Relative protection factor optimisation of natural antioxidants in biodiesel B100

•Rosemary, oregano and basil were effective in biodiesel protection.•The induction periods were used to determine the relative protection factor.•The relative protection factor was effective in evaluate the efficiency of the extracts.•Rosemary showed higher activity and total phenolic content.•The thermogravimetry showed that basil extract was the most stable.

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.