New insights into altering the structures and improving the functional properties of walnut protein: Synergistic high-pressure homogenization/ limited enzymatic hydrolysis

Walnut protein (WP) is a high-quality plant protein with remarkable nutritional value. However, the limited solubility of WP hinders its widespread application. This study investigated the effects of high-pressure homogenization (HPH) and limited enzymatic hydrolysis and their synergistic influence on the structure and functionality of WP. All treatments increased the surface hydrophobicity (H0) and free sulfhydryl content (-SH) and reduced the particle size. The use of HPH in synergy with alcalase (HWP-A) and trypsin (HWP-T) altered the structure of walnut proteins and enhanced the hydrolysis process and functional properties of the proteins. Structural analysis showed an increase in the content of random coils in the secondary structure, endogenous fluorescence spectroscopy resulted in a red-shift, atomic force microscopy (AFM) indicated distinct changes in surface morphology, with the height of the bulges increasing from 5.6 nm for WP to 52.0 nm for HWP-A and 52.7 nm for HWP-T. Small-angle X-ray scattering (SAXS) analysis revealed the disruption of internal protein aggregates. Regarding the functional properties, the foaming capacity increased from 20.86 % for WP to 90.41 % for HWP-A and 83.33 % for HWP-T, and the emulsion activity index rose from 21.07 m2/g for WP to 44.10 m2/g for HWP-A and 46.29 m2/g for HWP-T. The synergistic effect of HPH and limited enzymatic hydrolysis represents a promising approach to improving the functionality and applicability of walnut meal proteins.