Comparison of the Rancimat and the ACL Instrument for Measuring the Oxidative Stability of Corn Oil

A comparison was undertaken between two machines that utilise accelerated methods to measure oxidative stability: the Rancimat (Metrohm, Switzerland) and the single channel chemiluminescence instrument (ACL Instruments, Switzerland). The results from the machines showed good correlation for the measurement of the oxidation induction time of corn oil. For the ACL Instrument, the effect of the sample holder material (aluminium or borosilicate glass) was also investigated and clear differences were noted. Finally, a stability study was carried out over a period of 6 months, with corn oil, stored in the dark at three temperatures: ~4, ~27, ~40 °C and it was observed that it was possible to track subtle changes in oxidative stability using chemiluminescence.     

Kinetic parameter determination of vegetable oil oxidation under Rancimat test conditions

In this research, five different vegetable oils were oxidized at four different temperatures (373, 383, 393, and 403 K) under Rancimat test conditions. An increasing rate of oxidation could be observed as temperature increased. The natural logarithms of the kinetic rate constant (k value) varied linearly with respect to temperature, with the temperature coefficients (T_Coeff) ranging from 6.95×10^–2 to 7.40× 10^–2 K^–1 for the vegetable oils. On the basis of the Arrhenius equation and the activated complex theory, frequency factors (A), activation energies (E_a), Q₁₀ numbers, activation enthalpies (ΔH⁺⁺), and activation entropies (ΔS⁺⁺) for oxidative stability of the vegetable oils were calculated. The A, E_a, Q₁₀, ΔH⁺⁺, and ΔS⁺⁺ values for the vegetable oils ranged from 6.38×10³ to 28.03×10³ h^–1, from 86.86 to 92.42 kJ/mol, from 2.08 to 2.18, from 83.64 to 89.20 kJ/mol, and from –116.66 to –104.35 J/mol K, respectively.     

Wet Air Oxidation Of Wastewater From Olive Oil Mills

The oxidation of wastewater from olive oil mills has been carried out in the liquid phase at high temperatures and pressures. Synthetic urban wastewater has been used to dilute the raw effluent (dilution rate 1:10). Experiments conducted using air as the oxygen source showed a positive effect of the previous neutralization of the wastewater if compared to the oxidation conducted at the original pH of the effluent (pH = 5.3). In terms of chemical oxygen demand depletion and final biodegradability characteristics of the effluent, the use of free radical promoters, for instance hydrogen peroxide, resulted in a significant enhancement of the process. Experiments completed in the presence of two commercially available catalysts (platinum supported on alumina and copper oxide supported on active carbon) showed not only an improvement in the chemical oxygen demand removal rate but also a high degree of the mineralization of the wastewater contaminant load.     

Enhancement of Antioxidants in Olive Oil by Foliar Fertilization of Olive Trees

Oxidative stability (OS) of virgin olive oil is affected by different antioxidants whose levels may be influenced by nutrients availability. Changes in OS of virgin olive oil and antioxidants levels were evaluated according to foliar application of six nutrient-based treatments: T1 (rich in nitrogen), T2 (rich in boron, magnesium, sulfur and manganese), T3 (rich in phosphorus and potassium), T4 (rich in phosphorus and calcium), T5 (application of T1 and T2) and T6 (application of T1, T2, T3 and T4). The foliar applications were carried out during two successive growing seasons and oils were extracted and analyzed at the end of the experiment (after 2 years). T3 and T6 treatments improved oil stability by increasing the content of antioxidants, while T2 and T4 affected negatively the antioxidant profile of oils. Measured correlations between OS and compositional variables showed that total phenols had the highest value (R = 0.937, p < 0.001), followed by α-tocopherol (R = 0.775, p < 0.001) and oleic/linoleic ratio (R = 0.625, p < 0.05). These findings suggest that the changing levels of antioxidant compounds, due to fertilization, may be used to obtain oils with the highest quality.     

