Oxidative Stability Index Values Research Articles

Euphorbia tirucalli stem bark and phylloclades’ oil quality variability and implication for energy use

Liquid biofuels have emerged as a worldwide alternative fuel with potential to replace fossil fuels. Due to their wide availability as derivatives of organic materials from plants, they have attracted much attention and investment in developing countries including Tanzania, as alternative sources of energy. This study examined effects of oil quality from stem barks and phylloclades of Euphorbia tirucalli trees of different girth sizes (viz., 20 cm, 30 cm, 40 cm, 50 cm, 60 cm, 70 cm, and 80 cm) from semi-arid, coastal, and southern highlands in Dodoma, Dar es Salaam, and Mbeya Southern highland, agro-ecological zones in Tanzania. Using Soxhlet extraction method, oils were extracted from E. tirucalli stem barks with different girth sizes while oils from phylloclades were extracted from matured apical phylloclades collected from shoots of E. tirucalli trees from which the stem bark samples had been collected. Oil yields were determined by measuring the weight of oil (g) by the total weight of sample extracts used (20 g), and the average oil yield on each sample was determined. Oil quality was evaluated as oxidative stability index (OSI), acid values (AVs), and percent free fatty acids (%FFAs). Their results were then compared with the European Union (EU) oil quality standard specifications prescribed in EN 14214 of 6 h, 0.5 mg KOH/g, max and 0.020 maximum wt% limits, respectively. Differences in the quality of E. tirucalli (stem bark and phylloclades) oil were analyzed statistically with paired-sample t test (two-tailed) using the SPSS 15.0 software package. Results showed that the difference in OSIs from stem barks were not significantly higher (3–5 h) than phylloclades (3–4 h) at the p > 0.5 level. Also, the difference in AVs and %FFAs from the stem barks (7.6–7.4 mg KOH and 3.8–3.6%) was not significantly lower than those from the phylloclades (8.4–8.1 mg KOH and 4.3–4.0%) respectively. The quality of oil from stem bark and phylloclades samples at different stem girth sizes semi-arid agro-ecological zone was not significantly higher than from southern highland and coastal agro-ecological zones, respectively. Thus, there were no significant differences in the quality of E. tirucalli oil (stem bark and phylloclades) among stem girth sizes in different agro-ecological zones. The AVs and %FFAs of oils from stem bark and phylloclades were higher than the recommended standards, while the OSIs were below the biofuel standard limit. High AVs and %FFAs reduced oil quality by producing considerably low OSIs values than recommended standards. Finally, the study concluded that E. tirucalli oil requires purification to reduce levels of AV and %FFA contents so that the oil becomes suitable for application as liquid biofuel for energy generations.

Prediction of Walnut Deterioration Using Kernel Oxidative Stability.

Monitoring walnut oxidation is essential to control walnut quality during storage. An accelerated oxidation method for differentiating the oxidative stability index (OSI) of walnut kernels was examined and the effects of instrument operational parameters such as temperature and airflow were evaluated. Four cultivars, Chandler, Solano, Durham, and Howard were analyzed at 110, 120, and 130 °C with 15, 20, and 25 L h−1 airflow. Analysis using 110 °C with 25 L h−1 yielded the lowest coefficients of variance (4.4) than other operational parameters; analysis using the same temperature at lower airflow, 15 L h−1, yield the highest coefficient of variance (10.5). Kernel OSI values were independent of airflow, however, dependence of temperature coefficient and Q10 were demonstrated. The results from selected parameters were correlated with fat and moisture content, peroxide value, UV absorbances, oil oxidative stability, hexanal, and rancidity to establish the relationships between OSI values and quality changes during storage. Using 0.5 g of ground kernels, at 110 °C with 25 L h−1 airflow gave a lower coefficient of variance and higher correlation with kernel quality and oxidative markers comparing to other combinations of operating parameters.

