Structural evolution of citrus peel polysaccharides during aging modulates the in vitro digestive stability of EGCG and its transmembrane transport across Caco-2 monolayers

Aged citrus peel (Chenpi) is traditionally consumed with tea in Asian for synergistic flavor and health benefits. However, the structural evolution of citrus peel polysaccharides (Chenpi polysaccharides, CP) during aging and their regulatory role in the bioavailability of tea polyphenols remain poorly understood. In this study, CP from Chenpi aged 1–15 years were investigated for their impact on the digestive stability, epithelial transport, and delivery efficiency of epigallocatechin gallate (EGCG). Progressive depolymerization of CP altered their binding affinity toward EGCG (CP1 > CP15 > CP10 > CP5). Stronger binding led to greater digestive retention; CP1 showed the highest affinity (K_a = 3.02 × 10³ M^-1), enhancing EGCG retentionto 92.4 μg/mL (+376% vs. control), along with improved antioxidant capacity. However, its tight complexation hindered transmembrane transport. In contrast, CP15 formed compact nanospherical structures that enabled sustained EGCG release via weak multivalent interactions. Western blotting, TEM, and immunofluorescence revealed that CP15 downregulated efflux transporters (P-gp, MRP2) and reversibly remodeled tight junction protein ZO-1, promoting paracellular transport (P_app = 97.5 × 10^-7 cm·s^-1, 22.7-fold increase). These findings suggest a functional transformation of CP during aging—from stabilizing agents to barrier-modulating carriers—offering novel insights into structure-function relationships and a promising strategy for natural polysaccharide-based polyphenol delivery systems.