Evaluation of Oxygen-Limitation on Lipid Oxidation and Moisture Content in Corn Oil at Elevated Temperature

The role of oxygen-limitation on lipid oxidation and moisture content were tested in corn oil heated to 60, 100, and 140 °C. The degree of oxidation was determined by analyzing headspace oxygen content, conjugated dienoic acids (CDA), and p-anisidine value (p-AV). The moisture content in bulk oil was analyzed by the Karl Fischer method. Oxygen-limited samples heated to 100 and 140 °C had significantly more lipid oxidation than oxygen-unlimited samples at early timepoints (p < 0.05). After this period, the oxygen-unlimited samples had more lipid oxidation based on CDA and p-AV assays. During those initial periods, oxygen-limited samples had significantly higher moisture content than oxygen-unlimited samples (p < 0.05), which implies that moisture content in oils plays an important role in the rate of lipid oxidation. The increased moisture content in bulk oil under oxygen-limited conditions is due to headspace moisture rather than moisture inside the oil. However, the effects of oxygen-limitation on lipid oxidation were less clear at 60 °C than at 100 or 140 °C.     

Oxidative Stability in Bulk Oil Containing Carbohydrates Such as Glucose,Sucrose, Maltose,Mannitol, and Starch

Effects of carbohydrates including glucose, sucrose, maltose, mannitol, and starch on the oxidative stability of corn oils were evaluated at 40 °C for 51 days, at 100 °C for 17 h, and at 180 °C for 90 min. The degree of oxidation was determined by headspace oxygen content, conjugated dienoic acid (CDA) assay, or p-anisidine value (p-AV) and the moisture content of the oils was analyzed. Starch showed pro-oxidant properties whereas mannitol acted as an antioxidant at all tested temperatures. However, glucose, sucrose, and maltose showed different properties depending on the temperature and type of assays. At 40 °C, glucose, sucrose, and maltose showed antioxidant properties in headspace oxygen and CDA assays. There were no significant differences in CDA between samples at 100 and 180 °C. p-AV in samples containing glucose were significantly higher than those in controls at 180 °C, which may be due to the formation of volatiles from caramelization rather than lipid oxidation. Moisture content of oils containing glucose and starch was significantly higher than that of controls, whereas that of oils containing mannitol was lower than in the control (p < 0.05). Changes in moisture content of oils may be due to the migration of moisture from added carbohydrates into the oils.     

Oxidative Stability and Volatile Formations in Linoleic Acid-D<Subscript>2</Subscript>O Models in the Presence of Deuteron or Electron Donors

Effects of deuteron (D⁺) and electron donors on the oxidative stability in linoleic acid–water model systems were evaluated by analyzing headspace oxygen content and headspace volatiles. Acetic acid‐d and tetrakis(dimethylamino)ethylene (TDAE) were selected as a deuteron and an electron donor, respectively. Samples containing acetic acid‐d had significantly lower headspace oxygen content than controls while those containing TDAE had significantly higher headspace oxygen content (p < 0.05). Combination of acetic acid‐d and TDAE accelerated the consumption of headspace oxygen. Volatiles including t‐2‐heptenal, 2‐octenal, or 2,4‐octadienal had higher mass to charge ratio (m/z) of (molecular weight +1)/molecular weight in samples with deuterium oxide than in samples with deuterium free water. However, no significant difference was observed in the m/z ratio of (molecular weight +1)/molecular weight of those volatiles among samples with or without deuteron or electron donors. Also, lipid hydroperoxides with deuterium, were not found in samples containing deuterium oxide and acetic acid‐d. Therefore, added acetic acid‐d may not be involved on the formation of lipid hydroperoxides and volatiles directly.     

