Synthesis and characterization of alkylated caseinate, and its structure-curcumin loading property relationship in water

Abstract

Alkylated caseinates (Cn-caseinates) containing selected C8–C16 alkyl groups were successfully synthesized through a two-step reaction between the protein and fatty acids. The substitution degree (SD) of the alkyl groups was 5.2–72.9%, which depended on the feed molar ratio of reagents and fatty acid chain length. The SD value was positively associated with the surface hydrophobicity index (S0) of the Cn-caseinate. Among the tested Cn-caseinates (n = 0, 8, 12, 14 and 16), C16-caseinate showed the best self-assembly and curcumin-loading properties in water. With increased palmitoyl group SD, the critical micelle concentration (CMC) of C16-caseinate was decreased from 5.15 to 3.77 mg/L and the encapsulation efficiency of curcumin-loaded C16-caseinate self-assemblies was increased from 31.16% to 69.87%. Transmission electron microscopy analysis demonstrated a desirable sphere assembly. In addition, the C16-caseinate self-assemblies had good re-dispersibility and storage stability at 4 °C for 6 weeks.