Redox Reactions in Wheat Dough as Affected by Ascorbic Acid |
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Institution: | 1. Leibniz-Institute for Food Systems Biology at the Technical University of Munich, Lise-Meitner-Strasse 34, 85354, Freising, Germany;2. Biotask AG, Schelztorstrasse 54-56, 73728, Esslingen am Neckar, Germany;1. Soft Matter, Rheology and Technology, Department of Chemical Engineering, KU Leuven, Celestijnenlaan 200F, Box 2424, BE 3001 Leuven, Belgium;2. Laboratory of Food Chemistry and Biochemistry & Leuven Food Science and Nutrition Research Center (LFoRCe), Department of Microbial and Molecular Systems, KU Leuven, Kasteelpark Arenberg 22, Box 2463, BE 3001 Leuven, Belgium;3. Polymer Technology, Department of Mechanical Engineering, TU Eindhoven, Box 513, 5600 MB Eindhoven, The Netherlands |
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Abstract: | Ascorbic acid (AA) is used as bread improver, as its addition to dough causes an increase in loaf volume and an improvement in crumb structure. To explain these effects we review the stereospecificity of the improver action and the properties of ascorbate oxidase and glutathione dehydrogenase and the occurrence of low molecular thiols in flour and their concentration changes during dough mixing in the presence and absence of AA. On the basis of the results the improver action of AA is explained by a reaction sequence leading to a rapid removal of endogenous GSH, which otherwise would cause dough weakening by sulphhydryl/disulphide interchange reactions with gluten proteins. To test this hypothesis the binding sites of endogenous GSH in gluten proteins have been determined by the addition of35S-labelled GSH as a tracer to flour before dough mixing. The distribution of radioactivity in the gliadin and glutenin fractions of gluten obtained from dough indicates that the major portion of GSH is bound to glutenins. The isolation and sequence analysis of radioactive cystine peptides from an enzymatic digest of glutenins demonstrates that GSH is almost exclusively linked to those cysteine residues of LMW subunits that have been proposed to form intermolecular disulphide bonds. |
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