Formation of gliadin-chitosan soluble complexes and coacervates through pH-induced: relationship to encapsulation and controlled release properties

This paper investigated the pH-induced interaction between gliadin and chitosan (CS), as well as its relationship with encapsulation and controlled release properties, by embedding curcumin. According to the turbidimetric analysis, the critical pH _c and pH _φ of gliadin-chitosan nanoparticles (GCNPs), as well as gliadin nanoparticles (GNPs), were obtained. Soluble complexes and coacervates were formed mainly at pH 4.0–5.0 and 5.0–7.0, respectively, in the gliadin-CS system through electrostatic associative interactions. The isothermal titration calorimetry (ITC) showed that the gliadin-CS interaction was a spontaneous exothermic process at pH 3.0 and 5.0. The soluble complexes of GCNPs with good homogeneity, and the coacervates with a large amount of aggregation, were observed via scanning electron microscopy (SEM). At pH 5.0, gliadin-CS soluble complexes were formed and showed smaller particle sizes (570.42 nm), lowest PDI (0.191), higher ζ-potential (+19.2 mV) and improved encapsulation efficiency (85.11%) of curcumin compared to at other pHs. The controlled release profile in vitro indicated that the gliadin-CS interaction decreased the release rate of curcumin in both pepsin and trypsin digestion. In conclusion, the encapsulation and controlled release properties of GCNPs could be improved by the pH-induced formation of gliadin-CS soluble complexes.