Thermal oxidation of synthetic triglycerides. II. Analysis of the volatile condensable and noncondensable phases

Tripalmitin, 1-lauryl dipalmitin, 2-lauryl dipalmitin, 1-oleyl dipalmitin and 2-oleyl dipalmitin were subjected to thermal oxidation at 200 C in the presence of air. The volatile consensable products of oxidation collected after 3 and 24 hours were analyzed for carbonyl and carboxyl compounds. The volatile non-condensable products were quantitatively examined for carbon monoxide, carbon dioxide, and hydrogen. The results indicated that long chain carbonyls were formed in the initial stages of oxidation. When the oxidation was allowed to proceed for 24 hours, saturated aldehydes from C₁ to C₁₆, methyl ketones, and other ketones were found in the volatile oxidation products. A variety of fatty acids from C₄ to C₁₆ were identified in the volatile fatty acids. The presence of dicarboxylic acids indicated that oxygen attacked the double bond of oleic acid in 1-oleyl dipalmitin. Possible mechanisms for the formation of the decomposition products were discussed. Portion of a thesis presented by Joseph G. Endres as partial fulfillment of the requirements for the degree of Doctor of Philosophy in Food Technology. Funds for the partial support of these studies were made available by the National Institute of health Grant A-1671.     

Volatile components from triolein heated in air

In a continuing study to identify volatile odor constituents and their precursors from heated soybean oil, the following model triglycerides were heated to 192 C in air for 10 min: (a) pure triolein, (b) a mixture of triolein (25%)-tristearin, and (c) a randomly esterified triglyceride composed of oleic (25%) and stearic acids. Each model system produced the same major compounds which were identified as heptane, octane, heptanal, octanal, nonanal, 2-decenal, and 2-undecenal. These seven compounds apparently are unique to the oxidation of the oleate fattyy acid in each triglyceride sample. Minor volatile compounds from oxidized triolein included saturated and unsaturated aldehydes andn-hydrocarbons and saturated primary alcohols, methyl ketones, gamma lactones, and monobasic acids. Incorporation of stearic acid in the triglycerides noticeably increased the amounts of saturated minor compounds and the range of their carbon chain lengths. Decomposition products characteristic of the oxidation of stearate were apparent among decomposition products associated with the oxidation of oleate.     

Thermal oxidation of polypropylene close to industrial processing conditions

Thermal oxidation of isotactic polypropylene (PP) at 220 and 280°C in air was studied. Gas chromatography–mass spectrometric analysis was used to separate and identify the volatile products of PP oxidation. Twenty-three products were identified and 15 substances were quantified. The aldehydes are the principal products formed, followed by ketones, acids, and alcohols. The main organic product quantified was acetaldehyde. The volatile organic products formed constitute about 3% of the amount of water formed. The relative amounts of the most volatile products formed in the range 220–280°C are practically independent on the temperature of oxidation. The mechanism of formation on the oxidation products is discussed.     

Oxidized rapeseed oil methyl ester as a bitumen flux: Structural changes in the ester during catalytic oxidation

Structural changes occurring in the rapeseed oil methyl ester upon catalytic oxidation at 200 °C were examined. Oxidative decomposition of fatty acid chains to lower molecular weight compounds and the formation of oligomers were the major oxidation pathways at 200 °C. FT-IR and ¹H NMR examinations, as well as the fall in iodine number, revealed the disappearance of double bonds. Quantitative analysis of the rapeseed oil methyl ester and the liquid products of its oxidation showed that oxidation of fatty acid methyl esters possessing three and two double bonds was practically complete whereas for structures possessing one double bond the loss of unsaturation amounted to 25% only. The decrease in iodine number from about 110 to about 65 and the 1.5-fold increase in molecular weight of the liquid products in the course of 25-h oxidation suggest that only a part of the unsaturated bonds in the fatty acid methyl ester was engaged in the formation of liquid oligomers and volatile oxidation products. The addition of dicumyl peroxide promoted the formation of organic peroxides during the initial stage of oxidation, which resulted in a higher molecular weight of the liquid products. The volatile oxidation products were found to contain lower molecular weight aldehydes, ketones, free fatty acids and their methyl esters, alkylfurans, lactones, n- and isoalkanes. The reaction schemes for their formation were presented. The results of the study are of importance to the optimization of the conditions for oxidation of the ester in order to obtain a quality ecological bitumen flux.     

