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.     

Capabilities of different cooking oils in prevention of cholesterol oxidation during heating

The potential of various cooking oils to prevent cholesterol degradation and/or oxidation, as measured by the production of 7-ketocholesterol during heating at different temperatures, was studied using a cholesterol model system. In the control group (without cooking oil), cholesterol was relatively stable, and 73% of its initial concentration was present after 30 min of heating at 125°C. Less than 30 and 10% of cholesterol remained at 150 and 175°C after 30 min, respectively, and 10% at 200°C after 10 min. In the treatment group, cholesterol mixed with corn, canola, soybean, or olive oil had significantly improved thermal stability. More than 60 and 40% of cholesterol remained at 150 and 175°C after 30 min, respectively. In the control group, 7-ketocholesterol was produced when samples were heated above 150°C, and levels increased consistently during 30 min of heating. At 175 or 200°C, the level of 7-ketocholesterol did not increase further after reaching the highest level after 10 min of heating. 7-Ketocholesterol is not stable above 175°C, and its degradation rate could be much faster than its production at 200°C. 7-Ketocholesterol was not found in samples of cholesterol mixed with corn oil or laboratory-prepared soybean and rice bran oils until the heating temperature was raised to 175°C for 20 min. The levels of 7-ketocholesterol in those treatment groups were greater than that in the control group at 175°C for 30 min. These oils may increase the thermal stability of 7-ketocholesterol and retard its degradation rate.     

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.     

Supercritical fluid extraction of vegetable oil seeds

The extraction of oil from canola seeds using supercritical carbon dioxide was investigated. The basic equations which govern the oil extraction from a bed of seeds were derived from first principles. The equations can be solved by standard numerical techniques using experimentally determined parameters for the concentration of oil in the solvent in equilibrium with seeds having a known oil content. Preliminary extraction rate data and equilibrium data are given for crushed canola seed during extraction using supercritical carbon dioxide at select temperatures and pressures. The research is directed at obtaining the basic information required for the design of continuous countercurrent extractors.     

Effects of thermal oxidation on the constitution of butterfat,butterfat fractions and certain vegetable oils

To evaluate the thermal oxidative behavior of butterfat in comparison to selected vegetable oils, samples of winter and summer butterfat, liquid and solid butterfat fractions, and selected vegetable oils were heated at 185 C in the presence of air (30 ml/min) for 8 and 16 hr. The resultant heated fats and oils, as well as the methyl esters of their fatty acids, were examined by gel permeation chromatography. The results indicated that butterfat is much more stable to thermal oxidation than canola, sunflower and soybean oils. This was evidenced by a substantially higher content of both dimeric and higher oligomeric triglycerides in the vegetable oils than in any of the butterfat samples after both 8 and 16 hr of heating. The corn oil also exhibited a high degree of stability to thermal oxidation after 8 hr of heating. The 16 hr corn oil data, however, was less certain due to the presence of a very viscous and dark colored material which could not be removed from the oxidation flask; this was believed to contain highly polymerized oil and was not observed with any of the other samples. There were some differences in the inter- and intramolecular polymerization of the butterfat fractions compared with each other and with whole butterfat. With the winter butterfat samples, after 8 hr of thermal oxidation, both the solid and liquid butterfat fractions exhibited more stability toward intermolecular polymerization than did the whole butterfat. After 16 hr of heating the ratio of trimeric and higher oligomeric triglycerides to dimeric triglycerides increased with increasing degree of unsaturation of the butterfat and with increased time of heating. Similar trends were observed with regard to the degree of intramolecular polymerization. Presented at the AOCS meeting in Philadelphia in May 1985.     

