Orthokinetic destabilization of emulsions by saturated and unsaturated monoglycerides

The influence of pure and mixed monoglycerides on the orthokinetic stability of fine sodium caseinate-stabilized oil-in-water emulsions (1 g 100 g(-1) protein, 40 mL 100 mL (1) groundnut oil, average droplet size <0.5 m), with tristearin (TS) crystals (12.5 g 100 g-1) dispersed in the oil phase, has been investigated under strictly controlled shearing conditions. The presence of pure glycerol monostearate (GMS) was found to produce a highly viscous flocculated: state which was resistant to shear-induced partial coalescence. Emulsions containing pure glycerol monopalmitate (GMP) were more shear-sensitive, although the destabilization was not so extensive as to generate the large well-defined. viscosity increases found previously for emulsions containing pure glycerol monooleate (GMO). Different levels of (in)stability for the three pure monoglycerides can be attributed to differences in the competitive protein displacement behaviour and in the fat crystal type. A GMO-rich commercial emulsifier was found to produce emulsions having both quiescent stability and shear sensitivity, but the emulsifier concentration range giving this behaviour was extremely narrow. Certain binary mixtures of GMO + GMS or GMO + GMP could also generate emulsions that were orthokinetically unstable but perikinetically stable. Overall, these results indicate that a small change in the amount of added saturated monoglyceride can be used to provide sensitive control over the orthokinetic stability of milk protein-based emulsions. (C) 2001 Elsevier Science Ltd. All rights reserved.