Application of near infrared spectrophotometry to the study of the autoxidation products of fats

Summary The usefulness and limitations of near infrared spectroscopy as applied to the oxygenated products of fat oxidation has been studied. Hydroperoxides, acids, alcohols, esters, aldehydes, and ketones all absorb in the narrow range from 2,700 mμ to 3,000 mμ. Alcohols may be distinguished from hydroperoxides and acids, but the latter are too close together to be resolved. In mixtures all the C=O absorptions attributable to esters, aldehydes, and ketones combine to form one band. In autoxidizing methyl oleate, the increase in alcohol, carbonyl, and combined acid-hydroperoxide can be followed in the near infrared spectra of CCl₄ solutions. In the absence of acid the increase in hydroperoxide absorbance is linear with peroxide value. The changes in the spectra of a reduced and bicarbonate-washed sample of oxidized methyl oleate correlate well with the expected chemical changes. Presented at the 31st Fall Meeting of the American Oil Chemists’ Society, Cincinnati, O., Sept.30–Oct. 2, 1957. American Meat Institute Foundation Journal Paper Number 156.     

A Simple and Highly Selective Biomimetic Oxidation of Alcohols with Hypervalent Iodine(III) Reagent Catalyzed by β-Cyclodextrin in Water

Abstract  

A simple, mild and highly efficient biomimetic oxidation of alcohols to the corresponding aldehydes or ketones with hypervalent iodine(III) reagent catalyzed by β-cyclodextrin was reported. β-cyclodextrin serves as a biological catalyst to enhance the reaction remarkably. The oxidation proceeded in water to afford aldehydes or ketones in excellent yields and high selectivity without remarkable over-oxidation to carboxylic acids. Selective oxidation of primary alcohols in the presence of secondary alcohols was also achieved. A possible mechanism for the oxidation was proposed.     

Lipid oxidation products of heated soybeans as a possible cause of protection from ruminal biohydrogenation

Heating oilseeds has been shown to improve the milk fatty acid profile when given to dairy cows, compared to raw oilseeds. However, results from published studies are conflicting. The conditions of heating and storage of the oilseeds could be responsible for these differences, probably partly through their effects on lipid oxidation, the products of which could act on ruminal biohydrogenation (BH). Thus, 15 different treatments were applied to ground soybeans: three levels of heating (no heating, 30 min at 110 or 150°C) × 5 ambient storage durations (0, 1, 2, 4, or 6 months). Soybeans were incubated in vitro with ruminal fluid for 6 h. Triacylglycerol (TAG) polymers, hydroperoxides and hydroxyacids (HOA), aldehydes, and fatty acids were assayed in soybeans and ruminal culture. No TAG polymer was detected in any treatment. Soybeans stored for a long time had a high content of HOA, whereas those heated at 150°C, whatever the storage duration, had high aldehyde contents. The percentage disappearance of cis‐9,cis‐12 18:2 and cis‐9,cis‐12,cis‐15 18:3 in incubates decreased significantly in cultures with heated soybeans, especially at 150°C, suggesting that this partial protection of polyunsaturated fatty acids (PUFA) from BH was at least in part linked to the aldehyde content of the heated soybeans. Practical applications: Oilseeds given to ruminants are often heated, and heat treatment is known to generate oxidation products. Knowing what oxidation products influence ruminal biohydrogenation of unsaturated fatty acids could result in technological processes allowing a better transfer of unsaturated fatty acids from oilseeds to ruminant products.     

Über die Autoxydation gesättigter Fettsäuren VI: Isolierung und Identifizierung von Oxydationsprodukten der Laurin-, Myristin-und Stearinsäure sowie ihrer Methylester

Autoxydation of Saturated Fatty Acids VI: Isolation and Identification of Cleavage Products Formed by the Oxidation of Laurie, Myristic and Stearic Acids and their Methyl Esters Besides primary reaction products, as reported earlier, also some other substances, considered to be secondary products were identified in the oxidation product of saturated fatty acids and their methyl esters. A large number of methyl ketones, aldehydes and carboxylic acids could be detected by these investigations.     

Headspace Volatile Oxylipins of Eastern Himalayan Moss Cyathophorella adiantum Extracted by Sample Enrichment Probe

Cyathophorella adiantum (Griff.) M. Fleisch. (Division-Bryophyta, Family-Daltoniaceae), an Eastern Himalayan moss was studied for the first time to identify the volatiles derived from cellular and membrane bound fatty acids. A high capacity sample enrichment probe (SEP) was used for extraction of headspace volatile (HSV) molecules followed by GC–MS analysis. Different short-chain oxylipins like alkenes, alkanes, saturated and unsaturated alcohols, saturated and unsaturated aldehydes, ketones were identified along with free and esterified fatty acids, cyclo compounds and some by-products of secondary metabolites. Fatty acid analysis of neutral lipids (NL) and phospholipids (PL) of this plant exhibits the predominance of C16 and C18 fatty acids. It also reveals some interesting information that might indicate the possible fatty acid precursors for volatile generation and their sources in this plant.     

