Oil Stability Index Research Articles

Oil and Seed Meal Quality Indices of Indian Rapeseed-Mustard Varieties

Variation in oil, protein, fatty acid profile, oil stability index, PUFA to SFA, MUFA to PUFA, ω-6 to ω-3 fatty acid ratio and glucosinolate content and their relationships were studied in 50 rapeseed-mustard (Brassica species) varieties. Variability was low for protein and oil content with CV 4.2% and 5.1%, respectively. The highest variation was recorded for oil stability index followed by oleic acid content. Erucic acid ranged from 0.4 % [TERI (00) R- 9903] to 55.3% (NDYS-2). The saturated fatty acids showed a range of 2.5–8.6% and most of the varieties had 10.0. All the varieties, in general had high glucosinolate content except GSC- 5, TERI (OE) R-03 and TERI (00) R-9903. Oil stability index had highly significant and positive correlation with oleic acid and MUFA to PUFA ratio. The relationship of oil content was significantly positive with ω-6 to ω-3 fatty acid ratio (r = 0.377**). Protein content and SFA were positively correlated (r = 0.314 *). Erucic acid exhibited negative and significant association with SFA (r = − 0.293*) and oleic acid (r = − 0.863**).

Physicochemical and Sensory Quality of Crude Brazilian Pecan Nut Oil during Storage

AbstractThe physicochemical and sensory characteristics of pecan nut [Carya illinoensis (Wangenh.) K. Koch] oil obtained by cold pressing and stored at room temperature (average of 22.5 °C) in amber glass flasks for 120 days were determined. The pecan nut oil had an iodine value of 98.4; a refraction index at 40 °C of 1.469; saponification value of 184.3 g/100 g; a peroxide value (PV) of 0.55 mequiv O2/kg; an Oil Stability Index (OSI), i.e. an oxidative stability of 9.8 h and an acid value of 0.13 mg KOH/g. During the storage period, changes in the peroxide value (PV), specific extinction (SE) at 232 nm, acid value, and color of the oil were observed but, after 120 days, the oil still had adequate quality characteristics according to the Brazilian legislation for crude oils. Sensory analysis (descriptive profile and acceptance) showed that the sensory characteristics of pecan nut oil were unaltered for up to 60 days of storage. After 90 days, there was a significant increase in oxidized taste and bitterness, with a reduction in nut taste and acceptability of the oil (p ≤ 0.05). After 120 days of storage, sensory changes became more pronounced and were unacceptable. It was concluded that crude pecan nut oil stored in amber glass flasks at room temperature had a shelf life of 90 days.

EFFECT OF BLANCHING ON STORAGE STABILITY OF HAZELNUT MEAL

ABSTRACT Influence of blanching on storage stability of hazelnut meal was investigated under accelerated storage conditions. Meals were obtained from unblanched and blanched hazelnut kernels, and stored at a relative humidity of 60% at 30C for 50 days. Total free fatty acid content, concentrations of individual free fatty acids, peroxide value and oil stability index were measured in the hazelnut meal samples during storage. No significant difference was found between peroxide values of the samples, however, the values of both samples increased during storage time. The concentrations of free fatty acids increased because of the activity of lipase in both meals, but the levels were lower in the blanched sample. Oil stability index of the unblanched sample was lower than that of the blanched sample. Blanching treatment was found to improve the oxidative stability of hazelnut meal, possibly because of partial inactivation of deteriorative enzymes. PRACTICAL APPLICATIONSHazelnut meal is a product obtained from hazelnut which is used as an ingredient in various food products. Hazelnut meal is more prone to degradation and quality loss during storage via oxidation compared with the whole counterpart. Stability of whole hazelnut has been studied to a great extent in the literature, but there is a scarcity of information regarding stability of processed hazelnut. In addition, there is no information in the literature about the amount of individual free fatty acids in hazelnut where the amounts of total free fatty acids have been reported extensively. This study provides data for quality and stability of hazelnut meal during storage which could be used by the food industry.

