Effect of acetic acid deamidation-induced modification on functional and nutritional properties and conformation of...

Acids are often used for deamidating proteins, but the literature on acetic acid deamidation of proteins is sparse. Previous research on acetic acid-induced modification of proteins has focused on peptide proteolysis by relatively high concentrations of acetic acid (>1.5 mol L(-1)) rather than on the accompanying effect of deamidation. Therefore the objective of this study was to determine the deamidation effect of acetic acid with as little peptide proteolysis as possible by employing low-concentration acetic acid (<0.05 mol L(-1)) to deamidate wheat gluten. Changes in surface hydrophobicity, conformation, functional properties and nutritional characteristics of acetic acid-modified samples were determined and compared with those of hydrochloric acid (HCl)-modified samples.

At similar degree of deamidation and nitrogen solubility index, samples deamidated with acetic acid showed less destruction of peptides bandings, better foaming properties and a more decompacted form (lower S--S content in protein as determined by Raman spectroscopy) than those deamidated with HCl and also exhibited improved emulsification capacity and emulsion stability compared with native wheat gluten. Acetic acid deamidation led to fewer changes in peptide molecular size and secondary structure of wheat gluten compared with HCl deamidation according to the results of sodium dodecyl sulfate polyacrylamide gel electrophoresis and Fourier transform infrared spectroscopy respectively. Amino acid analysis revealed that the nutritional characteristics of wheat gluten were well maintained after deamidation with acetic acid.

The results show that low-concentration acetic acid can modify wheat gluten mainly by deamidation, resulting in deamidated wheat gluten with good functional and nutritional properties.