Stability of Tocopherol Homologs in Bulk Oils at 60°C Oxidation and Chlorophyll Photosensitization by the Action of Moisture

The effects of deuterium oxide (D₂O) on the stability of tocopherol homologs were evaluated in corn oil stored at 60°C or in the process of chlorophyll photosensitization. The degree of oxidation, changes in moisture, and the levels of tocopherol homologs were analyzed. The moisture content in corn oil incubated with deuterium-free water (H₂O) was significantly (P < 0.05) higher than that in corn oil incubated with D₂O. The presence of D₂O accelerated the rate of lipid oxidation in corn oil, irrespective of whether it has been oxidized at 60°C or has been photosensitized by chlorophyll. After exposure to either of the oxidative stresses, the stability of β + γ-tocopherols present in corn oil was enhanced in the presence of D₂O compared to corn oil incubated in the presence of H₂O, or control corn oil without the addition of moisture. However, the stability of α-tocopherol in corn oil incubated with D₂O was significantly lower after oxidation at 60°C compared to the other conditions (P < 0.05), whereas it was significantly higher than under the other conditions after chlorophyll photosensitization (P < 0.05). The moisture and type of oxidative stress, therefore, play important roles in the stability of tocopherol homologs in bulk oils.     

Analysis of vegetable oil volatiles by multiple headspace extraction

Quantitative determination of the volatiles produced from oxidized vegetable oils is an important indicator of oil quality. Five vegetable oils, low-erucic acid rapeseed, corn, soybean, sunflower and high oleic sunflower, were stored at 60°C for four and eight days to yield oils with several levels of oxidation. Peroxide values of the fresh oils ranged from 0.6 to 1.8 while those of the oxidized oils were from 1.6 to 42. Volatile analysis by the multiple headspace extraction (MHE) technique, which includes a pressure and time controlled injection onto the gas chromatography (GC) column (a chemically bonded capillary column), was compared with that obtained by static headspace gas chromatography (SHS-GC). Several volatile compounds indicative of the oxidation of polyunsaturated fatty acids from the vegetable oils were identified and measured by MHE; pure compounds of twelve major volatiles also were measured by MHE, and peak area was determined. Multiple extractions of the oil headspace provided a more reproducible measure of volatile compounds than was obtained by SHS-GC. Concentration of all volatiles increased with increased oxidation as measured by peroxide value of the oil. Presented at the Annual American Oil Chemists' Society Meeting, May 8–12, 1988, Phoenix, AZ.     

Evaluating Electron Paramagnetic Resonance (EPR) to Measure Lipid Oxidation Lag Phase for Shelf-Life Determination of Oils

Lipid oxidation is one of the major causes of oil deterioration causing off-flavors and consumer rejection. Fast, easy, and dependable assays for predicting lipid oxidation rates in foods are important for shelf-life prediction. In this study, an electron paramagnetic resonance (EPR) spin-trapping technique with N-tert-butyl-α-phenylnitrone (PBN) was tested to determine the lag phase of lipid oxidation in stripped soybean oil (SSO), SSO with added α-tocopherol, and commercial soybean, canola and corn oils. EPR intensity of spin-trapped products from SSO correlated well with lipid hydroperoxides formation for samples stored at 37 and 55 °C respectively. When the antioxidant α-tocopherol was added, the EPR signal intensity of oil samples increased—indicating sample deterioration—after 50–65% of α-tocopherol was consumed. When using the EPR method with commercial soybean, canola or corn oil stored at 55 °C, there was a poor relationship between EPR intensity and lipid hydroperoxides lag phases. However, a linear correlation was found between EPR signal intensity and hexanal formation. For example, EPR signal intensity lag phases were 5, 13 and 27 days for soybean, canola and corn oils, respectively which was similar to the hexanal lag phases of 5, 13 and 25 days for the same oils. The EPR spin-trapping assay method has several advantages over headspace hexanal measurements, especially with regard to easier sample handling and shorter analysis times.     

Effects of processing on oxidative stability of sesame oil extracted from intact and dehulled seeds

Oxidative stability of oils extracted from intact and dehulled sesame seeds was determined by monitoring changes in fatty acid composition, iodine value (IV), peroxide value (PV), conjugated diene (CD), para-anisidine value (p-AV), and 2-thiobarbituric acid (TBA) value and by nuclear magnetic resonance spectroscopy after storage under Schaal oven conditions at 65°C for up to 35 d. The oils from coated seeds were more stable, as reflected in PV, CD, p-AV and TBA values, than those extracted from dehulled seeds after roasting at 200°C, steaming at 100°C, roasting at 200°C plus steaming, or microwaving at 2450 MHz, except for TBA values of oil from microwaved seeds. After 35 d of storage at 65°C, the CD, p-AV, and TBA values of extracted oil from dehulled microwaved seeds were 17.72, 10.20, and 1.22, respectively, while those of their coated counterparts were significantly (P<0.05) different at 14.20, 16.47, and 1.26, respectively. Few significant changes were evident in the fatty acid composition of oil obtained from either coated and dehulled seeds subjected to different treatments. Nuclear magnetic resonance analyses found that R_ao (aliphatic to olefinic protons) and R_ad (aliphatic to diallylmethylene protons) ratios increased steadily over the entire storage period, which indicated progressive oxidation of unsaturated fatty acids.     

