Research conducted at Istanbul Technical University in 2019 on propolis samples collected from different regions of Turkey investigated the antioxidant capacity under in vitro conditions. Also, the scientists measured the phenolic and flavonoid contents of samples. The results revealed a high level of phenolic compounds composed of 32 different structures, including the caffeic acid phenethyl ester (CAFE) and thereby a powerful antioxidant capacity. Besides, the samples harvested from the Marmara region showed the highest amount of CAFE.
Reference:Ozdal, T., et al., 2019. Investigation of antioxidant capacity, bioaccessibility, and LC-MS/MS phenolic profile of Turkish propolis. Food Research International, 122, pp.528–536.