The Protective Effect and Mechanisms of Milk Proteins on Goji Berry Polyphenols

This study investigated the protective effects and underlying mechanisms of milk proteins on Goji Berry polyphenols (GBP). An in vitro digestion experiment validated that milk proteins (whey protein [WP] and casein [CA]) significantly enhanced the retention rate of GBP during the digestion process, with CA showing a more pronounced protective effect. To elucidate the mechanisms, β-casein (βCN) and β-lactoglobulin (βLG) were employed as representative models for CA and WP, respectively. Both proteins formed complexes with predominant GBP (rutin and p-coumaric acid [PCA]) through static quenching driven by hydrogen bonding and hydrophobic interactions. βCN exhibited higher K_a values (40.41 and 15.89 × 10⁴ M^-1) for rutin (Ru) and PCA than βLG (35.93 and 3.92 × 10⁴ M^-1). Notably, a comparative analysis of dynamic light scattering (DLS) and low-field nuclear magnetic resonance (Lf-NMR) revealed distinct protective mechanisms: βLG formed loose aggregates with significantly increased particle size but retained high water mobility, whereas βCN formed a more compact micellar structure and significantly restricted water mobility. Molecular docking demonstrated that βCN provides a more robust structural barrier for Ru and PCA by encapsulating them within internal cavity. In contrast, βLG primarily binds polyphenols on its surface or hydrophobic pocket, thus showing a weaker protective property than βCN. Therefore, the excellent binding affinity and enclosed encapsulation mode of βCN may explain why CA exhibits a superior protective effect on GBP compared to WP. PRACTICAL APPLICATIONS: This study elucidates the protective mechanism of milk proteins on GBP, laying a theoretical and experimental foundation for the development of high-value dairy products rich in GBP.