Rancimat Method Research Articles

Evaluation of antioxidant action by electrochemical and accelerated oxidation experiments of phenolic compounds derived from cashew nut shell liquid

This paper describes the use of electrochemical methods and accelerated oxidation experiments (EN 14112, Rancimat method) for the determination of antioxidant activity of phenolic compounds (cardanol, cardol and tert-butylated cardanol) derived from cashew nut shell liquid (CNSL), a byproduct obtained during the processing of cashew nuts classified as a renewable raw material, natural of low-value. Through the electrochemical study, having as reference the anodic peak potential (Epa) and peak current (Ip), was observed that the cardol had the best performance, followed by tert-butylated cardanol and this by cardanol, showing that the presence of electron-donating groups as tert-butyl and hydroxyl exerts a positive influence on the antioxidant action of these compounds. These analyzes showed also that unsaturated compounds presented current values superior than saturated ones, indicating that the unsaturated molecules participate in greater number of the electro-oxidation process. The accelerated oxidation experiments were performed through analysis of biodiesel samples additivated with CNSL-based antioxidants at 500ppm, and the same sequence of activity presented by the electrochemical study was observed, showing that this class of compounds can be applied effectively to inhibit the oxidative process of biofuel.

Characterisation and use of single and double low temperature dry-fractionated olein and stearin from virgin olive oil

Single and double-fractionated olein and stearin were obtained by successive cooling of the virgin olive oil at 10 and 6 °C. Characteristics of the obtained fractions were compared with those of the virgin parent oil. Single-fractionated stearin (first stearin) constituted 65% (w/w) of the virgin oil, while double-fractionated stearin (second stearin) constituted 55% (w/w) of the single-fractionated olein (first olein). The fractionation process resulted in minor changes in the peak temperature and enthalpy change of the differential scanning calorimetry thermograms, and in minor changes in the physical, chemical sensory attributes of the oil fractions. The virgin oil and the stearin fractions were significantly (P≤0.05) more stable to oxidation as evaluated by the Rancimat method than the olein fractions. Mayonnaise and Italian salad dressing prepared from the double fractionated stearin had significantly (P≤0.05) superior consistency, smoothness and overall acceptability to those produced from the other...

Influence of extraction techniques on antioxidant properties and bioactive compounds of loquat fruit (Eriobotrya japonica Lindl.) skin and pulp extracts.

In this study, the bioactive compounds of loquat fruit (Eriobotrya japonica Lindl.) skin and pulp extracted by two extraction methods (solvent and ultrasound-assisted) with three solvents (ethanol, water and ethanol–water) were compared to supercritical fluid extraction. The antioxidant activities of skin and pulp extracts were evaluated and compared to tertiary butylhydroquinone (TBHQ) using 2, 2-diphenyl-1-picrylhydrazyl (DPPH˙) radical scavenging, β-carotene bleaching, and the Rancimat assays. In DPPH assay solvent extracts of skin by ethanol (SSE) and ethanol–water (SSEW) showed strong inhibitory activity. The SSEW also showed the highest inhibition percentage of 85.58% by the β-carotene bleaching assay and longest induction time of 4.78 h by the Rancimat method. The large amount of tocopherols and phenolics contained in the skin extract may cause its strong antioxidant ability. The results indicated that the solvent extraction with ethanol–water produced the maximum extraction yield of phenolic and tocopherol compounds from loquat fruit skin and pulp. Furthermore, solvent extraction was the most effective in antioxidant activity of the extracts compared to other extraction techniques.

Physico-chemical durability criteria of oils and linked bio-based polymers

The oxidative stability or durability is an important indicator of performance that depends on the composition of the sample. The fatty oil or polymer degradation processes have generally been established as being free radical mechanism yielding primary oxidation products. We propose to explain in detail all the analytical methods and tools used for the determination of the initial physico-chemical properties of oils and the properties in ageing conditions. Chemical titrations for acid or peroxide value, Rancimat method or thermogravimetric measurements are discussed. Accelerated ageing tools for thermal or photochemical exposures are also shown. After the assessment of oil durability, the development of new bio-based polymer with vegetable oil is tackled because of its industrial interest. It is essential to understand the long term behavior of oils and biopolymers and to assess exactly the durability which is useful to produce life cycle analysis of materials. At last we underline the advantages of a new Fourier transform infrared (FTIR) instrumentation with in-situ irradiation and gas cell to give a screening of the durability of various oils or polymers. Main durability criteria of oils and biopolymers are linked to the production of volatile organic compounds and the resistance to the oxidation process.

