Comparative evaluation of the total antioxidant capacities of plant polyphenols in different natural sources

Plant phenolic compounds are metabolites with a strong antioxidant capacity. Despite the fact that plants synthesize them mainly for their own defense against oxidative stress, these compounds retain the ability to act as ex-plant antioxidants and, therefore, they contribute greatly to the dietary and pharmaceutical properties of plant-food. These compounds have a wide range of structures and functions. Generally, they possess an aromatic ring with one or more hydroxyl substituents and have been classified into at least 10 different classes based on their basic chemical structure. The aim of this work was to carry out the characterization of the phenolic content and the determination of the antioxidant capacity of 4 plant matrices. Firstly, the plant matrices Lippia citriodora, Hibiscus sabdariffa, Olea europaea and Silybum marianum were chosen due to their high content of phenolic compounds. After that, a qualitative characterization of the phenolic profile from the selected plant extracts wasperformed using a high-performance liquid chromatography coupled to mass spectrometry. Finally, determination of the total content of polyphenols was carried out using the Folin-Ciocalteu method and the antioxidant capacity using the electron transfer methods, FRAP and TEAC, and hydrogen donation, ORAC. A comprehensive characterization and biological antioxidant properties of selected sources have been obtained. After the chromatographic analysis of the phenolic profile of each matrix, it was observed that in L. citriodora the abundance of the group of phenylpropanoids and iridoids stands out, in H. sabdariffa the groups of anthocyanins and flavonoids, in O. europaea secoiridoids and terpenes while in S. marianum the group of flavonoids. Regarding the antioxidant capacity, L. citriodora showed better results for the FRAP assay, while for the TEAC and ORAC assays the highest values were for S. marianum.