Avaliação antimicrobiana e efeito antioxidante de extratos naturais como aditivos no biodiesel B100

Abstract

Biodiesel is a fuel obtained from renewable energy sources, playing an important role in fostering the green economy. However, the presence of unsaturated fatty acids in its chemical composition is able to accelerate the oxidation process. In order to delay the oxidative process, synthetic antioxidants are used that have a high cost and although efficient, they can cause harmful effects to humans, thus, the use of natural antioxidants is a promising alternative. The objective of this work was to evaluate the oxidative stability of Biodiesel B100 and the antimicrobial activity of natural extracts of cherry leaves (Eugenia involucrata), surinam cherry (Eugenia uniflora), java (Eugenia jambolana) and peach-bush (Eugenia myrcianthes), by conventional extraction method, in oil and fat extractor - Goldfish, using as solvents ethyl alcohol, ethyl acetate and hexane in a concentration of 1:10 mass/volume. The samples were characterized phytochemically, using the colorimetry and precipitation method, demonstrating the presence of flavonoids and tannins in all plant specimens. The antimicrobial activity of the extracts was tested against the strains of Bacillus cereus, Staphylococcus aureus, Escherichia coli and Salmonella sp, by the Minimum Bactericidal Concentration (CBM), with the ethanolic extract being the only one to eliminate all microorganisms, even obtaining the smallest CBM, 2,5 mg/mL for surinam cherry extract against E. coli. The content of total phenolic compounds (TFT) was evaluated by the Folin-Ciocalteau method, and the determination of antioxidant activity by the methods 2,2–Difenil–1–picril–hidrazila (DPPH) and Iron-reducing antioxidant method (FRAP). The results showed that all extracts obtained by ethanol were quantitatively higher in their concentration of phenolic compounds and antioxidant effects when compared to extracts of ethyl acetate and hexane. The ethanolic extracts at a concentration of 1000 ppm, were then evaluated by the Accelerated Oxidation test at 110C in Rancimat equipment. The tested biodiesel was synthesized from commercial soybean oil, showing satisfactory results for the analyzed physical-chemical parameters. B100 biodiesel (control sample) had an induction period (PI) of 5h21min. The cherry extract was the only one to improve the oxidative stability of biodiesel, presenting PI of 6h16min, being superior to the control. However, it is well below the limit established by the National Petroleum Agency (ANP), which requires a minimum time of 12 hours, yet, the synthetic antioxidant Butyl-hydroxy-toluene (BHT) showed a greater antioxidant effect (7h50min). The samples added with extracts of surinam cherry, java and peach-bush didn’t show antioxidant action, with PI of 3h42min, 4h24min and 3h60min, respectively. The ethanol extracts evaluated in the present study weren’t satisfactory for replacing synthetic antioxidants in biodiesel, however, they show good results in terms of their antimicrobial activity. Natural compounds are influenced by many factors, and more tests are needed for each purpose.