Characterization of Oil Extracted from Buriti Fruit (Mauritia flexuosa) Grown in the Brazilian Amazon Region

AbstractFive samples of buriti oil from industrial and artisanal suppliers were characterized in terms of nutritional quality parameters (nutraceutical levels) and acidity. As a first screening, each sample was analyzed by titration, spectrophotometry and an HPLC method, and the results were compared. As expected, artisanal samples showed lower acidity and higher levels of carotenes and tocols (tocopherols and tocotrienols). A blend of industrial and artisanal samples in suitable proportions was completely characterized in terms of analytical and physico‐chemical properties, i.e., fatty acid composition, iodine value, partial and total acylglycerol contents, refractive index (40 °C), saponification value, unsaponifiable matter, acidity (expressed as % of oleic acid), peroxide value, phosphorus content, oil stability index, tocol and carotene concentrations. The results of the present study showed that buriti oil is a valuable source of monounsaturated fatty acids, and vitamins A and E. No previous work in the literature has analyzed buriti oil to this extent. The chromatographic method using HPLC was effective in qualifying and quantifying tocopherols, tocotrienols and carotenes.

Comparative Oxidative Stability of Fatty Acid Alkyl Esters by Accelerated Methods

AbstractSeveral fatty acid alkyl esters were subjected to accelerated methods of oxidation, including EN 14112 (Rancimat method) and pressurized differential scanning calorimetry (PDSC). Structural trends elucidated from both methods that improved oxidative stability included decreasing the number of double bonds, introduction of trans as opposed to cis unsaturation, location of unsaturation closer to the ester head group, and elimination of hydroxyl groups. Also noticed with EN 14112 was an improvement in oxidative stability when a larger ester head group was utilized. Methyl esters that contained ten or less carbons in the fatty acid backbone were unacceptable for analysis at 110 °C (EN 14112) due to excessive sample evaporation. With respect to PDSC, a correlation was noticed in which the oxidation onset temperature (OT) of saturated fatty esters increased with decreasing molecular weight (R2 0.7328). In the case of the monounsaturates, a very strong inverse correlation was detected between molecular weight and OT (R2 0.9988), which was in agreement with EN 14112. Lastly, a strong direct correlation (R2 0.8759) was elucidated between OT and oil stability index (OSI, EN 14112, 80 °C). The correlation was not as strong (R2 0.5852) between OSI obtained at 110 °C and OT.

Characterization of artisanally and semiautomatically extracted argan oils from Morocco

AbstractThe present study was conducted to know the possible influence of the seed treatment, method of extraction and geographical origin on the quality and chemical composition of argan oil. Artisanally and semiautomatically extracted argan oils, from roasted and unroasted seeds, from interior and coast areas, were studied. The quality parameters analyzed were acid value, peroxide value, K232 and K270, triacylglycerols and fatty acid composition, polar compounds, total phenols, tocopherol content and oil stability index (OSI). Seed treatment and extraction method showed a higher influence on quality parameters than geographical area; the quality parameters of the different oils were discussed. The total phenolic content in all analyzed samples was lower than 10 ppm. γ‐Tocopherol was the major tocopherol (84.4–86.4%) with a high contribution to the total tocopherol content (383–485 ppm). The OSI of the argan oil samples were well correlated (R = 0.97) with the tocopherol contents. The argan oil samples obtained from roasted seeds presented higher stability (26–38 h) than the oils from unroasted seeds (16–32 h).

Influence of Blending Canola, Palm, Soybean, and Sunflower Oil Methyl Esters on Fuel Properties of Biodiesel

Single, binary, ternary, and quaternary mixtures of canola (low erucic acid rapeseed), palm, soybean, and sunflower (high oleic acid) oil methyl esters (CME, PME, SME, and SFME, respectively) were prepared, and important fuel properties were measured, such as oil stability index (OSI), cold filter plugging point (CFPP), cloud point (CP), pour point (PP), kinematic viscosity (40 °C), lubricity, acid value (AV), and iodine value (IV). The fuel properties of SME were improved through blending with CME, PME, and SFME to satisfy the IV (<120) and OSI (>6 h) specifications contained within EN 14214, the biodiesel standard from the European Committee for Standardization. SME was satisfactory according to ASTM D6751, the American biodiesel standard, with regard to OSI (>3 h). The CFPP of PME was improved by up to 15 °C through blending with CME. Statistically significant relationships were elucidated between OSI and IV, OSI and saturated fatty acid methyl ester (SFAME) content, OSI and CFPP, CFPP and IV, and CFPP and SFAME content. However, the only relationship of practical significance was that of CFPP versus SFAME content when SFAME content was greater than 12 wt %.