Reductive ozonolysis for monoenoic fatty acid structure determination in the microreactor apparatus

An improved method of double bond location in unsaturated monoenoic fatty acids has been developed for the “integrated microreactor apparatus” (MRA) system. Solid triphenylphosphine (TPP), as contrasted with previously employed TPP solutions, effectively reduces ozonides to aldehydes and eliminates interferences of solvents with desired aldehyde peaks and the selective loss of volatile aldehydes. The need for separating homologous series of volatile aldehydes at subambient temperatures (beginning at −40 C) and of long chain aldehyde esters (up to 270 C) places stringent requirements upon column stability, polarity and resolution. An effective substrate system for gas liquid chromatography (GLC) has been developed that gives results amenable to digital computer analysis; also developed are techniques of utilizing temperature measurements from temperature programming and for eliminating detector poisoning by TPP. This improved MRA system has been applied to the analysis of isomeric fatty acids formed in hydrogenation of fats. Presented at the Fifth Great Lakes Regional ACS Meeting, June 1971, Peoria, Illinois. No. Market. Nutr. Res. Div., ARS, USDA.     

Fish oil sensory properties can be predicted using key oxidative volatiles

The high level of PUFA in fish oil, primarily eicosapentaenoic acid (EPA) and DHA result in rapid oxidation of the oil. Current methods used to assess oxidation have little correlation with sensory properties of fish oils. Here we describe an alternative method using solid phase microextraction (SPME) combined with GC‐MS to monitor volatile oxidation products. Stepwise discriminant function analysis (DFA) was used to classify oils characterized as acceptable or unacceptable based on sensory analysis; a cross‐validated success rate of 100% was achieved with the function. The classification function was also successfully validated with tasted samples that were not used to create the method. A total of 14 variables, primarily aldehydes and ketones, were identified as significant discriminators in the classification function. This method will be useful as a quality control method for fish oil manufacturers. Practical applications: This paper describes an analytical method that can be used by fish oil manufacturers for quality control purposes. Solid phase microextraction and GC‐MS were used to monitor volatile oxidation products in fish oil. These data, combined with results of analyses by a sensory panel, were used to create a function that classified fish oil samples as acceptable or unacceptable. The volatile oxidation products used to in the function were primarily aldehydes and ketones. This method can be used by fish oil manufacturers as an alternative to expensive sensory panels.     

Volatile compounds in oils after deep frying or stir frying and subsequent storage

Soybean oil (900 g) was heated by deep frying at 200°C for 1 h with the addition of 0, 50, 100, 150 and 200 mL water, and then stored at 55°C for 26 weeks. Soybean oil, corn oil and lard were heated by stir frying and then stored at 55°C for 30 weeks. The volatiles and peroxide values of these samples were monitored. All samples contained aldehydes as major volatiles. During heating and storage, total volatiles increased 260-1100-fold. However, aldehyde content decreased from 62–87% to 47–67%, while volatile acid content increased from 1–6% to 12–33%; especially hexanoic acid which increased to 26–350 ppm in the oils after the storage period was completed. Water addition to the oils heated by deep frying tended to retard the formation of volatile compounds. The total amount of volatile constituents of lard heated by stir frying increased more during storage than that of corn oil or soybean oil. Peroxide values did not reflect the changes of volatile content in the samples.     

Mass spectral determination of aldehydes,ketones, and carboxylic acids using 1,1-dimethylhydrazine

Analyses of nanogram to milligram quantities of aliphatic aldehydes, fatty acids, and unhindered aliphatic ketones such as those typically found in pheromonal blends have been effected by treating these mixtures with 1,1-dimethylhydrazine. The aldehydes and ketones formN,N-dimethylhydrazones, while the fatty acids form methyl esters. Structural elucidation of the reaction products was achieved using EI and CI gas chromatography-mass spectrometry.Mention of a company or trade name is solely for identification of material used and does not imply endorsement by the United States Department of Agriculture.     

