Oil stability index correlated with sensory determination of oxidative stability in light-exposed soybean oil

Validity of the oil stability index (OSI) as an accelerated test of oxidative stability has been questioned because of its high holding temperature, 110°C, which may cause reactions that would not occur at lower temperatures. The purpose of this study was to characterize the usefulness of OSI as an accelerated oxidative stability test for oil of varying metal catalyst content by correlating OSI with the sensory induction period of light-exposed soybean oil. Five 400-g aliquots of soybean oil were placed in Erlenmeyer flasks and treated with increasing levels of a metal pro-oxidant, Cu²⁺ 2-ethylhexanoate. Pro-oxidant concentration ranged from 0 to 3.13×10⁻⁵ M. Five-gram aliquots were taken from duplicate flasks and immediately tested using the Oxidative Stability Instrument. Heating block temperature was 110°C. Sample flasks were then exposed to 800 footcandles of light and held at ambient temperature for 3 wk. One-gram aliquots were regularly withdrawn and evaluated for rancidity by 10 trained panelists to determine the sensory induction period of each sample. Aliquots were also taken to determine OSI of light-exposed oil samples. Sensory induction periods were correlated with OSI, resulting in a squared partial correlation coefficient (r ²) of 0.920. The r ² for OSI of light-exposed oil samples ranged from 0.897 to 0.979. OSI appears to be an acceptable accelerated method for measuring the oxidative stability of light-exposed soybean oil that varies in metal catalyst content.     

Oil stability index correlated with sensory determination of oxidative stability in canola oil

The usefulness of the Oil Stability Index (OSI) as an accelerated oxidative stability test for canola oil was studied by correlating the OSI with the induction period as determined by sensory analysis. Canola oil was treated by holding it for differing times (0, 1, 2, 3, 4, and 6 d) at elevated temperature (60°C) in the dark with agitation. The sensory induction period (SIP) was determined by storing the five treatments of oil and the control at 60°C in the dark with agitation and removing aliquots of oil for a nine-member sensory panel to evaluate over a 9-d period. The time it took for a treatment to reach an average sensory score of 5 (10-point scoring scale) was defined as the treatment’s SIP. OSI values were obtained on day 0 using a heating block temperature of 110°C and an air pressure of 6 psi. The relationship between SIP and OSI had a 0.89 coefficient of determination (r ²). This relationship may be sufficiently strong to warrant use of the OSI in industry applications but may not be ideal for more precise experimental studies of canola oil shelf life.     

Establishment of a model substrate oil for antioxidant activity assessment by oil stability index method

A model substrate oil using methyl linoleate was established for the determination of the antioxidant activity by Oil Stability Index (OSI) method. OSI values for methyl linoleate with different concentrations (5–100%) in silicone oil were measured at different temperatures (70–120°C). As the temperature increased, the OSI value decreased in each concentration of methyl linoleate. Optimal temperature and concentration of antioxidants, α-tocopherol, and butylated hydroxytoluene on OSI values for 10% methyl linoleate model oil was measured at 90, 100, 110, and 120°C. The logarithmic relationship between temperature and OSI using model substrate oil was similar to that of soybean oil. Furthermore, application of some spice extracts to this model oil system was carried out to give results thhat compared well with those available in the literature. Thus, the procedure using methyl linoleate-silicone oil as a model substrate oil is available for evaluating the antioxidant activity by the OSI method.     

Oxidative stability of soybean oil fatty acid methyl esters by oil stability index (OSI)

Biodiesel, an alternative diesel fuel derived from transesterification of vegetable oils or animal fats, is composed of saturated and unsaturated long-chain FA alkyl esters. During long-term storage, oxidation caused by contact with air (autoxidation) presents a legitimate concern with respect to monitoring and maintaining fuel quality. Extensive oxidative degradation may compromise quality by adversely affecting kinematic viscosity, acid value, or PV. This work examines the oil stability index (OSI) as a parameter for monitoring the oxidative stability of soybean oil FAME (SME). SME samples from five separate sources and with varying storage and handling histories were analyzed for OSI at 60°C using an oxidative stability instrument. Results showed that OSI may be used to measure relative oxidative stability of SME samples as well as to differentiate between samples from different producers. Although addition of α-tocopherol or TBHQ increased OSI, responses to these antioxidants varied with respect to SME sample. Variations in response to added antioxidant were attributed to aging and other effects that may have caused oxidative degradation in samples prior to acquisition for this study. Results showed that OSI was more sensitive than iodine value in detecting the effects of oxidative degradation in its early stages when monitoring SME during storage.     

