Abstract
The formation of peroxides by the oxidation of fats and oils is an important problem for cosmetics in terms of their stability and safety. In this study, effect of the composition of fatty acids on the rate of peroxidation was elucidated by the photo-irradiation of various triglycerides. Effect of the peroxides thus formed on the skin irritancy and cytotoxicity was also investigated.
After photo-irradiation of synthetic and/or purified triglycerides with an artificial light source, the peroxide value (POV) was measured and their skin irritancy was tested on the back of rabbit and guinea pig. The results indicated that POV increased linearly with irradiation time and that the rate of peroxidation (POV/hr) was dependent on the degree of unsaturation of the fatty acids moiety (F1, F2 and F3). The relationship between POV/hr and unsaturation was approximately given as a following equation:
POV/hr=2×(% of C18F1)+70×(% of C18F2)+90×(% of C18F3)
Furthermore, the peroxides in triglycerides revealed cytotoxicity which increased linearly with increase in POV. On the contrary, skin irritancy was unaltered with changes in POV. In general, skin irritancy of peroxides in fats and oils were reported to be augmented as POV increased which did not agree with our results. Some discussion was done on the discrepancy.
