Kinetics of Lipid Oxidation in Ternary Mixtures of Grape, Sesame and Sunflower Oils by Rancimat Method

O óleo extraído das sementes de uva é um produto com excelentes características antioxidantes e nutricionais, que pode ser utilizado na indústria de alimentos. Devido a essas características, este óleo foi incorporado, juntamente com o óleo de gergelim, em diferentes proporções, ao óleo de girassol, mantido na proporção de 50% em todas as misturas. Os óleos puros e misturas foram avaliados quanto à estabilidade termo-oxidativa (índice de estabilidade do óleo, OSI), compostos fenólicos, DPPH, cromatografia em fase gasosa, cinética de oxidação, entalpia e entropia e prazo de validade (a 25 ° C). A equação de Arrhenius e a teoria do complexo ativado foram utilizadas para estimar as energias de ativação, entalpias e entropia de ativação, variando de 80,66 a 90,37 kJ / mol, 77,84 a 86,61 kJ / mol e -129,46 a -104,37 J / mol K, respectivamente. O óleo de uva puro e as misturas com a maior proporção destes adicionados (B1 e B2) apresentaram os melhores valores em todos os parâmetros analisados. Os valores de energia livre de ativação (ΔG), que variaram de 27,68 a 38,59 kJ / mol, unificaram e verificaram os resultados dos outros parâmetros cinéticos, que indicam uma menor taxa de oxidação lipídica para a mistura B1, com maior proporção de uvas adicionadas

Effect of the natural antioxidant eugenol on quality preservation of commercial biodiesels produced with soybean oil or waste frying oil during storage at different temperatures

The objetive of this study was to evaluate the eugenol antioxidant efficiency on the oxidation stability of commercial biodiesel synthesized from soybean oil (SB) and wast fring oil (ORB) by determining induction period (IP) and acid number (AN) during storage at 10 °C or in accelerated oxidation test at 85 °C. For the oxidation stability evaluation, the Rancimat method (EN 14112) and AN (ASTM D664) analyses were used. The initial studies showed that the antioxidants eugenol and TBHQ when added separately increased IP values for the two types of biodiesel analyzed. During the storage at 10 °C, the IP was reduced for all samples. However, the lowest reduction percentages were for samples containing eugenol (-2.07 and -11.30% for SB and ORB, respectively). In relation to AN, the samples with the antioxidant eugenol led a greater decrease of this index, with the 10000 mg kg-1 concentration being the most efficient in the conservation of biodiesel. In the accelerated oxidation test in oven at 85 °C, pure BS presented higher susceptibility to degradation than the sample containing 10000 mg kg-1 of eugenol. In both storage studies, the eugenol natural antioxidant efficiency in the control of oxidative degradation of biodiesel becomes evident

Evaluation of Natural Antioxidants Action in Oxidative Stability of Commercial Biodiesel

The use of biodiesel has grown year-by-year, mainly due the low emission of pollutant gases. In addition, the raw materials used in its production are renewable, different from petroleum fuel. However, the biodiesels are more susceptible to oxidative degradation during the storage period, what damages the product quality. According the actual legislation, the use of antioxidant additives is necessary in order to provide a good resistance against oxidative reactions, which can be determined through accelerated oxidation tests, known as Rancimat method. The synthetic antioxidants tert-butylhydroquinone and butylated hydroxytoluene are among the most used, but several natural antioxidants could also be used. Thus, this work aims to evaluate the antioxidant properties of some natural antioxidants by using the Rancimat method. Two commercial biodiesel samples were added of three types of antioxidant at different levels of concentrations and submitted to accelerated oxidation in order to determine the induction periods. Different from vitamin E and grape seed oil, the eugenol additive presented the highest induction periods, being the most promising antioxidant additive for using in commercial biodiesel. DOI: http://dx.doi.org/10.17807/orbital.v10i1.1027</p

Evaluation of Potentiometric Methods for Acid Number Determination in Commercial Biodiesel Samples and Proposal of Alternative Method

The acid number (AN) is an important parameter that informs the quantity of free fatty acids (FFA) and acids originating from degradation reactions of biodiesel during production process and its storage. Due to the need to research and evaluate new environmentally friendly methods that reduce the toxic use solvents and minimize amounts of sample without significant loss of precision in the AN measurements by ASTM D664 method, the aims of this work were: i) to establish a procedure of cleaning and hydration of glass electrode to perform AN analyzes according ASTM D664 method in two commercial B100 biodiesel samples produced at Brazilian central-west region; ii) to propose the modification of the ASTM D664 method by reducing the amount solvent mixture and the sample size and to compare AN values obtained for cited samples with those obtained by ASTM D664 and EN 14104 methods. We proposed a simple procedure of cleaning and hydration of electrode. In this procedure, after each titration of the sample, electrode is rinsed with small portion of ethanol (approximately 5 mL) and then the electrode is immersed in distilled water by 15 min. The method proposed in this work is a modification ASTM D664 method, reducing by half the amount of sample and using only 50 ml solvent mixture against 125 for the official method. The acid number values determined indicate that biodiesel samples are in agreement with the maximum value stipulated by ANP resolution. By statistical analysis with confidence level of 95%, the results obtained with the proposed method are significantly equivalent to the official method ASTM D664, presenting satisfactory results, since the modification reduced the amount of solvent mixture by 60% and the sample amount by 50% used in the analysis, contributing to environmentally friendly analyzes and favoring both sustainable development and economic issues linked to biofuel research. DOI: http://dx.doi.org/10.17807/orbital.v10i1.1034 </p

