Induction Period Values Research Articles

Comparison of OXITEST and RANCIMAT methods to evaluate the oxidative stability in frying oils

The oxidation of fatty acids in the presence of atmospheric oxygen is recognized as one of the main factors affecting the shelf life of oils and fats causing rancidity by the formation of off-flavors due to aliphatic aldehydes or other volatile compounds. Therefore, the oxidative stability is one of the most important parameters to be evaluated in the formulation of commercial frying oils. In this regard, the induction period of 15 frying oils has been measured using two different methods of accelerated oxidation, OXITEST and RANCIMAT, and correlated to their fatty acid content previously detected by gas chromatographic technique. Frying oils containing high contents of saturated fatty acids mainly from the palm oil achieved an improved oxidative stability by increasing their induction period. Moreover, the linear regression analysis showed a good correlation between the induction period values of the two instruments. Hence, the innovative OXITEST method may be an easy, fast, and eco-friendly alternative to the official RANCIMAT method for evaluating the oxidative stability in oil- and fat-containing products.

Alternative binary blends and their synergistic effect on stability of soybean biodiesel

The primary antioxidant tert-butylhydroquinone (TBHQ) and an alternative additive, named 1,4-bis(ethylamino)-9,10-anthraquinone, were mixed to yield a potent blend able to be used in the field of biodiesel preservation. Physicochemical parameters such as peroxide value, total acid number, density and induction period were used to evaluate the effectiveness of the combination in stabilising soybean biodiesel during the accelerate storage period of degradation. The induction period values were also used to calculate the occurrence of synergistic effect, and it was observed a high percentage of synergism for the combined additives. The results showed that the presence of target alternative additive also enables lower the concentration of the primary antioxidant (TBHQ) in the blend. The cost-effective comparison was evaluated, and it was verified that the final cost of biodiesel can also be lowered, since the amount of additives (in the blend) required to meet the biodiesel specifications was reduced between 70 and 88%.

Comparison of the effect of sinapic and ferulic acids derivatives (4-vinylsyringol vs. 4-vinylguaiacol) as antioxidants of rapeseed, flaxseed, and extra virgin olive oils

The aim of the work is to compare the antioxidant activity of 4-vinylguaiacol (4-VQ) and 4-vinylsyringol (4-VS) added to stabilize three (flaxseed, olive and rapeseed) commercial oils. The phenolics were added at concentration of 20, 40 and 80mg per 100g of oil. The oils were oxidized in a Rancimat test at 110°C. The linear dependences between the concentrations of each of these compounds and the induction period (IP) were found. Generally, 4-VQ was more effective, since the determined IP increase after its addition was from 5 to 25-fold higher than for the same addition of 4-VS. The highest increase was noted for flaxseed oil, for which 80mg 4-VQ addition per 100g of oil resulted in 50% IP increase. The highest absolute values of IP were reached by extra virgin olive oil, naturally abundant in phenolic compounds and with the lowest fatty acids oxidation index.

<b>Oxidative stability of biodiesel blends derived from waste frying oils

The high cost of biodiesel production is mainly linked to the price of raw material.This factor has favored the use of alternative fats and oils such as those used in frying. Since biodiesel can be obtained from several vegetable and animal raw materials, the physicochemical characteristics of the fuel may vary considerably. One of these characteristics is the fatty acid composition. It directly affects the oxidative stability of biodiesel, which can be impaired when the fuel undergoes exposure to sunlight, metals, oxygen and high temperatures. In order to improve the oxidative stability of biodiesels produced from waste frying oil some studies involving blends of different raw materials have been carried out. In this sense, this work aimed to assess the characteristics resulting from the blending of soybean waste frying oil with other waste biodiesels in what concerns to oxidation. The blends of fatty materials were obtained by means of a 2² factorial design. The induction periods of biodiesel blends were enough to meet the ASTM D6751 standard. Swine fat was responsible for the increase in the induction period values.