Oxidative Stability of Chia (Salvia hispanica L.) and Sesame (Sesamum indicum L.) Oil Blends

AbstractChia and sesame oils are important sources of essential fatty acids; however, their ω‐3:ω‐6 proportions do not comply with nutritional recommendation. A feasible approach to improve the ratio is to blend different oils, but only after understanding physical and chemical changes of the new matrix. Objective of the investigation was to determine the physico‐chemical characteristics and the oxidative stability index (OSI), using the Rancimat method, of chia‐sesame oil blends. The four ω‐3:ω‐6 blends tested (1:4, 1:6, 1:8, and 1:10) were exposed to temperatures of 110, 120, and 130 °C. The OSI values of the mixtures varied between 6.24–8.08, 3.07–4.00, and 1.62–2.01 hours for each temperature, respectively. In addition, their mean activation energy, enthalpy, entropy, and Q10 were 88.4 kJ/mol, 85.2 kJ/mol, −41.1 J/mol K, and 2.0. Finally, a shelf life prediction performed at 25 °C indicated stability times between 80 and 123 days. Therefore, combining chia and sesame oils produced blends with a good balance of essential fatty acids.

Antioxidant recovery from hydrodistillation residues of selected Lamiaceae species by alkaline extraction

Aqueous solution of potassium hydroxide (KOH) was used in order to obtain rich in antioxidant activity extracts from Origanum dictamnus, Origanum hirtum, Origanum onites, Rosmarinus officinalis and Satureja thymbra, after removal of the essential oil via hydrodistillation. The increase of extraction time induced lower values of total phenolic content and DPPH radical scavenging ability of the extracts, while lower alkaline concentrations, i.e. 1% and 3%, proved to be more effective than 5% (v/w) KOH. The antioxidant activity of the extracts in sunflower oil was also measured by the oxidative stability index (OSI) method. OSI values decreased as extraction time increased, while the effect of KOH concentration at short extraction time was not significant. S. thymbra, O. hirtum and R. officinalis extracts showed high total phenolic content and good antiradical and antioxidant activity in just 30 min of extraction with KOH 1% (w/v). LC–MS analysis showed that all extracts were rich in phenolic acids, such as caffeic acid and rosmarinic acid, while R. officinalis was also rich in carnosic acid.

Estabilidad oxidativa y estimación de la vida útil del aceite de sacha inchi (Plukenetia volubilis L.)

Sacha inchi oil is rich in polyunsaturated fatty acids that may rust, limiting their shel flife. The Rancimat method is official, for evaluations of oxidative stability accelerated in oils. Industrially conventional techniques based on physical and chemical indicators are used; there are no studies of correlation between them and Rancimat. This work has for objective correlate the oxidative stability index (OSI) Sacha inchi oil obtained by Rancimat at temperatures of 80°, 90°, 100° and 110 °C under an air flow of 15 L/h, with the values of physic-chemical indicators such as Index peroxide, p-anisidine, totox and density. Also estimated by mathematical extrapolation, the shelf life of sacha inchi oil to usual storage temperatures. OSI values were: 0.493 ± 0.01 h at 110 oC, 1.590 ± 0.06 h at 100 oC, 4.645 ± 0.1 h at 90 oC and 20.512 ± 0.02 h at 80 oC. High correlation has been established between values of OSI vs physicochemical quality indices (0.9322 < r < 0.9965). The activation energy was found 137.90 kJ/mol, which explains the high oxidative stability for the oil, estimating a lifetime of 3.29, 1.79 and 0.79 years at 20, 25 and 30 °C respectively.

