Evaluation of Functional Stability and Batch-to-Batch Reproducibility of a Castanea sativa Leaf Extract with Antioxidant Activity

A growing body of evidence suggests that free radicals are generated by UV irradiation being responsible for skin injury. In this regard, the topical use of formulations composed of plant extracts with antioxidant activity could represent a useful strategy for the prevention of photoaging and oxidative-stress-mediated diseases. The aim of this study was to assess the reproducibility of the extraction method and the functional stability of a Castanea sativa leaf extract in view of its application as topical antioxidant. Measurements of 1,1-diphenyl-2-picryl hydrazyl (DPPH) scavenging activity, total phenols (measured by the Folin Ciocalteu assay) and phenolic composition (high-performance liquid chromatography unit coupled to a UV detector) were carried out on three different batches. The influence of pH and temperature on the extract's DPPH scavenging activity was assessed in aqueous and glyceric solutions (0.025% w/v) over a 3-month period. Minor differences were found between the three extract batches for all the evaluated parameters, and therefore the reproducibility of the extraction method can be inferred. pH presented a great influence in the extract functional stability. Major antioxidant activity decrease was found at pH 7.1, while lower changes were observed at pH 5. Glyceric solutions were stable throughout the test period. At 40 degrees C and pH 5, a marked decrease of activity was observed. Again, glyceric solutions were the most stable, even at 40 degrees C. Proper selection of pH and solvent is mandatory to ensure the stability of the studied extract after being incorporated in semisolid forms. In view of these results, glycerine is proposed as the best vehicle for topical formulations incorporating C. sativa leaf extract, which should have a pH around 5.