Effect of antioxidants on the stability and corrosiveness of palm biodiesel upon exposure of different metals

The properties of biodiesel get aggravated when metals are exposed into it. The present study aims to investigate the effect of antioxidants on the fuel properties of palm biodiesel upon exposure to copper and mild steel. The used antioxidants include pyrogallol (PY) and butylated hydro-oxy toluene (BHT). Static immersion tests of metal coupons in palm biodiesel in the absence and presence (500 ppm) of antioxidants were conducted at room temperature (25˚C-27 °C) for 60 days. The investigated fuel properties include induction period, density, viscosity, acid number and calorific values. Results showed that pyrogallol was more effective to suppress the degradation of metal surface, fuel composition and fuel properties.

Design of flavonoid microparticles with channel forming properties to improve oxidative stability of sunflower oil

Quercetin (Q) and epicatechin (E) microparticles were designed using an oil‐insoluble polymer (inulin [In]) as encapsulating agent and with or without an oil‐soluble polymer (soy protein isolate [SPI]) by spray‐drying. Encapsulation efficiencies were significantly higher for the E systems than for Q systems, suggesting that the spatial arrangement may affect the hydroxyl groups availability to form hydrogen bonds. The microencapsulated flavonoids were added to sunflower oil (SO) in order to evaluate its oxidative stability. The induction period (IP) of SO, determined in Rancimat at 60°C, significantly increased when Q‐microparticles with or without SPI were added, showing those with SPI the highest IP value. In the case of E systems, the IP of SO increased only when E–In microparticles with SPI were added. These results suggest that SPI may favor the diffusion of flavonoids to the lipid medium by the formation of channels into the microparticles. The channels formation was observed for Q–In–SPI and E–In–SPI by a confocal laser scanning microscopy study. Additional oxidation studies under conditions of lower oxygen availability resulted in overall more retarded oxidation and no clear effect of SPI incorporation was observed.Practical application: The results show that it is possible to design flavonoid microparticles with antioxidant activity in bulk oils. The inclusion of a lipid‐soluble polymer such as soy protein isolate in the microparticles favors the flavonoid release from the microparticles to bulk oil by channel formation.Epicatechin (E) and quercetin (Q) microparticles designed with inulin (IN, encapsulating agent) and soy protein isolate (SPI, channelizing agent) are incorporated to sunflower oil (SO). The channels formation is observed for Q–In–SPI and E–In–SPI by confocal laser scanning microscopy. The induction period (IP) of SO (Rancimat at 60°C) significantly increases when Q‐microparticles with or without SPI are added, showing those with SPI the highest IP value. Regarding E systems, the IP of SO increases only when E–In microparticles with SPI are added. No clear effect of SPI incorporation is observed in additional oxidation studies under conditions of lower oxygen availability.

In situ growth and physio-electrical characterization of bis-thiourea cadmium-iodide (BTCI) single crystal

The basic understanding of nucleation kinetics is very important for any useful material. In the present investigation, the solubility of BTCI (2:1 ratio) has been determined at various temperatures. The metastable zone width and induction period values were estimated in order to optimize the growth parameters. The Nucleation parameter such as interfacial energy has been determined using the experimentally determined induction period values. Various critical nucleation parameters like Gibbs free energy, radius of critical nucleus, and nucleation rate have also been investigated. It is observed that the nucleation rate increases with the increase of supersaturation. The growth parameters of the titled materials have been optimized for the growth of bulk size single crystals of BTCI. The single crystals of thiourea cadmium iodide have been grown by slow evaporation solution technique. The DSC study reveals that the melting point and the specific heat of BTCI have been found to be ~155.25 °C and 54.319 J/g °C respectively. The mechanical study has been carried out by Vickers method. DC conductivity study indicates NTCR–type behavior in BTCI single crystal and the activation energy was found to be 0.57 eV.

