Avaliação de extratos naturais na estabilidade termo-oxidativa do biodiesel e antimicrobiana na fermentação alcoólica

Abstract

The fossil fuels are non-renewable sources of energy, which motivates the search for new alternatives that besides clean and renewable it should present good quality and performance. Biodiesel and ethanol are the main liquid biofuels used in Brazil. Biodiesel has unsaturated fatty acids in its structure that facilitate processes of accelerated oxidation by temperature and humidity. Ethanol, on the other hand, is produced by fermentation processes, due to the biological action of yeasts. Contaminant microorganisms are one of the conditions responsible for the inhibition and decrease of yeast viability, besides reducing the fermentation yield. In order to increase the oxidative stability of biodiesel and control the contaminating microorganisms of ethanol's alcoholic fermentation, natural extracts can be used as an alternative to synthetic agents. The extracts from the leaves of Persea americana, Sambucus nigra and Esenbeckia grandiflora extracted with the fat extractor - Goldfish were tested, using ethylic alcohol, ethyl acetate and hexane as solvents at a concentration of 1:10 mass/volume. The effect of the extracts on the thermo-oxidative stability of methyl soy biodiesel was evaluated by the Differential Exploratory Calorimetry (DSC) technique, the extract that presented the best result was submitted to the Rancimat Accelerated Oxidation test. For microbiological contamination, the quantity of colony forming units (CFU/mL) of absolute broth, treated broth and fermented broth was determined and the bacteria Gram was identified. Determining the minimum inhibitory concentrations (MIC) of extracts, classifying them according to their bactericidal and bacteriostatic potential. From the results obtained with the DSC and confirmed by the Rancimat method, it is noted that the E. grandiflora leaves can be used to obtain extracts with antioxidant activity, considering it a possible substitute for synthetic antioxidants. In the fermentation process, Gram-positive bacteria were predominant, with contamination levels higher than 107 UFL/mL, which results in significant losses. The natural extracts were shown to be efficient in inhibiting most microorganisms. The leaves of E. grandiflora were efficient in all microorganisms analyzed, with bacteriostatic action in all concentration variations. The leaves of the P.americana extracted with the solvents ethyl acetate and hexane showed the lowest MIC of 1,25 mg/mL compared to Lactobacillus casei bacteria, being the only one with bactericidal action. These extracts have a high capacity to be used as substitutes for synthetic antimicrobials. However more tests are needed for this purpose.