Stability studies of L-ascorbic acid and ascorbyl palmitate in topical cosmetic formulations
The present study aimed to formulate and evaluate a topical skin-care cream (o/w emulsion) from l-ascorbic acid and ascorbyl palmitate at 2% versus its vehicle. Formulations were stored at 8°C, 25°C and 40°C (in incubator) for a period of four weeks to investigate their stability. In the physical analysis, the evaluation parameters consisted of colour, phase separation, centrifugation, and liquefaction. Cosmetic stability, established by HPLC analysis, relies quantitative chemical determinations of active components during 28 days. In the chemical analysis, the formulation with ascorbyl palmitate was more stable than that with l-ascorbic acid. The microbiological stability of the formulations was also evaluated. The findings indicated that the formulations efficient against the proliferation of various spoilage microorganisms, including aerobic plate counts as well as Pseudomonas aeruginosa, Staphylococcus aureus, and yeast and mould counts. Results emphasize the importance of studying the parameters by showing the relation of components degradation, physical and microbiological stability aspects of cosmetic formulations containing vitamins C and ascorbyl palmitate.
L-Ascorbic acid (Vitamin C) has been used in pharmaceutical and cosmetic preparations for a long time on the basis of its many favourable effects on the skin (1). It is an important antioxidant that protects the skin by scavenging and destroying free radicals and reactive oxygen-derived species (2). It could improve the morphogenesis of dermal epidermal junction, and is also known for its skin lightening properties (3, 4). L-Ascorbic acid is also used topically because of its ability to reduce wrinkles by promoting collagen synthesis and its skin-depigmenting activity (5). However, its low stability is a serious limitation. It is easily oxidized, especially under aerobic conditions and light exposure, being degraded first in a reversible step to dehydroascorbic acid and second to oxalic acid in an irreversible fashion (6). Chemical modification of ascorbic acid has led to more stable derivatives such as ascorbyl esters with C6 to C18 fatty acids or ascorbyl phosphate salts. Among the lipophilic derivatives, ascorbyl palmitate is often used in topical preparations against oxidative changes of biological components of the skin, and as an anti- ...