Effects of β-carotene and lycopene thermal degradation products on the oxidative stability of soybean oil

The relative oxidative stability of soybean oil samples containing either thermally degraded β-carotene or lycopene was determined by measuring peroxide value (PV) and headspace oxygen depletion (HOD) every 4 h for 24 h. Sobyean oil samples containing 50 ppm degraded β-carotene that were stored in the dark at 60°C displayed significantly (P<0.01) higher HOD values compared with controls. Lycopene degradation products (50 ppm) in soybean oil significantly (P<0.05) decreased HOD of samples when stored in the dark. PV and HOD values for samples containing 50 ppm of either β-carotene or lycopene degradation products stored under lighted conditions did not differ significantly from controls (P<0.05). However, soybean oil samples containing 50 ppm of unheated, all-trans β-carotene or lycopene stored under light showed significantly lower PV and HOD values than controls (P<0.01). These results indicated that during autoxidation of soybean oil held in the dark, β-carotene thermal degradation products acted as a prooxidant, while thermally degraded lycopene displayed antioxidant activity in similar soybean oil systems. In addition, β-carotene and lycopene degradation products exposed to singlet oxygen oxidation under light did not increase or decrease the oxidative stability of their respective soybean oil samples.     

Effects of bleached and unbleached rosemary oleoresin and rosmariquinone on light-sensitized oxidation of soybean oil

Synthetic rosmariquinone (RQ), an antioxidant naturally present in rosemary (Rosmarinus officinalis L.), tertiary butylhydroquinone (TBHQ) and rosemary oleoresin (bleached and unbleached), was tested for antioxidant activity in stripped and nonstripped soybean oil in a light-induced oxidation system. In the stripped soybean oil system, RQ was significantly less (P<0.05) effective than TBHQ at controlling oxidation of the oil. In light-induced oxidation of nonstripped soybean oil, RQ had significantly lower (P<0.05) peroxide values (PV) than TBHQ after 36 h. RQ had PV that was significantly (P<0.05) lower than those for both the bleached and nonbleached rosemary oleoresin throughout the 72-h study.     

Effects of thermally oxidized triglycerides on the oxidative stability of soybean oil

Soybean oil purified by silicic acid column chromatography did not contain peroxides, free fatty acids, phospholipids or oxidized polar compounds. The purified soybean oil was thermally oxidized at 180°C for 96 hr in the presence of air. The thermally oxidized compounds (31.3%) were separated from the purified soybean oil by gradient elution silicic acid chromatography. Thermally oxidized compounds contained hydroxyl groups, carbonyl groups andtrans double bonds according to the infrared spectrum. Thermally oxidized compounds were added to soybean oil and purified soybean oil at 0, 0.5, 1.0, 1.5 and 2.0% to study the effects of these compounds on the oxidative stability of oil. The oxidative stabilities of oils were determined by gas chromatographic analysis of volatile compound formation and molecular oxygen disappearance in the headspace of oil bottles. The thermally oxidized compounds showed prooxidant effects on the oxidative stabilities of both refined, bleached and deodorized soybean oil and purified soybean oil. Duncan’s Multiple Range Test showed that thermally oxidized compounds had a significant effect on the volatile compound formatiion and oxygen disappearance in the headspace of oil at α=0.05.     

Oxidative instability of CLA concentrate and its avoidance with antioxidants

This study evaluated the effectiveness of antioxidants, such as BHA, BHT, TBHQ, propyl gallate (PG), α-tocopherol (α-1), green tea extract (GTE), and rosemary extract (RE) on oxidative stability of CLA concentrate. Stability of CLA concentrate stored in air at 45°C up to 44 d was assessed by PV. During the storage period, the PV of the control CLA concentrate sample increased from 0.20 (fresh oil) to 1654 meq/kg (oxidized oil). On the other hand, the PV for CLA concentrates treated with 200 ppm of the single synthetic antioxidants, BHA, BHT, TBHQ, and PG, increased from 0.20 to 81, 107, 78, and 101 meq/kg, respectively. Also, the PV of CLA concentrate with the addition of 200 ppm single natural antioxidants α-T, GTE, and RE lowered the final PV to 122, 140, and 110 meq/kg, respectively. Under our experimental conditions, the protective effect of 200 ppm antioxidant was in the order of TBHQ>BHA>PG>BHT>RE>α-T> GTE. These results suggest that the appropriate use of antioxidants prolongs the oxidative stability of CLA concentrate.     

