Effect of some additives on wheat gluten solubility: a structural approach

The effects of KCl, NaCl and cysteine on the solubility in water of partially hydrolyzed gluten were studied at different pH values. As expected, solubility was shown to depend on solution pH. It decreased to reach a minimal value at the isoelectric pH (pH 6) and then it increased. In the presence of additives, the same behaviour was observed with an increase in solubilities values. In fact, an improvement of solubility of 28–30% was observed in the case of KCl and cysteine, while NaCl was much less efficient. The solubilisation effect of such additives was found to decrease with the initial concentration of wheat gluten. The structural investigation, by analysis of the amide I region of the infrared spectra of gluten samples, solubilised in the presence of additives, showed an increase in the proportion of β-turns and extended structures, accompanied by a decrease in the α-helix proportion. Such results confirm and explain the improvement of wheat gluten solubility by enhancing water–protein bonding and reducing protein–protein interactions. Structural changes result in a better accessibility of more water molecules to the protein and in greater hydration and solubilisation effects.