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

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.