提高润滑油基础油氧化安定性的方法

南阳石蜡精细化工厂由于在南阳稀油中掺炼南阳稠油,使润滑油基础油氧化安定性变差。本文介绍了南阳混合原油润滑油基础油性质及氧化安定性与油品组成的关系。通过对提高糠醛溶剂精制深度、对精制溶剂的改性、糠醛溶剂加入抗氧剂、WSQ—2脱氮剂液相脱氮工艺等方法的比较,探讨了如何利用现有装置改善基础油氧化安定性的途径。     

Determination of oxidation stability of soybean oil with the oxidative stability instrument: Operation parameter effects

Operation parameters of the oil stability index instrument were evaluated to determine their effect on the oxidative stability of commercial soybean oil. A factorial design was developed to evaluate the following three parameters, each at two levels, sample weight (2.5 or 5.0 g), conductivity tube temperature (20 or 30°C), and air flow rate (12 or 20 L/h), for a total of eight observations. Significance testing indicated that sample size and air flow rate affected oil oxidative stability independently (P<0.001), but not in combination. The conductivity tube temperature did not affect the oxidation stability index. Presented at the 1993 American Oil Chemists’ Society Meeting in Anaheim, California.     

Effects of tocopherols and their mixtures on the oxidative stability of olive oil and linseed oil under heating

The tested tocopherols (γ,δ,α) showed antioxidative activity at all levels of addition to the monounsaturated olive oil, the effects increased as a function of concentrations (maximum: +287% with 800 mg γ‐tocopherol/100 g oil compared to the control oil). In the highly unsaturated linseed oil, which contains 58 mg/100 g initial concentration of γ‐tocopherol, γ‐tocopherol showed antioxidative behavior up to the addition of 100 mg/ 100 g oil. Additions of more than the 100 mg/100 g affected the oil, resulting in a faster oxidation. Mixtures of γ/δ‐tocopherols in olive oil were found to protect more efficiently than both vitamins when added separately α‐tocopherol reduced effects of other tocopherols in both plant oils. The stabilizing effect of added tocopherols and their mixtures (100 mg/100 g oil each) in olive oil are γ/δ‐T>γ‐T>δ‐T>γ/α‐T>δ/α‐T>α‐T and in linseed oil γ‐T>γ/δ‐T>δ‐T>γ/α‐T>α‐T>α/δ‐T.     

Effects of seed damage on the oxidative stability of poppy seed oil

This study was conducted to assess the reduction of life time and quality of poppy seeds considering a mechanical damage, which may occur during harvesting. Vienna, Vienna, Austria Poppy seeds were crushed to receive 90%, 80%, 70%, 60% and 50% intact seeds, the undamaged 100% intact seeds served as controls. The samples were stored at 40 °C for 175 d and oxidation experiments performed periodically by assessing conjugated dienes, p‐anisidine reactive products, the iodine value, the acid value and γ‐tocopherol content. With increasing degree of mechanical damage the shelf life declined, the oxidation products were formed more rapidly and the main antioxidant in poppy seeds γ‐tocopherol was consumed. Considering the reduction of life time by including all quality parameters the shelf life of the 10% damaged seeds was reduced by 50.5%. This reduction was reached up to 82% for the 50% damaged seeds compared to the control. A high correlation was found between the increase in oxidation products and the degradation of γ‐tocopherol. This study show that increased damage during harvesting (10‐50%) is responsible for a faster loss of product quality especially in seeds containing high amounts of polyunsaturated fatty acids like poppy seeds.     

