mixing and baking performance and baked goods quality. For soft wheat flour applications, the solvent-accessible arabinoxylans play a dominant role in both sweet and savory products. It is well documented that aqueous extracts of wheat flour arabinoxylans form permanent gels when treated with oxidizing agents at room temperature. Chlorination is an essential soft wheat flour treatment for production of high-ratio cakes in the USA, frequently with a post-milling treatment to reduce flour particle size. Effects of milling yield, extent of chlorination, and flour particle size on cake flour functionality and batter viscosity were explored by solvent retention capacity (SRC) and Bostwick flow. The effects of the extent of chlorination were dramatic, but milling yield and additional milling to reduce particle size were less significant factors. Bostwick flow showed a characteristic pattern as a function of the extent of chlorination: a significant increase in flow for lightly chlorinated flours, due to the large decrease in glutenin network swelling (decrease in lactic acid SRC); but a dramatic decrease in flow for heavily chlorinated flours, due to the exaggerated increase in arabinoxylan network swelling (sharp increase in sucrose SRC) caused by oxidative gelation of solvent-accessible arabinoxylans. The difference in Bostwick flow, without and with added hydrogen peroxide, exactly mirrored the pattern measured by sucrose SRC, suggesting oxidative gelation of solvent-accessible arabinoxylans had occurred during chlorination. Treatment with endoarabinoxylanase resulted in increased Bostwick flow and decreased SRC values in water and sucrose. The increased flow was much greater for heavily chlorinated flours than for lightly chlorinated flours, suggesting significant depolymerization of oxidative gels that were created during extensive chlorination. Most importantly, addition of hydrogen peroxide after incubation with endoarabinoxylanase caused no further change in Bostwick flow.

Technical Abstract: Solvent retention capacity (SRC) and Bostwick flow were used to explore the effects of milling yield, extent of chlorination, and flour particle size on cake flour functionality and batter viscosity. The effects of the extent of chlorination were dramatic, but milling yield and additional milling to reduce flour particle size were less significant factors. Bostwick flow showed a characteristic pattern, as a function of the extent of chlorination. The difference in Bostwick flow, without and with added hydrogen peroxide, exactly mirrored the pattern measured by sucrose SRC, suggesting that oxidative gelation of solvent-accessible arabinoxylans had already occurred during chlorination. Treatment with endoarabinoxylanase resulted in increased Bostwick flow and decreased water and sucrose SRC values. The increased flow was much greater for heavily chlorinated flours than for lightly chlorinated flours, suggesting a significant depolymerization of oxidative gels that had been created during extensive chlorination. Based on our results, it was shown that sucrose SRC is a powerful predictor of the functional contributions resulting from extensive chlorination of soft wheat cake flours, and especially from the creation of oxidative arabinoxylan gels during heavy chlorination. It is suggested that lactic acid SRC is a revealing indicator of the effect of the extent of chlorination for lightly chlorinated flour, because it illustrates the diminished capacity to form glutenin networks. Moreover, these SRC responses provide a more reliable indicator of the extent of chlorination than does the traditional measurement of flour pH, as well as providing a functional alternative to the analytical measurement of chlorine uptake.