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Enzymes modifications of macromolecules from wheat from used in bread making

Final Activity Report Summary - BREAD ENZYMES (Enzymes modifications of macromolecules from wheat from used in bread making)

For many years, the only way used to modify dough properties has been to interfere in the gluten protein reticulation. This has been achieved by controlling the balance between SH groups and S-S bridges using chemicals (potassium bromate, ascorbic acid). Potassium bromate has been used extensively, as it enhances the baking performance and aids the development of a strong and resilient gluten matrix. But due the potential hazards associated with potassium bromate (Fischer et al., 1979; Dupuis, 1997), its use in bread making has been largely limited in American countries and prohibited in European countries. Therefore, an active research is devoted to oxidoreducing enzymes which can be proposed as bromate-replacers.

Another possibility to improve bread dough is to reticulate the major non-starch polysaccharides of wheat flour, i.e. Arabinoxylans (AX). AX are important in determining dough-handling properties and bread quality. They have the ability to form viscoelastic gels in the presence of oxidative agents like H2O2 / Peroxidase (POD), Polyphenol oxidase (PPO) or chemicals. Free radicals-forming oxidants are the more efficient ones. Although conflicting results have been published about the functional properties of AX in bread making, it appears that the water extractable AX content of wheat flours was positively correlated to their bread making potential in a French-type bread making process.

Among other oxidative systems, Horseradish POD (HRP) and laccase have been used successfully as gelling agents of AX solutions. The general aim of this work was to select enzymatic systems that could be used as bromate-replacers in order to modify the rheological properties of dough. Among the objectives, we wished to find out if the gluten network and the polysaccharide network are totally independent or if it is possible to create mixed cross-linking between proteins and AX by using oxidoreducing enzymes. Work was performed on model systems using free ferulic acid to represent the arabinoxylans and tyrosine to represent gluten proteins. We found the conditions where cross-linking between FA and Tyrosine was achieve. The ratio Tyr / FA necessary for the reaction to occur is very far from the natural Tyr / FA ratio in the flour. Then work was made on flour doughs. Gluten protein reticulation was followed by size exclusion HPLC. Proteins were less extractible from dough then from flour meaning that reticulation could limite the extraction process. Glucose oxidase (GOX), was added to the dough and a strengthening effect was observed, which was attributed to the activation of endogenous peroxidase by the hydrogen peroxide produced by GOX. This strengthening effect can be counteracted by the addition of free ferulic acid. Finally, rheological properties of the dough's were analysed using a texturometer: GOX dough's are more elastic than the control dough's. Ferulic acid dough's are less elastic than the control dough's.

We have not identified at time if a new mixed network between polysaccharide and protein was created or if the polysaccharide network promoted by POD (activated by GOX activity) can physically block the gluten macro polymers but experiments are currently done in order to answer the question.