Effects of light, oxygen and concentration on vitamin A1

Raman spectroscopy was used to demonstrate the effects of UV light and oxygen on vitamin A, (alltrans retinol) in an oily solvent. The retinol concentrations tested were those used in cosmetics. UVA light transformed this retinoid into several derivatives in a few hours. UVA light was more destructive than UVB. A UVA filter protected the active principle and confirmed the damage was due to UVA light. Aeration also accelerated retinol photodegradation, while an antioxidant limited the number of photoproducts detected. Thus retinol photodamage is amplified by oxygen. Raman measurements allow 'in situ' observation and identification of these complex processes. The changes in retinol, retinal and anhydrovitamin A concentrations were quantified directly. Retinol was converted to an electrocyclized retinoid (1606 cm(-1)) and a deconjugated oxidized species (1629.5 cm(-1)). Little anhydrovitamin A was formed and enough accumulated for the formation of carotene-like species (1527 cm(-1)). Copyright (C) 2004 John Wiley Sons, Ltd.