1H NMR spectral analysis as a new aspect to evaluate the stability of some edible oils

Oxidative stability is one of the most important indicators for maintaining the quality of edible oils. 1H NMR fingerprinting is used to evaluate the stability of edible oils at room temperature. The assignments of the 1H NMR signals of the major and minor components of unoxidized edible oils and the oil stability prediction were given. Minor components of the oils are playing an essential role in defining oil authenticity and quality. Extra virgin olive oil (EVOO) showed β-sitosterol, whereas, moringa oil (MO) showed β-sitosterol and stigmasterol. MO showed nonglyceride fraction, aliphatic chains and olefins. Sunflower oil (SO) could be easily distinguished due to its high linoleic acid content followed by apricot kernel oil (AKO). The order of stability of edible oils under study was: MO>EVOO>AKO>SO. 1H NMR spectral data agreed with the results obtained from Rancimat method for the determination of oxidative stability of edible oils under study. The main advantages of this method are the short time of analysis, the possibility to analyze samples without any preliminary treatment, and the small quantity of sample required.

Determining the aging degree of domestic heating oil blended with biodiesel by means of dielectric spectroscopy

To raise the share of renewable energies in the domestic heating market, the use of bio heating oil becomes increasingly important and popular. Considering the German heating market, bio heating oil blended with 10% biodiesel is already available. The affinity of biodiesel to forming oxidation products requires fast and reliable measuring methods which cannot be covered with conventional methods such as the Rancimat method according to DIN EN 15751. Therefore, a new measuring technique is introduced in this work, where oxidation products from heating oil blended with 10% biodiesel (HO B10) and for comparative purposes neat heating oil (HO B0) were investigated by dielectric spectroscopy. The results were verified by gel permeation chromatography (GPC) and by measuring of the total acid number (TAN). The alteration of dielectric parameters during the accelerated aging is used to determine the oxidation stability.

Assessment of the Oxidative Stability of Flaxseed-Enriched Lasagna Using the Rancimat Method

The oxidative stability of flaxseed-enriched lasagna during thermal processing was quantified using the Rancimat method. Lasagna was processed at high temperatures (120 and 180C) and oxidation was assessed from the electric conductivity of a water solution dissolving volatile secondary oxidation products. The oxidative stability of the lasagna was defined as the time to increase the conductivity by 5 μS/cm. The oxidative stability of the lasagna was higher than pure flaxseed oil, showing the protective effect of the lasagna matrix against the development or diffusion of oxidation products. Rolling the lasagna multiple times in the sheeter and reducing the processing temperature increased resistance to oxidation. The oxidative stability of the lasagna was independent of the extraction of flaxseed oil prior to enrichment. For both flaxseed enrichment levels (10 and 20%), the oxidative stability at 120C was approximately 10 times longer than the time required to dry lasagna at this temperature. Practical Applications The enrichment of lasagna with flaxseed improves its nutritional quality because of flaxseed omega-3 fatty acid, lignan and fiber content. However, the oxidation of flaxseed lipids during enriched lasagna processing is a major concern because of their high degree of unsaturation. This work validates the use of the Rancimat method to determine the processing parameters with a significant impact on flaxseed lipids oxidative stability and indicates that the number of passes in the sheeter, the processing temperature and the flaxseed enrichment level should be carefully considered to limit flaxseed lipids oxidation during processing.

