Autoxidation Of Unsaturated Fatty Acids Research Articles

Macro peroxide initiators based on autoxidized unsaturated plant oils: Block/graft copolymer conjugates for nanotechnology and biomedical applications

AbstractThe autoxidation of unsaturated fatty acids and their esters is one of the most important reactions in food and biological systems. Autoxidation is a type of reaction between air oxygen and unsaturated plant oils. This reaction starts with a hydrogen abstraction on the methylene group adjacent double bond, leaving a radical onto the carbon atom. Molecular oxygen attacks this radical leading to produce peroxide and hydroperoxide derivatives of the oligomerized unsaturated plant oils. Because peroxide groups thermally cleave to produce free radicals, hydroperoxide derivatives of unsaturated plant oil oligomers can be used in the free radical polymerization of vinyl monomers leading to the related block/graft copolymers. The obtained copolymers combined with the biodegradable natural plant oil gain superior properties such as biodegradability and softness. In this review article, the in vitro autoxidation of well‐known unsaturated plant oils‐soybean oil, linseed oil, and castor oil and some related unsaturated fatty acids‐oleic acid, linoleic acid, and ricinoleic acid was carried out under atmospheric conditions with or without exposing white light. Because the autoxidized unsaturated oil/fatty acids contain peroxide/hydroperoxide groups (they are referred to as macro peroxide initiators) that they are used in the free radical polymerization of vinyl monomers to obtain block/graft copolymers. The improved polymerization conditions, characterization, and applications of the obtained products will be discussed.

Lipid-derived flavor and off-flavor of traditional and functional foods: an overview

Flavor is an important aspect of both traditional as well as functional food acceptability and can be favorable or unfavorable depending on the chemical nature of the volatile compounds present, their potency, and the presence of non-volatile components. Lipid, as a major food component, contributes to the food flavor formation via both interactions with other components and/or due to its own degradation during food processing, cooking, and storage. This is particularly important when dealing with functional foods that may contain a high proportion of highly unsaturated oils. Lipid may be involved in the Strecker degradation and Maillard reaction, which occurs during food processing, and as a result, it forms a myriad of volatile compounds. Lipoxygenases and autoxidation of unsaturated fatty acids also play an important role in the development of volatile compounds as well as the storage conditions of oils under display lights in the supermarkets, if kept in clear bottles. In this contribution, a cursory account of the role of lipids in flavor formation is provided.

Structural properties of vegetable oil thermosets: Effect of crosslinkers, modifiers and oxidative aging

The present work is focused on the study of the formulation effect of cationically polymerized vegetable oil thermoset on their aging behavior. Toward this aim, tung oil-based biopolymers were prepared using different comonomers or adding a modifier. Specifically, synthetic and natural comonomers (styrene, divinylbenzene and a methyl ester of tung oil) and a modifier (acrylated epoxidized soybean oil) were used to prepare different crosslinked samples with a fixed weight ratio of tung oil/comonomer (or modifier) = 70/30. The chemical aging suffered by the fatty acid segments of the matrix, which is known as autoxidation of unsaturated fatty acids in oils and alkyd resins, was followed by Fourier transformed infrared spectroscopy, dynamic-mechanical analysis, positron annihilation lifetime spectroscopy and thermogravimetric analysis. As a result, values of the glass transition temperature, the storage moduli, tanδ and the free nanohole volumes were obtained. To study the influence of the aging process on the network structures at molecular level, the evolutions of the experimental parameters mentioned were followed for one year at two different aging conditions: room temperature and 50 °C.The chemical changes leading to nanostructural variations in all the studied samples are discussed in terms of the formed networks and the degradative processes during aging.

