Effect of milk protein composition on physicochemical properties, creaming stability and volatile profile of a protein-stabilised oil-in-water emulsion.

Casein, whey proteins and monoglycerides are emulsifiers that adsorb at the oil-water interface to form and stabilise emulsions. This study aims to understand the effect of different milk protein compositions (ratio of sodium caseinate and whey protein concentrate (WPC)) with glycerol monooleate (GMO) on physicochemical properties, creaming and oxidative stability of the emulsions. Model emulsions with five different protein compositions were prepared by microfluidisation. The physicochemical properties were characterised by droplet size, zeta potential, viscosity and creaming index. Oxidative stability was assessed using volatile lipid oxidation compounds during ageing (28 days at 45 °C). Results showed that the emulsion with only sodium caseinate produced smaller droplets (174.7 nm), higher zeta potential (-50.8 mV) and a more viscous emulsion (1.89 mPa s) compared to the emulsion with only WPC (191.4 nm; -38.8 mV; 1.65 mPa s). Protein composition had no significant effect on creaming stability. Eleven volatile compounds were identified as lipid oxidation markers and six compounds (2-pentylfuran, octanal, nonanal, 3-octen-2-one, 2,4-heptadienal, 3,5-octadien-2-one isomers) demonstrated that emulsions with mixed protein types (sodium caseinate and WPC) had better oxidative stability than emulsions with a single protein type. Therefore, mixed proteins with GMO form stable emulsions with both good physicochemical properties and oxidative stability.