Oxidative stability of fat substitutes and vegetable oils by the oxidative stability index method

Oxidative Stability Index (OSI) of carbohydrate fatty acid polyesters, fat substitutes and vegetable oils were measured with the Omnion Oxidative Stability Instrument according to the new AOCS Standard Method Cd 12 B-92 (The Official Methods and Recommended Practices of the American Oil Chemists' Society, edited by D. Firestone, AOCS, Champaign, 1991). The stability of crude and refined, bleached and deodorized (RBD) vegetable oils (soybean, hydrogenated soybean and peanut) were determined at 110°C. In addition, OSI times for sucrose polyesters of soybean oil, butterfat, oleate:stearate and methyl glucoside polyester of soybean oil were determined in the absence and in the presence of 0.02 wt% antioxidants, [Tenox TBHQ (tertiary butylhydroquinone, Tenox GT-2 (from Eastman Chemical Products (Kingsport, TN); and vitamin E (from BASF, Wyandotte, MI)], and the results were compared with those of vegetable oils. Crude oils were most stable (20.4–25.9 h), followed by RBD oils (9.3–10.4 h) for soybean and peanut oils, respectively, and fat substitutes (3.8–6.8 h). Overall, Tenox TBHQ was the best antioxidant for improving the oxidative stability of both vegetable oils and fat substitutes. The sucrose polyester made with oleic and stearic acid was more stable than fat substitutes containing more polyunsaturated fatty acids, such as those from soybean oil, or from short-chain fatty acids, such as from butterfat. Antioxidants enhanced the stability of RBD oils (222% increase) and synthetic fat substitutes (421–424% increase) more than that of crude oils (33% increase). The shapes of the induction curves, not the actual OSI times for fat substitutes and vegetable oils, were similar and sharply defined.     

Comparison of oxidative stability of high- and normal-oleic peanut oils

A peanut breeding line with high-oleic acid and an isogenic sister line with normal fatty acid composition were obtained. Oil was extracted with dichloromethane and processed in the laboratory by alkali neutralization and bleaching. Fatty acid compositions were determined by gas chromatography and application of theoretical response factors. Oils were extracted and processed in duplicate. The oxidative stability of the oils was measured by the Schall oven test (80°C), active oxygen method (AOM) (112°C) and by comparison of oxidation rates on thin-layer chromatography-flame ionization detector (TLC-FID) rods (100°C). Fatty acid analysis indicated that the high-oleic line had 75.6 and 4.7% oleic and linoleic acids, respectively, compared to 56.1 and 24.2% for the normal line. The induction times for the Schall test were 682 and 47 h for high- and normal-oleic oils (P<0.01). The AOM induction times were 69 and 7.3 h for high and normal oils, respectively (P<0.01). The times to reach 50% loss in triglyceride area on TLC-FID were 847 and 247 min for high-oleic compared to normal-oleic oils (P<0.01). The results indicate that high-oleic peanut oil has much greater autoxidation stability as compared to normal oil.     

Effects of free fatty acids on oxidative stability of vegetable oil

The effect of free fatty acid (FFA) content on the susceptibility to thermooxidative degeneration of vegetable oils was determined by Rancimat analysis. A prooxidant effect of FFA was observed in all filtered oils, independently of lipidic substrate and of its state of hydrolytic and oxidative alteration. The intensity of this effect was related to FFA concentration, but regression analysis of the experimental data did not show a general correlation law between FFA concentration and induction time (I _t). Different results were obtained for freshly processed virgin olive oils, characterized by postpressing natural suspension-dispersion: opposite behavior was observed of FFA content as regards oxidative stability, depending on the presence of suspended-dispersed material. This fact is of interest because the dispersed particles play a double stabilizing effect on both oxidative and hydrolytic degradation. These results showed that avoidance of oil filtration is highly desirable to extend olive oil’s shelf life.     

Pan-frying stability of NuSun oil,a mid-oleic sunflower oil

Pan-frying is a popular frying method at home and in many restaurants. Pan-frying stabilities of two frying oils with similar iodine values (IV)—mid-oleic sunflower oil (NuSun oil; IV=103.9) and a commercial canola oil (IV=103.4)—were compared. Each oil sample was heated as a thin film on a Teflon-coated frying pan at ∼180°C to a target end point of ≥20% polymer. High-performance size-exclusion chromatography analysis of the mid-oleic sunflower and canola oil samples indicated that the heated samples contained 20% polymer after approximately 18 and 22 min of heating, respectively. The food oil sensor values increased from zero to 19.9 for the canola sample and from zero to 19.8 for the mid-oleic sunflower sample after 24 min of heating. The apparent first-order degradation rate for the mid-oleic sunflower sample was 0.102±0.008 min⁻¹, whereas the rate for the canola sample was 0.092±0.010 min⁻¹. The acid value increased from approximately zero prior to heating to 1.3 for the canola sample and from zero to 1.0 for the mid-oleic sunflower sample after 24 min of heating. In addition, sensory and volatile analyses of the fried hash browns obtained from both oils indicated there were no significant differences between the two fried potato samples.     