Quality parameters for the evaluation of cold-pressed edible argan oil

Seventeen argan oils from Swiss and German markets were evaluated regarding the sensory quality, identity, oxidative state as well as contaminants in order to give an overview about the characteristics of this high-value product on the market. At least one sensory defect was detected in each argan oil by a trained sensory panel showing that the sensory quality in most oils should be improved. Adulterations of expensive argan oil with cheaper oils are detectable by the dominant occurrence of γ-tocopherol and α-spinasterol and 7-stigmastenol (Schottenol) as characteristic Tocopherol and Phytosterols, respectively. Only one oil exceeded the limit of the total oxidation value (TOTOX) of 20; the shelf-life calculated from the induction period (Rancimat method at 120 °C) was 196–435 days. Some oils contained higher amounts of mineral oils while the content of Benzo[a]pyrene in all oils was remarkably below the limit of 2 µg/kg.

Antioxidant activity of Peanut (Arachis Hypogaea L.) Skin Extract: Application in Soybean and Mustard Oil

Total phenolics of peanut skin obtained by different methods were estimated; the effect of different solvents on extractability of total phenolic compounds has also been evaluated. The effect of peanut skin extract, possessing highest phenolics and DPPH radical scavenging activity, was evaluated by schaal oven test in the soybean oil, while oxidative stability of mustard oil was evaluated by Rancimat method. Total phenolics were obtained highest (76.0 ± 2.12 to 101.7 ± 5.54 mg/g GAE dw) in the roasted samples, followed by the dry samples (54.7 ± 1.78 to 89.1 ± 3.78 mg/g GAE dw), and lowest (14.5 ± 0.95 to 21.6 ± 1.02 mg/g GAE dw) in the blanched samples; 80% methanol extraction provided better extractability of phenolic compounds than the aqueous and 80% ethanol extraction method. The peroxide value and induction period of different oils was also evaluated in the present study, which clearly showed that peanut skin extract offered significantly (P < 0.05) better or at least similar protection against oxidation in the oils; than the synthetic antioxidant (BHT). Thus, peanut skin may be a good source of natural antioxidants for stabilization of various vegetable oils, during harsh processing and unavoidable storage conditions.

Comparative evaluation of the effect of antioxidants added into peanut (arachis hypogae l.) oil biodiesel by P-DSC and rancimat

Biodiesel, a blend of long-chain fatty acid alkyl esters, undergoes oxidation due to the degradation of unsaturated esters upon the contact with atmospheric oxygen or changes in temperature and moisture. In peanut biodiesel, oleate and linoleate represent more than 80 % of the overall ester content, which are the quality-determining esters. In the present work, oxidative stability of peanut oil biodiesel obtained by the methanolic and ethanolic routes was evaluated by P-DSC and Rancimat methods. The efficiency of different concentrations of antioxidant substances, α-tocopherol, TBHQ (tert-butylhydroquinone), and green tea extract (Camellia sinensis L.) added into biodiesel was investigated. The results showed that α-tocopherol acted as pro-oxidant in the two biodiesels, for all studied concentrations. The synthetic antioxidant substance, TBHQ, corrected the stability of biodiesels with high efficiency while green tea extract showed an antioxidant additive potential for use in biodiesel.

Elaboração de farofa de grãos, sementes oleaginosas e castanha de caju: composição de fibras, ácidos graxos e aceitação

O trabalho objetivou a elaboração de farofa salgada, composta de sementes oleaginosas e castanha de caju, bem como a avaliação de seus atributos nutricionais, comparando-os às recomendações atuais de ingestão e sua aceitação sensorial. As matérias-primas utilizadas na elaboração da farofa foram: gergelim, linhaça dourada, girassol, soja tostada, aveia, flocos de milho, gérmen de trigo, castanha de caju, farinha de milho, óleo de girassol, tempero desidratado e sal. A análise sensorial foi realizada por 120 avaliadores, voluntários, não treinados, de ambos os sexos, frequentadores do campus. A análise físico-química foi realizada considerando teores de fibra alimentar total, solúvel, insolúvel; ácidos graxos; gorduras saturadas, monoinsaturadas, poli-insaturadas, trans; índice de peróxidos e estabilidade oxidativa. Quanto à fibra total, a porção de 30 g apresentou 11% dos valores diários recomendados; ácidos graxos ω-6 e ω-3, com proporção de 5:1, razão adequada segundo as recomendações da Organização Mundial de Saúde; ácido graxo oleico representou 15 g da composição lipídica do produto. Quanto à estabilidade, a farofa mostrou-se estável pelo método Rancimat e índice de peróxido aceitável pela legislação brasileira. Apresentou excelente aceitação entre os avaliadores, com 98% de aprovação e 89% de intenção de compra.