Chemical Changes of Canola Oil During Frying Under Atmospheric Condition and Combination of Nitrogen and Carbon Dioxide Gases in the Presence of Air

The effects of different frying methods; frying under atmospheric condition and frying in the presence of different ratios of nitrogen and carbon dioxide gases; were investigated on chemical changes of canola oil. The tests were conducted four times per day during four consecutive days. The chemical changes of oil samples were determined by analyzing peroxide value (PV), p-anisidine value (p-AV), totox value (TV) and acid value (AV). Irrespective of the test methods, PV increase was observed on the first day followed by significant (p < 0.05) reduction in the subsequent days. On the first day, the highest p-AV and TV was observed in oil fried under atmospheric condition and the lowest p-AV and TV for those fried under gases. However, from the second day, the p-AV and TV in frying under different ratios of nitrogen and carbon dioxide gases were significantly (p < 0.05) higher than the frying under atmospheric condition. Additionally, hydrolysis and oxidation of oil during frying resulted in continuous AV increase that among them atmospheric frying had the highest AV. In conclusion, atmospheric frying accelerates the rate of oil deterioration and application of nitrogen and carbon dioxide gases in the fryer could reduce the rate of oil disintegration.     

Chemical and sensory properties of gas-purged,minimum-refined,extruded-expelled soybean oil

Developing low-cost oil refining methods is critical to business that use low-cost extrusion-expelling (E-E) to crush soybeans so they can capture the full value-added potential by marketing finished oils. Normal commodity (CO) and high-oleic (HO) E-E soybean oils were minimum-refined, gas-purged, and evaluated in frying applications. Degummed commodity oil (DCO) and minimum-refined (degummed and deacidified by Magnesol® adsorption) CO and HO oils were gas-purged with N₂ for 1 h at 150°C. For DCO, gas purging did not affect PV, oxidative stability index (OSI), FFA, color, and total tocopherol content, but p-anisidine value (AV) increased. For CO, the minimum-refined, gas-purged oil did not differ from degummed, gas-purged oil in terms of p-AV, OSI, tocopherol content, and color. PV and FFA were lower in minimum-refined, gas-purged oil. Minimum-refined, gas-purged HO had much higher OSI, tocopherol, and FFA levels than did minimum-refined, gas-purged CO. The oils were used to fry bread cubes at 185°C. Fried bread cubes were stored under various conditions and evaluated for flavor attributes. These oils were different in toasty/nutty, beany/grassy, and oxidized flavors, as well as overall flavor intensity and desirability. Minimum-refined, gas-purged oils produced fried bread cubes having initial flavor profiles similar to those fried in commercial oil; however, when fresh oils were used they were less stable to oxidation. Longer heating times of the minimum-refined, gas-purged oils produced bread cubes with better oxidative stabilities than those produced with commercial oil.     

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.     

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.     

Study of deuterium transfer,isotope effects and structural distributions of products of reactions of coals in deuterated tetralin using 2H and 13C FT-n.m.r. and solid-state 13C FT-n.m.r.

Four coals (bituminous, subbituminous, lignite and canneloid) are treated with tetralin-1,1,4,4,-d₄ or — 1,1 -d₂ or mixtures of tetralin-d₄ and tetralin-d₀ at 427 °C in degassed Pyrex vessels for times between 5 and 60 min. Deuterium depletion and scrambling in solvent-derived products are determined for degassed and air-saturated experiments. Deuterium distributions are determined for preasphaltene and asphaltene fraction (A + P) and light oils (LTO) by ²H FT-n.m.r., and solid coals and products are characterized by ¹³C CP/MAS and ¹³C FT-n.m.r. Illinois No. 6, PSOC 837 and PSOC 531 coals selectively consume tetralin-d₀ over tetralin-d₄ and exhibit isotope effects in the scrambling of deuterium from 1 — to 2-positions. Intersite deuterium scrambling in recovered tetralin is negligible at 10 min or shorter reaction times, but deuterium depletion from tetralin is significant at all reaction times. Deuterium is detected predominantly at benzylic-type and secondary aliphatic positions and to a lesser extent at aromatic positions of A + P and LTO fractions at reaction times of 5 min. The presence of air significantly enhances both the extent of deuterium scrambling and the rearrangement of tetralin to 1-methylindan at reaction times of 30–60 min.     

