The influence of Annona muricata L. peel extract as a potent source of natural antioxidant on soybean oxidation stability: A influência do extrato de Annona muricata L. peel como uma potente fonte de antioxidante natural na estabilidade da oxidação da soja

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