Industrial Crops and Products 80 (2016) 109–114 Contents lists available at ScienceDirect Industrial Crops and Products jo ur nal home p age: www.elsevier.com/locate/indcrop Relative protection factor optimisation of natural antioxidants in biodiesel B100 Kelly Roberta Spacino, Elisangela Tavares da Silva, Karina Gomes Angilelli, Ivanira Moreira, Olívio Fernandes Galão, Dionisio Borsato ∗ State University of Londrina, Chemistry Department, Fuels Analyses and Research Laboratory, PO Box: 10.011, 86057-970 Londrina, Paraná, Brazil a r t i c l e i n f o Article history: Received 29 June 2015 Received in revised form 3 November 2015 Accepted 9 November 2015 Available online 6 December 2015 Keywords: Biodiesel Rosemary Oregano Basil Simplex-centroid design a b s t r a c t Soybean oil is currently the most widely used raw material for biodiesel production, but its main fatty acids are unsaturated, which makes the addition of antioxidants necessary. This study used alcoholic extracts of natural antioxidants rosemary, oregano and basil to evaluate the protection factor in biodiesel. The analysis of total phenolics content of the extracts showed that the highest values were found for rosemary extract, followed by oregano and basil. Thermogravimetric analysis indicated that the most stable extract was basil, followed by rosemary and oregano. After drying, the extracts were added to the B100 biodiesel and the samples were subjected to accelerate oxidative stability testing at temperatures of 110, 115, 120 and 125 ◦ C following the experimental simplex–centroid design for mixtures. Through the relationship between the values of induction periods, from the different tests and control, the values of the relative protection factor (RPF) were determined. The multiresponse optimisation of predictive equations showed that the greatest value of the RPF was 3.73 for the test containing 50% of rosemary and 50% of oregano and the lowest was 2.94 for biodiesel containing only basil extract as an antioxidant. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Biodiesel is a mixture of mono-alkyl esters of long chain fatty acids obtained by the transesterification of oil or fat with an alco- hol and catalyst (Martínez et al., 2014; Daud et al., 2015). In Brazil, as in many other countries, energy production has caused serious environmental problems due to the large-scale use of fossil fuels (Kaercher et al., 2013). Therefore, the use of this biofuel becomes important as it is biodegradable and not toxic, and reduces the emission of exhaust gases from diesel engines, such as particu- late matter, unburnt hydrocarbons and carbon monoxide, making it environmentally friendly (Bouaid et al., 2012; Daud et al., 2015). However, biodiesel is susceptible to oxidation, an undesirable phenomenon, because it can increase the viscosity and formation of insoluble species, which can cause clogging of the fuel lines and pumps (Almeida et al., 2015). The oxidation is related to the vari- ety of oils and fats used in the manufacture of biodiesel, making it difficult to ensure their quality in order to meet all compliance parameters required for commercialisation such as specific mass at 20 ◦ C, acid value, iodine value, flash point, ester content, kinematic ∗ Corresponding author. E-mail address: dborsato@uel.br (D. Borsato). viscosity, cold filter plugging point, and others (En 14112, 2003; Martins et al., 2015). Several oilseed crops (soybean oil, cottonseed oil, macauba oil) with have been studied for use in biodiesel production, some more efficiently, but factors such as climate and region of the country, can determine and influence the choice (Cremonez et al., 2015). Currently, soybean is the main oilseed with regard to production and international trade and its oil is the most commonly used in the production of biodiesel. However, 84% of its fatty acids are unsatu- rated, such as oleic acid (C 18:1 ), linoleic acid (C 18:2 ) and linolenic (C 18:3 ), which makes it susceptible to oxidation by atmospheric oxygen (Ferrari et al., 2005; Lee et al., 2011; Issariyakul and Dala, 2014; He et al., 2015). In order to avoid the oxidation process of biodiesel, synthetic antioxidants have been employed. However, despite its efficiency, most of these compounds have low biodegradability and are toxic and expensive (Sousa et al., 2014). Natural antioxidants are an alter- native and have proven to be effective in controlling lipid oxidation in edible oils (Cordeiro et al., 2013), but are still not being used in practice in biodiesel (Coppo et al., 2014). Some plants used as condiments are good sources of phenolic compounds that have antioxidant activity, due to their ability to inhibit free radicals by donating hydrogen atoms, regenerating the ester molecule and interrupting the oxidation mechanism (Borsato http://dx.doi.org/10.1016/j.indcrop.2015.11.034 0926-6690/© 2015 Elsevier B.V. All rights reserved.