Interaction of polyphenols and multilayered liposomal-encapsulated grape seed extract with native and heat-treated proteins

•Polyphenols in grape seed extract formed aggregates with all proteins used.•Highest precipitation capacity was determined for sodium caseinate.•Uncoated liposomes formed large-sized protein-liposome aggregates.•Chitosan-coated liposomes reduced interactions with proteins in acidic milieu.•Pectin-chitosan coated liposomes formed precipitates with proteins.

Soy lecithin liposomes with incorporated grape seed extract (GSE) were prepared by high-pressure homogenization and coated with chitosan as a first layer and pectin as a second layer. The GSE and the uncoated and coated liposomes were mixed with native and heat-treated protein solutions of bovine serum albumin (BSA), whey protein isolate (WPI) and sodium caseinate (Na-caseinate) to investigate their interactions. Uncoated liposomes without GSE had the smallest particle size (34 nm); when GSE (0.1% w/w) was entrapped into liposomes; its size increased three-fold (102 nm). The particle sizes of chitosan-coated liposomes were 80 nm and 197 nm containing GSE as well as of pectin-chitosan-coated liposomes 227 nm and 157 nm, respectively. The ζ-potential changed from −23 over +49 to −31 mV (liposomes) and −26 over 46 to −29 mV after second layering (GSE-liposomes). Prior to centrifugation, the particle diameters of the chitosan-coated liposomes were smaller than in the other samples containing GSE and the ζ-potentials were the highest of all liposome–protein mixtures (∼45 mV). After centrifugation, the polyphenols and proteins could be recovered in the supernatant, which proved that chitosan-coated liposomes have reduced precipitation properties. Additionally, only small protein concentrations too low for determination with SDS-PAGE electrophoresis were found in the residues. Na-caseinate, however, was precipitated by the positively charged chitosan-coated liposomes due to more hydrophobic forces. GSE and negatively charged liposomes (uncoated liposomes and chitosan-pectin-coated liposomes) precipitated and sedimented the proteins. This was demonstrated by increased particle sizes and reduced protein contents in the supernatants.

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