Utilization of green seed canola oil for biodiesel production

Increasing percentage of green canola seed every year is a serious problem for canola growers. Chlorophyll content of this oil is very high, which makes it more susceptible to photo‐oxidation and ultimately the oxidation stability of the oil is very reduced. Hence green seed canola oil is underutilized for edible purposes. The present work is an attempt to produce high‐quality biodiesel from green seed canola oil and methanol, ethanol and various mixtures of methanol and ethanol using KOH as a catalyst. A mixture of alcohols improved the rate of reaction. After transesterification of green seed canola oil using KOH, the chlorophyll content of the oil was decreased substantially (from 22.1 ppm to 10.3 ppm). Characteristics of the esters prepared from green seed canola oil were well within the limits of ASTM standards. Lubricity of the green seed oil esters was excellent (20% decrease in wear scar area) when added at 1 vol% to the base fuel. Oxidation stability is crucial for long‐term storage of the fuel. Oxidation stability index (OSI) of green seed esters was 4.9 h at 110 °C, which is much less than the European Standard (6 h at 100 °C). The low oxidation stability of green seed esters is attributed to its higher chlorophyll (10.3 ppm) content. An attempt was also made to reduce the chlorophyll content of the oil before transesterification using activated carbon treatment, and it was observed that chlorophyll content was reduced from 22.1 to 2.2 ppm. Copyright © 2006 Society of Chemical Industry     

Evolution of thermograph parameters during the oxidation of extra virgin olive oil

The modulated differential scanning calorimetry (M‐DSC) was used as a rapid and effective method to characterize the olive oil at different levels of oxidation. Thermograph parameters have been related to oxidative degradation of the triglycerides. In this study, their relation to the characteristic off‐flavor compounds, correlated to the oxidative degradation of the oil, was also investigated. Extra virgin olive oil samples were subjected to the following oxidation treatments: a) purged with air using glass washing bottles at two flow rate values, b) heated in a conventional oven at two area/oil mass ratios, and c) heated in a microwave oven also at two area/oil mass ratios. Samples were withdrawn and analyzed at predetermined intervals. Flavor and off‐flavor compounds were isolated using a dynamic thermal stripping apparatus and transferred into a gas chromatograph by using a thermal desorption unit. All oil samples were analyzed by M‐DSC during cooling from 25 °C to ?60 °C at 7 °C/min, and heating back to 40 °C at 10 °C/min. High correlation values were obtained between various M‐DSC thermograph parameters and certain volatile compounds. Results showed that M‐DSC could be used as a simple method to indicate compositional changes in olive oil during oxidation.     

Acceleration of the thermoxidation of oil by heme iron

Transition metals, including iron, occur naturally at significant concentrations in meat. Iron can be extracted from the food into the oil and potentially decrease the stability of the oil during frying by accelerating thermoxidation. The objective was to examine the thermoxidative stability of partially hydrogenated soybean oil after addition of heme iron. Heme iron (2.7 ppm) was added to the oil, and then oil samples were heated continuously at 160, 180, or 200°C for 72 h. Oil samples were removed for analysis every 12 h. The acid values, color, food oil sensor readings, and TAG polymer content of the heated oil samples were compared with oil samples containing no added iron that were held at the same temperatures. Generally, each oxidative index increased with (i) an increase in temperature, (ii) an increase in heating time, and/or (iii) the addition of iron. Generally, the extent of oxidation was greater for samples heated at 200°C than for oil samples heated at 160 or 180°C. The oil samples heated at 200°C reached the target polymer content of 20% after 27 h of heating. If heme iron accumulates in the oil, it will increase the rate of oxidation and thermal degradation and reduce the frying life of the oil.     

Stability of low linolenic acid canola oil to frying temperatures

The effect of heating on the oxidation of low (1.6%) linolenic acid canola oil (C18∶3) at frying temperature (185 ±5°C) under nitrogen and air was examined and then compared to a laboratory deodorized (9.0%, C18∶3) and a commercially deodorized (8.5%, C18∶3) canola oil sample. A significantly lower development of oxidation was evident for the low C18:3 canola oil, based on the measurement of peroxide value (PV), thiobarbituric acid (TBA), free fatty acids (FFA), dienals and carbonyls. The greater stability of the low C18:3 canola oil was also reflected by a corresponding improvement in heated room odor intensity scores. Heating under nitrogen (rather than air) not only improved the odors but limited the oxidation in all oils. While the low C18:3 canola oil heated under nitrogen was acceptable in 94% of odor judgments the same oil heated in air was acceptable in only 44%. This suggests that even low levels of C18:3 may contribute to the development of the heated room odor phenomenon.     

