Droplet composition affects the rate of oxidation of emulsified ethyl linoleate |
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Authors: | J N Coupland Z Zhu H Wan D J McClements W W Nawar P Chinachoti |
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Affiliation: | (1) Department of Food Science, University of Massachusetts, 01003 Amherst, Massachusetts |
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Abstract: | Our objective was to study the influence of droplet composition on the rate of lipid oxidation in emulsions. A series of oil-in-water
emulsions stabilized by a nonionic surfactant (Tween 20) was studied. These emulsions had the same total oil concentration
(5 wt%) and initial droplet diameter (0.3 μm), but contained droplets with different ratios of ethyl linoleate (substrate)
andn-tetradecane (inert diluent). Lipid oxidation was measured as a function of time by three different methods: gas-chromatographic
determination of residual substrate; ultraviolet-visible spectrophotometric determination of conjugated dienes; and measurement
of aqueous thiobarbituric acid-reactive substances. All three methods showed similar trends for emulsions of similar composition.
The progress of lipid oxidation in the emulsions was dependent on the concentration of ethyl linoleate in the emulsion droplets.
At low concentrations (1% oil as substrate), oxidation proceeded at a relatively slow and constant rate. At intermediate concentrations
(20%), the oxidation rate was rapid initially and then slowed down with time. At high concentrations (100%), the oxidation
rate was slow at first, and then increased with time. An explanation of our results is proposed in terms of the distribution
of substrate molecules between the droplet interior and interface, and the ingress of aqueous radicals into the emulsion droplets. |
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Keywords: | Emulsions lipids micelles oxidation rancidity |
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