031: Blackcurrant Polyphenols Interact With Micellar Caseins Compared to Whey Proteins

Introduction

The delivery of polyphenols using milk proteins holds the potential to enhance their biological activities, however, the interactions of milk proteins with fruit polyphenols in mixed systems are still not well understood.

Methods

HPLC was employed to profile polyphenols extracted from blackcurrant. Multi-spectroscopic techniques, including UV-vis spectroscopy, intrinsic fluorescence quenching, and FTIR, were used to determine the mechanisms, binding forces, and structural changes in milk proteins (casein micelles, whey proteins, and a mixture of casein micelles and whey proteins in a 50:50 ratio) upon interaction with blackcurrant polyphenols in protein to polyphenol concentration ratios of 40:1, 20:1, and 10:1. Additionally, the total phenolic content combined with loading efficiency tests were conducted to quantify the polyphenols bound to specific milk proteins.

Results

The total phenolic content of blackcurrant powder was 5.90 ± 0.16 mg gallic acid equivalent per g dry weight. Cyanidin 3-O-glucoside was the most abundant polyphenol, accounting for 20.2% of the total quantified polyphenols, followed by rutin (17.0%). Blackcurrant polyphenols quenched milk proteins through both dynamic and static quenching mechanisms. Milk proteins interacted with blackcurrant polyphenols spontaneously, forming protein-polyphenol complexes primarily through hydrophobic interactions found by fluorescence quenching. The interactions led to an increase in β-sheet content in micellar caseins (p < 0.0001) and the protein mixture (p = 0.0124), whereas a decrease in β-sheet content was observed in whey proteins (p < 0.0001), at the protein to polyphenol concentration ratio of 40:1. The loading efficiency test revealed that blackcurrant polyphenols preferred to bind to casein micelles compared to whey proteins (p < 0.0001), with up to 15.8 times greater binding at the mixed protein to polyphenol concentration ratio of 40:1.

Significance

The findings demonstrated the ability of polyphenols to stabilize the structures of caseins and proteins within a 50:50 whey protein-to-micellar casein mixture, highlighting the potential development of desirable and shelf-stable functional dairy products with fruit polyphenols. Additionally, the results provide valuable insight into designing efficient milk protein-based delivery systems for protected polyphenol transport in the digestive system.

Authors: Ting Mao, Maneesha S. Mohan