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Cross-Linking of Wheat Gluten Using a Water-Soluble Carbodiimide

¹Laboratoire de chimie agro-industrielle, Institut National Polytechnique, Ecole Nationale Supérieure de Chimie de Toulouse, 118 route de Narbonne, 31077 Toulouse cedex 4, France. ²Institute for Agrotechnological Research (ATO-DLO), Division Industrial Proteins, Bornsesteeg 59, PO Box 17, 6700 AA Wageningen, The Netherlands. ³Corresponding author. Phone: +33(0)562885720. Fax: +33(0)562885730. E-mail: vtropini@ensct.fr

Wheat gluten was cross-linked using water-soluble 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide HCl (EDC). To enhance cross-linking, N-hydroxysuccinimide (NHS) was added to the reaction mixture. The cross-linking efficiency was evaluated by the decrease in the amount of amino groups, the solubility of the protein in aqueous solutions with different pH levels, and by the change in the molecular weight distribution of the cross-linked compounds. Cross-linking was dependent on the reaction time, the molar ratio of added reactants, and the pH level of the reaction mixture. If the reaction was carried out at pH 3, no decrease in the amount of amino groups or solubility was observed. At pH 5–7, the amount of amino groups decreased from 15 to 10 mmol/100 g of protein. This was accompanied by a large decrease in the water solubility of the protein (<10%, w/v). Finally, reaction at pH 11 decreased the amount of amino groups from 15 to 8 mmol/100 g of protein. However, hardly any decrease in the water solubility was observed. Based on these results and SDS-PAGE experiments, two cross-link mechanisms are suggested: one resulting in inter- and the other resulting in intramolecular cross-links.