Investigating the effect of whey protein isolate:proanthocyanidin complex ratio on the stability and antioxidant capacity of Pickering emulsions

Whey protein isolate (WPI) has the potential to be a Pickering stabilizer, but its applications in emulsions are restricted due to its structural susceptibility to external environments. Proanthocyanidin (PAC) is a natural antioxidant polyphenol that can improve protein properties and enhance the stability and longevity of emulsions. In the current work, PACs were employed to bind WPIs, forming a complex to stabilize Pickering emulsion. Fluorescence spectroscopy, infrared spectroscopy, confocal microscopy, quartz crystal microbalance with dissipation monitoring (QCM-D), and antioxidant stability of the emulsion were performed to characterize the structural changes of the protein/polyphenol complexes and their effects on the interfacial properties and stability of the emulsion. Results indicated that PACs and WPIs might bind through hydrogen bonding and hydrophobic interactions, effectively increasing the hydrophilicity of the complexes. QCM-D and emulsion stability showed that adsorption at the oil-water interface of the complexes was the largest, and the stability of the Pickering emulsion was optimal when the concentration ratio of PAC to WPI exceeded 1:1. The antioxidant properties of Pickering emulsions were positively correlated with the addition of PACs. These findings demonstrated that PACs could improve the properties of WPIs and enhance the stability and antioxidant properties of WPI Pickering emulsions.