Okra Flower Polysaccharide–Pea Protein Conjugates Stabilized Pickering Emulsion Enhances Apigenin Stability, Bioaccessibility, and Intestinal Absorption In Vitro

The covalent interactions of polysaccharides and protein can improve the emulsification and stability of Pickering emulsions, which are promising systems for the delivery of active substances. Okra flowers, which commonly represent agricultural waste, have high-viscosity polysaccharides that can be used for the development of protein-polysaccharide-based emulsifiers. In this study, the Maillard reaction was performed under optimized conditions (70 °C, pH 10, and 12 h) with a 1:1 mass ratio to generate pea protein isolate (PPI)-okra flower polysaccharide (OP) conjugate with the highest grafting degree of 22.80 ± 0.26%. The covalent binding of OP facilitated variations in the secondary and tertiary structures of PPI, decreasing its particle size (from 535.70 to 212.05 nm) and zeta-potential (from -30.37 to -44.39 mV). The emulsifying stability of the emulsion stabilized by OP-PPI conjugates was significantly improved due to the formation of a stable interfacial layer, showing an 80.39% increase compared to that of free PPI. Simultaneously, the emulsions prepared with the conjugates demonstrated excellent stability across diverse environmental conditions by enhancing the interaction between the lipid and protein. Moreover, the conjugate-stabilized emulsion not only exhibited a higher encapsulation efficiency of 91.52 ± 0.75% and superior protective efficacy but also controlled the release of apigenin (API) during gastrointestinal digestion, achieving the highest API bioaccessibility (74.58 ± 1.19%). Furthermore, it also contributed to the absorption and transmembrane transport efficiency of API in Caco-2 cells, improving its bioavailability. These results confirmed that covalent conjugation with OP is a valuable strategy for enhancing the emulsifying features of PPI. The PPI-OP emulsion delivery system holds great potential for nutrient delivery.