Effect of baicalein and acetone extract of Scutellaria baicalensis on canola oil oxidation

There is an increasing interest in natural antioxidants present in traditional Chinese herbal medicines. The present study examined the antioxidant activity of heane, acetone, and methanol extracts, as well as baicalein purified from the dry roots of Scutellaria baicalensis Georgi (common name: Huangqin), in heated canola oil. Oxygen consumption and decreases in linoleic acid linolenic acid content were monitored in canola oil held at 90–93°C. Among the three extracts, the acetone extract was most effective against oxidation of canola oil, followed by the methanol extract of the dry roots. The antioxidant activity of these three extracts correlated well with their content of baicalein, which provided strong protection to canola oil from oxidation. The antioxidant activity of Huangqin acetone extract was dose-dependent. The acetone extract at 100 ppm or above was even more effective than butylated hydroxytoluene at 200 ppm in protecting canola oil from oxidation. The present results suggest that the acetone extract of these roots should be further explored as a potential source of natural antioxidants for use in the processed foods.     

Efficacy of tertiary butylhydroquinone on the storage and heat stability of liquid canola shortening

The sensory (odor and flavor) and physicochemical characteristics of tertiary butylhydroquinone (TBHQ) treated and butylated hydroxyanisole/toluene (BHA/BHT) treated liquid canola shortenings, subjected to accelerated storage (Schaal oven test at 65°C) and deep fat heating (at 185°C), were determined. Data for the Schaal oven test indicate that TBHQ was effective in retarding oxidative rancidity in liquid canola shortenings. However, addition of the commonly used mixture of BHA/BHT to canola shortenings resulted in only a slight decrease in oxidation during schaal oven storage. The results obtained from deep fat heating of canola liquid shortening show that neither TBHQ nor BHA/BHT was effective in enhancing oxidative and thermal stability of this product.     

Enzyme-aidedvs. two-stage processing of canola: Technology,product quality and cost evaluation

The investigation focussed on the use of carbohydrase enzymes to enhance oil extraction during pressing in a laboratory expeller. Enzyme-treated seeds at 6% moisture were pressed in the expeller set at full-press conditions. Control seeds were pressed at wider choke openings but at the same barrel pressures as enzyme-treated samples. Time of pressing and temperature and pressure inside the expeller barrel were used to calculate throughput and energy requirements per unit weight of processed material. Treatment with enzymes improved throughput of the expeller, increased oil flow rate and oil recovery. Material throughput was increased by 30–50%, depending on canola variety. The recovery of the oil was increased from 72% of the seed oil for control samples, to 90–93% for enzyme-treated samples. The average residual oil content in presscakes from enzyme-treated seeds was 7.4%. The oil quality was inferior to cold-pressed control but was much better than has been reported for solvent-extracted oil.     

Antioxidant activity of amino acid sodium and potassium salts in vegetable oils at frying temperatures

Previous studies reported that several amino acids had strong antioxidant activity in vegetable oils under frying conditions. In this study, amino acids were converted to their sodium or potassium salts, and a heating study was conducted with 5.5 mM amino acid salts in soybean oil (SBO) at 180°C. Sodium salts of amino acids including alanine, phenylalanine, and proline and disodium glutamate had significantly stronger antioxidant activity than the corresponding amino acids, and potassium salts had stronger antioxidant activity than sodium salts. Potassium salts of alanine and phenylalanine more effectively retained tocopherols in SBO than the corresponding amino acids during heating. Phenylalanine potassium salt had stronger antioxidant activity than phenylalanine in other vegetable oils including olive, high oleic soybean, canola, avocado, and corn oils. Phenylalanine potassium salt at 5.5 mM more effectively prevented oil oxidation than tert-butyl hydroquinone, a synthetic antioxidant, at its legal concentration limit (0.02%) indicating its feasibility as a new antioxidant for frying.     

