pH-dependent interactions in OPI/CS composites drive emulsion stability and β-carotene bioaccessibility

Composite particles of oat protein isolate (OPI) and chitosan (CS) were fabricated under different pH and ratio to investigate their interactions, and then used as stabilizers to prepare emulsions for β-carotene delivery. The heat treatment of OPI yielded OPI′, and the binding of OPI′ to CS was enhanced due to the unfolding of its structure. With increasing OPI′:CS ratio and pH value, the particle size and turbidity initially increased and then decreased, accompanied by a shift in the dominant interaction from electrostatic to hydrophobic forces. The strongest hydrophobic interaction was observed at OPI′:CS = 5:1 and pH 7. The emulsion prepared under these conditions exhibited the smallest droplet size (1.55 μm), excellent storage stability, and a high bioaccessibility of β-carotene (36.78%) during in vitro digestion. Furthermore, the OPI′/CS emulsion markedly enhanced the retention of β-carotene under various storage temperatures and UV irradiation, demonstrating great potential for delivering lipophilic bioactive compounds.