Optimization of solvent extraction and HPLC-DAD method parameters for determination of phenolic compounds in various Brazilian propolis

Propolis is an organotherapeutic product collected by honey bees that contains a large number of phytoconstituents, possessing excellent pharmacological properties. In this study, phenolic composition and antioxidant capacity were evaluated in different types of Brown, Green and mixture of Red, Green I and Brown II (RGB) Brazilian propolis. Ultrasonic-assisted extraction was performed by direct solvent extraction (DSE) and successive solvent extraction (SSE) methods. The ethanolic extract of Green I propolis by SSE was higher in total phenolics (403.88 mg GAE/g extract), flavonoids (311.57 mg QE/g extract), and DPPHGreek ano teleia scavenging activity (82.33 mu Mol TE/g extract) compared to other Brazilian propolis samples. Moreover, different solvent phases were used in the HPLC-DAD analysis and the results were validated by linearity and sensitivity. The optimized method was proven to be precise revealing good separation of standard phenolic compounds. Thermal stability of the compounds was accessed by using different column oven temperatures (40, 50 and 60 degrees C), and the results showed that lower temperature (40 degrees C) retains the maximum contents of total phenolics in the 80% ethanolic extract of Green I propolis (253.71 mg/g extract) by DSE compared to other propolis samples. This extract (109.35 mg/g extract) also obtained a higher amount of total phenolic compounds in the SSE compared to ethyl acetate and acetone extracts. Among the phenolic compounds, artepillin C (60.10 mg/g extract) was higher in the SSE of Green I propolis 80% ethanolic extract. Thus, this study optimized the extraction and HPLC analytical conditions for the determination of phenolic composition and antioxidant capacity in different samples of Brazilian propolis.