Autoxidized Oleic Acid Bifunctional Macro Peroxide Initiators for Free Radical and Condensation Polymerization. Synthesis and Characterization of Multiblock Copolymers

Autoxidation of unsaturated fatty acids gives fatty acid macroperoxide initiators containing two functionalities which can lead to free radical and condensation polymerizations in a single pot. The oleic acid macroperoxide initiator obtained by ecofriendly autoxidation (Pole4m) was used in both the free radical polymerization of styrene and the condensation polymerization with amine-terminated polyethylene glycol (PEGNH2) to obtain triblock branched graft copolymers. The narrow molar masses of the poly oleic acid-g-styrene (PoleS) and poly oleic acid-g-styrene-g-PEG (PoSG) graft copolymers were successfully obtained. The inclusion of oleic acid decreased the glass transition temperature of the polystyrene segment because of the plasticizing effect of oleic acid. In addition, a mechanical property of the copolymer was improved when compared with the pure PS. Structural characterization, morphology of the fracture surface, micelle formation, thermal analysis and molar masses of the obtained products were also evaluated.

Enhancement of the Oxidative Stability of Whey Butter through Almond (P runus dulcis ) Peel Extract

Whey butter is characterized with higher concentration of unsaturated fatty acids; the autoxidation of unsaturated fatty acids limits the shelf life of whey butter. We investigated the effect of almond peel extract on oxidative stabilization of whey butter at refrigeration temperature as the butter is put at refrigeration temperature in supermarkets for sale. Whey butter was added with 100 (T1), 200 (T2), 300 (T3) and 400 (T4) ppm concentrations of ethanolic almond peel extract, compared with a control, stored at refrigeration temperature (6 ± 1C). Changes in chemical characteristics were studied at the interval of 45 days. Supplementation of whey butter with almond peel extract did not show any effect on compositional attributes, rather it strongly inhibited the peroxidation of unsaturated fatty acids (P < 0.05). The iodine value of whey butter was greater than normal butter with no difference in refractive index and unsaponifiable matter. The peroxide value of 90-day stored whey butter added with 400 ppm almond peel extract and control was 0.62 and 1.59 (meqO2/kg). Supplementation of whey butter with almond peel extract markedly improved the induction period. Sensory characteristics of supplemented whey butter were not different from the normal butter (P > 0.05). Almond peel extract can be used for the long-term preservation of whey butter at refrigeration temperature. Practical Applications The increased awareness of health benefits of natural antioxidant and professed of synthetic antioxidants has opened new arrays of the application of natural antioxidants. Almond peel extract can be used to improve the shelf stability of whey butter.

Effects of processing on soybean nutrients and potential impact on consumer health: An overview

Production of soybeans and consumption of soy products is increasing worldwide mainly due to acclaimed health benefits. Processing can alter soybean sensory appeal, nutritive value and potentially affect consumer health. This review of the literature examines these issues. Despite potential changes in nutritive value during processing, soy foods processing below 100oC for short periods, may not adversely affectnutritive value. However, heat inactivation of trypsin inhibitors, denaturation of soybean globulins and haemagglutenins, increases soy protein bioavailability. Excessive heating can impair nutritive value by making lysine unavailable, as serine, cystine and cysteine are converted to a dehydroprotein intermediate that reacts with lysine to form lysinoalanine. Tryptophan and methionine are also lost duringexcessive heating. The acylation reaction catalyzed by alkali, generates lysinoalanine, an unavailable and potentially toxic compound. In rats, ingestion of lysinoalanine results in diarrhoea, pancreatic hyperplasia, and loss of hair. At levels present in foods, protein-bound lysinoalanine does not cause nephrotoxicity in humans. Heat treatments at alkaline pH result in destruction of arginine, which is converted to ornithine, urea, citrulline and ammonia, while cysteine is converted into dehydroalanine. Serine, threonine and lysine are also reduced at alkaline pH. Theseconditions may be present during alkali refining of soy oil. Carbohydrates with free reducing groups react with carbonyl groups on proteins as part of the Maillard reaction. Heat treatments at alkaline pH and above 200oC cause isomerization of amino acids, leading to formation of racemic mixtures of L and D forms. Since Disomers have reduced bioavailability and some including D-proline are reported to be toxic, racemization of an essential amino acid reduces its nutritional value. Changes in lipids include oxidation, loss of lipid-soluble vitamins and change of fatty acids from cis to trans isomers. Autoxidation of unsaturated fatty acids initiates free radicalformation leading to destruction of unsaturated fatty acids, with potential reduction of essential fatty acid content. Oxidized lipid-protein interaction products are important precursors of atherosclerotic plaques in vivo. Carotenoids are lost on bleaching, thereby reducing Vitamin A potential. Vitamin E is lost during oil refining. Roasting and toasting have no effect on soy isoflavones, but organic solvents remove them, while fermentation increases their bioavailability. Dehulling reduces total mineral content but most soy minerals follow protein or meal, while sodium and potassium are lost in wash water. To minimize adverse changes, minimal washing, fermentation, reduction of hydrogenation temperature and thermal processing below 100oC for short periods, are recommended.

