Alkaline extraction pH has significant effects on the structural and functional properties of chickpea protein isolates and their foams

Abstract

Alkaline extraction and isoelectric precipitation are commonly used to obtain plant protein isolates. Although the effects of pH on chickpea protein isolates (CPI) in solutions and emulsions have been studied, a comprehensive investigation into the impact of extraction pH in the extraction process and foaming properties is still lacking. Therefore, we investigated the effects of extraction pH (8, 9, and 10) on the structural, functional, and compositional properties of CPI and foams made from it. FTIR results indicated that CPIs extracted at pH 10 had significantly lower carbohydrate-to-protein and lipid-to-protein ratios with lower protein carbonylation and lipid peroxidation levels. In CPI foam samples lipid-to-protein ratios were higher. At pH 10, protein denaturation was apparent based on amide II/ Amide I ratios in CPI samples. Protein carbonylation was found to decrease with increasing pH. Lipid extracts of CPI foams indicated higher levels of phosphate-containing lipids in pH 10 foam samples. In addition, aliphatic chain length was higher in pH 10 foam samples as well. CPI extracted at pH 10 had higher surface hydrophobicity, particle size, and zeta potential, protein hydration differences and more protein denaturation levels. Similarly, foaming stability increased with the pH but not the foaming capacity. No significant differences in antioxidant activity, surface tension, and SDS-PAGE profile were detected among the samples. The results suggest that alkaline extraction pH has significant effects on the composition, structure, and functional properties of CPIs and their foams, especially in terms of their lipid contents. In addition, alkaline-induced conformational changes can be leveraged to optimize techno-functional performance for the development of plant protein ingredients intended for aerated and foam-based food systems.