The heat stability of Rhamnolipid containing egg-protein stabilised oil-in-water emulsions

The heat stability of egg white stabilised emulsions was studied in the presence of monoglycerides, lecithin and rhamnolipid biosurfactants. Rhamnolipids have a greater effect on the reduction of emulsion droplet particle size than either lecithin or monoglycerides, with both the latter having virtually no effect even at high concentration. The effect of all surfactants on heat stability is concentration dependent. There is trend towards a minimum in heat stability (represented by the first order rate constant, k) for emulsions stabilised by all surfactants at a molar ratio (R) of egg protein to surfactant of R = 50 for monoglycerides, R = 34 for lecithin and R = 61 for rhamnolipids. However, this trend is only statistically significant for the rhamnolipid emulsions. The largest decrease in heat stability is observed for the rhamnolipid stabilised emulsion. The rhamnolipid biosurfactant is also the only one of the three surfactants that is able to provide heat stability to the emulsion at high molar ratios, presumably due to competitive displacement of the protein from the emulsion droplet surface. Analysis of the thermodynamics of the heat-induced destabilization of the emulsions suggests differing mechanisms for the three surfactants, probably related to the way in which the different surfactants interact with the adsorbed protein layer. Molecular docking and molecular dynamics simulations confirm different binding affinity to egg proteins for the rhamnolipid and lecithin surfactants.