Isolation and characterization of Glyoxal–Arginine modifications

Glyoxal is generated in foods and in vivo by autoxidation of unsaturated fatty acids and by the Maillard reaction of reducing sugars and amines. Due to its high reactivity, the α-dicarbonyl easily reacts with protein-bound lysine and arginine residues. The quantitatively most important modification of the ε-amino group of lysine is Nε-carboxymethyllysine [1]. Reaction with glyoxal also leads to cross-linking of proteins by formation of amides (glyoxal–amide cross-link [2]), imidazole (MODIC [3]) and imidazolium structures (GOLD [4]).Concerning the reaction of glyoxal with the guanidino group of arginine, inconsistent results have been published in the literature. We could now verify 1-(4-amino-4-carboxybutyl)-2-imino-4,5-dihydroxy-4,5-dihydroimidazolidine (dihydroxyimidazolidine) as the single primary product in incubations of Nα-t-BOC-arginine with glyoxal under physiological conditions [5]. The structure was identified as a cis/trans-isomer mixture of ca. 1:4. In a much slower reaction, dihydroxyimidazolidine is degraded to N7-carboxymethylarginine (CMA), representing a novel stable endproduct. Both structures were unequivocally established by 1H-, 13C-, HMBC-NMR and high-resolution mass spectra. Other structures could not be found under these reaction conditions. Synthesis of 1-(4-amino-4-carboxybutyl)-2-imino-5-oxo-imidazolidine (imidazolinone), which has been published earlier as the only modification so far , could not be verified [6]. However, both arginine modifications, dihydroxyimidazolidine and CMA can be transformed to the imidazolinone under acid conditions. Therefore, the detection of the imidazolinone in incubations under physiological conditions must be evaluated as an artifact of the acid sample workup procedures applied.The mechanistic relationship of all three structures was clarified in incubations at various temperatures, pH values and in the presence of o-phenylenediamine and aminoguanidine. The latter experiment using α-dicarbonyl trapping reagents proved that the reaction to the dihydroxyimidazolidine can be reversed to regenerate arginine and a glyoxal derivative. As trapping reagents are commonly used to measure ‘free’ glyoxal in foods and in vivo samples, the published data has to be evaluated very critically. In addition, it was possible to elucidate the mechanism leading from the dihydroxyimidazolidine to CMA and to exclude any participation of the imidazolinone.

Addition of Palatase M (Lipase from Rhizomucor miehei) to Dry Fermented Sausages: Effect over Lipolysis and Study of the Further Oxidation Process by GCMS

Three doses [0.150, 0.300, and 1 LU/g (where 1 LU is the amount of enzyme that liberates 1 μmol of butyric acid/min from an emulsified tributyrin substrate at pH 7.0 and 30°C)] of Palatase (lipase from Rhizomucor miehei) were added to a dry fermented sausage formulation to study their effect over the lipid fraction and some sensory properties. The enzyme caused significant increments for all free fatty acids analyzed, which were proportionally lower for linolenic acid and linoleic acid. No differences in rancid odor or taste were observed in the sensory evaluation of sausages elaborated with enzyme with regard to the control. However, an acceleration of the oxidation process after a period of storage under freezing conditions was found in the lipase added sausages. The analysis of volatile profiles by GC-MS showed that aldehydes, which basically originate by autoxidation of unsaturated fatty acids, were 43.59% for control sausage and 64.26, 65.65, and 59.99% for sausages with 0.150 LU/g, 0.300 LU/g, and 1 LU/g of lipase, respectively.

