The wheat flour qualities for bread making can vary widely from one cultivar to another and from one year to another, whereas the bakers need a constant quality to obtain a bread of constant and good quality. Actually, the wheat flour qualities are corr ected by a mix of chemical additives. For many of them, these additives help in obtaining the adequate rheological properties of dough during the mixing process. They modify the dough properties by mainly acting on the cross-linking reactions leading to gluten network formation during mixing. The use of some of them is either limited or prohibited due to potential hazards (potassium bromate) or regulations for traditional products (ascorbic acid). The purpose of this project is to find enzymatic syste ms, which could be able to be used as alternatives to chemical additives leading to safer final products (mainly bread) with better organoleptic qualities. The enzymes, which will be studied, are mainly laceases (and other polyphenol oxidases) and perox idases. These enzymes could enhance the dough rheological properties by promoting the cross-linking of wheat flour macromolecules, the gluten proteins through their tyrosine residues and the pentosanes (arabino-xylans AX) through their ferulic acid (FA) moieties. For each enzymatic system, we will first study their ability to polymerise tyrosine and FA and to form covalent links between tyrosine and FA. Then, we will follow the FA incorporation in gluten proteins. Lastly, the effects of the selected e nzymes will be followed by two criteria. Firstly, by using a mixer developed in the laboratory, we will follow the effect of enzyme addition on the oxygen uptake and on the dough consistency during mixing. Secondly, the aggregation state of the gluten pr oteins will be analysed by size exclusion chromatography (SEC) and the formation of a mixed cross-linking between gluten and AX will be checked by the presence of xylose moieties covalently linked in the protein fractions separated by SEC.
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