Kinetics of commercial olive oil oxidation: Dynamic differential scanning calorimetry and Rancimat studies

Four samples of olive oil were oxidized under polythermal (dynamic) conditions in the cell of a normal‐pressure differential scanning calorimeter (DSC) and in the Metrohm Rancimat apparatus. The DSC experiments were carried out in an oxygen flow atmosphere using different linearly programmed heating rates in the range of 4–20 °C/min. Through DSC exotherms, the extrapolated onset temperatures were determined and used for the assessment of the thermal‐oxidative stabilities of the samples. Using the Ozawa‐Flynn‐Wall method and the Arrhenius equation, the activation energies (E_a), pre‐exponential factors (Z) and reaction rate constants (k) for oil oxidation under DSC conditions were calculated. The Rancimat measurements of oxidation induction times were carried out under isothermal conditions in an air atmosphere at temperatures from 100 to 140 °C with intervals of 10 °C. Using the Arrhenius‐type correlation between the inverse of the induction times and the absolute temperature of the measurements, E_a, Z, and k for oil oxidation under Rancimat conditions were calculated. The primary kinetic parameters derived from both methods were qualitatively consistent and they help to evaluate the oxidative stabilities of oils at increased temperatures.     

Oxidative stability of potato chips determined by Rancimat

During recent years the Rancimat apparatus has been used extensively to determine the stability of fats and oils. Most stability tests for fat-containing foods are performed on the extracted oil. The objective of this research was to observe the behavior of potato chips in the racimat without oil extraction. Determinations were carried out at 110°C and 20 L/hr air flow. The curves for the ground chips were completely different from those obtained with extracted oils. Curves for fresh potato chips showed two inflection points after approximately 5 and 20 hr, respectively. Sensory analyses (odor score) of samples withdrawn from the Rancimat after 0, 5, 10, 20 and 25 hr showed significant differences (P < 0.01). An odor score of 5 was considered the rejection point, and was equivalent to 10.8 hr and corresponded to 150 μs of electric conductivity. At this point, the curves started to level off between the first and second inflection points. Curves obtained with potato chips stored at 25°C for 2, 4, 6, 8, 10 and 12 wk showed the same basic pattern, although prolonged storage corresponded with lower induction time. Correlation of induction values between ground potato chips and extracted oil was high (r > 0.87). From these results, it seems that it is possible to estimate the oxidative stability of fatcontaining foods without prior extraction. Presented at 81st AOCS Annual Meeting, Baltimore, MD, 1990.     

Influence of the Rancimat Apparatus Operating Parameters on Oxidative Stability Determination of Cold-Pressed Camelina and Hemp Seed Oil

The study investigates the impact of operating parameters such as temperature (90, 100, 110, 120 °C), airflow rate (10, 15, 20 L h⁻¹), and sample weight (3, 6, 9 g) on the oxidative stability of cold-pressed camelina and hemp seed oils using the Rancimat apparatus. Conducted analysis indicates a significant influence of temperature on oils' induction time. Moreover, higher airflows should be selected at high analysis temperatures. Based on the calculated parameters of the oxidation kinetics, it was shown that hemp oil has higher activation energy values than camelina oil. Response surface methodology (RSM) indicates that to minimize the determination time of camelina oil oxidation, the following analysis conditions should be selected: sample weight (SW) = 33.5 g, airflow (AF) = 20 L h⁻¹, and temperature (T) = 120 °C. However, for hemp oil, these parameters should be SW = 5.56 g, AF = 15 L h⁻¹, T = 120 °C. Sample mass does not significantly impact oils induction time, which depends mainly on the temperature and airflow. Practical applications: The conducted research shows that the parameters of the cold-pressed camelina and hemp oils oxidative stability have to be determined experimentally. The determined parameters for assessing the oxidative stability will reduce the analysis time and the possibility of interpolating the obtained result at different temperatures and analysis parameters.     

Fish Oil and Olive Oil Supplementation in Late Pregnancy and Lactation Differentially Affect Oxidative Stress and Inflammation in Sows and Piglets