Evaluation of oxidative stability of canola oils by headspace analysis

Lipid oxidation is a major factor affecting flavor quality and shelf life of vegetable oils. Oxidative stability is therefore an important criterion by which oils are judged for usefulness in various food applications. In this study a method based on headspace analysis was developed to evaluate relative oxidative stability of canola oils. The method does not require the use of chemicals, involves minimal sample preparation, and can be performed on a relatively small sample size in comparison with traditional wet chemical methods. Canola oils freshly extracted in the laboratory from different seed samples were subjected to accelerated oxidation and analyzed for PV by standard methods and headspace volatiles by solid phase microextraction/GC-MS. Forward stepwise regression analysis of the data revealed a relationship between PV and headspace concentration of the volatile lipid oxidation products hexanal and trans,trans-2,4-heptadienal. The PV calculated using this formula correlated (R ²=0.73) with those measured by conventional methods. Presented in part at the 96th Annual Meeting of the AOCS, 1–4 May 2005, Salt Lake City, UT.     

Effects of Moisture and Amphiphilic Compounds on the Oxidative Stability of Microwave-Treated Corn Oil

Effects of moisture and amphiphilic compounds, including oleic acid, lecithin, and monoacylglycerols (MAGs), on the oxidative stability are evaluated in microwave-treated corn oil. Moreover, the physical properties including critical micelle concentration (CMC) and moisture content are determined in oils treated by microwave irradiation. The CMC of lecithin and moisture content of oils decreases remarkably, whereas the temperature of the oil increases rapidly with microwave irradiation. The addition of lecithin results in increased moisture content significantly in the edible oils, whereas oleic acid and MAGs do not exhibit these effects. Primary oxidation products in all the oil samples increase, despite the type of amphiphilic compounds used. Corn oil containing oleic acid and samples with lecithin exhibits lower and higher p-anisidine values (p-AV), respectively. Remarkably high moisture content in corn oils containing lecithin may contribute to the formation of volatile compounds and high p-AV. Collectively, moisture and amphiphilic compounds affect the degree of lipid oxidation in microwave-irradiated bulk oils. Practical application: A microwave oven is an irreplaceable home appliance and is widely used in households nowadays. Effects of amphiphilic compounds and moisture on the oxidative stability are evaluated and it is found that the amphiphilic compounds in lipids affect heat transfer and oxidative stability of oils. The results of this study can provide fundamental insights into lipid oxidation in edible oils, and can provide a direction to the food industry with respect to the development of more efficient and safe methods for the preparation of microwavable foods.     

AOCS collaborative study on sensory and volatile compound analyses of vegetable oils

An AOCS collaborative study was conducted to determine the effectiveness of sensory analysis and gas chromatographic analyses of volatile compounds in measuring vegetable oils for levels of oxidation that ranged from none to high. Sixteen laboratories from industry, government, and academia in Canada and the United States participated in the study to evaluate the flavor quality and oxidative stability of aged soybean, corn, sunflower, and canola (low-erucic acid rapeseed) oils. Analytical methods included sensory analyses with both flavor intensity and flavor quality scales and gas-chromatographic volatiles by direct injection, static headspace, and dynamic headspace (purge and trap) techniques. Sensory and volatile compound data were used to rank each of the oils at four levels of oxidation—none, low, moderate, and high. For soybean, canola, and sunflower oils, 85–90% of laboratories correctly ranked the oils by either analysis. For corn oil, only 60% of the laboratories ranked the samples according to the correct levels of oxidation by either analysis. Variance component estimates for flavor scores showed that the variation between sensory panelists within laboratories was lowest for the unaged oils. As storage time increased, the variance also increased, indicating that differences among panelists were greater for more highly oxidized oils. Between-laboratory variance of sensory panel scores was significantly lower than within-laboratory variance.     