Oxidation stability of biodiesel fuels and blends using the Rancimat and PetroOXY methods. Effect of 4-allyl-2,6-dimethoxyphenol and catechol as biodiesel additives on oxidation stability.

In the present work, several fatty acid methyl esters (FAME) have been synthesized from various fatty acid feedstocks: used frying olive oil, pork fat, soybean, rapeseed, sunflower, and coconut. The oxidation stabilities of the biodiesel samples and of several blends have been measured simultaneously by both the Rancimat method, accepted by EN14112 standard, and the PetroOXY method, prEN16091 standard, with the aim of finding a correlation between both methodologies. Other biodiesel properties such as composition, cold filter plugging point (CFPP), flash point (FP), and kinematic viscosity have also been analyzed using standard methods in order to further characterize the biodiesel produced. In addition, the effect on the biodiesel properties of using 4-allyl-2,6-dimethoxyphenol and catechol as additives in biodiesel blends with rapeseed and with soybean has also been analyzed. The use of both antioxidants results in a considerable improvement in the oxidation stability of both types of biodiesel, especially using catechol. Adding catechol loads as low as 0.05% (m/m) in blends with soybean biodiesel and as low as 0.10% (m/m) in blends with rapeseed biodiesel is sufficient for the oxidation stabilities to comply with the restrictions established by the European EN14214 standard. An empirical linear equation is proposed to correlate the oxidation stability by the two methods, PetroOXY and Rancimat. It has been found that the presence of either catechol or 4-allyl-2,6-dimethoxyphenol as additives affects the correlation observed.

Phytochemical contents and oxidative stability of oils from non‐traditional sources

Non‐traditional plant oils, such as cold pressed black cumin (Nigella sativa) seeds oil and oils extracted by n‐hexane in the lab conditions from food industry by‐products, namely, apricot kernels (Prunus armeniaca), wheat germ (Triticum vulgare), grape seeds (Vitis vinifera), and tomato seeds (Lycopersicon esculentum) were investigated. Bioactive compounds such as phytosterols, tocopherols, and tocotrienols, and also fatty acid composition were determined by GLC and HPLC. The oxidative stability index of oils was evaluated by rancimat method. The fatty acid composition of lipids from apricot kernels was different from the other oils. The contribution of oleic acid in apricot oil amount 66.77%, while in the other oils ranged from 12.39% to 21.86%. The highest level of α‐linolenic acid was determined in wheat germ oil (7.58%). Concerning phytosterols, β‐sitosterol was major component in all oils extracted from non‐traditional sources, with wheat germ oil being the richest in total phytosterol content. Wheat germ oil was very rich in campesterol and sitostanol. It was found that wheat germ, black cumin seed, tomato seed, and apricot kernel oils contained significant amount of citrostadienol. Concerning the vitamin E, it was found that black cumin seed oil contained highest amount of tocotrienols and gamma tocopherols, while, tomato seed oil contain highest amount of gamma‐tocotrienols. Wheat germ oil was unique in having a high content of alpha‐tocopherol. Apricot kernel and wheat germ oils showed the highest oxidative stability as shown from its induction period compared to the other investigated oils. It is recommended that these oils can be utilized as sources of value added products, natural antioxidants, edible, and healthy oils.Apricot kernels, black cumin, grape, and tomato seeds and wheat germ oils were investigated. Bioactive compounds such as phytosterols, tocopherols, and tocotrienols, and also fatty acid composition were determined by GLC and HPLC. The oxidative stability index of oils was evaluated by rancimat method. It is recommended that these oils can be utilized as sources of value added products, natural antioxidants, edible and healthy oils.

