Investigation of the relation between interfacial properties of milk protein ingredients and their emulsifying properties

This study aimed to investigate the relationship between emulsifying properties and oil-water (O-W) interfacial properties of casein dominated milk protein ingredients. The ingredient samples were milk protein concentrate 80 (MPC80), milk protein isolate 85, milk protein isolate 90, micellar casein concentrate (MCC), and sodium caseinate (NaCN). Emulsions were prepared using 20% (wt/wt) sunflower oil as the dispersed phase and 1% (wt/wt) protein dispersion as the continuous phase. Emulsifying activity is indicated by mean droplet size (e.g., D4,3 and D3,2) in fresh emulsions. Emulsion coalescence stability was expressed by particle size change after cold storage up to 60 d. The interfacial properties tested were interfacial tension (IFT), O-W interface adsorption dynamics (for a 12,600-s period), and dilatational modulus. Interfacial tension at a quasi-equilibrium state showed a fair correlation with the droplet size change after 30 d of storage. The statistical correlations between interfacial properties and emulsion characteristics suggest that this study provided empirical evidence showing IFT and interfacial modulus may be used as convenient and effective parameters for indicating emulsion properties of milk protein ingredients. Although MCC, MPC80, and NaCN resulted in comparable quasi-equilibrium IFT, NaCN showed a unique interfacial rheological behavior. This work showed that the interfacial rheological response to dilatational deformation was relevant to emulsion property.