Improving the oxidative stability of polyunsaturated vegetable oils by blending with high-oleic sunflower oil

Mixing different proportions of high-oleic sunflower oil (HOSO) with polyunsaturated vegetable oils provides a simple method to prepare more stable edible oils with a wide range of desired fatty acid composition. Oxidative stability of soybean, canola and corn oils, blended with different proportions of HOSO to lower the respective levels of linolenate and linoleate, was evaluated at 60°C. Oxidation was determined by two methods: peroxide value and volatiles (hexanal and propanal) by static headspace capillary gas chromatography. Determination of hexanal and propanal in mixtures of vegetable oils provided a sensitive index of linoleate and linolenate oxidation, respectively. Our evaluations demonstrated that all-cis oil compositions of improved oxidative stability can be formulated by blening soybean, canola and corn oils with different proportions of HOSO. On the basis of peroxide values, a partially hydrogenated soybean oil containing 4.5% linolenate was more stable than the mixture of soybean oil and HOSO containing 4.5% linolenate. However, on the basis of volatile analysis, mixtures of soybean and HOSO containing 2.0 and 4.5% linolenate were equivalent or better in oxidative stability than the hydrogenated soybean oil. Mixtures of canola oil and HOSO containing 1 and 2% linolenate had the same or better oxidative stability than did the hydrogenated canola oil containing 1% linolenate. These studies suggest that we can obviate catalytic hydrogenation of linolenate-containing vegetable oils by blending with HOSO. Presented at the AOCS/JOCS joint meeting, Anaheim, CA, April 25–29, 1993.     

Clarifications of the Carbonyl and Water Absorptions in Fourier Transform Near Infrared Spectra from Extra Virgin Olive Oil

The Fourier transform near infrared (FT-NIR) spectrum of extra virgin olive oils (EVOO) shows two minor carbonyl absorptions at 5280 and 5180 cm^–1 that has been used to assess their authenticity. To establish components absorbing at 5280 cm^–1, volatile aldehydes and ketones, triacylglycerol (TAG), diacylglycerols (DAG), free fatty acids (FFA), phenolics, and water are investigated and sometimes added to refined olive oil (ROO). Except TAG, the remaining carbonyls contribute to 5280 cm^–1 by broadening peak. Water absorption is demonstrated by its removal using Na₂SO₄ or deuterium oxide addition; FT-NIR spectral changes are reconstituted by water addition. Water absorption depends on being free or complexed with polar compounds in oil. The size of absorption is not related to abundance, but on unique absorption specificity of components; water shows the strongest absorption. Heat removes water and volatiles, leaving behind DAG, FFA, and phenolics, and makes it possible to differentiate absorption of water, volatile and non-volatile carbonyls. Cloudy olive oils are analyzed using FT-NIR methodology after warming for 3 min at 50 °C. FT-NIR index values are replaced by a new calibration model based on correlating gravimetric mass loss of water plus volatiles with spectral changes. The FT-NIR methodology is expanded to include EVOOs with 15.5% to 21% linoleic acid. Practical Applications: Testing for authenticity of EVOOs remains a challenge because adulterations continue to be a problem due to economic gains. Spectroscopy methods, specifically FT-NIR, are much preferred to targeted chemical methods because they measure all constituents in products and are non-destructive and fast. The current universal FT-NIR methodology assesses 13 different parameters: five major FAs, and the DAG and FFA contents. The FT-NIR index value measuring the content of moisture plus volatiles is now replaced by a gravimetric determination. The methodology identifies four major types of adulterants, high in oleic acid, linoleic acid, palm olein or ROO. The composition of olive oils makes it necessary to develop five oil-specific groups, but cloudy samples still need to be clarified by slight warming before measuring. The value of this universal FT-NIR methodology will increase after being adopted by commercial and in regulatory settings.     