Quantitative determination of hydroxy fatty acids as an indicator of in vivo lipid peroxidation: Oxidation products of arachidonic and docosapentaenoic acids in rat liver after exposure to carbon tetrachloride

An improved gas chromatography-mass spectrometry method has been applied to the quantitation of both in vitro and in vivo products of lipid peroxidation in rat liver stimulated with carbon tetrachloride. The method avoids problems of autoxidation of unsaturated fatty acids during sample preparation, and the sensitivity permits assays on as little as 1 mg of tissue. This permits small samples of tissue to be obtained by biopsy from the same organ, thus making it possible to perform in vivo time studies on a single animal. Lipids from whole tissue or cell preparations are simultaneously extracted and reduced by catalytic hydrogenation and then saponified and derivatized to their pentafluorobenzyl esters and trimethylsilyl ethers. Quantitation is accomplished by negative ion chemical ionization gas chromatography-mass spectrometry, using either deuterated compounds or naturally occurring fatty acid metabolites as internal standards. Hydroxy fatty acids which result from reduction of the hydroperoxides of arachidonic and docosapentaenoic acids are found to increase within 20 min after exposure of liver or hepatocyte suspensions to carbon tetrachloride.

Effect of preoperative stress on serum lipoperoxide levels

To test the concept of intense psychogenic stress manifesting as organic lesion, effect of pre-operative stress on serum lipid peroxide levels in 30 otherwise healthy patients to undergo major abdominal elective surgery has been studied and compared with healthy controls. Significant elevations in serum lipid peroxide levels both on hospitalization and at pre-operative stage were noticed in comparison with healthy controls. However, serum lipid peroxide levels at pre-operative stage did not show significant fluctuations in comparison with those at the time of admission, suggestive of no probable further increment in autoxidation of unsaturated fatty acids of membrane lipids and proper handling by scavenging enzyme system.

Changes in volatile constituents of bell peppers immediately and 3o minutes after stir frying

AbstractBell peppers(Capsicum annuum var. grossum. Sendt) were stir fried for two min, and their volatile constitu‐ents were analyzed immediately and 30 min after stir frying. Autoxidation of unsaturated fatty acids in stir frying and aging is the main cause of changes in volatile compounds.

ENDOR, triple resonance and ESR studies of spin-trapped radicals in autoxidized linoleic acid and its deuterated derivatives

Radicals generated in autoxidized linoleic acid; 11,11-dideuterio-9- cis,12- cis-linoleic acid ( 2H 2); 9,10,12,13-tetradeuterio-9- cis,12- cis-linoleic acid ( 2H 4) and 9,10,11,11,12,13-hexadeuterio-9- cis,12- cis-linoleic acid ( 2H 6), have been detected by ESR and ENDOR using the spin trap 2-methyl-2-nitrosopropane. The coupling constants obtained from the ENDOR spectrum of the linoleic acid systems have been unambiguously assigned by comparison with spectra obtained from deuterated derivatives. The radicals identified confirm the accepted mechanism for autoxidation of unsaturated fatty acids. Autoxidation of the 2H 2-compound identified the presence of an alternative, but kinetically less favourable route for the autoxidation of linoleic acid.

Inhibition of antithrombin III by lipid peroxides

A study was made of the inhibition of antithrombin III (At III) activity by lipid peroxides prepared from autoxidation of unsaturated fatty acids. Lipid peroxides markedly reduced the thrombin neutralising activity of plasma and purified At III with or without albumin carrier. Heparin Sepharose chromatography and heparin co-factor assays suggested that the primary target of lipid peroxides on the At III molecule may be the heparin binding site. Results from electrophoretic studies suggested that interaction between lipid peroxides and At III increased the negative charge of the At III molecule; however, no aggregation of the At III molecule was observed. Lipid peroxidation is being increasingly recognised as a factor in the pathogenesis of several disease states, and it is possible that local inhibition of At III by lipid peroxides could contribute towards the development of a thrombotic event.

