Conformational changes and functional properties of acid-modified soy protein.

Changes to the conformation and functional properties of soy protein caused by mild acid treatment were investigated.Whena 2% soy protein solution in 0.05 n HC1was heated for 30min at 95°C, the functional properties of the protein, including its solubility, emulsifying properties and foaming properties, were greatly improved.It was found that the soy protein can be deamidated preferentially without significant cleavage of the peptide bonds under these carefully controlled conditions in dilute acid (0.05n HC1at 95°C for 30min).The functional properties of the soy protein were increased greatly with an increase in surface hydrophobicity at an early stage of the mild acid treatment.These results suggest that the improvement in the functional properties of acidmodified soy protein may be mainly due to an increase in surface hydrophobicity induced by deamidation and acid-induced denaturation.Plant proteins contain a large amount of asparagine and glutamine.The amide groups in the side chains of these amino acids play an important role in stabilizing the protein structure through hydrogen bonding.However, it is known that the amide groups are readily modified by relatively mild treatment.