STABILITY OF ASCORBIC ACID IN COSMETIC FORMULATION: PROTECTIVE ROLE OF RESVERATROL AND MELATONIN

The degradation of ascorbic acid (AA) has been considered one of the causes of quality and color changes during processing and storage of cosmetic products. The degradation process of AA is very complex and proceeds toward a number of oxidation/reduction and intermolecular rearrangement reactions [1]. In particular, AA is highly unstable in aqueous solution with the formation of degradation products such as dehydroascorbic acid, 2-furoic acid, 3-hydroxy-2-pyrone, furfural, etc. The nature of the degradation products depends on the reaction conditions. In the presence of oxygen (aerobic) the oxidation of ascorbic acid leads to the formation of several intermediates [2] and the final formation of various five carbons compounds such as 2-furoic acid and 3-hydroxy-2-pyrone. Under anaerobic conditions ascorbic acid was found to degrade via several steps to furfural [3]. The aims of our study was to investigate the AA stability in an aqueous cosmetic formulation, containing resveratrol (R), melatonin (M). The degradation kinetics of AA have been studied in single solutions, in the presence of resveratrol and melatonin, and in the commercial sample at different temperature (25, 40 and 60 °C). A reverse phase chromatographic method with gradient elution was developed by using both UV and mass spectrometric detection (HPLC-UV, LC-ESI-MS). The separation of the components of the cosmetic solution and the main degradation products (2-furoic acid, 3-hydroxy-2-pyrone, furfural, dehydroascorbic acid) was achieved on a Phenomenex LUNA C18 (4,6 x 150 mm ID; 5m) column. It was found that the main degradation products were deriving from the degradation of AA, and that their relative abundance and formation rates were influenced by the presence of M and R. In particular, in the absence of melatonin and resveratrol the degradation led to the preferential formation of dehydroascorbic acid, 2-furoic acid and 3-hydroxy-2-pyrone, representative aerobic degradation products. On the other hand, M and R presence in solution caused a slower AA degradation rate and the preferential formation of furfural, typical anaerobic reaction product. In aqueous solution at 40°C, the contemporary presence of R and M decreased AA degradation rate to t1/2 =267 days, instead of 66 days when AA was alone, demonstrating a protective role in AA degradation . Since R and M are potent antioxidant and free radical scavenger [4,5], it can be hypothesized that they protect AA from oxidation process and promote AA anaerobic degradation to furfural.