Effectiveness of natural versus synthetic antioxidants in a rice bran oil-based structured lipid

Antioxidants were evaluated for their ability to improve oxidative stability index (OSI) of enzymatically prepared rice bran oil-based structured lipid (RBOSL) containing caprylic acid. RBOSL was purified by short-path distillation. Vitamin E concentration decreased significantly in RBOSL after enzymatic modification. Total γ-oryzanol concentration after modification was not significantly different. OSI of RBOSL containing rosemary extract (RE), carnosic acid (CA), tertiary butyl hydroquinone (TBHQ), ethylenediamine tetraacetic acid (EDTA), and α-tocopherol (TOC), and 50:50 (w/w) combinations in concentrations of 200, 300, 400 and 500 ppm were determined. The OSI of unmodified rice bran oil (RBO) was 12.4 ± 0.2 h and significantly higher than RBOSL which was 11.4 ± 0.0. Mean peroxide and p-anisidine values for antioxidant treatments in RBOSL with the highest OSI values were determined after incubation at 60 °C for 21 days and sampled every 3 days. Mean peroxide and p-anisidine values for CA and CA/RE were comparable to TBHQ.

Characterization of Cold‐Pressed Onion, Parsley, Cardamom, Mullein, Roasted Pumpkin, and Milk Thistle Seed Oils

Cold-pressed onion, parsley, cardamom, mullein, roasted pumpkin, and milk thistle seed oils were characterized for their fatty acid (FA) composition, tocopherol content, carotenoid profile, total phenolic content (TPC), oxidative stability index (OSI), color, physical properties, and radical-scavenging capaci- ties against peroxyl (oxygen radical-scavenging capacity) and sta- ble DPPH (diphenylpicrylhydrazyl) radicals. Parsley seed oil had the highest oleic acid content, 81 g/100 g total FA, and the low- est saturated fat among the tested oils. Roasted pumpkin seed oil contained the highest level of total carotenoids, zeaxanthin, β- carotene, cryptoxanthin, and lutein at 71 μmol/kg and 28.5, 6.0, 4.9, and 0.3 mg/kg oil, respectively. Onion seed oil exhibited the highest levels of α- and total tocopherols under the experimental conditions. One of the parsley seed oils exhibited the strongest DPPH· scavenging capacity and the highest oxygen radical ab- sorbance capacity (ORAC) value of 1098 μmol Trolox equiv/g oil. However, ORAC values of the tested seed oils were not nec- essarily correlated to their DPPH· scavenging capacities under the experimental conditions. The highest TPC of 3.4 mg gallic acid equiv/g oil was detected in one of the onion seed oils. The OSI values were 13.3, 16.9-31.4, 47.8, and 61.7 h for the milk thistle, onion, mullein, and roasted pumpkin seed oils, respec- tively. These data suggest that these seed oils may serve as dietary sources of special FA, tocopherols, carotenoids, phenolic com- pounds, and natural antioxidants. Paper no. J11246 in JAOCS 83, 847-854 (October 2006). Edible seed oils are a group of important food ingredients. Novel specialty seed oils rich in factors beneficial to health are in high demand because of consumers' interest in disease pre- vention and health promotion through improved diets. These beneficial factors include special FA compositions such as high content of monounsaturated FA (MUFA) or n-3 FA, tocopher- ols, carotenoids, and antioxidative phenolic compounds (1-4). A number of edible oils from herb, spice, and fruit seeds have been shown to contain special FA profiles (4). For instance, American ginseng seed oil contains about 87% oleic acid, and basil seed oil has 57-63% α-linolenic acid (18:3n-3), the es- sential n-3 FA (4). The cold-pressed edible seed oils may be preferred by consumers because the cold-pressing procedure involves neither heat nor chemicals, and may increase the re- tention of beneficial phytochemicals. Previous studies showed that cold-pressed carrot seed oil had about 82% oleic acid (18:1n-9), which has been associated with lowering the risk of cardiovascular disease (5). Cold-pressed edible hemp and berry fruit seed oils contain significant levels of α-linolenic acid (18:3n-3), which may be converted to the longer-chain n-3 PUFA, EPA (20:5n-3) and DHA (22:6n-3), in vivo through elongation and desaturation reactions. EPA and DHA poten- tially reduce the risk of cancer, heart disease, hypertension, and autoimmune disorders (6-8). These data suggest the possibility of developing novel edible seed oils with special FA composi-

Characterization of cold‐pressed onion, parsley, cardamom, mullein, roasted pumpkin, and milk thistle seed oils

