Functional and digestive properties of pea protein–sour cherry concentrate complexes: effects on solubility, foaming, emulsifying, and antioxidant capacity

This study explored the formulation of diluted sour cherry concentrate (SC) and pea protein (PP) mixtures and emulsions and investigated their effects on protein functional properties and the bioaccessibility of phenolic compounds during in vitro gastrointestinal digestion. The total phenolic content (TPC) of sour cherry concentrate was found to be 1156.59 mg GAE/100 mL, with chlorogenic acid being the most abundant phenolic compound. The addition of SC (0.05–1 mg GAE/mL) to PP (5 mg/mL) solutions (SC-PP mixtures) improved protein solubility from 261.50 ± 15.10 mg BSA/g protein to 690.07 ± 18.10 mg BSA/g protein at 0.4%. SC-PP mixtures exhibited reduced foaming capacity (FC: 24.17–33.33%) and stability (FS: 9.12–13.13%) compared to PP alone (36.67 ± 4.71% and 26.79 ± 2.52%, respectively). Emulsions containing SC exhibited higher emulsion capacity (EC) and stability (ES) at 50% oil compared to 25% oil, and the formulation with SC at 0.2 mg GAE/mL (SPE-0.2) showed the most optimal performance. Zeta potential measurements indicated increased stability in emulsions, especially for 50% oil emulsions with SC, attributed to enhanced electrostatic repulsion. In vitro digestion revealed that SC improved protein availability, especially in the intestinal phase, and enhanced antioxidant capacity, with higher concentrations of SC resulting in greater retention and improved antioxidant properties throughout digestion. Overall, SC enhanced protein solubility, emulsifying properties, and antioxidant stability, suggesting potential benefits for functional food applications.