A Novel Photometric Method for Evaluation of the Oxidative Stability of Virgin Olive Oils

The Oxitester method, a novel, simple, and fast photometric method for the evaluation of the antioxidant capacity of olive oils, was validated and compared to the official oil stability index (Rancimat) method. The Oxitester method appeared to be a good alternative to the Rancimat method with adequate correlation for a wide range of virgin olive oil samples, including extrissima virgin olive oils (correlation coefficient 0.88), and extra virgin olive oils of increased acidity (free fatty acids >0.45%, correlation coefficient 0.89). Other quality factors (flavor, free fatty acids content, specific absorbance at 270 and 232 nm, peroxide value, and content of oleic, linoleic, and linolenic acids) were also measured and correlated to the antioxidant capacity values of the Oxitester and Rancimat methods. The Oxitester method, in contrast to the Rancimat method, was indicative of the flavor characteristics of the olive oils and the content of linolenic acid.

Oxidative Stability of Conventional and High‐Oleic Vegetable Oils with Added Antioxidants

AbstractThe oxidative stability of conventional and high‐oleic varieties of commercial vegetable oils, with and without added antioxidants, was evaluated using the oil stability index (OSI). Oil varieties studied were soybean (SOY), partially‐hydrogenated soybean (PHSOY), corn (CORN), sunflower (SUN), canola (CAN), high‐oleic canola (HOCAN), very high‐oleic canola (VHOCAN), oleic safflower (SAF) and high‐oleic sunflower (HOSUN). One or more commercial antioxidants were added to the four most stable oils at supplier‐recommended levels: rosemary extract (RM; 1,000 ppm), ascorbyl palmitate (AP; 1,000 ppm), tert‐butylhydroquinone (TBHQ; 200 ppm), and mixed tocopherols (TOC; 200 ppm). OSI in hours (h) at 110 °C of the conventional oils were 5.2, 7.6, 8.4, 9.8, 10.9 and 14.3 h for SUN, SOY, CAN, CORN, PHSOY and SAF, respectively. OSI of high‐oleic variants were 12.9, 16.5 and 18.5 h for HOCAN, HOSUN and VHOCAN, respectively. Maximum OSI values for the four most stable oils when treated with antioxidants, were 40.9, 48.5, 48.8 and 55.7 h for HOCAN, VHOCAN, SAF and HOSUN, respectively. Addition of TBHQ, alone and in combination with other antioxidants, resulted in the greatest increase in oxidative stability of SAF and other high‐oleic oils evaluated. AP had a positive synergistic effect when used with TBHQ, while RM decreased TBHQ effectiveness.

Comparison of two seed oils used in cosmetics, moringa and marula

Comparison of the seed oil of Moringa pterygosperma (moringa) and Sclerocarya birrea (marula) showed a marked difference in fatty acid composition and oxidative stability. Moringa, with 1000 ppm tocopherols, had an oil stability index (OSI) of 133 h at 110 °C while marula with 1000 ppm tocopherols yielded 37 h at 110 °C. This correlated well with the fatty acid composition of these two oils. Moringa had less than 1% polyunsaturates and marula had 6.7% of these oxidatively unstable materials. In addition, fatty acid compositions of seven species of moringa are presented. All of these species had levels of behenic acid ranging from 1 to 7% with oleic acid levels from 68 to 79%. The highest amount of polyunsatures was found in the moringa species was in Moringa drouhardii with 3.6%.

Effect of Temperature on the Oil Stability Index (OSI) of Biodiesel

Biodiesel, an alternative fuel derived from lipid feedstocks, such as vegetable oil or animal fat, is mainly composed of saturated and unsaturated fatty acid alkyl esters. Fuel suppliers, terminal operators, and users are becoming more concerned with monitoring and maintaining good biodiesel fuel quality with respect to oxidative degradation during storage. The oil stability index (OSI), a parameter that measures the relative oxidative stability of fatty materials, is typically measured isothermally at elevated temperatures to accelerate oxidation. The present work investigates the effects of block temperature (T) on the OSI of biodiesel from soybean oil fatty acid methyl esters (SME) and used cooking oil fatty acid methyl esters (UCOME). Results were compared to those for pure methyl oleate (MO). An increasing temperature accelerated the oxidation reaction causing a decrease in OSI. Response factors (RF) determined with MO as the reference methyl ester showed little variation with respect to the temperat...

