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(phi) 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 zeta-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.