Thermally-induced protein–polyphenol co-assemblies: beta lactoglobulin-based nanocomplexes as protective nanovehicles for EGCG

Abstract

Delivery of sensitive water-soluble compounds in foods is an important challenge. (−)-Epigallocatechin-3-gallate (EGCG), the major catechin in green tea, is a potent antioxidant with numerous attributed health benefits. However, its sensitivity to oxidation limits its enrichment in the diet for preventive medicine. We have studied the possibility of using thermally modified β-lactoglobulin (β-Lg) to form co-assembled nanovehicles for delivery of EGCG, as a model system for delivery of polyphenols by heat-modified proteins. Using fluorescence spectroscopy, DLS and spectrophotometry we found that optimal nano-entrapment is obtained when EGCG is added to preheated (75–85 °C, 20 min) β-Lg solution during cooling and vortexing. The measured association constant with the heated protein was 3.7 × 10 5 M −1, about 3.5-fold higher than that with the native protein: 1.05 × 10 5 M −1. Thermally-induced protein-EGCG co-assemblies were smaller than 50 nm, thus excellent transparency was maintained, enabling their application in clear beverages. These complexes conferred considerable protection to EGCG against oxidative degradation: A 33-fold lower initial degradation rate, and a 3.2-fold slower degradation over 8 days were observed for nano-entrapped compared to unprotected EGCG.