Shear stability of sodium caseinate emulsions containing monoglyceride and triglyceride crystals

Shear destabilization of sodium caseinate oil-in-water emulsions has been investigated under carefully controlled conditions. Protein stabilized emulsions with tristearin (TS) crystals in the groundnut oil phase were cooled and destabilized under strictly controlled shearing conditions using a Bohlin CVO rheometer. Glycerol monooleate (GMO) was added as emulsifier in order to promote shear sensitivity in the emulsions. Emulsion systems with monoglyceride contents or triglyceride crystal concentrations, which exceeded certain well-defined limits, could be readily destabilized under shear. Shear-induced destabilization occurred very suddenly at a certain critical shear stress. The critical destabilizing stress was found to decrease with increasing levels of GMO, but shear-sensitive emulsions containing up to 3.25 wt.% GMO in the oil phase were found to be stable to quiescent storage over a time-scale of weeks. The shear sensitivity of emulsions was also found to be dependent on the concentration of triglyceride crystals within the droplets. The enhanced shear-sensitivity of crystal-containing emulsions with added GMO can be interpreted partly to a displacement of protein from the interface and partly to a template effect, with triglyceride crystals being encouraged by the emulsifier to grow beyond the droplet surface.