Relevance of various components present in plant protein ingredients for lipid oxidation in emulsions

Abstract

Plant protein ingredients (isolates, concentrates) are increasingly used for food formulation due to their low environmental impact compared to animal‐based proteins. A specific application is food emulsions, of which the physical and oxidative stability need to be supported. The emulsifying properties of diverse plant proteins have already been largely covered in literature, whereas only in a few studies the chemical stability of such emulsions was addressed, especially regarding lipid oxidation. In the few examples available mostly the effects caused by proteins were elaborated, whereas those caused by non‐protein components have hardly been considered. Yet, plant protein ingredients are characterized by high compositional complexity, with notably a plethora of non‐protein components. Topics covered in this review, therefore, include the composition of various types of plant protein ingredients (i.e., legumes, oil seeds) in relation to the fractionation processes used, and the potential effects on lipid oxidation in emulsions. The composition varies greatly among species and depends on the harvest conditions (i.e., year, location), and genetics. In addition, fractionation processes may lead to the accumulation or dilution of components, and induce chemical changes. Both protein and non‐protein components can act as pro‐ or antioxidants contingent on their concentration and/or location in emulsions. Since the chemical composition of plant protein ingredients is often hardly reported, this makes a‐priori prediction of an overall effect difficult, if not impossible. Standardizing the fractionation process and the starting material, as well as in‐depth characterization of the resulting fractions, are highly recommended when aiming at rationally designing food emulsions.

Effect of Nonprotein Components for Lipid Oxidation in Emulsions Stabilized by Plant Protein Extracts

“…Next to non-protein components, the initial level of protein oxidation was positively correlated with lipid oxidation in emulsions ( r = 0.91; p < 0.05 for hydroperoxides). Radical-mediated protein and lipid oxidation can mutually promote each other. ,− Therefore, it may be expected that an initial level of protein oxidation, as a result of the protein fractionation process used (i.e., defatting and wet processing), would be a driver for subsequent lipid oxidation in emulsions formulated with those ingredients, although systematic experimental evidence on this matter is still missing . The protein-bound carbonyl content in the fresh emulsions (between 2.94 and 7.01 μmol/g soluble protein) was consistent with values from literature for commercial plant protein ingredients (∼3–20 mmol/kg), , which clearly points to an aspect of protein materials that is generally overlooked, but that could turn out to be highly relevant for their use.…”

“…In addition, proteins in isolates and concentrates differ in their oxidative state due to the production conditions, which may affect the oxidative emulsion stability. 9 To try to rationalize and deconvolute the effects of the multitude of factors at play, a correlation matrix was prepared containing the chemical composition of the soluble plant protein solutions and oxidation data of the emulsions (hydroperoxide concentration at day 3 and 7, and aldehyde concentration at day 3) (Table S2). The key factors are summarized in Table 2, focusing on the hydroperoxide concentration at day 7: only correlation values (r) exceeding an absolute value of 0.8 are shown.…”

“…Besides proteins, that generally account for 50–80 wt % of the ingredient, plant protein concentrates and isolates still contain substantial amounts of non-protein components such as lipids, phytic acid or polyphenols . Depending on their localization and concentration, these components may affect lipid oxidation by acting as pro- or antioxidants . However, the detailed composition of plant protein ingredients, in particular regarding the non-protein component part, is generally not determined nor reported in literature.…”

“…This has been extensively studied and exemplified with animal-derived proteins, such as dairy proteins (whey proteins and caseins). When plant protein ingredients are used as alternative emulsifiers, it has been shown that this can lead to emulsions having a better oxidative stability than references stabilized by animal proteins. − In a recent review, we focused on how plant protein ingredients may modulate lipid oxidation in emulsions, and more specifically on the potential influence of the protein fractionation process and of the environmental conditions applied (pH, ionic strength) . We concluded that it is highly challenging to ascribe lipid oxidation in emulsions to specific components present as the ingredient composition depends on the crop and cultivar as well as on the fractionation process .…”

“…When plant protein ingredients are used as alternative emulsifiers, it has been shown that this can lead to emulsions having a better oxidative stability than references stabilized by animal proteins. − In a recent review, we focused on how plant protein ingredients may modulate lipid oxidation in emulsions, and more specifically on the potential influence of the protein fractionation process and of the environmental conditions applied (pH, ionic strength) . We concluded that it is highly challenging to ascribe lipid oxidation in emulsions to specific components present as the ingredient composition depends on the crop and cultivar as well as on the fractionation process . Besides proteins, that generally account for 50–80 wt % of the ingredient, plant protein concentrates and isolates still contain substantial amounts of non-protein components such as lipids, phytic acid or polyphenols .…”