Continuous-phase fat crystals strongly influence water-in-oil emulsion stability

To elucidate the role of continuous-phase fat crystals on emulsion destabilization, water-in-canola oil emulsions prepared with 0-2% (w/w) added solid fat (hydrogenated canola stearine or hydrogenated cottonseed stearine) were examined using pulsed NMR droplet-size analysis, sedimentation, and microscopy. Droplet-size analysis showed that addition of either fat prior to emulsification (precrystallized fat) or fat quench-crystallized in situ following emulsification (postcrystallized fat) decreased the degree of droplet coalescence, based on volume-weighted (d(33)) mean droplet diameters, with postcrystallized emulsions being more stable against coalescence. Sedimentation studies corroborated these results, with greatly enhanced stability against sedimentation in postcrystallized emulsions. Precrystallized fat had very little effect on emulsion sedimentation at levels as high as 2% (w/w). Postcrystallized cottonseed stearine produced slightly less resistant emulsions than did canola stearine, even if both were in the beta-form. Surface energetics revealed that canola stearine had greater affinity for the oil/water interface and hence a greater displacement energy. The presence of micronsized (Pickering) crystals located directly at the droplet interface, resulting from in situ crystallization or generated by the shearing of precrystallized fats, provided enhanced stability vis-a-vi's preformed crystals. These stabilized emulsions via the formation of crystal networks that partially immobilized droplets.