Effects of droplet size on the oxidative stability of oil-in-water emulsions.

The effects of droplet size and emulsifiers on oxidative stability of polyunsaturated TAG in oil-in-water (o/w) emulsions with droplet sizes of 0.806 +/- 0.0690, 3.28 +/- 0.0660, or 10.7 +/- 0.106 microm (mean +/- SD) were investigated. Hydroperoxide contents in the emulsion with a mean droplet size of 0.831 microm were significantly lower than those in the emulsion with a mean droplet size of 12.8 microm for up to 120 h of oxidation time. Residual oxygen contents in the headspace air of the vials containing an o/w emulsion with a mean droplet size of 0.831 microm were lower compared with those of the emulsion with a mean droplet size of 12.8 microm. Hexanal developed from soybean oil TAG o/w emulsions with smaller droplet size showed significantly lower residual oxygen contents than those of the larger droplet size emulsions. Consequently, oxidative stability of TAG in o/w emulsions could be controlled by the size of oil droplet even though the origins of TAG were different. Spin-spin relaxation time of protons of acyl residues on TAG in o/w emulsions measured by H NMR suggested that motional frequency of some acyl residues was shorter in o/w emulsions with a smaller droplet size. The effect of the wedge associated with hydrophobic acyl residues of emulsifiers was proposed as a possible mechanism to explain differences in oxidative stability between o/w emulsions with different droplet sizes.