Effect of Spray‐Dried Flavonoid Microparticles on Oxidative Stability of Methyl Linoleate as Lipid Model System

AbstractMicroencapsulated quercetin (Q) and epicatechin (E) were prepared by spray‐drying using inulin (IN) as encapsulating agent (Q–IN and E–IN) as well as with Capsul (C) as channelizing agent (Q–IN–C and E–IN–C). Microparticles were added to methyl linoleate (ML) and results showed that Q microparticles markedly improved its oxidative stability by increasing the induction period values and delaying the formation of oxidation compounds, as determined by high‐performance size‐exclusion chromatography, with respect to E microparticles, thus suggesting the importance of flavonoid C‐ring substitution. Remaining levels of Q in the lipid system throughout oxidation of ML added with Q microparticles seemed to show two releasing zones: the first one corresponds to the equilibrium zone, when Q released from microparticles replaces Q that is being degraded; the second zone corresponds to the degradation of Q, when the release rate of the encapsulated Q is slower than its degradation rate. In contrast, E microparticles showed only one zone corresponding to the release of surface E. The end of the induction period was in line with the exhaustion of Q and E and the initiation of formation of advanced oxidation products (polymers). In conclusion, Q microparticles have a potential application to extend the shelf‐life of lipid matrixes.

Biodiesel oxidative stability from Rancimat data

It is conventional to quantify the oxidative stability of oils and biodiesel through an induction time determined by a Rancimat instrument. European Standard EN 14112 for the Rancimat method describes two procedures for determining this induction period. The automated method relies on finding the position of the peak in the second derivative of the conductivity vs. time curve. The manual method is based on the intersection of two tangents lines. It is shown that this method can also be automated by a curve fitting approach based on a novel Rancimat response function. This analysis demonstrates that the induction period values determined by the two methods differ with the second derivative method returning slightly higher estimates for the induction period.Biodiesel was prepared using base-catalysed methanolysis of sunflower oil. It was stabilized using the hindered phenol antioxidant tetrakis[methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)]methane. It was found that stability increases linearly with stabiliser concentration and that the effect of the measurement temperature follows Arrhenius kinetics. The effectiveness of the antioxidant stabiliser diminished with increasing temperature.

Influence of Water and Ultraviolet Irradiation on the Induction Period of the Oxidation of Biodiesel

Biodiesel degrades due to oxidative processes, causing a decrease in its quality. In the present work, it has been clearly shown that the incidence of ultraviolet radiation on biodiesels obtained from soy, canola, linseed and microalgae oils initiate oxidative processes which lead to the decrease in the induction period (IP) of the fuel. The influence of the residual water content of the same biodiesels on the oxidation process was also investigated with and without the incidence of ultraviolet radiation. Between 190 and 850 ppm of water in the biodiesel and without UV irradiation, no significant change in the IP values was observed under the experimental conditions.

Relative protection factor optimisation of natural antioxidants in biodiesel B100

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.

Tetrahydrocurcuminoids as potential antioxidants for biodiesels

This work demonstrates the potential use of tetrahydrocurcuminoids (THCs) as natural antioxidants to enhance the oxidation stability of biodiesels. Fatty acid methyl esters produced from cottonseed and residual cooking oils were doped with three different THCs, curcumin and synthetic antioxidants for comparison. The THC derivative with a phenol group in meta-position of the linking chain and a neighboring methoxy group provided higher oxidation stability (induction period values) in both biodiesels in comparison with other THCs and curcumin. Moreover, this THC derivative presented better efficiency than butylated hydroxytoluene in one of the studied biodiesels. This result is in agreement with antioxidant activity data for the three TCHs and curcumin reported in the literature. Additionally, THCs are colorless (instead of curcumin) which increases the market acceptance of such additives for biodiesel.

Дослідження кінетики осадження нікелю з розчину

Background. In the nickel-containing catalysts production there is the technological stage of the intermediate insoluble nickel compounds. The studies of the nickel precipitation kinetics by the urea from the nickel nitrate solution were carried out that are useful for the design and characteristics calculation of these processes,Objective. The purpose is in constructing of mathematical model for the nickel precipitation process.Methods. A thermodynamic evaluation of possible reactions in solution was carried out. In isothermal conditions at the temperatures of 90 and 100 °C the kinetic curves of nickel precipitation from solutions were obtained at different initial concentrations. On the curves several sections were marked: the induction period and the main reaction period that are analyzed by different methods. The dependence of the induction period value from the conditions of the process was analyzed using multiple regression approach. The kinetic equation of first order reaction was chosen for the main period and the temperature dependence of the rate according to Arrhenius equation was determined.Results. It is established that the value of the induction period depends on the process temperature and the concentration of nickel, the regression equation was obtained. It is shown that the basic section of the precipitation process kinetic curves are described by the equation of the first order at the different initial concentrations of metal in all the investigated temperature range, reaction rate constant of the first order and the activation energy of the process were calculated.Conclusions. The proposed kinetic model of precipitation that consists of equations system for calculating the time of reaction was obtained. The value of the activation energy of the process indicates a kinetic stage of process tendency.