Oxidative Stability of Conjugated Linoleic Acid Rich Soy Oil

This study was conducted to determine the oxidative stability of conjugated linoleic acid rich soy oil (CLARSO) and the effects of conjugated linoleic acid (CLA) levels on volatile oxidation products formed during CLARSO oxidation. CLARSO oxidative stability was determined by gravimetric analysis, peroxide value, headspace oxygen analysis and p-anisidine value. Volatile oxidation compounds were analyzed by solid phase microextraction–gas chromatography with a flame ionization detector and a mass spectrometer. CLA oxidation results were highly dependent on analytical methods used and oxidation parameters measured. The gravimetric study showed a CLA concentration effect on oxidation, which was not seen in the headspace oxygen depletion and peroxide value. Volatile oxidation data indicate that CLARSO had significantly higher (p < 0.05) levels of pentanal and trans-2-heptenal than the other oils, but there was no significant difference between the amounts of any volatiles present in 8 and 15% CLARSO. This suggests that oxidation was greater in CLARSO and that CLA concentration did not affect oxidation.     

Evaluation of the Oxidative Stability of Diacylglycerol-Enriched Soybean Oil and Palm Olein Under Rancimat-Accelerated Oxidation Conditions

The oxidative stability of diacylglycerol (DAG)-enriched soybean oil and palm olein produced by partial hydrolysis using phospholipase A1 (Lecitase Ultra) and molecular distillation was investigated at 110 °C by the Rancimat method with and without addition of synthetic antioxidants. Compared with triacylglycerol oils, the DAG-enriched oils displayed lower oxidative stability due to a higher content of unsaturated fatty acids and a lower level of tocopherols. With the addition (50–200 mg/kg) of tert-butylhydroquinone (TBHQ) or ascorbyl palmitate (AP), the oxidative stability indicated by induction period (IP) of these DAG-enriched oils under the Rancimat conditions was improved. The IP of the diacylglycerol-enriched soybean oil increased from 4.21 ± 0.09 to 12.64 ± 0.42 h when 200 mg/kg of TBHQ was added, whereas the IP of the diacylglycerol-enriched palm olein increased from 5.35 ± 0.21 to 16.24 ± 0.55 h when the same level of AP was added. Addition of TBHQ, alone and in combination with AP resulted in a significant (p ≤ 0.05) increase in oxidative stability of diacylglycerol-enriched soybean oil. AP had a positive synergistic effect when used with TBHQ.     

Oxidative stability of hydrogenated menhaden oil shortening blends in cookies,crackers, and snacks

The oxidative stability of partially hydrogenated menhaden fish oil (PHMO) shortening/canola oil blends with added antioxidant tertiary butylhydroquinone (TBHQ) and various blended partially hydrogenated vegetable oil (PHVO) shortenings without antioxidant in aged cookies and crackers was analyzed by anisidine value (AV), peroxide value (PV), and Totox value. The results showed no significant differences (P<0.05) for PV, AV, or Totox value between the PHMO shortening containing TBHQ and the PHVO shortening in cookies, crackers, and deep-fried extruded snacks, except for the AV and Totox value of crackers.     

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.     

Effect of Bene Kernel Oil on the Frying Stability of Canola Oil

Canola oil (CAO) with (0.05–0.4%) and without added bene kernel oil (BKO) and tert-butylhydroquinone (TBHQ, 100 ppm) was used for deep-fat frying of potatoes at 180 °C for 48 h. Frying stability of the oil samples during the frying process was measured based on the variations of total polar compounds (TPC) content, conjugated diene value (CDV), acid value (AV), carbonyl value (CV) and total tocopherols (TT). In general, frying stability of the CAO significantly (P < 0.05) improved in the presence of the TBHQ and BKO. The best frying performance for the CAO was obtained by using of 100 ppm TBHQ and 0.1% BKO. The effectiveness of TBHQ and BKO at these levels was found to be nearly the same. Increasing the level of BKO from 0.1 to 0.4% caused a decrease in the oxidative stability of the CAO, indicating the pro-oxidant effect of the oils added at these levels.     

