Antioxidant Capacity of Rhizophora mangle Bark Extracts : A Contextualized Approach in the Teaching of Analytical Chemistry (Journal Article)

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Abstract: Antioxidants are molecules that act against free radicals, and this effect can bring many benefits to health and society. Antioxidants can be found in various matrices of nature, such as fruits and plants. Some studies have shown that Rhizophora mangle, a typical mangrove plant, is rich in antioxidants. People report its use for medicinal purposes, such as treating diabetes and high blood pressure. In Espírito Santo, Brazil, the bark extract of the plant is used as a waterproofing agent in the making of the capixaba clay pan, a cultural symbol of the state. Thus, this context was used as a reference for the application of chemical knowledge addressed in the teaching of Instrumental Analytical Chemistry. The participants were undergraduate chemistry students at the Federal University of Espírito Santo (Ufes). Two experiments were designed to be performed by groups of four to five students during 2–4 h laboratory classes. The students employed analytical techniques for spectrophotometric (FRAP, ferric reducing antioxidant power) and electrochemistry (CRAC, ceric reducing antioxidant capacity) determination of the total antioxidant capacity of R. mangle bark extracts. The experimental results indicated that the extracts of the plant have significant antioxidant capacity compared to trolox. By performing different extraction procedures and analytical techniques, students were able to compare, analyze, and evaluate strategies aimed at determining antioxidant capacity. The antioxidant capacity assays can be expanded to analyze other matrices of interest to professors and students.