Chemical changes which take place in an edible oil during thermal oxidation

Johnson, Ogden C.; Kummerow, Fred A.

doi:10.1007/bf02637894

Cited by 46 publications

(16 citation statements)

References 12 publications

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“…Yoon et al (1985) reported that the refractive index of rice bran oil and double fractioned palm olein increased almost linearly with the increase in heating time. In another study, Johnson and Kummerow (1957) investigated the chemical changes that take place in corn oil during thermal oxidation, and they reported that the corresponding refractive index of samples increased with thermal treatment duration at a constant temperature and with the increase of temperature at a constant treatment time.…”

Section: Physicochemical Properties Of the Control Mixed Oilmentioning

confidence: 99%

A response surface methodology study on the effects of some phenolics and storage period length on vegetable oil quality: change in oxidation stability parameters

Karaman¹,

Toker²,

Öztürk³

et al. 2014

Turk J Agric For

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In the present study, response surface methodology was conducted for the determination of effects of some phenolics (gallic acid, ellagic acid, and quercetin) on some stability parameters of mixed oil prepared with sunflower and hazelnut oils (50:50, v/v). In this respect, peroxide value (PV), free fatty acids (FFAs), p-anisidine value, induction period, and refractive index of mixed oil were investigated. Predictive regression equations were constructed for the estimation of each studied parameter (R 2 > 0.861). The storage period caused a significant increase in the peroxide value, FFAs, p-anisidine, and refractive index values of the mixed oil, while it decreased the induction period value of oil (P < 0.01). The addition of gallic acid significantly retarded oxidation (P < 0.05), and in general gallic acid and quercetin were found to be effective for preserving oil against oxidation.

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Section: Physicochemical Properties Of the Control Mixed Oilmentioning

confidence: 99%

A response surface methodology study on the effects of some phenolics and storage period length on vegetable oil quality: change in oxidation stability parameters

Karaman¹,

Toker²,

Öztürk³

et al. 2014

Turk J Agric For

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“…Such polymeric species rarely become larger than trimers or tetramers 12,23,42 , although an explicitly stated reason for this cannot be found in the open literature. One of the obvious results of polymer formation is an increase in the oil viscosity 18,43 . Under conditions where oxygen is available, fatty acid moieties are joined by both C-O-C linkages 3,23,42 and C-C linkages 42 .…”

Section: Secondary Products Of Oxidationmentioning

confidence: 99%

“…Once this isomerization has begun, a conjugated diene group from one fatty acid chain can react with a single olefin group from another fatty acid chain to form a cyclohexene ring 2,42 . This reaction between a conjugated di-olefin and a mono-olefin group is called the Diels Alder reaction, and it becomes important at temperatures of 250-300°C or more 8,18,23 . The products formed are called dimers.…”

Section: Thermal Polymerizationmentioning

confidence: 99%

“…A very sensitive wet method to detect carbonyl compounds 11 and a UV adsorption method used to determine unsaturated carbonyls compounds 18 have been reported. The thiobarituric acid (TBA) test was an early test to measure the levels of aldehydes produced during the oxidation of fatty oils 26 .…”

Section: Secondary Oxidation Productsmentioning

confidence: 99%

“…Kinematic viscosity appears to be the most often used procedure 18,50,96,100 , although absolute viscosity could also be used. Several studies have used refractive index as a way to show the formation of polymers 13,14,16,18 . The fact that fatty oil or ester polymers have higher refractive indices is undoubtedly the reason why a refractive index detector is used in the BS EN ISO 16931 procedure.…”

Section: Physical Propertiesmentioning

confidence: 99%

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Characterization of Biodiesel Oxidation and Oxidation Products

2005

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This report must be reproduced in full,unless SwRI approves a summary or abridgement. iii EXECUTIVE SUMMARY Stability Chemistry FundamentalsChemical reactivity of fatty oils and esters can be divided into oxidative and thermal instability. Both of these types of instability are determined by the amount and configuration of the olefinic unsaturation on the fatty acid chains. Many of the plant-derived fatty oils, including soy and rapeseed, contain polyunsaturated fatty acid chains that are methylene-interrupted rather than conjugated. This structural fact is key to understanding both oxidative and thermal instability.In oxidative instability, the methylene carbons between the olefinic carbons are the sites of first attack. After hydrogen is removed from such carbons oxygen rapidly attacks and a hydroperoxide is ultimately formed where the polyunsaturation has been isomerized to include a conjugated diene. This reaction is a chain mechanism that can proceed rapidly once an initial induction period has occurred. The greater the level of unsaturation in a fatty oil or ester, the more susceptible it will be to oxidation. Once the hydroperoxides have formed, they decompose and inter-react to form numerous secondary oxidation products including aldehydes, alcohols, shorter chain carboxylic acids, and higher molecular weight oligomers often called polymers. Another polymerization mechanism, vinyl polymerization, has been proposed as being part of the degradation process of fatty oils and esters. However, conventional understanding of oxidation chemistry would imply that such processes would not be significant when oxygen was abundant, so its precise level of importance has not been determined.Metals, free fatty acids, acidic fuel additives, the size of the alcohol group (for mono-esters), and the presence of natural antioxidants can all impact the oxidative stability of fatty oils and/or esters. Oxidation can also be catalyzed by light, but such photo-oxidation should not be a significant factor for the manufacture and transportation of biodiesel fuel.Thermal polymerization of fatty oils and esters does not become important until temperatures of 250-300°C are reached. This is because the methylene-interrupted polyunsaturated structure cannot participate in such reactions until it isomerizes into a conjugated configuration, and such isomerization will not occur until that temperature range is reached. Thermal polymerization occurs by the Diels Alder reaction, and two fatty acid chains are linked by a cyclohexene ring. Higher order oligomers are also possible, although the exact mechanism is still not established. Certain thermal polymerization products in used cooking oils may carry over to non-distilled biodiesel. The verification of such compounds and their impact on fuel quality has not been determined. Thermal polymerization may be of limited importance in biodiesel fuel that is repeatedly heated by the engine and recycled to the fuel tank before actual combustion. However, thermal polymerization will not impact stor...

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Studies of the changes in edible fats during heating and frying

Gere

1982

Nahrung

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For detecting the changes in edible fats during the frying operation and for quality assessment of used frying fats 5 relatively simple methods were proposed: determination of polymer content by gel permeation chromatography, measurement of total polar artefacts by TLC followed by densitometry or by adsorption column chromatography. determination of decrease in essential fatty acid concentration and photometric measurement of absorbance at 232 nm.Using the above methods degradation of sunflower oil, rapeseed oil and lard was investigated by running 12 laboratory experiments with different heating or frying conditions. The results showed that both the composition of fat and the frying parameters greatly influence the rate of deterioration.Study of relationships between values obtained by different methods (using data from 110 samples) indicated that high, linear correlations depending on the nature of fat can be found. Correlation coefficients and equations of regression lines were calculated.

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Chemical changes which take place in an edible oil during thermal oxidation

Cited by 46 publications

References 12 publications

A response surface methodology study on the effects of some phenolics and storage period length on vegetable oil quality: change in oxidation stability parameters

A response surface methodology study on the effects of some phenolics and storage period length on vegetable oil quality: change in oxidation stability parameters

Characterization of Biodiesel Oxidation and Oxidation Products

Studies of the changes in edible fats during heating and frying

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