The phenolic profile of walnut meal protein isolate and interaction of phenolics with walnut protein

Abstract

The aim of this study was to interpret the interaction of phenolics with walnut protein and determine their effects on protein functional properties. The phenolic profiles of walnut meal (WM) and walnut meal protein isolate (WMPI) were established using UPLC-Q-TOF-MS. A total of 132 phenolic compounds were detected, including 104 phenolic acids and 28 flavonoids. Phenolic compounds bound to protein via hydrophobic interactions, hydrogen bonds, and ionic bonds were identified in WMPI. They were also present as free forms, but the hydrophobic interactions and hydrogen bonds were the main non-covalent binding forces between phenolics and walnut proteins. The interaction mechanisms were further supported by the fluorescence spectra of WMPI with ellagic acid and quercitrin. In addition, changes in the functional properties of WMPI after removal of phenolic compounds were evaluated. Dephenolization significantly increased water holding capacity, oil absorptive capacity, foaming capacity, foaming stability, emulsifying stability index, and the in vitro gastric digestibility. However, in vitro gastric-intestinal digestibility was not significantly affected. These results provide insights into the interactions between walnut protein and phenolics, which indicates potential strategies for removing phenolics from walnut protein.