Study of the mechanisms of action of ascorbic acid and azodicarbonamide during wheat (Triticum aestivum L.) bread making

Wheat bread is an important staple food for a significant part of the world population. Its recipe contains the essential ingredients wheat flour, water, yeast and salt, and optionally also some non-essential ingredients. Straight-dough wheat bread making, the most commonly used bread making process, starts by mixing the ingredients to form visco-elastic dough. During dough mixing, the wheat gluten proteins, which consist of glutenins and gliadins, form a continuous network which relies on non-covalent interactions and covalent bonds. During dough mixing, air, and thus also molecular oxygen (O2), is incorporated. The latter is involved in several reactions including the oxidation of sulfhydryl (SH) groups into disulfide (SS) bonds. The gluten network allows wheat flour dough to retain gas during fermentation and the early phases of baking. During further baking, the gas cells are opened up which results in bread with a typical spongy crumb structure. Chemical redox agents are often part of the recipe as non-essential ingredients to optimize wheat flour bread making performance or to overcome deficiencies in wheat flour quality. Ascorbic acid (AH2) and azodicarbonamide (ADA) are two important components in this context. During dough mixing, AH2 is oxidized by O2 into dehydroascorbic acid (DHA) through action of AH2 oxidase. However, the O2 in dough necessary for DHA formation is rapidly consumed by yeast and in reactions catalyzed by enzymes present in wheat flour. DHA oxidizes glutathione (GSH) in the presence of GSH dehydrogenase to its dimer GSSG. Otherwise, GSH would react with SS bonds of the glutenin component of wheat gluten proteins through SH/SS exchange reactions which would depolymerize glutenin to some extent resulting in dough weakening and low bread quality. It has been suggested that ADA rapidly oxidizes free SH groups of proteins during dough mixing resulting in additional SS bonds between and within glutenin proteins. The bread volume enhancing effect of ADA has mainly been linked to a reduction in the amount of work input needed during mixing. A major drawback of the use of chemical agents in bread making is that, in most territories where its use is allowed, they need to be listed on labels. In order to develop clean label alternatives, it is essential to fully understand their mechanisms of action. Against this background, the main objective of this doctoral dissertation was to study the mechanisms of action of AH2 and ADA during wheat b