Flavonoid- and limonoid-rich extracts from lemon pomace by-products: Technological properties for the formulation of o/w emulsions

Lemon pomace, the by-product derived from the industrial processing of citrus fruits for juice production, is a matrix rich in flavonoids and limonoids, bioactive compounds with interesting functional properties. The aim of the present work was to investigate the technological properties of flavonoids and limonoids-rich extracts recovered from lemon pomace by-products in model oil-in-water (o/w) emulsions. Two extracts, obtained with different extraction procedures, were characterized in terms of surface properties, either as pure extract or in combination with pea protein isolate. Then, the most surface-active extract was used to enrich, at increasing concentrations (0.5%, 1% and 2%), o/w emulsions (20% w/w) stabilized by pea proteins. Droplet size distributions, microstructure, flow behavior and oxidative stability were investigated. The extracts were able to lower the surface tension of the protein interfacial layer, with a concentration dependent behavior. In emulsions, depending on the amount added, the extract significantly altered the dispersion degree, by increasing oil droplet size and inducing flocculation at the highest extract to pea protein ratios. The emulsions showed a Newtonian behavior, with the exception of the sample with the highest amount of extract (2%) which also presented a yield stress. In accelerated oxidation tests, the extracts were shown to improve the chemical stability of the emulsions; however, the physical stability was impaired in the systems with the highest extract amounts (1%, 2%). Limonoids- and flavonoids-rich extracts recovered from lemon pomace can be considered promising as multifunctional ingredients in o/w emulsions, provided that their effect on the colloidal properties is properly addressed.