This study was conducted to compare the effects of fish oil and olive oil supplementation in late pregnancy and during lactation on oxidative stress and inflammation in sows and their piglets. A total of 24 sows were fed a basal diet supplemented with additional corn starch (CON), fish oil (FO) or olive oil (OO). Sows fed an OO diet during late gestation had a higher piglet birth weight compared with CON‐fed and FO‐fed sows (P < 0.05). Furthermore, sows from the OO group had a higher milk fat content than sows from CON and FO groups, and a lower pre‐weaning mortality of piglets was observed in the OO group (P < 0.05). Maternal FO supplementation resulted in increased malondialdehyde concentration in sow plasma, colostrum, milk and piglet plasma than in CON and OO groups (P < 0.05). However, an increased total antioxidant capacity (T‐ACC) and activities of glutathione peroxidase (GSH‐Px) and total superoxide dismutase (T‐SOD) were also observed in the FO group (P < 0.05). Sows fed an OO diet had significantly decreased interleukin‐1β (IL‐1β), interleukin‐6 (IL‐6) and tumor necrosis factor‐α (TNF‐α) concentrations in milk compared with CON and FO fed sows (P < 0.05). Moreover, lower plasma IL‐1β and TNF‐α levels were observed in piglets from the OO group compared with the CON group (P < 0.05). Collectively, these results suggest that an OO diet is most beneficial in late gestation and during lactation in sows. However, FO increases the susceptibility to oxidative stress in sows and piglets.     

A Kinetic Approach to the Oxidation of Linseed Oil as Influenced by Fruit Peel and Seeds of Pomegranate

The objective of this research is to analyze the kinetic parameters of linseed oil by treating it with pomegranate peel and seeds at 353, 368, and 383 K using Rancimat. There are no significant differences (p < 0.05) between the oxidative stability indices of samples containing pomegranate peel and pomegranate seeds. In addition, the indices pertaining to the oxidative stability of linseed oil increase in value as the concentrations of pomegranate peel and seeds increase. Apart from the pomegranate peel at 0.1% and the quercetin, all other antioxidants are able to reduce the severity of temperature‐related parameters (i.e., temperature coefficient and Q₁₀ values). In addition, these antioxidants are able to form an activated complex with lower levels of thermal energy (by reducing activation energy and enthalpy) but of more structured configuration (by reducing the frequency factor and entropy). A high correlation is found between the Gibbs free‐energy of activation and the oxidative stability index of samples. The most substantial increase in the Gibbs free‐energy of activation occurs by TBHQ, followed by gallic acid, quercetin, and pomegranate peel at 1%. Practical Applications: Linseed oil is characterized by its high amounts of essential polyunsaturated fatty acids (PUFAs). The high PUFA content of linseed oil contributes to its rapid oxidation. Pomegranate peel and seeds are valuable sources of natural antioxidants. Investigating the effect of pomegranate peel and seeds in reducing the dependence of linseed oil oxidation on temperature provides a range of valuable kinetic parameters. Nevertheless, this subject has received little attention so far. There are few published data regarding the effect of natural antioxidants on lipid oxidation by this approach. Accordingly, this study is designed to investigate the oxidation kinetics and mechanisms of linseed oil as manipulated by fruit peel and seeds of pomegranate. The results show that the fruit peel and seeds of pomegranate can improve the oxidative stability of linseed oil and reduce the severity of effects caused by undesirable temperatures that may increase the oxidation rate of linseed oil.     

The Effect of Operational Parameters of the Rancimat Method on the Determination of the Oxidative Stability Measures and Shelf-Life Prediction of Soybean Oil

Operational parameters of the Rancimat method, including oil sample size, airflow rate, and temperature, were evaluated to determine their effects on the oxidative stability index (OSI), temperature coefficient, Q ₁₀ number, and shelf-life prediction for soybean oil. Operational parameters of the Rancimat method had statistically significant effects (P < 0.05) on the OSI. Whenever the oil sample size and airflow rate at a given temperature were such that the air-saturated condition could be established, the OSIs showed no statistically significant differences. As temperature increased, OSIs decreased, while their average coefficient of variation (CV) increased. In general, the conditions where the sample was saturated with air and had a relatively lower CV were an oil sample size of 6 g at all temperatures and airflow rates, then 3-g oil sample size at low temperatures (100 and 110 °C) and low airflow rates (10 and 15 L h⁻¹). The temperature coefficient and Q ₁₀ number were found to be independent of the oil sample size and airflow rate, and their mean values for soybean oil were calculated to be −3.12 × 10⁻² °C⁻¹ and 2.05, respectively. Oil sample size and airflow rate showed a significant effect on shelf-life prediction for soybean oil. Therefore, choosing the right levels of these operational parameters in the Rancimat method may produce the least possible difference between predictions from long-term storage studies and the OSI test.     

