EFFECT OF DRY HEATING ON THE PHYSICOCHEMICAL PROPERTIES AND ANTIOXIDANT ACTIVITIES OF WHEY PROTEIN ISOLATE CONJUGATED WITH LACTOSE AND GLUCOSE VIA THE MAILLARD REACTION

Whey protein isolate (WPI) is commonly used as a food ingredient, and its functional properties can be modified through Maillard conjugation with reducing sugars. However, the influence of sugar type on the resulting physicochemical changes and the resulting antioxidant properties under mild dry-heating conditions remains insufficiently understood. This study aimed to investigate the effects of lactose and glucose on the physicochemical characteristics and antioxidant properties of WPI during dry-heating at 60 °C and controlled relative humidity for up to 7 days. Commercial WPI (95% protein) was conjugated with lactose or glucose at a 1:1 (w/w) ratio and incubated for 0, 1, 4, and 7 days. Changes in color, browning intensity, and functional groups (FT-IR spectra) were analysed, and antioxidant activity was evaluated using DPPH and ABTS radical scavenging assays. Prolonged heating resulted in significant color changes (p < 0.05) in both WPI-lactose and WPI-glucose conjugates, with greater browning development observed in WPI-glucose. Correspondingly, WPI-glucose exhibited higher UV-Vis absorbance at 420 nm and a stronger radical scavenging activity than WPI-lactose after 7 days of conjugation. These findings highlighted that the choice of reducing sugar critically governed the progression of the Maillard reaction and enhanced the antioxidant activity of WPI under mild dry-heating conditions. Comparative insights into the selection of suitable reducing sugars for developing Maillard-conjugated whey protein ingredients with antioxidant potential were provided.