Oxidative reaction has to be considered in the choice of raw materials (vegetable oils, waxes, phospholipids) and in cosmetics products’ formulation. Fatty acid oxidation (or oxidative rancidity) is a chemical phenomenon observed when unsaturated fatty acids are in the presence of atmospheric oxygen. Light and temperature accelerate this reaction.
The appearance of a rancid flavor is characteristic of the organoleptic degradation resulting from this chemical phenomenon and determines the shelf life product. Add to changement of the marketable quality characteristics, different degradation product families can be formed: peroxides from free radicals, aldehyde, ketones and hydrocarbons. Methods exist to measure the oxidation. First, when stability or compatibility analysis we can measure the peroxide value of oil; it will be possible to know if the oil oxidizes and also the duration that it takes to oxidize.
This analysis can also permit to knowi if the packaging is good (opaque, transparent). There is also gas chromatography. It will be able to follow fatty acid content in order to measure the decomposition of substrate, or allows to target primary or secondary compounds of degradation (hydroperoxides, volatile aldehydes, …).
Références: [1] M.V. Piretti, C. Cavani, and F. Zeli, Mecanism of the formulation of hydroperoxides from methyl oleate, Rev.Fse Corps Gras 25(2): 73-79, 1978 [2] A. Judde, Oxidation prevention of fatty acids in a cosmetic product: mechanisms, effects, measuring mean, what antioxidants for which applications? , OCL 11(6): 414-418, 2004. [3] LD Metcalfe, AA Schmitz, The Rapid Preparation of Fatty Acid Esters for Gas Chromatographic Analysis, Analytical Chemistry, 1961 – ACS Publications.
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