FTIR assessment of the oxidation process of castor oil FAME submitted to PetroOXY and Rancimat methods

This short communication reports an assessment of the oxidation process of castor oil fatty methyl ester samples submitted to Rancimat (EN 14112) and PetroOXY (ASTM-D7545) oxidation methods. Fourier Transformed Infrared Spectroscopy (FTIR) was used to evaluate the FAME degradation products resulting from the accelerated oxidation, following the area of the carbonyl band (~ 1740 cm⁻¹) of the samples at different oxidation times. Our results indicate that the level of oxidation of castor oil FAME, using the Rancimat method, follows a similar pattern of the oxidized samples using the PetroOXY method.     

Impact of Aromatization by Citrus limetta and Citrus sinensis Peels on Olive Oil Quality,Chemical Composition and Heat Stability

The objectives of this work were to study the impact of aromatization by sweet lemon and sweet orange peels on olive oil quality, chemical composition and heat stability. Flavored olive oils were prepared by maceration of sweet lime and sweet orange zests at 1, 3 and 5 %. The oil samples were kept at 60 °C for 40 days. Physicochemical tests (FFA, PV, oxidative stability, polyphenols and pigments contents) were carried out. The antioxidant activity (β‐carotene‐linoleate bleaching assay, DPPH radical scavenging and reducing power) was also tested. Results indicated that the addition of citrus zests contributed to the increase in polyphenols and carotenoids contents. Moreover, it led to an increase in the DPPH‐radical scavenging activity (99.50 % for flavored olive oil with sweet orange zests at 5 %). Flavored olive oils with sweet orange zests were more stable to heat treatment than those flavored with sweet lemon zests. The degradation rate of bioactive compounds was lower for virgin olive oil comparing to flavored oils.     

Thermal Oxidation Kinetics of Refined Hazelnut Oil

In this study, oxidation kinetics of refined hazelnut oil heated at the temperature range from 80 to 180 °C was evaluated. The changes in peroxide value, p‐anisidine value, polymer triglyceride content, α‐tocopherol content, and color values during oxidation were best fitted to zero‐order kinetic model. The rate constants for the p‐anisidine value, polymer triglyceride content, and degradation of α‐tocopherol of hazelnut oil increased at the temperatures between 80 and 160 °C, while the rate constant for peroxide value decreased at the temperatures between 80 and 140 °C. The activation energies for the formation of peroxides (at 80–140 °C), secondary oxidation products such as alkenals, the polymer triglycerides, and degradation of α‐tocopherol were found as 47.49, 29.95, 52.65, and 14.22 kJ mol^?1, respectively. The induction period of hazelnut oil was observed to reduce with increasing oxidation times. The increase in the b* value with the oxidation time and temperature was attributed to the fact that the heating process intensified the yellow color of the oil.     

Kinetic study for the development of an accelerated oxidative stability test to estimate virgin olive oil potential shelf life

This study proposes an accelerated test performed at mild temperature (40–60 °C) to measure oxidative stability and estimate the potential shelf life of extra‐virgin olive oil (EVOO). The kinetic behavior of normalized oxidation indices (PV, K₂₃₂ and K₂₇₀) and the oxidizing substrate [unsaturated fatty acids (UFA)] during storage of different virgin olive oil samples in darkness and at different temperatures (25–60 °C) is reported for the first time. PV and K₂₃₂ followed an apparent pseudo zero‐order kinetics (R² >0.951) at all the experimental temperatures in all samples, whereas the evolution of K₂₇₀ apparently better fitted a pseudo first‐order kinetics (R² >0.926). The temperature‐dependent kinetics of the oxidation indices and the UFA were well described by the linear Arrhenius equation between 25 and 60 °C (0.960< R² <0.999, p <0.05). The best correlation between loss of PUFA and increase of oxidation product indices was K₂₃₂ (0.581< R² <0.924). The time required to reach the upper limits for PV, K₂₃₂ and K₂₇₀ established for the EVOO category in the current EU legislation correlated well with temperature using a potential equation, making it possible to set up an accelerated stability test at temperatures below 60 °C to estimate the potential shelf life under normal storage temperature conditions.     