Rapid determination of oxidative stability of edible oils by FTIR spectroscopy using disposable IR cards

Disposable polytetrafluoroethylene (PTFE) polymer IR (PIR) cards were used as substrates to rapidly oxidize edible oils and simultaneously monitor the extent of oxidation by FTIR spectroscopy. Four edible oils were oxidized on PIR cards and in bulk at moderate temperature (58°C), and real-time oxidation plots were obtained by measuring changes in the IR hydroperoxide (ROOH) absorbance as a function of time. The relationship between the ROOH absorbance and PV was developed using a reference method to define absorbances corresponding to PV end points of 100 and 200 meq ROOH/kg for the oils oxidized in bulk and on cards, respectively. The real-time oxidation plots obtained for the oils oxidized in bulk and on cards were similar in appearance, but the oils on the cards reached the PV end point 20 times faster than the oils oxidized in bulk. The results indicate that the use of disposable PIR cards coupled with moderate heating and aeration provides a simple, practical, and rapid means for monitoring oxidation and determining the oxidative stability of edible oils at a normal storage temperature.     

Steaming,boiling after pre-frying,and stir-frying influence the fatty acid profiles and oxidative stability of soybean oil blended with docosahexaenoic acid algal oil

The objective of this study was to improve the content of docosahexaenoic acid (DHA) and obtain the blended oils used for different cooking methods (steaming, boiling, and stir-frying) by blending 0%–15% DHA algal oil into soybean oil. It was shown that the addition of DHA algal oil increased saturated fatty acid (SFA) (1.57%) but decreased monounsaturated fatty acid (MUFA) (0.76%) and polyunsaturated fatty acid (PUFA) (0.68%). Various cooking methods significantly changed the fatty acid (FA) compositions. Steaming is a more effective way to prevent DHA loss and the production of trans-fatty acid than boiling and stir-frying. Besides, a positive result from free fatty acid (FFA) and peroxide value also demonstrated that steaming was a better way to protect oils. Overall, the soybean oil blended with 3% DHA algal oil with better oxidative stability and could be recommended for daily application by steaming.     

Influence of interesterification on the oxidative stability of marine oil triacylglycerols

To understand the relationship between triacylglycerol structure of marine oils and their oxidative stability, peroxide values and absorbed oxygen levels of whale, sardine, cod liver and skipjack oils, interesterified by lipase and NaOCH₃, were compared with those of native oils during storage at 40°C. Triacylglycerol structures of marine oils were characterized by high-performance liquid chromatography and differential scanning calorimetry analyses. Enzymatically interesterified fish oils were more stable than native oils because the level of highly unsaturated triacylglycerols was decreased. However, the oxidative stability of interesterified whale oil was more susceptible to oxidation than the native oil.     

Comparative study on the stability of crude and refined rice bran oil during long‐term storage at room temperature

The effect of the full refining process on the stability of rice bran oil during storage at room temperature was studied. Crude and refined rice bran oil were kept in the dark and were exposed to light for 240 days, and every 10 days samples were drawn and analysed. The storage stability of crude and fully refined rice bran oil was determined and compared with respect to fatty acid composition, tocopherols, tocotrienols, sterols and γ‐oryzanol content. In addition, the oxidative status was evaluated by determining the concentration of polar compounds and the oil stability index (OSI). A good correlation between the decrease of total tocopherols and the OSI was found. α‐Tocopherol had the highest correlation coefficient (r² = 0.9653) in crude rice bran oil kept in the dark, and γ‐tocopherol showed the lowest in the refined sample (r² = 0.4722). The order of stability of tocopherols and tocotrienols in crude oil was completely different from that in refined oil. In comparison to tocopherols, sterols showed a better stability during the entire storage period. The exposure to daylight heavily affected the composition and the stability of both crude and refined rice bran oil.     