AbstractCold‐pressed onion, parsley, cardamom, mullein, roasted pumpkin, and milk thistle seed oils were characterized for their fatty acid (FA) composition, tocopherol content, carotenoid profile, total phenolic content (TPC), oxidative stability index (OSI), color, physical properties, and radical‐scavenging capacities against peroxyl (oxygen radical‐scavenging capacity) and stable DPPH (diphenylpicrylhydrazyl) radicals. Parsley seed oil had the highest oleic acid content, 81 g/100 g total FA, and the lowest saturated fat among the tested oils. Roasted pumpkin seed oil contained the highest level of total carotenoids, zeaxanthin, β‐carotene, cryptoxanthin, and lutein at 71 μmol/kg and 28.5, 6.0, 4.9, and 0.3 mg/kg oil, respectively. Onion seed oil exhibited the highest levels of α‐ and total tocopherols under the experimental conditions. One of the parsley seed oils exhibited the strongest DPPH scavenging capacity and the highest oxygen radical absorbance capacity (ORAC) value of 1098 μmol Trolox equiv/g oil. However, ORAC values of the tested seed oils were not necessarily correlated to their DPPH scavenging capacities under the experimental conditions. The highest TPC of 3.4 mg gallic acid equiv/g oil was detected in one of the onion seed oils. The OSI values were 13.3, 16.9–31.4, 47.8, and 61.7 h for the milk thistle, onion, mullein, and roasted pumpkin seed oils, respectively. These data suggest that these seed oils may serve as dietary sources of special FA, tocopherols, carotenoids, phenolic compounds, and natural antioxidants.

Fatty Acid Composition and Antioxidant Properties of Cold-Pressed Marionberry, Boysenberry, Red Raspberry, and Blueberry Seed Oils

Cold-pressed marionberry, boysenberry, red raspberry, and blueberry seed oils were evaluated for their fatty acid composition, carotenoid content, tocopherol profile, total phenolic content (TPC), oxidative stability index (OSI), peroxide value, and antioxidant properties. All tested seed oils contained significant levels of alpha-linolenic acid ranging from 19.6 to 32.4 g per 100 g of oil, along with a low ratio of n-6/n-3 fatty acids (1.64-3.99). The total carotenoid content ranged from 12.5 to 30.0 micromoles per kg oil. Zeaxanthin was the major carotenoid compound in all tested berry seed oils, along with beta-carotene, lutein, and cryptoxanthin. Total tocopherol was 260.6-2276.9 mumoles per kg oil, including alpha-, gamma-, and delta-tocopherols. OSI values were 20.07, 20.30, and 44.76 h for the marionberry, red raspberry, and boysenberry seed oils, respectively. The highest TPC of 2.0 mg gallic acid equivalents per gram of oil was observed in the red raspberry seed oil, while the strongest oxygen radical absorbance capacity was in boysenberry seed oil extract (77.9 micromol trolox equivalents per g oil). All tested berry seed oils directly reacted with and quenched DPPH radicals in a dose- and time-dependent manner. These data suggest that the cold-pressed berry seed oils may serve as potential dietary sources of tocopherols, carotenoids, and natural antioxidants.

Changes in chemical quality indices during long‐term storage of palm‐olein oil under heated storage and transport‐type conditions

AbstractSix quality indices, namely free fatty acids (FFA), peroxide value (PV), anisidine value (AV), oxidative stability index (OSI), total tocopherols and headspace volatiles (hexanal, t‐2‐hexenal and t,t‐2,4‐decadienal), were evaluated in a long‐term storage trial of 52 weeks at 50 °C of palm‐olein, a monounsaturated oil. Three concentrations of copper (0.035, 0.17 and 0.69 mg kg−1) were added. FFA values for all the sample treatments increased slightly over the storage period but remained within acceptable limits. PV of the copper‐containing samples declined initially and then remained stable up to week 40, after which it increased slightly for the 0.035 and 0.17 mg kg−1 samples. However, PV of the control (no added copper) increased steadily to above the acceptable limit. AV of the copper‐containing samples increased much more than that of the control. OSI and total tocopherol values of the copper‐containing samples were markedly lower than those of the control. t‐2‐Hexenal did not increase during the storage period, whereas hexanal increased in the copper‐containing samples but at a slower rate than in the control. Conversely, the copper‐containing samples had high levels of t,t‐2,4‐decadienal but the control had none. AV, OSI and total tocopherols are the most valuable quality indices for assessing monounsaturated oil quality, whereas FFA, PV and headspace volatiles can be misleading. Copyright © 2003 Society of Chemical Industry

