Modification of soy protein hydrolysates by Maillard reaction: Effects of carbohydrate chain length on structural and interfacial properties

This study investigated the effects of carbohydrate chain length on the structural and interfacial properties of the Maillard reaction conjugates of soy protein hydrolysates (Mw > 30 kDa). The covalent attachment of sugars to soy peptides was confirmed by amino acid analysis and examination of the Fourier-transform infrared spectra. The results suggested that the emulsion stability of the conjugates increased as the length of the carbohydrate chains increased. The surface activity measurement revealed that the soy peptide–dextran conjugates were closely packed and that each molecule occupied a small area of the interface. It was further confirmed that the soy peptide–dextran conjugates formed a thick adsorbed layer at the oil–water interface, as observed in the confocal laser scanning micrographs. The interfacial layer of soy peptides was rheologically complex with broad linear viscoelastic region and strong elastic modulus, and the soy peptide–dextran conjugates might form multilayer adsorption at the interface. This study suggested that the improved surface properties of the soy peptide–dextran conjugates were a result of the strong membrane formed by the closely packed molecular and multilayer adsorption at the interface, which provided steric hindrance to flocculation.