Antioxidant capacity is a surrogate measure of the quality and stability of vegetable oils

Total antioxidant capacity (TAC) may be a comprehensive oil quality index because of its potential association with chemical composition, oxidative stability, and fresh oil quality. We aimed to investigate the chemical determinants of the oxidative stability and TAC of oils using multivariate statistical analyses and the use of the TAC assay as a predictor of oil stability. Fatty acids, tocols, phenolic compounds, peroxide value, acid value, induction period (by the Rancimat test) and TAC (by the TEAC assay) were determined in refined canola, corn, soybean, and sunflower oils as well as cold‐pressed nut oils. Principal component analysis was used for data reduction and variable extraction. Generalized linear models successfully estimated the TAC (R2 = 90.3%, p < 0.005) and oxidative stability (R2 = 91.6%, p < 0.001) of the oils, and γ‐tocopherol was the most important predictor in both of the models. The peroxide value and induction period were linearly associated with antioxidant capacity (R2 = 0.65, p < 0.01 and R2 = 0.70, p < 0.01, respectively), allowing the prediction of the initial quality and oxidative stability of the oils by the TEAC assay. Additionally, the proposed minimum TAC value for good quality refined oils was 2.2 mmol TE/kg.Practical Applications: Lipid oxidation is one of the major causes of vegetable oil degradation, affecting its global quality and limiting its shelf life. Therefore, a quality index applicable for estimating oxidative stability and initial quality of refined and cold‐pressed vegetable oils might be an important tool for quality control of oils in the food industry. We show that the TEAC assay, a simple and rapid spectrophotometric assay of antioxidant capacity, may be a useful tool for the determination of the global quality of oils due to its significant associations with the induction period and peroxide value. A minimum TAC value is advisable for good quality refined plant oils, especially when the initial quality and the shelf life are of concern.Antioxidant capacity is a surrogate measure of the quality and stability of vegetable oils. 2.2 mmol trolox equivalents/kg was proposed as a minimum total antioxidant capacity value for good quality refined oils.

Effect of temperature on the oxidation of soybean biodiesel

This paper proposes to examine the effect of temperature on the oxidation behavior of biodiesel. Soybean biodiesel was oxidized at different temperatures (room temperature, 60, and 110 °C), and the increase in primary and secondary oxidation products was determined based on the peroxide and anisidine values, respectively, during the induction period (IP). The results indicated that the evolution of hydroperoxides followed zero-order reaction kinetics during the IP at all temperatures, and their rate of formation was exponentially affected by temperature. It was also deduced that temperature influenced the ratio between primary and secondary oxidation products formation, which decreased as the temperature increased. Additionally, it was possible to predict the oxidation behavior of the soybean biodiesel at room temperature by an exponential model fitted to the IP values at different temperatures (70, 80, 90, 100, and 110 °C) using the Rancimat apparatus.

Developing the complex antioxidant from walnut leafs and calendula extracts

This article is devoted to research the oils and fats oxidation processes. The methods of protection oils, fats and fat-containing products from oxidative damage are given. The most attention is paid to products protection from oxidation with the help of inhibitors. Natural antioxidants from plant material are reviewed. Complex antioxidant based on walnut leaves and calendula extracts are developed and investigated. The ability of the developed oxidation inhibitor to inhibit the oxidation of sunflower oil is demonstrated. The antioxidant feature was estimated from the values of induction periods. By adding an extract of the walnut leaves in amount of 0,025 % (counting dry substance) and calendula extract in amount of 0,025 % (counting dry matter) into sunflower oil, the induction period is doubled. The synergy between sunflower oil tocopherols and antioxidants based on walnut leaves extracts and calendula extract was found. Thus, the complex herbal antioxidant that can increase the stability of sunflower oil to oxidation is developed.