Changes in Total Polar Compounds,Peroxide Value,Total Phenols and Antioxidant Activity of Various Oils Used in Deep Fat Frying

In this study, the effect of deep fat frying on oil degradation, total phenols (TP) and total antioxidant activity (TAA) of hazelnut, corn, soybean and olive oils were investigated. Oil degradation and oxidation were monitored by measuring the total polar compounds (TPC) and the peroxide value (PV). The amount of TPC in corn, soybean and olive oils increased significantly with the time increment (p < 0.05). The PV of the oils did not exceed the maximum acceptable limit of 10 mequiv O₂/kg after 125 min frying except for hazelnut oil (10.64 mequiv O₂/kg). Deep-fat frying did not cause any significant change in the TP of corn oil, soybean oil and olive oil (p < 0.05). A significant decrease in the antioxidant activity was observed after 50 min frying using hazelnut oil and corn oil (p < 0.05). However, the antioxidant activity of soybean oil and olive oil significantly decreased after 75 and 25 min frying, respectively.     

Effect of natural antioxidants in virgin olive oil on oxidative stability of refined,bleached, and deodorized olive oil

The factors influencing the oxidative stability of different commercial olive oils were evaluated. Comparisons were made of (i) the oxidative stability of commercial olive oils with that of a refined, bleached, and deodorized (RBD) olive oil, and (ii) the antioxidant activity of a mixture of phenolic compounds extracted from virgin olive oil with that of pure compounds andα-tocopherol added to RBD olive oil. The progress of oxidation at 60°C was followed by measuring both the formation (peroxide value, PV) and the decomposition (hexanal and volatiles) of hydroperoxides. The trends in antioxidant activity were different according to whether PV or hexanal were measured. Although the virgin olive oils contained higher levels of phenolic compounds than did the refined and RBD oils, their oxidative stability was significantly decreased by their high initial PV. Phenolic compounds extracted from virgin olive oils increased the oxidative stability of RBD olive oil. On the basis of PV, the phenol extract had the best antioxidant activity at 50 ppm, as gallic acid equivalents, but on the basis of hexanal formation, better antioxidant activity was observed at 100 and 200 ppm.α-Tocopherol behaved as a prooxidant at high concentrations (>250 ppm) on the basis of PV, but was more effective than the other antioxidants in inhibiting hexanal formation in RBD olive oil.o-Diphenols (caffeic acid) and, to a lesser extent, substitutedo-diphenols (ferulic and vanillic acids), showed better antioxidant activity than monophenols (p- ando-coumaric), based on both PV and hexanal formation. This study emphasizes the need to measure at least two oxidation parameters to better evaluate antioxidants and the oxidative stability of olive oils. The antioxidant effectiveness of phenolic compounds in virgin olive oils can be significantly diminished in oils if their initial PV are too high.     

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

The 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.     

Effect of extraction solvents on oxidative stability of crude soybean oil

Oxidative stabilities of crude soybean oils obtained by different extraction solvents such as hexane, water and Folch's solvent (mixture of two volumes of chloroform and one volume of methanol) were determined by gas chromatographic analyses of headspace and peroxide value of oil samples. For the determination of oxidative stability of oil samples, total volatile compounds formation, molecular oxygen disappearance in the headspace and peroxide value of oil samples were measured. Iodine value (133–136), saponification value (195–198), unsaponifiable matters (0.3–0.4%), iron (0.6 ppm), sterols content (2,400–2,590 ppm), tocopherols content (1,250–1,520 ppm) and fatty acid composition of crude oils obtained by different solvent extraction were not significantly different. Acid value of Folch-extracted oil was the highest as 1.3, whereas those of hexane-and aqueous-extracted oils were 0.5 and 0.4, respectively. Crude soybean oil extracted by Folch's method was found to contain the most phosphorus, while hexane- and aqueous-extracted oils contained similar amounts of phosphorous. Crude soybean oil obtained by Folch extraction was most stable in oil oxidation, and oxidative stabilities of oils obtained by hexane and aqueous extraction, which were significantly much less stable than Folch-extracted oil, were not significantly different during ten weeks storage.     

Ziziphi spinosae Semen Oil Enhance the Oxidative Stability of Soybean Oil under Frying Conditions

The objective of this study is to improve the oxidative stability of soybean oil by using Ziziphi spinosae semen oil (ZSSO). In the present study, the oxidative stability, fatty acid composition, tocopherol, and phenolic changes of soybean oil without additives and soybean oil mixed with 5% ZSSO are evaluated during frying at 180 ℃ for 18 h. Tert-butyl hydroquinone (TBHQ) and vitamin E (VE) as common antioxidants are incorporated into soybean oil for comparison. According to the results of oxidative stability assays of conjugated diene value, thiobarbituric acid value, acid values, and total polar compounds, the incorporation of ZSSO significantly restrain the lipid oxidation of soybean oil. After 18 h of frying, the soybean oil samples with ZSSO has more polyunsaturated fatty acids, tocopherols, and DPPH radical scavenging capacity, and less trans fatty acids, compared with TBHQ and VE. In addition, ZSSO-containing soybean oil maintains a high content of phenols during the frying period, which is correlated with the increase in oxidative stability. Therefore, replacing part of soybean oil with ZSSO can effectively reinforce the performance of soybean oil under frying conditions.     