Evaluation of the stability of blends of sunflower and rice bran oil

AbstractBlends of sunflower oil (SFO) and rice bran oil (RBO) were evaluated for their stability. Additionally, known amounts of natural antioxidants extracted from RBO were added to SFO, and their protective effect was compared to that of the blends. The results found indicate that by raising the amount of RBO, from 10 to 50%, an increase of OLO, OLP, PPL, OOO, PPO, OPO, 18:1 and 16:0 occurred, followed by a decrease of LLL, LLO, and 18:2. These changes in fatty acid and triacylglycerol (TAG) composition led to an increase of the oil stability index at 120 °C and a reduction of polymer TAG formation in the heated blends at 180 °C during 8 h. A comparable protective effect of natural antioxidants to that of blending was observed in a 50 : 50 blend, by remarkably increasing the induction period.

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

AbstractThe 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.

1,1‐DI‐(2′,5′‐DIHYDROXY‐4′‐TERT‐BUTYLPHENYL)ETHANE: A NOVEL ANTIOXIDANT

ABSTRACT A novel antioxidative compound, namely 1,1‐di‐(2′,5′‐dihydroxy‐4′‐tert‐butylphenyl)ethane (DHPE) was synthesized by condensation reaction between tert‐butylhydroquinone (TBHQ) and acetaldehyde. The antioxidant and free‐radical scavenging activities of this compound were compared to other common antioxidants, namely butylated hydroxyanisole, butylated hydroxytoluene, TBHQ and propyl gallate by 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical assay and oil stability index experiment, deep‐fat frying and Schaal oven test. DHPE was the most potent antioxidant among all antioxidants tested using 10% emulsion and deep‐fat frying at 180C. It was also a very good antioxidant at room temperature in lard and soybean oil. DPPH radical scavenging assay showed that DHPE was a strong free‐radical scavenger.

Effect of dewaxing pretreatment on composition and stability of rice bran oil: Potential antioxidant activity of wax fraction

AbstractThe effect of dewaxing pretreatment on rice bran oil composition and stability was investigated, as well as the possibility to use rice bran oil waxes as natural antioxidants at high temperatures. A correlation between wax content and dewaxing time was noticed. The pre‐dewaxing process led to a loss of minor compounds, which negatively affected the oxidative stability index (OSI) of the dewaxed oil. The addition of rice bran oil waxes improved the oil stability index and heat stability of sunflower oil. An increase of 60% of the OSI and a significant decrease in polymer formation (59.2%) were observed.

Oxidative Stability Measurement of High-Stability Oils by Pressure Differential Scanning Calorimeter (PDSC)

High-stability oils are used as coatings on food products that require long shelf life. The high stability oils produced from high-oleic oils require less processing and bring additional nutritional benefits such as lower trans and saturated fat contents. Accurate and reproducible oxidative stability measurement of these oils is necessary to assess the performance. The accelerated oxidative stability measurement method often used in the fats and oils industry, the oxidative stability index (OSI, AOCS Cd 12b-92) is unreliable for higher stability oils due to poor reproducibility. This study presents a pressure differential scanning calorimetry (PDSC) method, which is highly reproducible and versatile and applies to oils from low to very high oxidative stability. PDSC has been used in industrial applications such as lubricants (ASTM D 6186-98) and measures the oxidative induction time (OIT) of oils under high temperature and pressure in the presence of pure oxygen. The OITs of a number of hydrogenated oils with different unsaturation and oxidative stability are measured. Unlike OSI data, the PDSC OIT measurement is highly reproducible and precise and requires only a small sample and a couple of hours. The regression analysis of the PDSC data indicated the natural log OIT of all samples linearly correlated with the temperature. The equation derived from this relationship helps to compare the oxidative stabilities of the same or different oils determined at different temperatures. The development of this method into an approved method will benefit the fats/oils and food industry.

