Effect of ultrasound assisted heating on structure and antioxidant activity of whey protein peptide grafted with galactose

This work investigated the structure and antioxidant activity of Maillard reaction products of whey protein peptides grafted with galactose through ultrasound assisted water bath heating. The Maillard reaction time was 180 min including 0, 15, 30, 45, and 60 min ultrasound assisted water-bath heating performed at the beginning of the reaction. The results revealed that the intermolecular motion of the amino group and the carboxyl group of each amino acid was accelerated, and the secondary structures of whey protein peptides were changed by grafted galactose through ultrasound assisted heating. When subjected to the ultrasound treatment for 60 min, the reducing power of whey protein isolate (WPI) and conjugated whey protein peptides (WPP) reached 0.481 and 0.686, respectively. Additionally, the ABTS(+) radical-scavenging activity of WPI and WPP reached 42.19% and 49.05%, respectively. These results were significantly higher (P < 0.05) than those obtained using the water bath alone. The maximum of DPPH radical scavenging activity of WPI and WPP conjugates was 54.89% and 81.50%, respectively, with an ultrasound treatment of 30 min, which was also higher than that of the water bath alone (P < 0.05). WPP-Ga showed significant structural, differences and higher antioxidant activity than WPI-Ga (P < 0.05).