Covalent and non-covalent modification of sunflower protein with chlorogenic acid: Identifying the critical ratios that affect techno-functionality

Abstract

Phenolic compounds are removed from plant protein extracts because their interaction with proteins can lead to undesirable sensory and techno-functional changes. The trend toward less refined plant protein fractions requires clarification of the degree to which removal is necessary. Chlorogenic acid (CGA) was added to sunflower protein solutions to obtain apparent CGA-protein molar ratios between 1:10 and 10:1. The samples were incubated either at pH 7 to induce non-covalent interactions or at pH 9 to induce covalent interactions. The type and extent of protein modification, physicochemical properties, solubility, and gelling ability were evaluated. Both binding modes of CGA had a positive effect on protein solubility. Covalently modified samples showed color changes upon a molar ratio of 1:1 and higher. All solutions were able to form gels (protein concentration 10% w/v). Maximum gel strength was obtained at a 1:1 ratio in case of covalent modification. Higher molar ratios led to lower gel strengths and this effect was more pronounced for covalently modified samples than for non-covalent ones. Depending on the applications, complete removal of CGA is not necessary, since CGA improves the solubility of the sunflower proteins. However, CGA removal to a more favorable ratio between 5:1 and 1:1 is recommended if the material is used for gel formation. Under conditions that promote covalent binding with CGA, ratios above 1:1 lead to significant green coloration. It remains to be tested whether this observation also applies to less refined sunflower ingredients with multiple components.