β-Elimination reactions and formation of covalent cross-links in gliadin during heating at alkaline pH |
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| Authors: | Ine Rombouts Bert Lagrain Kristof Brijs Jan A Delcour |
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| Institution: | a Laboratory of Food Chemistry and Biochemistry and Leuven Food Science and Nutrition Research Centre (LFoRCe), Katholieke Universiteit Leuven, Kasteelpark Arenberg 20, Box 2463, B-3001 Leuven-Heverlee, Belgium |
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| Abstract: | The aim of this study was to increase insight into gluten polymerisation. While previous research on this topic focused on disulfide (SS) bonds, the present paper focuses on cross-links based on dehydro-protein formation through β-elimination reactions. Gliadin, the monomeric fraction of gluten containing no free sulfhydryl (SH) groups, was heated for 120 min at pH 8.0 and 130 °C, and cross-link formation was evaluated by determining extractability in sodium dodecyl sulfate containing buffer, reaction products of β-elimination reactions, and cross-links involving the latter. Heating decreased gliadin extractability. Reduction of SS bonds increased extractability of heated gliadin, but did not restore it to that of non-heated gliadin, suggesting contribution of both SS and non-SS bonds to gliadin cross-linking. Decreased SS levels and the presence of dehydroalanine and SH groups in heated gliadin samples indicated cleavage of SS bonds by β-elimination reactions. Some of the formed free SH groups were then involved in oxidation and/or SH–SS interchange reactions leading to intermolecular SS bonds. In addition, amino acid analysis revealed formation of an irreversible non-SS cross-link between dehydroalanine and the free SH group of cysteine, namely lanthionine. In conclusion, non-SS bonds may well contribute to the gluten network under specified reaction conditions. |
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| Keywords: | Gliadin polymerisation Dehydroalanine Lanthionine Lysinoalanine |
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