Structure-function guided design of sequential whey protein-polyphenol-pectin conjugates for enhanced lutein...

The development of efficient delivery systems for sensitive lipophilic bioactives like lutein remains a significant challenge. This study engineered a series of binary and ternary conjugates of whey protein (WP) with pectin (PE) and polyphenols (gallic acid, GA; tannic acid, TA) through Maillard reaction and alkaline-driven conjugation to create tailored lutein carriers. Comprehensive characterization (SDS-PAGE, FTIR, fluorescence) confirmed successful covalent bond formation, with sequential dual-covalent conjugation (WP-GA/TA-PE) achieving the most significant depletion of free amino and sulfhydryl groups. The dual-covalent conjugates, particularly WP-TA-PE, exhibited exceptional emulsification performance (Emulsion Stability Index increased by ∼94%), resulting from synergistic covalent cross-linking and polysaccharide coating. This structure provided a robust multi-faceted protection system for lutein: the highest UV, thermal, and storage stability were achieved. Furthermore, the conjugates allowed for controlled digestibility, with WP-TA-PE showing the lowest free fatty acid release and lutein bioaccessibility, indicating a strong barrier function. Conversely, native WP provided the highest lutein bioaccessibility, benefiting from its readily digestible interface. A key structure-function finding was a clear trade-off governed by the conjugation pathway: covalent polyphenol conjugates (WP-GA/TA) were optimal antioxidants, while sequential dual-covalent conjugates (WP-GA/TA-PE) were superior emulsifiers and protectants, albeit at the cost of reduced bioaccessibility. This work demonstrates a rational design strategy for creating multi-functional food-grade colloidal systems with tunable properties for specific applications in fortified foods and supplements.