Color changes in olive oil
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Summary and Conclusions
That yellow olive oil packed in tin may turn green, and that this reaction is brought about by reduction of the yellow color through the action of the free fatty acids of the oil on the tinplate.
That this reaction will not take place at normal temperatures in the presence of light.
That the green color of olive oil, so formed, reverts to yellow by the action of light.
That the formation of green color in olive oil is dependent on the acid strength of the oil and depth of the original yellow color and increases proportionately with these.
That, in general, most olive oils on the market packed in tin, are of a greenish color, while the bottled product is yellow. This, of course, does not apply to fresh oil, but only that which is sufficiently old to have permitted any color change to have taken place.
That it is not possible to pack olive oil in cans without development of greenish color unless the original oil is rendered neutral or bleached. As it is not practical to render the oil absolutely neutral or to bleach it, the formation of green color in tin cannot be entirely prevented in practice but may be controlled to a certain extent.
That the development of excessive green color, which might be objectionable, can be prevented either by packing in cans only oil of low acidity (below 0.25%) or oil, the original color of which is light yellow. In the latter case the acidity is of little consequence as far as color is concerned.
That green-colored oil in cans can be reconditioned by transferring to bottles and exposing to light, whereby the original yellow color is restored.
KeywordsFree Fatty Acid Color Change Yellow Color Green Color Stannic Chloride
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