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Antioxidants are an alternative to prevent or retard biodiesel degradation. Soursop (Annona muricata L.) is a native tropical fruit with important antioxidant activity, besides high concentration of phenolic compounds. Peels form about 20 % of the soursop fruit composition and are usually discarded as a waste product. In this study the antioxidant potential of different peel extracts was evaluated by oxidative stability when used as an additive into soybean biodiesel. All samples were analyzed by the Rancimat® 873, using 32 experimental design. The tests were performed with biodiesel B100 with solutions extracted in different conditions, such as pH and residue concentrations. Results demonstrated that all experiments were able to increase significantly the induction period (IP), when compared to a pure biodiesel control sample, and showed similar efficiency with synthetic antioxidants (BHT). Among all experiments, each neutral and alkaline extractions presented induction periods over 8 h, achieving and surpassing the minimum allowed by European standard. However, the highest IP was found to be 10.30 h, with 3 g L-1 in neutral extraction. Results corroborate that soursop peel has a high antioxidant capacity and efficiency to improve the oxidation stability, and could be used as an inexpensive natural antioxidant to biodiesel.

A incorporação do biodiesel na matriz energética brasileira é de extrema importância para reduzir a importação de óleo diesel e diminuir os impactos ambientais gerados pelos gases de efeito estufa. Atualmente no Brasil a adição de biodiesel no óleo diesel é de 10%. Devido à biodegradabilidade do biodiesel, antioxidantes sintéticos são adicionados para aumentar sua vida útil, porém, esses compostos são derivados do petróleo e possuem potencial toxicidade e caráter carcinogênico. O objetivo deste trabalho foi utilizar extratos do Pleurotus ostreatus (P.O) como antioxidantes para biodiesel. Foram utilizadas técnicas rigorosas como: teste de oxidação acelerada (Rancimat® 873) e delineamento experimental simplex centróide. Para uso do P.O foram executadas a extração aquosa ácida, orgânica neutra e orgânica básica para extrair os compostos com potencial antioxidante e transferir-los para o biodiesel. A metodologia de extração aquosa ácida do P.O apresentou rendimento de 31,9%. Quando o biodiesel foi purificado com a solução ácida do Pleurotus ostreatus 5 g/L, o período de indução do biodiesel foi de 9,28 h (aumento de 183%), apresentando conformidade com a norma EN 14214.