Thermo-oxidative degradation of low-density polyethylene close to industrial processing conditions

Thermo-oxidative degradation of low density polyetylene (LDPE) at a low degree of volatilization (about 4%) at 264–289°C was studied. Gas chromatography—mass spectrometric analysis was used to separate and identify the products of LDPE decomposition. Altogether 44 compounds representing hydrocarbons, alcohols, aldehydes, ketones, acids, cyclic ethers, cyclic ethers, cyclic esters, and hydroxycarboxylic acids were identified. Sixteen oxygen-containing products were quantified. Among the components identified, the fatty acids and aldehydes predominated. The most abundant product was formic acid. The mechanism of formation of the degradation products is discussed.     

Microbial conversions of alkanes and fatty acids

Alkanes are attacked readily by a wide variety of microorganisms. The most frequently encountered mode of oxidation is for one of the terminal methyl groups to be oxidized, through the alkanol, then the alkanal, to the corresponding fatty acid. Alkanes may be attacked subterminally also, and various ketones as well as the corresponding secondary alcohols can be produced. Subsequent degradation of these ketones occurs via introduction of oxygen into the chain to give a corresponding ester, which is then hydrolyzed to give a primary alkanol 2 carbon atoms shorter than the original alkane. The fatty acids arising by either route of oxidation, or by gratuitous introduction to the microbial system, may be oxidized by: (a) β-oxidation to give a number of acetyl-CoA units—intermediates of the process cannot be isolated from this pathway due to the tightly coupled nature of the substrates to the enzymes; (b) α-oxidation; or (c) oxidation at the other end of the molecule. In the latter case, ω- and ω—1-hydroxyfatty acids can be produced. ω-Hydroxyfatty acids are subsequently oxidized to give dicarboxylic acids, which can be isolated, sometimes in high yield, by use of appropriate microbial mutants lacking in certain of the key metabolizing enzymes. With some yeasts, the fatty acids, including the ω-hydroxyfatty acids, can be esterified to various sugars to give a series of glycolipids. In some cases, wax esters are formed between fatty acid and alkanol; these wax esters can include diunsaturated molecules having a close chemical similarity to those of sperm whale and jojoba oils. Various recent innovations have occurred using isolated enzyme systems which can be used in transesterification reactions to convert cheap triacylglycerols into high value added commodities such as cocoa butter.     

Formation of triacylglycerol core aldehydes during rapid oxidation of corn and sunflower oils with tert-butyl hydroperoxide/Fe2+

The lipid ester core aldehydes formed during a rapid oxidation (7.8 M tert-butyl hydroperoxide, 90 min at 37°C) of the triacylglycerols of purified corn and sunflower oils were isolated as dinitrophenylhydrazones by preparative thin-layer chromatography and identified by reversed-phase high-performance liquid chromatography with on-line electrospray ionization mass spectrometry and by reference to standards. A total of 113 species of triacylglycerol core aldehydes were specifically identified, accounting for 32–53% of the 2,4-dinitrophenylhydrazine (DNPH)-reactive material of high molecular weight representing 25–33% of the total oxidation products. The major core aldehyde species (50–60% of total triacylglycerol core aldehydes) were the mono(9-oxo)nonanoyl- and mono(12-oxo)-9,10-epoxy dodecenoyl- or (12-oxo)-9-hydroxy-10,11-dodecenoyl-diacylglycerols. A significant proportion of the total (9-oxo)nonanoyl and epoxidized (12-oxo)-9,10-dodecenoyl core aldehydes was found in complex combinations with hydroperoxy or hydroxy fatty acyl groups (6–10% of total triacylglycerol core aldehydes). Identified were also di(9-oxo)nonanoylmonoacylglycerols (0.5% of total) and tri(9-oxo)nonanoylglycerols (trace). The identification of the oxoacylglycerols was consistent with the products anticipated from tert-butyl hydroperoxide oxidation of the major species of corn and sunflower oil triacylglycerols (mainly linoleoyl esters). However, the anticipated (13-oxo)-9,11-tridecadienoyl aldehyde-containing acylglycerols were absent because of further oxidation of the dienoic core aldehyde. A significant proportion of the unsaturated triacylglycerol core aldehydes contained tert-butyl groups linked to the unsaturated fatty chains via peroxide bridges (2–9%). The study demonstrates that rapid peroxidation with tert-butyl hydroperoxide consitutes an effective method for enriching natural oils and fats in triacylglycerol core aldehydes for biochemical and metabolic testing.     

