Improving solubility and emulsifying property of wheat gluten by deamidation with four different acids: Effect of replacement of folded conformation by extended structure

Abstract Deamidation was performed under different conditions to find the best way for preparing soluble wheat gluten and the conformation was also investigated to understand the mechanisms responsible for the functional changes. Wheat gluten was heated at 70 °C for 20 h with hydrochloric acid (0.08 M), malic acid (1.6 M), tartaric acid (0.8 M) and citric acid (1.0 M) or at 121 °C for 15 min with tartaric acid (0.8 M). Comparison of the degree of deamidation and hydrolysis showed that high temperature (121 °C) could accelerate deamidation and tartaric acid (0.8 M) could be the most appropriate acid to replace hydrochloric acid (0.08 M) for preparing deamidated wheat gluten of similar properties. It was confirmed by the results that the solubility and emulsifying property of deamidated wheat glutens were significantly improved, and the essential amino acid contents were enhanced. Circular dichroism and Fourier-transform infrared spectroscopy showed there was a decrease in β-sheet and a slight increase in random coil of deamidated wheat glutens. Wheat glutens of largely folded conformation tended to extend after deamidation based on fluorescence measurement showing the exposure of tryptophan residue to hydrophilic environment and enhanced surface hydrophobicity. The size of protein increased upon deamidation, which was observed by atomic force microscope, further illuminating that an extended conformation was adopted. The extended structure could at least partially contribute to the improvement of solubility and emulsifying property.