CHEMILUMINESCENCE OF SOYBEAN SEEDS: SPECTRAL ANALYSIS, TEMPERATURE DEPENDENCE AND EFFECT OF INHIBITORS

Abstract— The spontaneous light emission of soybean seeds is enhanced 4–8 times during the first minute after water imbibition. Other solvents are also effective. The temperature dependence of soybean chemiluminescence identifies two reactions with activation energies of 20 and 68 kJ/mol corresponding to the lipoxygenase reaction and to the autoxidation of unsaturated fatty acids, respectively. Free radical scavengers and lipoxygenase inhibitors decrease soybean photoemission. The singlet oxygen probe 1,4‐diazabicyclo‐[2,2,2]‐octane (DABCO) increases soybean photoemission. The emission spectra of soybean seeds under a variety of conditions show bands between 450 and 720 nm with 50–70% of the emission over 600 nm. The experimental evidence is consistent with singlet oxygen being one of the emitting species, however, due to the complexity of the system it is likely that other chemiluminescent species are also formed.

Oxidative reactions of unsaturated lipids

Monohydroperoxides, which are the products of free radical autoxidation of unsaturated fatty acids, can under go further free radical chain reactions initiated by abstraction of hydrogen to reform peroxy radicals. In the autoxidation of methyl linolenate, the peroxy radicals corresponding to ‘inner’ hydroperoxides may cyclise and, after further oxygenation, yield diperoxides. The mixtures of the two peroxidic species, monohydroperoxides and diperoxides, obtained from linolenate can be identified and determined chromatographically. Mechanistic studies showed that the oxygenation of pentadienyl radicals to form peroxy radicals—an important propagation step in autoxidation—is reversible. H-donors can be used to control the relative rates of the forward and reverse reactions and so determine the relative proportions of different peroxidic species formed. α-Tocopherol was shown to be an effective H-donor and drastically altered the distribution of products formed in linolenate autoxidation. Such control of peroxide formation may be a factor determining the manifestations that are specific to the oxidative deterioration of a food product.

The stability of wheat starch lipids in untreated and chlorine‐treated cake flours

AbstractUntreated flour and flour treated with chlorine (2.2 g Cl2 kg‐1) were stored in air at 25°C for 4 months. Starch samples prepared from the original flours were stored in air at 25°C for 4 months. Starch samples were also prepared from the fresh flours (control starches) and from the stored flours. Some of the starches from the stored flours were subsequently held at 70°C for 1 month. Starch lipids were not affected by flour chlorine treatment, or by storage at 25°C. There was slight hydrolysis of starch lysophospholipids at 70°C, but negligible autoxidation of unsaturated fatty acids in the total starch lipids. There was appreciable hydrolysis of non‐starch lipids in the untreated stored flour, but no detectable autoxidation of unsaturated fatty acids. Chlorine treatment of flour caused an immediate loss of approximately half of the oleic, linoleic and linolenic acids in all the non‐starch lipids which were examined. There was no further change in the fatty acid composition of the non‐starch lipids when the treated flour was stored, but lipid hydrolysis was substantially reduced compared with the untreated stored flour.

