Impact of succinylation on pea protein-curcumin interaction, polyelectrolyte complexation with chitosan, and gastrointestinal release of curcumin in loaded-biopolymer nano-complexes

Abstract

The influence of pea protein succinylation on the nature and strength of interaction with curcumin for a potential role in encapsulation and gastrointestinal delivery was investigated. Succinylation neutralized the positive charge on lysine residue and increased the effective negative charge on the protein from −34.4 ± 0.2 to −59.9 ± 0.9 mV with corresponding decrease in surface hydrophobicity and binding with curcumin. The binding constants (K) of 6.9 (± 0.21) × 104 M−1 and 4.2 (±0.05) × 104 M−1 were obtained for the native protein-curcumin (CUR/PPI) and succinylated protein-curcumin (CUR/SPPI) interactions, respectively. These values increased to 14.5 (± 0.64) × 104 M−1 and 187.9 (± 12.40) × 104 M−1 for curcumin-native pea protein-chitosan (CUR/PPI/CHI) and curcumin-succinylated protein-chitosan complexes (CUR/SPPI/CHI), respectively. Incorporation of chitosan to the protein-curcumin complex favoured static interaction. Transmission electron microscopy and dynamic light scattering confirmed the formation of spherical nano-complexes within the size range of 100–194.5 nm. FTIR showed that curcumin was stabilized more in the native protein complex than in the succinylated form. Polyelectrolyte complexation with chitosan by electrostatic interaction stabilized the succinylated protein-curcumin complex. The encapsulation efficiency decreased with a decrease in protein hydrophobicity and binding as a result of succinylation, from 34.65 ± 0.10% in CUR/PPI to 24.92 ± 0.03% in CUR/SPPI and from 85.01 ± 1.43 in CUR/PPI/CHI to 62.05 ± 2.95% in CUR/SPPI/CHI nano-complex. Although polyelectrolyte biopolymers enhance curcumin-loaded complex stability at the gastric phase, the release profile demonstrated that pea protein isolate effectively encapsulated and released curcumin without protein modification or incorporation of chitosan.