我国润滑油氧化安定性试验方法标准及研究进展

将国内23项润滑油氧化安定性试验方法标准分为旋转氧弹法、氧化管法、设备模拟法和仪器分析法进行了归纳总结;概述了热失重分析仪、差示扫描量热仪、高效液相色谱测定仪和傅立叶变换红外光谱测定仪等现代分析仪器在润滑油安定性试验中的应用和研究进展情况。     

大豆油与过氧甲酸的环氧化动力学研究

通过大豆油中的双键与过氧酸发生环氧化反应,合成了环氧大豆油(ESO)。从动力学的角度,对反应过程中的各种影响因素,进行了较详细的研究。得知大豆油与过氧甲酸反应,大豆油的反应级数为1级,过氧甲酸的反应级数为2级,其反应活化能为22.77 kJ/mol。生成的环氧大豆油与体系内的甲酸发生水解开环反应,环氧大豆油的反应级数为0.5级,甲酸的反应级数为1级,该反应活化能为4.91 kJ/mol。通过所得动力学参数设定了无催化剂的环氧大豆油合成工艺,得到了环氧值高达6.85的环氧大豆油。     

Development and Validation of a Simple Reversed‐Phase HPLC‐UV Method for Determination of Malondialdehyde in Olive Oil

A simple, precise, accurate and selective method was developed and validated for determination of malondialdehyde (MDA) in olive oil. Separation was achieved on a reversed‐phase C₈ column using a mobile phase consisting of methanol/0.8 % phosphoric acid (10:90, v/v), at a flow rate of 1.0 ml/min and UV detection at 220 nm. This method was validated according to the requirements for new methods, which include accuracy, precision, selectivity, robustness, a limit of detection, limit of quantitation (LOQ), linearity and range. The current method demonstrated good linearity over the range of 0.5–1000 ppm of MDA with r² greater than 0.999. The recovery of MDA in olive oil ranged from 97.1 to 99.1 %. The method was selective where MDA was distinctly separated from other compounds of the oil with good resolution. The method was also precise where the RSD of the peak areas of replicate injections of MDA standard solution were less than 1 %. The degree of reproducibility of the results obtained as a result of small deliberate variations in the method parameters and by changing the analytical operators proved that the method is robust and rugged. The low LOQ of MDA (0.5 ppm) using this method enables quantitation of MDA at low concentration.     

Adulteration and Presence of Polycyclic Aromatic Hydrocarbons in Extra Virgin Olive Oil Sold on the Brazilian Market

Seventy samples sold in the Brazilian market as extra virgin olive oil (EVOO) were evaluated for the presence of the 13 polycyclic aromatic hydrocarbons (PAH) classified as carcinogenic and genotoxic by the Joint FAO/WHO Expert Committee on Food Additives (JECFA), to verify if the products were adulterated and to evaluate if there is a correlation between PAH presence and adulteration. PAH were detected in 93% of the samples, with summed levels varying from not detected to 41.10 μg/kg. Five samples showed BaP concentration above acceptable levels set by European legislation and by Brazilian regulation (2.0 μg/kg) and 7 presented PAH4 levels above the limit set by European legislation (10.0 µg/kg). The levels of fatty acid composition, sterols content, stigmastadiene and specific extinction did not comply with both Brazilian and International Olive Council (IOC) standards in 18, 31, 30 and 21% of the samples, respectively. The tolerance levels for these analyses in the Brazilian standards are 55.0–83.0 g/100 g (oleic acid), 3.5–21.0 g/100 g (linoleic acid), ≤0.05 g/100 g (trans-oleic acid), ≤0.05 g/100 g (trans-linoleic + trans-linolenic acid), ≤0.15 mg/kg (stigmastadiene), ≤2.50 (K232), ≤0.22 (K270), ≤0.01 (?K), 1000–1600 mg/kg (Σ sterols). Results indicate that 19 samples were adulterated. According to principal component analysis, samples were distinguished as: (1) EVOO with addition of vegetable oil from another source, (2) EVOO with addition of refined oil and (3) samples possibly not adulterated. The variable ΣPAH was related mainly to samples of EVOO with addition of vegetable oil from another source.