Frying stability of soybean and canola oils with modified fatty acid compositions

Pilot plant-processed samples of soybean and canola (lowerucic acid rapeseed) oil with fatty acid compositions modified by mutation breeding and/or hydrogenation were evaluated for frying stability. Linolenic acid contents were 6.2% for standard soybean oil, 3.7% for low-linolenic soybean oil and 0.4% for the hydrogenated low-linolenic soybean oil. The linolenic acid contents were 10.1% for standard canola oil, 1.7% for canola modified by breeding and 0.8% and 0.6% for oils modified by breeding and hydrogenation. All modified oils had significantly (P<0.05) less room odor intensity after initial heating tests at 190°C than the standard oils, as judged by a sensory panel. Panelists also judged standard oils to have significantly higher intensities for fishy, burnt, rubbery, smoky and acrid odors than the modified oils. Free fatty acids, polar compounds and foam heights during frying were significantly (P<0.05) less in the low-linolenic soy and canola oils than the corresponding unmodified oils after 5 h of frying. The flavor quality of french-fried potatoes was significantly (P<0.05) better for potatoes fried in modified oils than those fried in standard oils. The potatoes fried in standard canola oil were described by the sensory panel as fishy.     

Canola and high erucic rapeseed oil as substitutes for diesel fuel: Preliminary tests

A cooperative project using the facilities of the POS Pilot Plant Corporation, the Saskatchewan Research Council and the Agricultural Engineering Department, University of Saskatchewan, and funded by Agriculture Canada, was initiated in 1980 to investigate the feasibility of using canola and high erucic rapeseed oil as a replacement/extender to diesel fuel in direct-injection diesel engines. Work carried out included the documented production and refining of canola and R500 (high erucic) vegetable oils, preparation of methyl ester and of blends of all these fuels with methanol and ethanol. These fuels were evaluated by ASTM and improvised tests to determine their usefulness as diesel fuel. Engine tests involved a 2-cylinder Petter diesel and a 6-cylinder John Deere turbocharged diesel. Results were similar for both engines in short-term performance tests, and indicated that: (a) maximal power was essentially the same when burning canola oil as when burning diesel fuel; (b) specific fuel consumption was ca. 6% higher when burning canola oil, but because canola oil has a heating value 14% less than diesel fuel, the thermal efficiency is somewhat higher when operating on canola oil; (c) there were no starting problems down to 10 C; (d) there were fewer particulates in the exhaust when burning canola oil; and (e) there was generally less combustion noise when burning canola oil. The high viscosity of canola oil (ca. 35 times that of disel fuel at 20 C) poses a major problem in using the oil at low temperature. Blending with diesel fuel and the creation of a methyl ester from the canola oil both proved effective in reducing viscosity, but neither lowered the pour point apprecibly. Efforts on reduction of pour points and further work on blends and on heating the fuel are described.     

Antioxidant Activity of Sesamin in Canola Oil

The present study presents the antioxidant activity of sesamin in canola oil compared with that of butylated hydroxytoluene (BHT) by monitoring the oxygen consumption and the decrease in linoleic acid and α-linolenic acid. The oxidation of canola oil was conducted at 35, 60, 90, 120 and 180 °C with addition of 50–400 ppm sesamin. Results from the oxygen consumption test showed that sesamin dose-dependently inhibited the oxidation of canola oil at concentrations of 50–200 ppm at temperatures of 60–180 °C, however, sesamin lost its antioxidant activity at a low temperature of 35 °C. The fatty acid analysis also demonstrated that sesamin at 50, 100 and 200 ppm dose-dependently prevented the oxidation of linoleic acid and α-linolenic acid in canola oil. Both the oxygen consumption and the fatty acid analysis demonstrated sesamin was less effective than BHT as an antioxidant at temperatures of 60–180 °C. It was therefore concluded that sesamin could prevent the lipid oxidation of frying fats and oil, however, its antioxidant activity was not as potent as that of BHT.     

Antioxidative effect of ethanol tea extracts on oxidation of canola oil

There is an increasing interest in the biological effects of natural antioxidants present in teas on formation ofin vivo free radicals, carcinogenesis, and atherogenesis. Teas are traditionally classified into six major groups, namely, green, yellow, white, black, dark-green, and oolong teas. The present study examined the antioxidative activity of ethanol extracts from these six major groups of teas against oxidation of heated canola oil. The oxidation was conducted at 100°C by monitoring oxygen consumption and changes in linoleic and linolenic acids in canola oil. The ethanol extracts of green, yellow, and white teas strongly inhibited oxidation of canola oil compared to butylated hydroxytoluene, probably due to the presence of natural polyphenols. In contrast, oolong teas examined exhibited only moderate antioxidative activity because of the partial destruction of natural polyphenols by semifermentation. The ethanol extracts of black, dark-green, and ginseng teas studied showed little or no protection to canola oil from lipid oxidation, probably due to the complete destruction of natural polyphenols by fermentation during manufacturing processes.     

