Avaliação do potencial antioxidante dos ácidos anacárdicos no biodiesel de girassol

Abstract

The Cashew Nut Shell Liquid (CNSL) is a phenolic oil contained in the bark of cashew nut (anacardium occidentale), consisting of a mixture of four phenols: anacardial acid, cardanol, cardol and 2-methylcardol. The anacardic acids are the major constituents of the natural CNSL (72-82%) presenting not only antibiotic, but also cytotoxic and anxiolytic activities. As a phenolic derivative, anacardic acids may present antioxidant activity, and the present work aims to study these acids as antioxidant in sunflower biodiesel. The process of obtention was performed by means of column chromatography, since the methodology described by Paramashivappa et al. (2001) did not present high separation efficiency, and high-efficiency liquid chromatography techniques were employed for the isolation of the anacardic acids, as well as techniques of Fourier-transform infrared spectroscopy and nuclear magnetic resonance for characterization. Oxidative stability was performed by an accelerated method in Rancimat, employing increasing concentrations of the natural antioxidant and using salicylic acid as a synthetic compound for comparison with the anacardic acids in its concentration of greater efficiency. Through this study it was possible to develop a methodology of obtaining anacardic acids in three chromatography steps. The aforementioned acids, however, did not present significant gains in stability for sunflower biodiesel, not adapting the stability biodiesel to a minimum (8 hours) established by the ANP. Nevertheless, it was possible to observe the influence of some orto-substituent to phenolic hydroxyl carbonylic compounds and the effect of aliphatic substituents on antioxidant activity. Moreover further studies are needed to determine the mechanisms of action of compounds derived from hydroxybenzoic acid.