Impact of fat and water crystallization on the stability of hydrogenated palm oil-in-water emulsions stabilized by whey protein isolate

The influence of aqueous phase composition (0-40 wt.% sucrose, 0 and 150 mmol kg(-1) sodium chloride, NaCl) on the stability of 20 wt.% hydrogenated palm oil-in-water emulsions stabilized by 0.9 wt.% whey protein isolate (WPI) to chilling and freezing was studied. Emulsion stability was measured after emulsions had been cooled to temperatures where (i) only the oil phase crystallized or (ii) both the oil and aqueous phases crystallized. Emulsion stability was assessed by DSC measurements of fat destabilization after cool-heat cycles (-40 to 40 degreesC or -10 to 40degreesC), and by measurements of mean particle size, free oil, gravitational separation, and shear viscosity after isothermal storage (-40 to 37 degreesC). Sucrose improved emulsion stability to droplet coalescence and gravitational separation, particularly at temperatures where part of the aqueous phase froze. The cryo-protective affect of sucrose was attributed to its ability to increase the amount of unfrozen water (UW), modify ice crystal structure, alter interfacial protein structure, and/or reduce the frequency of droplet-droplet collisions. NaCl promoted emulsion instability, particularly at holding temperatures where the oil was partially crystalline, which was attributed to its ability to facilitate the close approach of droplets by screening the electrostatic repulsion between them. These results have important implications for the formulation of emulsions that are stable to chilling and freezing. (C) 2004 Elsevier B.V. All rights reserved.