Composition and Pathway of Formation of Stale Aldehydes in Bottled Beer

Volatile aldehydes formed during storage of bottled beer on the shelf are generally considered to cause a stale flavor in beer. Oxidation of higher alcohols by melanoidins, oxidative degradation of isohumulones, Strecker degradation of amino acids, and autoxidation of unsaturated fatty acids are all involved in the formation of many kinds of volatile aldehydes. Evidence was presented in a previous paper that the aldehydes formed by oxidation of higher alcohols plus isohumulones may be the “stale aldehydes” specifically responsible for the stale flavor. Volatile aldehydes of oxidized beer were isolated as their 2,4-dinitrophenylhydrazone derivatives, and subjected to chromatography on a magnesia-Celite 545 column and thin-layer chromatography (TLC) on PEG 6000-impregnated silica gel plates. They were identified by gas chromatography (GC) and mass spectrometry (MS). The concentrations of alkenals and alkadienals, with six to twelve carbon atoms, formed by oxidation of higher alcohols plus isohumulones, were higher in oxidized beer than in fresh beer or oxidized unhopped beer, and a few of these compounds were only detected in oxidized beer. The aldehydes derived from higher alcohols and isohumulones underwent aldol condensation to form these unsaturated aldehydes. When a mixture of these unsaturated aldehydes (Table II) was added to fresh beer, a taste panel reported that the beer had a typical stale aroma.

Composition and Pathway of Formation of Stale Aldehydes in Bottled Beer

Volatile aldehydes formed during storage of bottled beer on the shelf are generally considered to cause a stale flavor in beer. Oxidation of higher alcohols by melanoidins, oxidative degradation of isohumulones, Strecker degradation of amino acids, and autoxidation of unsaturated fatty acids are all involved in the formation of many kinds of volatile aldehydes. Evidence was presented in a previous paper that the aldehydes formed by oxidation of higher alcohols plus isohumulones may be the “stale aldehydes” specifically responsible for the stale flavor. Volatile aldehydes of oxidized beer were isolated as their 2,4-dinitrophenylhydrazone derivatives, and subjected to chromatography on a magnesia-Celite 545 column and thin-layer chromatography (TLC) on PEG 6000-impregnated silica gel plates. They were identified by gas chromatography (GC) and mass spectrometry (MS). The concentrations of alkenals and alkadienals, with six to twelve carbon atoms, formed by oxidation of higher alcohols plus isohumulones, were higher in oxidized beer than in fresh beer or oxidized unhopped beer, and a few of these compounds were only detected in oxidized beer. The aldehydes derived from higher alcohols and isohumulones underwent aldol condensation to form these unsaturated aldehydes. When a mixture of these unsaturated aldehydes (Table II) was added to fresh beer, a taste panel reported that the beer had a typical stale aroma.

Lipid Utilization in Viable and Non-Viable Protea compacta Embryos during Germination

Summary An inability to convert free fatty acids to carbohydrate appears to be the main obstacle to germination in non-viable Protea compacta seeds. This block to energy release is apparently due to the fact that no glyoxysomes develop, a situation that may be related to the state of the nuclei, and to inability of the embryos to produce growth promoting substances. Autoxidation of unsaturated fatty acids and the subsequent formation of free radicals during dry storage, do not appear to be responsible for the loss in seed viability.

Proposed Pathways for the Formation of Volatile Aldehydes during Storage of Bottled Beer

Volatile aldehydes formed during shelf storage of bottled beer seem to be the main cause of the stale flavor in beer. However, the origin of these aldehydes in beer has been controversial. Evidence is presented in this paper that oxidation of higher alcohols by melanoidins, oxidative degradation of isohumulones, Strecker degradation of amino acids, and autoxidation of unsaturated fatty acids are all involved in the formation of these volatile aldehydes in bottled beer. Moreover, the saturated aldehydes resulting from these reactions subsequently undergo aldol condensation to give longer-chain unsaturated aldehydes in beer. Conversely, unsaturated aldehydes tend to be oxidized to shorter-chain saturated aldehydes. Melanoidins act as hydrogen acceptors in the oxidation of higher alcohols and also as antioxidants in the oxidation of isohumulones and unsaturated fatty acids. Isohumulones in beer undergo oxidative degradation to form volatile aldehydes and also inhibit the oxidation of higher alcohols, amino acids, and unsaturated fatty acids by acting as an electron donor in these oxidations. Thus, the reactions involved in formation of volatile aldehydes are interrelated through the electron-transfer system in beer. On the basis of these findings, a mechanism is proposed for the formation of volatile aldehydes in bottled beer.