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

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 beta-lactoglobulin (beta-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 degrees C, 20 min) beta-Lg solution during cooling and vortexing. The measured association constant with the heated protein was 3.7 x 10(5) M-1, about 3.5-fold higher than that with the native protein: 1.05 x 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. (C) 2010 Elsevier Ltd. All rights reserved.