Quantitative determination of total lipid hydroperoxides by a flow injection analysis system

A flow injection analysis (FIA) system coupled with a fluorescence detection system using diphenyl-1-pyrenylphosphine (DPPP) was developed as a highly sensitive and reproducible quantitative method of total lipid hydroperoxide analysis. Fluorescence analysis of DPPP oxide generated by the reaction of lipid hydroperoxides with DPPP enabled a quantitative determination of the total amount of lipid hydroperoxides. Use of 1-myristoyl-2-(12-((7-nitro-2-1,3-benzoxadiazol-4-yl)amino) dodecanoyl)-sn-glycero-3-phosphocholine as the internal standard improved the sensitivity and reproducibility of the analysis. Several commercially available edible oils, including soybean oil, rapeseed oil, olive oil, corn oil, canola oil, safflower oil, mixed vegetable oils, cod liver oil, and sardine oil were analyzed by the FIA system for the quantitative determination of total lipid hydroperoxides. The minimal amounts of sample oils required were 50 μg of soybean oil (PV=2.71 meq/kg) and 3 mg of sardine oil (PV=0.38 meq/kg) for a single injection. Thus, sensitivity was sufficient for the detection of a small amount and/or low concentration of hydroperoxides in common edible oils. The recovery of sample oils for the FIA system ranged between 87.2±2.6% and 102±5.1% when PV ranged between 0.38 and 58.8 meq/kg. The CV in the analyses of soybean oil (PV=3.25 meq/kg), cod liver oil (PV=6.71 meq/kg), rapeseed oil (PV=12.3 meq/kg), and sardine oil (PV=63.8 meq/kg) were 4.31, 5.66, 8.27, and 11.2%, respectively, demonstrating sufficient reproducibility of the FIA system for the determination of lipid hydroperoxides. The squared correlation (r ²) between the FIA system and the official AOCS iodometric titration method in a linear regression analysis was estimated at 0.9976 within the range of 0.35−77.8 meq/kg of PV (n=42). Thus, the FIA system provided satisfactory detection limits, recovery, and reproducibility. The FIA system was further applied to evaluate changes in the total amounts of lipid hydroperoxides in fish muscle stored on ice.     

Oxidative and flavor stabilities of soybean oils with low-and ultra-low-linolenic acid composition

The effects of linolenic acid (18∶3) concentration, combined with TBHQ addition, temperature, and storage time, on the oxidative and flavor stabilities of soybean oils (SBO) were evaluated. During storage under fluorescent light at both 21 and 32°C, the SBO with ultra-low-18∶3 concentration (1.0%, ULSBO) generally had greater oxidative stability than did SBO with low-18∶3 concentration (2.2%, LLSBO). The ULSBO had about half the p-anisidine value of LLSBO throughout storage. Although the ULSBO initially had significantly greater PV and poorer (lower) sensory scores for overall flavor quality than did LLSBO, significant differences disappeared with storage. The ULSBO had a lower content of polar compounds and greater oil stability indices than did LLSBO when TBHQ was present. All oils were more oxidatively stable with TBHQ addition, but the TBHQ addition did not result in improved flavor stability early in storage. In all tests, oils stored at 32°C were less stable than oils stored at 21°C. The TBHQ had a better antioxidant capacity when the 18∶3 concentration was lower. The retardation effect of TBHQ on lipid oxidation and the improved stability of ULSBO over LLSBO were more easily detected when the storage temperature was higher.     

