Physicochemical stability of lycopene-loaded emulsions stabilized by plant or dairy proteins

Abstract

Lycopene is a lipophilic bioactive compound that has many health benefits but can be challenging to deliver in vivo. To mediate this, delivery strategies should be developed, and protein-stabilized oil-in-water (O/W) emulsions have been suggested to improve the physicochemical stability, bioaccessibility and bioavailability of lycopene. In this research different proteins were compared to determine their impact on the physical stability (droplet size, charge, interfacial rheology) and lycopene retention in canola O/W emulsions. Two were of dairy (whey protein isolate, sodium caseinate) and two of plant (soy and pea protein isolate) origin; plant proteins being of interest due to their wider availability, reduced cost, and lower impact on the environment compared to dairy proteins.

Particle size distribution for sodium caseinate and pea protein-stabilized emulsions remained unchanged after 14 days of refrigerated storage, while whey and soy protein isolate-stabilized emulsions became unstable. The droplet charge was largely negative (~ -45 – -60 mV) for all emulsions and the lycopene concentration in plant protein-stabilized emulsions at 14 days of storage was similar to that in sodium caseinate-stabilized emulsions, but significantly higher than that in whey proteinstabilized emulsions. While sodium caseinate formed relatively viscous films at the oil-water interface, the other proteins showed more viscoelastic behaviour. In spite of this difference, both the caseinate and pea protein stabilized emulsions were promising delivery vehicles. This also indicates that plant-derived proteins can be feasible alternatives to dairy emulsifiers.