Effect of Operational Parameters on Determination of Oxidative Stability Measured by Rancimat Method

Operational parameters of Rancimat, including sample weight (3, 6, 9 g), airflow rate (10, 15, 20 L/h) and temperature (110, 120, 130°C) were evaluated to determine their effects on oxidative stability index, temperature coefficient, Q10 number, and shelf life prediction of ghee (anhydrous milk fat). These parameters showed statistically significant effects on the oxidative stability index. It was observed that when the sample weight and airflow rate at a given temperature were at saturated air condition, the oxidative stability indexes showed no significant differences (p < 0). As the temperature increased, oxidative stability index decreased and average coefficient of variation was minimal at 120°C. The conditions under which the ghee sample was saturated with air and had a relatively lower oxidative stability index, was with sample weight of 6 g, temperature at 120°C and an airflow rate of 15 L/h. Temperature coefficient and Q10 number were independent of sample weight and air flow rate, however, they had a significant effect on shelf life prediction of ghee.

Use of natural antioxidants in soybean biodiesel

The antioxidant activity of curcumin and β-carotene was studied as a method to control the oxidative process of methyl soybean biodiesel during a 180-day storage period. Initially, the antioxidant activity of curcumin and β-carotene against radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) was tested. Curcumin reduced the concentration of DPPH by 90% whereas β-carotene reduced it by 15%. The antioxidant activity was determined through both the Rancimat and Petro-OXY methods. Results obtained from the two methods were consistent. They showed that curcumin increased the induction period of biodiesel by 83%, indicating the potential use of this antioxidant on an industrial scale. However, the study showed that β-carotene acts as a pro-oxidant, reducing the induction period of biodiesel when subjected to the Rancimat and Petro-OXY tests.

Determination of the oxidative stability of hazelnut oils by PDSC and Rancimat methods

The present study was conducted to determine the oxidative stability of hazelnut oil and compare it with more common and previously tested olive oil and rapeseed oil. The oxidative stability was determined by means of two independent methods, pressure differential scanning calorimetry (PDSC), and oxidative stability index (OSI) using TA Instruments DSC and Metrohm Rancimat equipment, respectively. Both the PDSC and Rancimat devices were set at five different isothermal temperatures in the range of 100–140 °C. The times to reach peak maximum (τ max) obtained from PDSC exotherms were statistically related with the Rancimat induction times (τ on) to obtain correlation coefficient >0.99 within linear relation. Based on the Arrhenius equation and activated complex theory, activation energies (E a), pre-exponential factors (Z), and specific rate constants (k) for studied oils oxidations were calculated. To the best of our knowledge, this is the first study dealing with oxidative stability of hazelnut oil using PDSC technique. According to the results obtained, PDSC seems to be useful and quick method for kinetic analysis of lipid oxidation in hazelnut oil.

Physicochemical stability of egg protein‐stabilised oil‐in‐water emulsions supplemented with vegetable powders

SummaryThe effect of vegetable powders on the physicochemical stability of egg protein‐stabilised oil‐in‐water emulsions was studied. Vegetable powders (beetroot, broccoli, carrot, celery, green pea, red pepper, spinach, swede, tomato and yellow pea) were added at 2.5% (w/v) to emulsions prepared with rapeseed oil. The physical stability of the emulsions was characterised using the emulsifying activity (EAI) and the emulsifying stability indices (ESI) in addition to bright field microscopy. The oxidative stability of the emulsions was monitored by means of an accelerated oxidation test (Rancimat method). The addition of most vegetable powders did not markedly affect the physical stability of the emulsions although an adverse effect of tomato was observed. The oxidative stability of the emulsions was significantly improved in most cases as indicated by the Rancimat method with broccoli exhibiting the highest increase in induction time (98.2%) compared with the control. Both polar and nonpolar antioxidants are likely to contribute to the overall chemical stability of this complex food system in a concentration‐dependent manner.

