Exploring the possibility of predicting long-term oxidative stability in prototype skincare formulations using various lipid oxidation initiators.

Objective: The purpose of this study was to identify an effective lipid oxidation initiator which could predict, within 1 month, the long-term oxidative stability of a prototype skincare formulation. The main purpose was to find a potential initiator not to assess oxidation stability of the formulations.

Methods: Four initiators (below) were examined in three steps: Reaction kinetics using a Clark electrode (Oxygraph); Effect of adding an initiator on the product's physical and oxidative stability in prototype skincare formulations by visual observation, peroxide value and headspace GC-MS determination of volatile oxidation products; and Ability to differentiate unstable vs. stable prototype creams by initiator addition. The four initiators explored were: FeCl /H O , FeCl /ascorbic acid, 2,2'-Azobis(2,4-dimethylvaleronitrile) (AMVN) and 2,2'-Azobis(2-methylpropionamidine) dihydrochloride (AAPH) RESULTS: In Oxygraph, the initiator systems FeCl /H O and FeCl /ascorbic acid were good accelerators of oxygen consumption. The addition of FeCl /H O to prototype formulations did not affect the physical stability. However, the addition of FeCl /ascorbic acid to prototype formulations resulted in phase separation and FeCl /ascorbic acid was therefore deemed unusable. Moreover, the addition of AAPH or AMVN resulted in an increased and decreased viscosity respectively. In the oxidation stability study, peroxide value increased significantly when AMVN was added. However, the peroxide value remained low for the other initiators and the control (no initiator). The secondary volatile oxidation product, butanal, increased most with the FeCl /H O addition. Three out of the four initiators did not have the ability to rank the stable and unstable formulations in accordance with the result obtained for volatile oxidation products after 42 days of storage at 20°C of formulations without initiator. Only, FeCl /H O was able to rank the formulations in accordance with the oxidative stability observed for volatile oxidation products after 42 days of storage.

Conclusion: FeCl /H O showed potential as an initiator to predict the oxidative stability of skincare formulations, but more studies are needed to confirm the result in a broader range of products over a longer time.