Effect of different polyphenols on the stability and digestibility of multilayer emulsions fabricated from polyphenol-protein covalent complexes

Abstract

Whey protein isolate (WPI), as a common emulsifier, is sensitive to environment conditions, reducing the multilayer emulsion stability. The covalent binding between WPI and polyphenols is commonly used to improve the physicochemical properties of WPI, and further improve the performance of multilayer emulsions. However, minimal studies are available that systematically examine the effect of different polyphenol-WPI complexes on the performance of multilayer emulsions. This study used three common polyphenols (i.e. luteolin, epigallocatechin gallate (EGCG), and rutin) for covalent coupling to WPI. The degree of covalent coupling of WPI and polyphenols was determined, suggesting the degree of covalent binding was EGCG > luteolin > rutin. Fourier transform infrared spectroscopy confirmed the potential coupling sites of WPI-polyphenol complexes. Fluorescence spectrum and circular dichroism spectrum determined changes in WPI structures. Among three WPI-polyphenol complexes, the WPI-EGCG (WPI-E) complexes displayed the best physicochemical characteristics, including emulsification property, antioxidant property, and thermal property. Then, the WPI-polyphenols complexes were used to fabricate multilayer emulsions for caffeic acid phenethyl ester (CAPE) encapsulation. The WPI-E complexes stabilized multilayer emulsion demonstrated the highest stability on pH, ionic strength, and temperature. The WPI-luteolin (WPI-L) stabilized multilayer emulsion presented the highest encapsulation rate, while the non-covalent complex WPI stabilized multilayer emulsion demonstrated the highest release rate during simulated in vitro digestion. This study helped us to better understand the structure-function relationships associated with the fabrication of multilayer emulsions from polyphenols.