Experimental study of the factors affecting the oxidation stability of biodiesel FAME fuels

Oxidative stability of fatty acid alkyl esters or biodiesel during storage is very important as it yields products that degrade biodiesel quality and consequently affect engine performance. Accurate measurement, prediction and control of the oxidative stability of biodiesel from different feedstocks remain a challenging problem in biodiesel research. The current study relates to the investigation of the impacts of variation in feedstock on the oxidative stability of biodiesel, efficacy of various stability models (APE, BAPE, and OX) at predicting biodiesel oxidative stability, and the impacts of antioxidant loads in controlling oxidative instability of biodiesel. Firstly, oxidation stability for twelve different fatty acid methyl ester (FAME) biodiesels was measured to establish the effects of feedstock type on it. Then, fatty acid compositions were measured to establish the efficacy of the various models known as APE, BAPE, and OX proposed for characterizing the susceptibility of FAME to oxidation. Results showed oxidative stability and stability indices did not correlate well indicating that these models are inaccurate indicator for biodiesel stability. The response of the four biodiesel (Palm, Olive, Soyabean, and Jatropha) to the loading of the antioxidant (tertiary butyl-hydroquinone, TBHQ) was investigated to establish antioxidant threshold loading for delaying needed to delay oxidative degradation. It was found that biodiesel with high polyunsaturated fatty acids showed little improvement in oxidative stability to the same antioxidant dose. Finally, the efficacy of Rancimat methods in predicting the storage life of biodiesel was carried out by developing and extrapolating the oxidative stability Arrhenius temperature curves. The results for Sesame and Rapeseed FAME kept at 40°C showed under prediction of the storage life by the Rancimat method than obtained in real conditions.

Design and straightforward synthesis of novel galloyl phytosterols with excellent antioxidant activity

Novel galloyl phytosterols were rationally designed by incorporation of gallic acid into phytosterols through straightforward esterification. The esterification was successfully achieved by coupling of gallic acid and phytosterols through a mild chemical Steglich esterification reaction that is more straightforward than the enzymatic method. The identity of the newly synthesized galloyl phytosterols was confirmed by NMR, HPLC–MS and IR spectroscopies. Further evaluation of the novel galloyl phytosterols with radical scavenging, ferrous ion chelating, and Rancimat methods revealed its excellent antioxidant activities that are comparable to the most potent fat-soluble antioxidants. This novel antioxidant offers an intriguing solution for naturally derived antioxidants and will have great potential application as antioxidant in food industry. The methods developed in this study will be valuable for development of other phenolic phytosterols.

Optimization of ultrasonic-assisted extraction of phenolic compounds from bovine pennyroyal (Phlomidoschema parviflorum) leaves using response surface methodology

The ultrasound-assisted extraction (UAE) was applied to optimize the experimental conditions for the extraction of phenolic compounds from bovine pennyroyal (Phlomidoschema parviflorum) leaves by response surface methodology (RSM) and to compare its efficiency with maceration extraction (ME). The Box–Behnken design was employed for the optimization of three extraction parameters, including extraction time (X1, min), temperature (X2, °C) and pH (X3) for the achievement of high yields of dry matter (DM), total phenolics (TP) and antioxidant activity (AA) measured by the DPPH assay [expressed as 50% effective concentration (EC50)] and the Rancimat method [expressed as induction period (IP)]. The optimum extraction conditions were as follows: extraction time 49.3min, extraction temperature 41.5°C and pH 6.5. Under these conditions, DM, TP, EC50 and IP were 25,185mg/kg sample, 15.4mgGAE/g DM, 0.48mg/ml and 5.7h, respectively. The comparison between the UAE and ME methods showed the suitability of UAE for extracting phenolic compounds from bovine pennyroyal plant. The evaluation of antioxidant activity by DPPH assay indicated that the phenolic compounds from bovine pennyroyal plant had significant antioxidant activity. The results of HPLC analysis showed that caffeic acid and quercetin were the predominant phenolic acid and flavonoid in the plant extract, respectively.