Changes in virgin olive oil characteristics during different storage conditions

In this study we have examined the effect of olive oil storage outdoors on a comprehensive series of quality measures. The conditions used were at the extreme of those encountered during the production of bottle oil. Filtered and unfiltered oils were compared as was the influence of inert gas (nitrogen) in the headspace. Increases in K₂₃₂, K₂₇₀ and peroxides over time were very much reduced by inert headspace gas, which also reduced losses of total phenols and oxidative stability. Headspace nitrogen also reduced the rise in unconjugated phenolics as secoiridoid derivatives declined and minimised losses in polyunsaturated fatty acids. The pattern of volatile compounds detected in olive oils stored indoors or outdoors showed subtle differences. Moreover, when stored with air exposure the levels of some negative sensory components such as penten‐3‐ol and hexanal increased while other positives, like trans‐2‐hexenal were reduced. These changes would be expected to reduce quality. Finally, Panel tests were used. All oils lost perceived quality on storage and this was accelerated outdoors while headspace nitrogen slowed the deterioration significantly. Our data show that storage outdoors for 4 months in winter does not reduce olive oil quality significantly and that an inert gas in the headspace is beneficial. Practical applications : The storage of olive oil for bottling is carried out under a variety of conditions. Here we assess the effects of storage outdoors for oils from the main Greek cultivar (Koroneiki) of olive. Detailed analyses of quality (standard measures, different phenolics, lipids and volatiles) as well as Panel tests were used for evaluation. Our data show that, although storage outdoors causes deterioration quicker than indoors, changes are not serious up to 4 months. Furthermore, the use of an inert headspace gas significantly preserved quality both indoors and outdoors. Thus we would strongly recommend the latter measure to producers.     

Comparative Fingerprint Changes of Toxic Volatiles in Low PUFA Vegetable Oils Under Deep-Frying

The volatile fraction of three vegetable oils recommended for deep‐frying due to their high MUFA:PUFA ratios, namely extra‐virgin olive oil, peanut oil and canola oil, was compared before and after frying potatoes, with a particular focus on toxic volatiles. For the purpose, a headspace solid‐phase‐micro extraction technique coupled with gas chromatography and mass spectrometry was optimized, with semi‐quantification achieved using two internal standards. Significant qualitative and quantitative differences were observed, both before and after frying. From a total of 51 compounds, aldehydes were the main group formed after deep‐frying, their nature and abundance being highly associated with the initial fatty acid composition, particularly linoleic acid (r² = ?0.999, p ≤ 0.001). Globally, extra‐virgin olive oil revealed fewer formations of unsaturated aldehydes, including toxic ones, and correlated with lower amounts of degradation indicators, as polar compounds (r² = 0.998, p ≤ 0.001) and p‐anisidine value (r² = 0.991, p ≤ 0.001). Despite the similarities in total unsaturation degree between canola and peanut oils, the former presented lower amount of volatiles, including E,E‐2,4‐decadienal and acrolein, the more toxic ones. These results highlight for the pertinence of volatile analyses to evaluate and compare oil degradation under thermal and oxidative stress, while complementing other degradation indicators. Additionally, the optimized methodology allows a direct comparison of different oil matrices, supporting further developments into more general methods for volatiles quantification, enabling more efficient comparison of results between research teams.     

Antioxidant Activity of Raisin Extracts in Bulk Oil,Oil in Water Emulsion,and Sunflower Butter Model Systems

The antioxidant activities of the raisin extract (RE) in stripped corn oil, stripped corn oil emulsions, and sunflower butter stored at 60 °C for up to 15 days was evaluated. Peroxide values and hexanal content were measured on a half day, 2 or 3 day basis for the emulsion, sunflower butter, and bulk oil, respectively. The RE had the best antioxidant activity in the bulk oil system. Statistical contrasts indicated the oxidation of bulk corn oil treated with RE was significantly (p < 0.001 and p = 0.044) lower than bulk oil and bulk oil treated with tertiary-butylhydroquinone (TBHQ), respectively. No differences (p = 0.15) in hexanal concentrations were observed in stored bulk oils treated with RE and TBHQ. However, both these materials inhibited hexanal formation better (p < 0.001) when compared to the control corn oil. In contrast, 200 μg/g TBHQ had better (p = 0.0004) antioxidant activity than 3,000 μg/g RE in the oil in water(o/w) emulsion. No significant differences (p = 0.1637) in hexanal formation were observed in the emulsions treated with RE and TBHQ. However, the data indicated that the RE treated emulsion did undergo more secondary oxidation than the emulsion treated with TBHQ beyond 110 h. The 3,000 μg/g RE had antioxidant activity in sunflower butter, but was less effective than the 200 μg/g TBHQ and a lower RE concentration (200 μg/g). The observations supported the hypothesis that RE has antioxidant activity in the multiple model systems.