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Biodiesel is a renewable fuel produced from vegetable oils and animal fats transesterification. However, due to its chemical characteristics, it is susceptible to oxidation causing losses to its manufacturers and users. In this work a series of salicylates were synthesized and employed as secondary antioxidants in biodiesel B100. The accelerated oxidation tests were carried out against copper and iron. The biodiesel oxidation degree was followed by the acidity index. Among the synthesized compounds, isopropyl salicylate was able to inhibit the oxidation process by 55% when induced by copper and 52% when it was induced by iron after 8 hours exposure. The commercial antioxidant TBHQ was used as a positive control presenting lower inhibition values than isopropyl salicylate. It should be noted that salicylates are accessible molecules in just one reaction step, high yields and low cost, these being desirable characteristics for the biodiesel industry.

Abstract The antioxidants used in the food industry are essential to inhibit the formation of free radicals, preserving the existing properties in the different matrices. However, the insecurity of the synthetic antioxidants regarding human health propels search for natural substrates with potential antioxidant activity as an alternative to synthetic compounds. In this way, the work had as objective obtaining extracts from the seed pomace of the Hevea brasiliensis (rubber tree), relating the contents of flavonoids and total phenols in the application as an antioxidant. The methodology consisted of the extraction using four solvents, varying extractive methods, time, and seed concentrations. The antioxidant activity in vitro was evaluated by capturing the DPPH (2,2-diphenyl-1-picryl-hydrazil) radical. The optimized results demonstrate that the aqueous extracts produced in the Soxhlet in the concentrations of 85 g L−1 and retention time of 4 h reached 37.73 ± 1.69% in the antioxidant tests of the free radical DPPH capture, 1405.15 mg EAC 100 g−1 in the quantification of phenolic compounds and 223.34 mg 100 g−1 of total flavonoids. Thus, this work may contribute to the realization of studies and future research for characterization and identification concerning which phenolic compounds and flavonoids attribute the antioxidant characteristic to the extracts produced, enabling the discovery of products with high added value in the production chain. In addition, because the water used as a solvent showed greater antioxidant potential between the extracts, the non-toxic and environmentally friendly character is highlighted, allowing a wide variety of applications in the food industry.