Comparison of rancimat evaluation modes to assess oxidative stability of fish oils

Two Rancimat evaluation modes, the induction period (IP), and the time needed to achieve a selected difference in conductivity (tΔK) were compared for assessing relative stability of anchovy, sardine, and hake liver oils. Mean coefficients of variation were 2.5 and 2.4% for IP and tΔK values, respectively, for oils oxidized in the range 55–90°C. Natural logarithms of IP and tΔK values varied linearly with temperature (P<0.001). A linear relationship (r=0.999) was established between the IP and tΔK values (P<0.001). Relative oxidative stability of fish oils was determined with the same degree of confidence by either IP or tΔK values.     

Polyphenol oxidase from eggplant reduces the content of phenols and oxidative stability of olive oil

Activity of the polyphenol oxidase (PPO) from eggplant fruit (Solanum melongena L.) on phenolic compounds of an extra virgin olive oil (EVOO) was studied. In standardized reaction solutions, the eggplant PPO, isolated in the laboratory, depleted completely chlorogenic and caffeic acids, oleuropein, and verbascoside, while the levels of hydroxytyrosol reduced by half. Conversely, no activity of the PPO was observed on the gallic and protocatechuic acids nor on mono‐phenols, such as tyrosol and the p‐coumaric, o‐coumaric, and ferulic acids. PPO activity on phenols extracted from eggplant fruit and EVOO confirmed the enzyme substrate specificity and caused a significant decrease in the measure of total phenols and o‐diphenols. Similarly, PPO crude extract caused a significant decrease of polyphenols directly in the EVOO. Moreover, maximum degradation of EVOO polyphenols was observed when olive oil was homogenized with eggplant fruit pulp to form a cream‐like purée. In fact, immediately after the preparation, total phenols and o‐diphenols of the olive oil recovered from the eggplant‐oil purée were decreased by ～80% and 100% compared to those of the initial EVOO. As a consequence, the oxidative stability of the recovered oil was ～60% lower than that of the initial EVOO. In conclusion, in the preparation of vegetable preserves, a residual activity of phenol oxidase may adversely affect the quality and shelf life of the extra virgin olive oil used as covering.     

Composition and oxidative stability of soybean oil in mixtures with jojoba oil

Improvement of the oxidative stability of soybean oil (SBO) by blending with jojoba oil (JO) was investigated. SBO in the presence of 5, 10, 15 and 20 wt‐% of JO was subjected to accelerated storage at 60 °C. Peroxide values (PV), anisidine values (AV), UV absorption characteristics (K₂₃₂ and K₂₇₀ values), and headspace volatiles were determined to monitor the oxidative stability of oil samples. JO was effective in reducing the formation of hydroperoxides and volatile compounds in SBO. The effect was remarkable in SBO/JO blends containing 15 and 20% JO, which showed significant reductions in PV, AV and volatile content with respect to pure SBO. The increased oxidative stability of SBO/JO blends could not be attributed to JO tocopherols, since the addition of JO to SBO significantly reduced the tocopherol content of SBO. Besides the tocopherol content and unsaturation degree of SBO and JO, the effect of the JO ester structure on the oxidative stability of the blends is discussed. The enhanced chemical and flavor stabilities of SBO/JO blends with respect to pure SBO may make a significant contribution to improve the shelf life of SBO by reducing the deterioration reactions related to lipid peroxidation.     

原油对水相泡沫稳定作用机理研究进展

为了评述原油对水相泡沫稳定性的影响机理,分别介绍了原油在水相泡沫中的存在状态,原油对泡沫的稳定或破坏机理。原油对泡沫的稳定性有着显著影响,稳泡或消泡也极大程度上决定了石油与天然气开采作业中,诸如泡沫驱油、泡沫堵水、堵气、泡沫排液、泡沫压裂等作业效率。重点阐述了假乳液膜对泡沫稳定性的影响机理,总结出原油在水相泡沫体系中以溶解油或乳化油两种状态存在。原油溶解于水相胶束中(溶解油)可降低泡沫的稳定性。大多原油在水相泡沫中以乳化油滴形式存在,油滴与气泡之间被假乳液膜隔开,假乳液膜决定了泡沫体系的稳定性。假乳液膜稳定性好能促进三相泡沫的稳定性;而假乳液膜稳定性差就加剧了三相泡沫地破裂。通过评述指出了原油与水相泡沫相互作用研究领域今后的研究方向。