Phosphorylated walnut protein/chitosan nanocomplexes as promising carriers for encapsulation of caffeic acid phenethyl ester

Abstract BACKGROUND Walnut proteins display poor solubility and dispersity under acidic pH conditions, which limits their application in acidic beverages and foods. This study aimed to fabricate stable nanocomplexes between phosphorylated walnut protein (PWPI) and chitosan (CS) in an acidic pH and to investigate the encapsulation capacity of the complexes. RESULTS The PWPI/CS nanocomplexes prepared at a mass ratio of 2:1 showed small Z‐average sizes (approximately 285 nm at pH 5.5 and 222 nm at pH 3.5) with a narrow particle distribution (polydispersity index <0.3). Caffeic acid phenethyl ester (CAPE) can be effectively encapsulated into PWPI/CS with improved solubility. Circular dichroism analysis indicated that PWPI/CS and CAPE‐loaded PWPI/CS (PWPI/CS‐CAPE) had reduced α ‐helical content and increased β ‐sheet content. Fourier transform infrared spectroscopy analysis further identified the different driving forces for the complexation of PWPI and CS at pH 3.5 and 5.5 and confirmed the successful encapsulation of CAPE. The rheological results revealed that the PWPI/CS and PWPI/CS‐CAPE formed at pH 3.5 (PWPI/CS‐CAPE‐3.5) had a higher apparent viscosity and better viscoelasticity than the complexes formed at pH 5.5. The PWPI/CS‐CAPE‐3.5 also showed good stability under heat treatment, salt treatment, and long‐term storage. The PWPI/CS‐CAPE complexes showed controlled release of CAPE. CONCLUSION Walnut protein and chitosan nanocomplexes prepared at acidic pH levels were stable and promising carriers for CAPE, which could expand the application of walnut proteins in the food industry. © 2023 Society of Chemical Industry.