Lipase-catalyzed hydrolysis of canola oil in supercritical carbon dioxide

The effect of pressure, temperature, and CO₂ flow rale on the extent of conversion and the product composition in the enzyme-catalyzed hydrolysis of canola oil in supercritical carbon dioxide (SCCO₂) was investigated using lipase from Mucor miehei immobilized on macroporous anionic resin (Lipozyme IM). Reactions were carried out in a continuous flow reactor at 10, 24, and 38 MPa and 35 and 55°C. Supercritical fluid chromatography was used to analyze the reaction products. A conversion of 63–67% (triglyceride disappearance) was obtained at 24–38 MPa. Mono-and diglyceride production was minimum at 10 MPa and 35°C. Monoglyceride production was favored at 24 MPa. The amount of product obtained was higher at 24–38 MPa due to enhanced solubility in SCCO₂. Complete hydrolysis of oil should be possible by increasing the enzyme load and/or decreasing the quantity of the oil substrate. There was a drop in triglyceride conversion over a 24-h reaction time at 38 MPa and 55°C, which may be an indication of loss of enzyme activity. Pressure, temperature, and CO₂ flow rate are important parameters to be optimized in the enzyme-catalyzed hydrolysis of canola oil in SCCO₂ to maximize its conversion to high-value products.     

Antioxidant Activity of Amaranth Protein Hydrolysate Against Thermal Oxidation of Vegetable Oils

The antioxidant capacity of amaranth protein hydrolysate (AH) during the thermally induced oxidation of two different vegetable oils, sunflower oil (SO) and canola oil (CO), was assessed by differential scanning calorimetry by means of isothermal and non‐isothermal assays. Interactions between AH and tocopherols were also analyzed. In both oils, AH (10 % w/w) produced an increase in the induction period in isothermal assays, presenting a synergistic effect with tocopherols. In the case of non‐isothermal assays, thermograms of oils with AH showed a significant diminution in the second exothermic peak, suggesting an inhibition of the decomposition of primary to secondary oxidation products. In addition, AH produced an increase in the oxidation rate constant (k) value at low temperatures being more evident in the case of canola oil. However, this effect decreased as a function of the temperature increase, which suggests that AH would have a pro‐oxidant effect at low temperatures but a heat stabilizing effect at high temperatures (above 210 °C for SO and 190 °C for CO).     

Viscosity measurement and modeling of canola oil and its blend with canola stearin in equilibrium with high pressure carbon dioxide

During enzymatic reactions carried out in supercritical CO₂ (SCCO₂) media, CO₂ can expand the liquid reactant mixture, especially lipid-type substances, due to pressure increase and dissolution of CO₂, causing viscosity reduction, and improvement of the diffusion of reactants and products. For better understanding of the transesterification reaction of canola oil and canola stearin in SCCO₂ media, the viscosity of canola oil at 40, 50, 65, and 75 °C and its blend with canola stearin (30 wt%) at 65 °C in equilibrium with high pressure CO₂ was measured up to 12.4 MPa using a rotational rheometer equipped with a high pressure cell. The solubility of CO₂ in canola oil at 40 and 65 °C and its blend with canola stearin at 65 °C was also determined at pressures of up to 20 MPa using a high pressure view cell. The viscosity of canola oil at 40, 50, 65, and 75 °C and its blend with canola stearin at 65 °C decreased exponentially to 87.2, 84.7, 74.8, 66.2, and 74.2% of its value at atmospheric pressure, respectively, with pressure increase up to 12.4 MPa. The viscosity of the samples decreased with an increase in temperature, but the effect of temperature diminished above 10 MPa. The viscosities of CO₂-expanded canola oil and its blend with canola stearin at 65 °C were similar up to 12.4 MPa. The samples exhibited shear-thickening behavior as the flow behavior index reached almost 1.2 at elevated pressures. The mass fraction of CO₂ in canola oil at 40 and 65 °C and its blend with canola stearin at 65 °C reached 24 and 21% at 20 MPa, respectively. The Grunberg and Nissan model was used to correlate the viscosity of CO₂-expanded lipid samples.