Whey protein isolate-dextran conjugates: Decisive role of glycation time dependent conjugation degree in size control and stability improvement of colloidal nanoparticles

Whey protein isolate-dextran (WPI-dextran) conjugates were acquired via Maillard reaction for different durations (1-7 days) and their potential to govern the size and stability of colloidal nanoparticles formed from heating electrostatic complexes of WPI-dextran conjugates and chondroitin sulfates was assessed. The grafting degree and browning index gradually increased with the reaction time. The intensity of amide bands increased in the first 2 days and then declined. As the duration increased, the content of alpha-helix increased from 23.9% to 29.6%, while I3-sheet and random coil decreased from 23.8% and 38.1% to 19.6% and 32.7%, respectively. Moreover, the surface hydrophobicity was reduced as the conjugation progressed, while surface and total sulfhydryl content gradually increased from 5.3 and 15.4 mu mol/g to 11.0 and 17.9 mu mol/g, respectively. Meanwhile, fluorescence intensity of conjugates decreased with prolonged durations. These changes with increasing grafting degree prompted greater steric hindrance, weakened hydrophobic interaction, and improved stability of protein during heating, thus facilitating the decreasing diameter of the corresponding heat-induced nanoparticles. In comparison with the nanoparticles derived from non-conjugated mixture of WPI and dextran, those from WPIdextran conjugates showed an excellent stability to aggregation and dissociation upon synergistic influence of pH variation (1-10) and enhancing ionic strength (0-4 mol/L).

Automated summary

WPI-dextran conjugates were obtained through Maillard reaction for different durations, leading to increased grafting degree and browning index over time. The conjugates showed increased content of alpha-helix, reduced surface hydrophobicity, and increased sulfhydryl content as conjugation progressed, with a decrease in fluorescence intensity. These changes resulted in improved stability of nanoparticles and facilitated a decrease in diameter during heating. Compared to non-conjugated nanoparticles, those from WPI-dextran conjugates exhibited excellent stability against aggregation and dissociation under pH variation and increasing ionic strength.