Influence of Different Moisture Contents on the Stability of Tocochromanols in Bulk Oils at 25 °C Storage

The stabilities of tocochromanols including α‐tocopherol, α‐tocotrienol, γ‐tocopherol, γ‐tocotrienol, and δ‐tocotrienol in grape seed oil, palm oil, or stripped soybean oil with added tocotrienol mixtures (SOTT) were determined under relative humidity (RH) 0, 32, 75, and 93% at 25 °C for 8 months of storage. Stability of tocochromanols was significantly influenced by the presence of moisture and other tocochromanols. Tocochromanol stability in grape seed oil was high at RH 75%, whereas palm oil had significantly lower tocochromanol content at RH 75% compared to those under other RH (p < 0.05). Tocochromanol stability in SOTT was high at RH 0%. δ‐Tocotrienol had the highest stability followed by α‐tocotrienol, γ‐tocotrienol, and α‐tocopherol in SOTT. Moisture content in palm oil was the lowest while that in SOTT was the highest at the same RH. Oxidative stability of palm oil was the highest followed by grape seed oil and SOTT based on conjugated dienoic acid content and p‐anisidine values. Moisture in oils affects the stability of tocochromanols and oxidative stability in vegetable oils.     

The Effect of Natural and Synthetic Antioxidants on the Oxidative Stability of Biodiesel

A significant problem associated with the commercial acceptance of biodiesel is poor oxidative stability. This study investigates the effectiveness of various natural and synthetic antioxidants [α-tocopherol (α-T), butylated hydroxyanisole (BHA), butyl-4-methylphenol (BHT), tert-butylhydroquinone (TBHQ), 2, 5-di-tert-butyl-hydroquinone (DTBHQ), ionol BF200 (IB), propylgallate (PG), and pyrogallol (PY)] to improve the oxidative stability of soybean oil (SBO-), cottonseed oil (CSO-), poultry fat (PF-), and yellow grease (YG-) based biodiesel at the varying concentrations between 250 and 1,000 ppm. Results indicate that different types of biodiesel have different natural levels of oxidative stability, indicating that natural antioxidants play a significant role in determining oxidative stability. Moreover, PG, PY, TBHQ, BHA, BHT, DTBHQ, and IB can enhance the oxidative stability for these different types of biodiesel. Antioxidant activity increased with increasing concentration. The induction period of SBO-, CSO-, YG-, and distilled SBO-based biodiesel could be improved significantly with PY, PG and TBHQ, while PY, BHA, and BHT show the best results for PF-based biodiesel. This indicates that the effect of each antioxidant on biodiesel differs depending on different feedstock. Moreover, the effect of antioxidants on B20 and B100 was similar; suggesting that improving the oxidative stability of biodiesel can effectively increase that of biodiesel blends. The oxidative stability of untreated SBO-based biodiesel decreased with the increasing indoor and outdoor storage time, while the induction period values with adding TBHQ to SBO-based biodiesel remained constant for up to 9 months.     

Oxidative Rancidity in Refined Sunflower Oil with Respect to Storage Variation

Refined sunflower oil was stored in brown and colorless glass bottles at ambient temperature (18–32°C) and 37°C to assess the effect of light, heat and air on the stability fo the oil and to record the progress of oxidative rancidity especially the secondary stages with respect to storage variation and time. Oil sample stored in brown color bottle was found to be superior (FFA 0.15 to 0.53; PV 0.5 to 80; HV 3 to 12; oxirane oxygen 0.2 to 2.3) over oil stored in colorless bottle (FFA 0.15 to 0.60; PV 0.5 to 91; HV 3 to 8; oxirane oxygen 0.1 to 2.8) at ambient temperature. Samples stored at 37°C deteriorated very fast. Silver nitrate test, oxidised fatty acid formation, urea adduct formation, picric acid-TLC test, Kreis test, DNP-TLC test, DNP-precipitation test have been devised to detect and follow oxidative rancidity. These tests worked well even at the lower levels of oxycompounds. No conjugation was detected in any of the oil.     

Lipid oxidation in potato chips

Qualitative and quantitative analyses of volatile compounds in fresh and aged potato chips and unused fresh and aged frying oils showed that oxidation of oils was mainly responsible for volatile compound changes in potato chips during storage. The lipid oxidation of potato chips was determined by measuring the peroxide value of potato chips and the amount of volatile compounds and oxygen content in the headspace of potato chip bottles by gas chromatography. The correlation coefficients between volatile compounds and oxygen content, volatile compounds and peroxide value, and peroxide values and oxygen content were -0.93, 0.95 and -0.93, respectively. These high correlation coefficients indicated that volatile compound changes in potato chips during storage were mainly due to the oxidation of oil. The lipid oxidation of potato chips during storage can be studied by measuring oxygen content and the amount of volatile flavor compounds in the headspace. The potato chips produced in oil containing an antioxidant tertiarybutyl hydroquinone (TBHQ) had better oxidation stability than the chips fried in oil without TBHQ.