Phenolic compounds in walnut pellicle improve walnut (Juglans regia L.) protein solubility under pH-shifting condition

Xiangzhen Kong; Zilin Huang; Caimeng Zhang; Yufei Hua; Yeming Chen; Xingfei Li

doi:10.1016/j.foodres.2022.112156

Phenolic compounds in walnut pellicle improve walnut (Juglans regia L.) protein solubility under pH-shifting condition

Food Res Int. 2023 Jan:163:112156. doi: 10.1016/j.foodres.2022.112156. Epub 2022 Nov 19.

Authors

Xiangzhen Kong¹, Zilin Huang², Caimeng Zhang², Yufei Hua², Yeming Chen², Xingfei Li²

Affiliations

¹ State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, PR China; School of Food Science and Technology, Jiangnan University, Wuxi, PR China. Electronic address: xzkong@jiangnan.edu.cn.
² State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, PR China; School of Food Science and Technology, Jiangnan University, Wuxi, PR China.

PMID: 36596107
DOI: 10.1016/j.foodres.2022.112156

Abstract

This study focused on the interaction of walnut protein with phenolic extracts of walnut pellicle (PEWP) under alkaline condition, leading to enhancement of protein solubility under neutral condition. First, the change of PEWP under alkaline condition was determined by RP-HPLC and mass spectrometry, and the results showed that most ellagitannins in PEWP could be retained under alkaline condition within 3 h. Interaction between PEWP and walnut protein under pH-shifting condition resulted in the remarkable increase of protein solubility (above 90%) at neutral pH. The results from SDS-PAGE and SEC showed that the improved solubility lied in the formation of large and soluble protein aggregates due to the covalent interaction among walnut protein and polyphenols. A significant change in tertiary structure of protein-phenolic complex was witnessed by fluorescence spectrum and near-UV circular dichroism. Meanwhile, walnut protein-polyphenol interaction led to a slight increase in β-turn while a slight decrease in β-sheet. Combined with amino acid composition, it could be illustrated that the covalent bonding for walnut protein with polyphenol mainly occurred at Lysine residues.

Keywords: Alkaline condition; Phenolic compounds; Protein-phenolic complex; Solubility; Walnut protein.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Hydrogen-Ion Concentration
Juglans* / chemistry
Nuts / chemistry
Phenols / analysis
Polyphenols / analysis
Solubility

Substances

Phenols
Polyphenols