Detection of radical development by ESR spectroscopy techniques for assessment of oxidative susceptibility of fish oils

Detection of radical development by two different Electron Spin Resonance (ESR) spectroscopy techniques has been evaluated for obtaining objective analytical information about oxidative susceptibility of fish oils under mild oxidation conditions. Two oils from different by-products in the fish industry, salmon viscera oil (SVO) and cod liver oil (CLO), were used. In addition, radical formation in the ethyl ester of docosahexaenoic acid (DHA) was studied as representing polyunsaturated fatty acids in fish oils that are very prone to oxidation. The ESR spin trapping technique, using the spin trap α-phenyl-N-tert-butylnitrone, and the ESR spin scavenging technique, using the stable nitroxyl radical 2,2,6,6-tetramethyl-1-piperidinyl-1-oxyl (TEMPO) to be scavenged by radicals generated in the oxidative process, were applied to detect radical development at 40 °C in the dark. For comparative purposes, oxidative susceptibility was evaluated by determination of peroxide value (PV) and the TBARS test under the same oxidation conditions. Results were also compared to the oil stability index (OSI) obtained at 60 °C. Results obtained by ESR spin trapping were consistent with results obtained in the OSI test, as well as those obtained for PV and the TBARS test. Therefore, detection of radical formation by ESR spin trapping provided objective information upon the relative oxidative susceptibility of SVO and CLO. On the other hand, results obtained by ESR spin scavenging were not concluding to establish the different oxidative susceptibility of the two oils found by the other determinations applied. The kinetic curves of TEMPO were similar for both oils, which suggests that mechanisms other than that based on the expected radical-radical interactions might be involved.

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

AbstractBiodiesel, 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.

Relation between the Endogenous Antioxidant System and the Quality of Extra Virgin Olive Oil under Accelerated Storage Conditions

Three monovarietal extra virgin olive oils (EVOOs) were subjected to accelerated storage conditions (60 degrees C, dark) representative of the autoxidation process during shelf life. Oxidation markers, i.e., the peroxide value, conjugated dienes, the oil stability index, and minor components, were monitored. The changes in minor components, related to the stage of ongoing oxidation and expressed as a percentage of the induction period (IP), followed a similar pattern in all oils: o-diphenols diminished by the highest rate (halved within 15% of the IP), followed by alpha-tocopherol (halved within 35% of the IP). Carotenoids and chlorophylls were also affected by autoxidation, whereas squalene showed high stability (<20% loss within 100% of the IP). Polar phenols (especially o-diphenols) and alpha-tocopherol were deduced to be the most potent antioxidants of EVOO. They efficiently inhibited oxidative lipid deterioration and subsequent development of sensory defects (rancidity, discoloration), which occurred only after substantial depletion of these antioxidants. Therefore, they could also be used as markers for the oxidative status of EVOO particularly in the early stage of oxidation.

Antioxidant properties of prunes (Prunus domestica L.) and their constituents

Prunes contain large amounts of phenolics and show high antioxidant activity. The aim of this study is to clarify the contents of caffeoylquinic acid (CQA) isomers, and to estimate the contribution of these isomers to the antioxidant activity of prunes. Furthermore, structural elucidation and evaluation of antioxidant activity of prune components were also performed. CQA isomers in prunes were quantified by HPLC analysis, and it has become apparent that prunes contain relatively high amount of 4-O-caffeoylquinic acid. The contribution of CQA isomers to the antioxidant activity of prunes was revealed to be 28.4% on the basis of oxygen radical absorbance capacity (ORAC); hence, it was indicated that residual ORAC is dependent on unknown antioxidant components. Total 28 compounds were isolated and their structures were elucidated by NMR and MS analyses. Four abscisic acid related compounds, a chromanon, and a bipyrrole were novel. Each CQA isomer in prunes showed high antioxidant activities when measured by the oil stability index (OSI) method, O2- scavenging activity, and ORAC. Other isolated compounds such as hydroxycinnamic acids, benzoic acids, coumarins, lignans, and flavonoid showed high ORAC values. Furthermore, a novel chromanon indicated a remarkable synergistic effect on ORAC of CQA isomers.