Evaluating Antioxidant Eugenol on Oxidation Stability of Biodiesel Synthesized from Used Frying Oil

Due the environmental appeal, the demand of new processes and inputs has been increasing considerably in the last decade. Biodiesel is a biodegradable fuel obtained from vegetable oils or animal fats, including those discarded after use. The methyl and ethyl transesterification routes for biodiesel production were tested by using residual frying oil as raw material through the homogeneous basic catalyst, such as sodium hydroxide. In present work, it was evaluated the efficiency of the eugenol on the oxidation stability of the methyl and ethyl biodiesels synthesized from residual frying oil. The chromatographic analysis determined that the conversion of the yield to the methyl and ethylic esters (biodiesel) was 90.6 % and 87.3 %(m/m) respectively. For both biodiesel samples a rise of the eugenol concentration added resulted in an increase of the induction period (oxidation stability parameter evaluated by Rancimat method), with a consequent reduction of the acid number. Taking these results into account, it can be concluded that the samples obtained after eugenol addition can be used as biodiesel. DOI: http://dx.doi.org/10.17807/orbital.v10i1.1030 </p

Effect of Curcumin Natural Antioxidant on Oxidative Stability of Commercial Biodiesels from Different Raw Materials

Biodiesel emerges as an alternative biofuel for fossil ones because it is less polluting and can be produced from renewable sources. However, biofuels are generally more susceptible to auto-oxidation than fossil ones. Some fundamental characteristics in biofuel must be controlled in order to permit the correct operation of engines, so that the National Agency for Petroleum, Natural Gas and Biofuels (ANP) establishes specific resolutions about that. In most cases, the biofuel is poorly resistant to auto-oxidation, being required the addition of extrinsic antioxidant agents. In this work, it was demonstrated the curcumin is a natural product with excellent antioxidant behavior to be added to commercial biodiesel samples. The physical-chemical characteristics, induction period measured using Rancimat method EN14112 and acid number by ASTM D 664 method were investigated in present work for two commercial biodiesel samples prepared with different raw materials (soybean oil or soybean oil with beef tallow). The presence of beef tallow in one of the samples was positive for this biofuel quality in all of the aspects analyzed. Curcumin proved to be an efficient antioxidant for both biodiesel samples, increasing the induction period and reducing the acid number, guaranteeing good oxidative stability for commercial biodiesels studied. DOI: http://dx.doi.org/10.17807/orbital.v11i4.1225 </p

Evaluation of Antioxidant Potential and Chemical Composition Blends of Sunflower Oil (Helianthus annuus L.) with Coconut Oil (Cocos nucifera L.)

Coconut oil has more than 90% of saturated fatty acids. Of this percentage, about 47% of lauric acid, an important saturated acid that gives great stability to oxidation, in addition to benefic properties such as anti-inflammatory. Sunflower oil also presents important properties for daily balance of the body, however, the high amount of unsaturated fatty acids provides low oxidative stability. Knowing the nutritional values of both raw materials under study, the aim of this study was to mix them in two different proportions: 50% sunflower + 50% coconut (blend 1) and 70% sunflower + 30% coconut (blend 2), in order to evaluate the antioxidant potential and chemical composition, by analysis of fatty acids content; antioxidant activity (DPPH); phenolic compounds; oxidative stability, by accelerated oxidation test, Rancimat method. The acidity values for both pure oils and blends are within the values established by Anvisa and Codex Alimentarius, and phenolic compounds were proportional to the amount of sunflower oil incorporated into the coconut oil. The values of oil stability index (OSI), determined by Rancimat, were high, especially for coconut oil, and in the mixtures, the increase in oxidative stability was proportional to the amount of coconut oil added to sunflower oil. DOI: http://dx.doi.org/10.17807/orbital.v11i4.1226</p

Characterization, Oxidative Stability and Antioxidant Potential of Linseed (Linum usitatissimum L.) and Chia (Salvia hispanica L.) Oils

The aim of the present study was to assess the composition and oxidative stability of linseed and chia commercial oils, in addition to determining the kinetics of oxidation at temperatures of 100, 110, 120 and 130°C, as well as the quality parameters, acid value (AV), moisture and ash content. The data of oxidative stability index (OSI), moisture, acid value and ash content were acquired according to the methods: AOCS Cd 12b-92, EN ISO 8534 and AOAC, respectively. The fatty acid composition was assessed by gas chromatography coupled to flame ionization detector (FID). The antioxidant activity was assessed using the method of free radical scavenging of DPPH (2,2-diphenyl-1- picrylhydrazyl) and phenolic compounds using Folin-Ciocalteau reagent. The fatty acids identified in greater amount in the analyzed oils were the unsaturated acids linolenic, linoleic and oleic. Regarding the AV, linseed oil was more acid than chia oil. Chia oil offers better nutritional quality, resulting from the greater amount of unsaturations present in its composition, one of the factors that negatively affected its oxidative stability expressed as OSI. Regarding phenolic compounds and antioxidant potential, chia oil also showed better values, 319.12 mg g-1 and 149.57 µg mL-1, respectively. Linseed oil showed better oxidative stability with activation energy (Ea) and acceleration factor Q10 of 82.12 kJ mol-1 and 1.92, respectively, determined by kinetic studies for oxidative degradation performed using Rancimat method. DOI: http://dx.doi.org/10.17807/orbital.v11i4.1327 </p