Moringa oleifera: A potential source for production of biodiesel and antioxidant additives

This work reports the use of Moringa oleifera oil and leaves as potential sources for the production of biodiesel and antioxidant additives for biodiesels, respectively. The M. oleifera methyl ester was prepared by a two-step reaction and exhibited physical–chemical properties that met the minimum or maximum limits of the EN 14214, emphasizing the high induction period (IP) of 19.3h. Ethanolic extracts of M. oleifera leaves were evaluated as additives to increase the IP value of biodiesels. The results indicate that the 98% (v/v) ethanolic extract increased IP values of soybean biodiesel from 3.8 to 10.3h using the 100μgg−1 of extract, showing better performance than the synthetic antioxidant tert-butyl-hydroquinone. The extract also provided similar efficiency to methyl esters produced from sunflower, colza, corn and residual cooking oils. These results evidence the promising use of M. oleifera not only for biodiesel production but also as a source of antioxidant additives for biodiesels with low oxidation stability.

Development of an electrolytic method to obtain antioxidant for biodiesel from cashew nut shell liquid

An electrochemical method was applied in order to obtain a new antioxidant for soy biodiesel conservation, from the technical CNSL (tCNSL). The electrochemical modification occurred in an electrolytic tank under controlled conditions, including the voltage, electrical current and tCNSL flow. Physico-chemical analysis and Fourier Transform Infrared (FTIR) were carried out on tCNSL and eCNSL, while Gas Chromatography coupled to Mass Spectrometry (CG–MS) and Nuclear Magnetic Resonance (NMR) was carried out only on eCNSL to characterize the occured transformations after the electrolysis process. The Rancimat results showed that when eCNSL was added to the soy biodiesel, it was able to increased it is oxidative stability and the Induction Period (IP=7.31±0.20) values were higher than that required by ANP (Agency of Petroleum, Natural Gas and Biofuels). The electrolytic tests results combined with GC–MS displayed a significant decrease in the cardanol percentage which can promote the formation of dimers or oligomers that may be responsible for the increased antioxidant activity of the eCNSL. Therefore, the electrolysis process resulted in an effective biofuel antioxidant that presents interesting commercial advantages.

Investigations on critical parameters, growth, structural and spectral studies of beta-alaninium picrate (BAP) single crystals

Beta-alaninium picrate (BAP) salt has been synthesized and the solubility of the synthesized sample in double distilled water was determined at different temperatures. Solution stability was studied by observing the metastable zone width by employing the polythermal method. Induction period values for different supersaturation ratios at room temperature were determined based on the isothermal method. The nucleation parameters such as critical radius, critical free energy change, interfacial tension, and nucleation rate have been estimated for BAP salt on the basis of the classical nucleation theory. The lattice parameters of the grown BAP crystal were determined using the x-ray diffraction (XRD) technique. The reflection planes of the sample were confirmed by the powder XRD study and diffraction peaks were indexed. Fourier transform infrared spectroscopy and Fourier transform–Raman studies were used to confirm the presence of various functional groups in the BAP crystal. The nonlinear optical property of the grown crystal was studied using the Kurtz–Perry powder technique. UV–visible spectral studies were carried out to understand optical transparency and the type of band gap of the grown BAP crystal.

Nucleation kinetics and growth aspects of negative solubility lithium sulphate monohydrate single crystal

Nucleation and growth kinetics give valuable information about the crystal growth process, which can be employed in the growth of large size crystals. Accordingly, this paper discusses nucleation theory as applied to crystallizing negative solubility lithium sulphate monohydrate (LSMH) crystal. Solubility, metastable zone and induction period values were determined experimentally in order to optimize the growth parameters. The nucleation parameters such as interfacial energy, volume free energy, critical free energy and critical radius have been evaluated. The results have been discussed in detail. The good quality single crystal of LSMH was grown by the low temperature solution growth technique. The growth and dislocation behaviors were detected under the etching studies. It is shown that the classical approach explains the available nucleation data under most conditions used for growing LSMH crystals.