Comparison of methods for determining fatty acid oxidation produced by ultraviolet irradiation

Summary The thiobarbituric acid (TBA) reaction for fatty acid oxidation has been compared with Lundberg and Chipault's method for peroxides, the Kreis test for aldehydes, and with the degree of conjugation, using fatty acid esters exposed to ultraviolet light for various periods. The TBA test paralleled the other methods for methyl linolenate and methyl linoleate but was essentially negative for methyl oleate oxidation. The sensitivity of the TBA test for linolenate was 30–80 times that for linoleate at the same peroxide values. The TBA test appears to be a reliable method of estimating the oxidation products of linolenic and linoleic acids in tissues and other biological material. Supported by a grant from the Atomic Energy Commission.     

Carbonyls in oxidizing fat. V. The composition of neutral volatile monocarbonyl compounds from autoxidized oleate,linoleate, linolenate esters,and fats

The steam volatile monocarbonyl compounds in mildly autoxidized esters of oleic, linoleic, linolenic acids, and animal and vegetable fats were quantitatively estimated. The major aldehydes in oleate and linoleate were those that might be expected from the scission of reported monomeric hydroperoxide isomers. The predominance of hept-2,4-dienal and propanal in linolenate suggested that the major monomeric hydroperoxides were 12-and 16-hydroperoxy conjugated dienoic isomers. The number of minor aldehydes increased with degree of unsaturation of the fatty acid. The amounts of monocarbonyl compounds in the fats examined generally agreed with their average fatty acid composition. Appreciable amounts of heptanal in lamb and beef fat and heptanal and decanal in butterfat, under the conditions of oxidation, could not have come from the three unsaturated acids. Heating at 165°C. in all samples increased the proportions of the most unsaturated major aldehydes.     

Effect of n−3 fatty acid-rich fish oil supplementation on the oxidation of low density lipoproteins

This study was aimed at determining the effect of fish oil supplementation on copper-catalyzed oxidation of low density lipoproteins (LDL) from nine hypertriglyceridemic human subjects. A rapid headspace gas chromatographic method was used to measure the volatile oxidation products from LDL. Propanal and hexanal were the major volatile products formed in the oxidation of n−3 and n−6 polyunsaturated fatty acids (PUFA), respectively. Fish oil supplementation resulted in a significant increase in propanal formation from 3.7 to 13.4 nmol/mL LDL (P<0.01); it also resulted in small decreases in pentanal formation from 14.7 to 11.4 nmol/mL LDL and in hexanal formation from 138 to 108 nmol/mL LDL (P<0.05). The changes in peroxidation products paralleled the changes in LDL composition, which showed a significant increase in n−3 PUFA from 3.2 to 14.6% (P<0.01) and a decrease in n−6 PUFA from 43.7 to 35.0% (P<0.05). Propanal formation was highly and significantly correlated with n−3 PUFA content (r=0.950,P<0.001). Since total volatiles remained unchanged, this indicated that the two groups of LDL samples did not differ in overall oxidative susceptibility. Although fish oil intake did not alter the oxidative susceptibility of LDL, the chemically modified LDL particles generated a distinct pattern of volatile oxidation products that reflected changes in their fatty acid composition.     

Phospholipids and oxophospholipids in atherosclerotic plaques at different stages of plaque development

We identified and quantified the hydroperoxides, hydroxides, epoxides, isoprostanes, and core aldehydes of the major phospholipids as the main components of the oxophospholipids (a total of 5–25 pmol/μmol phosphatidylcholine) in a comparative study of human atheroma from selected stages of lesion development. The developmental stages examined included fatty streak, fibrous plaque, necrotic core, and calcified tissue. The lipid analyses were performed by normal-phase HPLC with on-line electrospray MS using conventional total lipid extracts. There was great variability in the proportions of the various oxidation products and a lack of a general trend. Specifically, the early oxidation products (hydroperoxides and epoxides) of the glycerophosphocholines were found at the advanced stages of the plaques in nearly the same relative abundance as the more advanced oxidation products (core aldehydes and acids). The anticipated linear accumulation of the more stable oxidation products with progressive development of the atherosclerotic plaque was not apparent. It is therefore suggested that lipid infiltration and/or local peroxidation is a continuous process characterized by the formation and destruction of both early and advanced products of lipid oxidation at all times. The process of lipid deposition appears to have been subject to both enzymatic and chemical modification of the normal tissue lipids. Clearly, the appearance of new and disproportionate old lipid species excludes randomness in any accumulation of oxidized LDL lipids in atheroma.