Effect of roasting oil composition on the stability of roasted high‐oleic peanuts

AbstractOff‐flavor due to lipid degradation is an important factor in the shelf life of peanut products. The use of recently developed peanuts with high‐oleic acid/linoleic acid (O/L) ratio has the potential to significantly extend the shelf life of roasted peanuts. To determine the full potential for shelf‐life improvement of oil‐roasted high‐O/L peanuts, a study was conducted to examine the effects of roasting high‐O/L peanuts (O/L=30) in high‐O/L (O/L=23.2) or conventional (O/L=1.5) peanut oil. Peanuts were roasted at 177°C to Hunter L values of 49±1. Roasted peanuts were stored at 30°C for 20 wk. Samples were taken at regular intervals to determine PV, oxidative stability index (OSI), moisture content, and water activity. The O/L ratio of high‐O/L roasted peanuts was 27.9 vs. 13.6 for the conventional oil‐roasted peanuts. After 20 wk of storage, PV of conventional oil‐roasted peanuts was 10.8 compared to 5.3 for the high‐O/L‐roasted peanuts. OSI values were 88.5 and 52.4 immediately after roasting for the high‐O/L‐roasted vs. conventional oil‐roasted peanuts. OSI for both decreased, but differences remained similar throughout the storage period. Shelf life of high‐O/L peanuts decreased when roasted in conventional O/L‐peanut oil vs. high‐O/L peanut oil.

Comparative studies of oxidative stability of edible oils by differential scanning calorimetry and oxidative stability index methods

A comparative study was conducted to determine the oxidative stability of twelve different edible oils with two different instruments: a differential scanning calorimeter and an oxidative stability index (OSI) instrument. The OSI instrument temperature was set at 110 °C. The differential scanning calorimetry (DSC) technique involved oxidation of oil samples in an oxygen-flow DSC cell. The DSC cell temperature was set at four different isothermal temperatures: 110, 120, 130 and 140 °C. A dramatic increase of evolved heat was observed with the appearance of a sharp exothermic curve during initiation of the oxidation reaction. The oxidative induction time (T0) was automatically determined by extrapolation of the downward portion of the DSC oxidation curve to the time axis. There was a good correlation (P<0.0001) between the DSC T0 and OSI values. The decrease in log10 (T0) with increasing DSC isothermal temperature was best fitted by a linear equation. DSC evidently provides a convenient way to determine the oxidative stability of various edible oils.

Stabilization of soybean oil with heated quercetin and 5-caffeoylquinic acid in the presence of ferric ion.

The effect of heated quercetin (400 mg/kg of oil) or 5-caffeoylquinic acid (5-CQA) and the presence of ferric ion (2.2 mg/kg of oil) on the stability of soya oil oxidized in an oxidative stability index (OSI) instrument was investigated. After heating the phenolic at 100 degrees C or 150 degrees C, the OSI values of treated oils were not significantly (p < 0.001) different, whereas, at 200 degrees C, the values decreased significantly with addition of quercetin, but not with 5-CQA. However, the antioxidative activity of quercetin remained significantly greater than that of 5-CQA. The antioxidative potency of quercetin was reduced significantly by addition of ferric palmitate (FP), but that of 5-CQA was not. Reaction between the ortho-dihydroxy groups of the quercetin and ferric ion may reduce the number of hydroxyls available to react with free radicals. Chelating action of 5-CQA might be provided by ortho-dihydroxy grouping of the quinic acid moiety.