Shelf life and rheology of emulsions containing vitamin C and its derivatives

Ascorbic acid (AA), or vitamin C, is widely used in the pharmaceutical, cosmetic and food industries as an antioxidant and cosmetics containing AA have been gaining popularity in the last few years for the treatment of photoageing. To solve the problem of its low stability, some esters have been synthesised, such as magnesium ascorbyl phosphate (MAP), also available encapsulated in collagen-based microspheres (EMAP). The aim of this research was to study the physical and chemical stability of O/W emulsions containing AA, MAP or EMAP, by rheological and HPLC analysis, respectively. These emulsions were stored at 25, 37 and 45°C for 28 days and samples tested weekly during storage. It was concluded that all the formulations showed pseudoplastic behaviour. The presence of MAP provoked an initial rise in thixotropy. The formulation containing AA did not show any marked change in rheological behaviour. In the chemical analysis, the formulation with EMAP was more stable than those with MAP and AA. Hence, replacement of AA with EMAP in this cosmetic formulation may be a viable way to enhance the stability of the active principle.