Propolis extract release evaluation from topical formulations by chemiluminescence and HPLC

Propolis is a resinous bee hive product that has many biological activities. Among these activities, the antioxidant activity deserves special interest since it suggests propolis could be successfully applied topically to prevent and treat skin damages. The skin is continuously exposed to free radicals generated in the aging process and by external stimuli such as sunlight. Thus, the development of topical formulations added with propolis extract is justified. However, it raises the necessity of being concerned about the methodologies that could be used to evaluate the propolis extract release from these formulations. So, p-coumaric acid content using HPLC and the antioxidant activity using chemiluminescence were used to assess the release of propolis extract from topical formulations. A low fat content formulation (F1) and a high fat content formulation (F2) were evaluated and they showed that after 6 h, 4.6 μg/cm2 (F1) and 2.75 μg/cm2 (F2) of the p-coumaric acid was released, while it was found that both formulations released about 0.85 μL/cm2 of the antioxidant activity as propolis extract equivalent (AAPEE). Thus, once the antioxidant activity of propolis extract may be the result of the synergic action of several compounds, the obtained results indicate that a release study would be more conclusive if the antioxidant activity was evaluated, besides the measurement of a marker compound content.