The antioxidant properties of caffeic and ferulic acids in biological systems have been extensively demonstrated. As antioxidants, these compounds prevent the production of reactive oxygen species (ROS), which cause cell lesions that are associated with the development of several diseases, including cancer. Recent findings suggest that the chemoprotective action of these phenolic acids occurs through the following mechanisms: regulation of gene expression, chelation and / or reduction of transition metals, formation of covalent adducts and direct toxicity. The biological efficacy of these promising chemoprotective agents is strongly related with their chemical structure. Therefore, in this study, we discuss the structural characteristics of ferulic and caffeic acids that are responsible for their biological activities, as well as the mechanisms of action involved with the anti-cancer activity. Several reports indicated that the antioxidant effect of these phenylpropanoids results from reactions with free radicals with formation of stable products in the cells. The chelating effect of these compounds was also reported as an important protective mechanism against oxidative. Finally, the lipophilicity of these agents facilitates their entry into the cells, and thus, contributes to the anticancer activity.

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Phenolic compounds are widely recognized because of their antioxidant capacity. In the present work, caffeic acid was shown to minimize the formation of oxidative radicals in soybean biodiesel, according to the induction period (IP) obtained by the Rancimat method. Its efficiency was much higher than usual antioxidants, such as butylated hydroxytoluene (BHT) and tertbutylhydroquinone (TBHQ). With a decomposition temperature of 170 °C, caffeic acid retained its properties, showing excellent antioxidant activity even when subjected to accelerated oxidation tests. While contamination with metals led to a meaningful decrease of the oxidative stability of soybean biodiesel, when small amounts of caffeic acid (500 mg L À1 ) were also present in the fuel, IP values higher than 6 h were obtained, reaching the limit specified by EN 14214.

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