Structure and antioxidant activity of whey protein isolate conjugated with glucose via the Maillard reaction under dry-heating conditions

The aim of this study was to investigate the structural characteristics and antioxidant activities of the Maillard reaction products obtained from whey protein isolate (WPI) and glucose (1:1 weight ratio) after dry-heating (60 °C and 79% relative humidity) for 0–7 d. The results revealed that the color (redness and yellowness), the UV–vis absorption, and the fluorescence intensity increased as the reaction time increased (P < 0.05). In addition, marked increases in the reducing power and the ABTS radical scavenging activities of the WPI–glucose conjugates were obtained with an increase in the reaction time (P < 0.05). The sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis illustrated that WPI and glucose formed high molecular weight conjugates. The increased Tmax demonstrated that the thermal stability of WPI was remarkably improved by its conjugation with glucose. The Fourier transform infrared (FT-IR) spectra suggested that the amide I, II, and III bands of WPI were altered by the Maillard reaction. All in all, these results suggested that WPI–glucose conjugates have high thermal stability and improved antioxidant properties.