Dissimilarity of the oxidations of rapeseed and butter oil triacylglycerols and their mixtures in the absence of tocopherols

Although fatty acid composition is the most important attribute used to control oxidation stability, all edible oils are affected by lipid oxidation irrespective of whether they are highly unsaturated or not. The aim of the study was to compare the oxidation of rapeseed oil (RO) and butter oil (BO) triacylglycerols (TAGs) and their mixtures containing 10% or 20% of the other. Oxidation of the TAGs at 40°C was followed by formation of primary and secondary products. Statistical methods were used to interpret the data. The RO and BO TAGs and their mixtures began to oxidise without any induction periods. In the RO TAGs more hydroperoxides and p‐anisidine reactive compounds were formed than in the BO TAGs. The BO TAGs oxidised more than would be expected by their fatty acid composition. High susceptibility of BO TAGs to oxidation was caused by the easy breakdown of their hydroperoxides. Heptadienal and heptenal were specific products of oxidised RO TAGs and heptanal and nonenal of oxidised BO TAGs. Mixtures of RO and BO TAGs behaved according to which was dominant in the mixture. However, as little as 10% of RO or BO TAG introduced its specific oxidation products to the mixture. © 1999 Society of Chemical Industry     

Measurement of oxidation of polyunsaturated fatty acids by spectrophotometric assay of conjugated derivatives

A procedure has been developed for measuring the extent of oxidative deterioration of polyunsaturated fatty acids. The method is based on the conversion of fatty acid hydroperoxides and compounds derived from them, oxodienes and hydroxydienes, to conjugated fatty acids with strongly chromophoric triene and tetraene structures. This is done in two steps in which reduction with sodium borohydride is followed by dehydration under acid conditions; the chromophores produced are measured by absorbance in the ultraviolet. The method has been investigated using methyl linoleate and methyl linolenate as model compounds. Dienoic fatty acid oxidation products give rise to a conjugated triene chromophore whilst the more polyunsaturated fatty acids form a conjugated tetraene chromophore. The sum of absorbance changes at 268 and 301 nm measure the degree of oxidation. The ratio of absorbance change at 301 nm divided by that at 268 nm varies from zero for a pure triene to 2.8 for a pure tetraene and is a measure of the type of polyunsaturated fatty acid being oxidised. The concentration of oxodiene component present in the original mixture may be estimated separately by the decrease in the 275 nm region during the reduction step.     

Impact of surfactant type, pH and antioxidants on the oxidation of methyl linoleate in micellar solutions

The oxidation of methyl linoleate micelles has been studied, aiming at elucidating the effect of various variables, including surfactant type, pH and antioxidants. The progress of the methyl linoleate oxidation was evaluated by measurement of conjugated dienes hydroperoxides (CDHP) and malondialdehyde (MDA). It was shown that the oxidative stability of methyl linoleate micelles was influenced by surfactant type, with oxidative rate being greater in SDS micelles than in Tween 20 micelles. Besides, the methyl linoleate micelles at pH 6.8 had greater rates of lipid oxidation than their pH 3.0 counterparts. Moreover, the incorporation of VE and VC in the methyl linoleate micelles successfully slowed the formation of hydroperoxides and their subsequent decomposition product MDA. However, the antioxidant activities of VE and VC were related to their concentrations.     

The high performance liquid chromatographic determination of total malondialdehyde in vegetable oil with dansyl hydrazine

A simple high-performance liquid chromatographic (h.p.l.c.) method has been developed for determining total malondialdehyde (MDA), including free MDA and MDA released from its precursor in vegetable oils. Free MDA was reacted with dansyl hydrazine in an acidic medium, and the product, 1-dansyl-pyrazole(DP), was determined by h.p.l.c. The reaction releasing MDA from its precursor requires Fe³⁺ in 5% hydrochloric acid medium. Recoveries of free MDA and tetramethoxypropane (used as an MDA precursor) in vegetable oils were satisfactory. During autoxidation, a remarkable difference between the DP values of methyl oleate, methyl linoleate and some vegetable oils, and that of methyl linolenate was observed. Only methyl linolenate released MDA during autoxidation. For autoxidised methyl linolenate the DP value correlated with the thiobarbituric acid(TBA) value, although the DP value was only 30% of the TBA value.     

Use of fatty acid methyl esters and edible fats and oils to reduce soft scald of apples

The incidence of soft scald that developed on Jonathan apples during cool storage was reduced by post-harvest dipping of the fruit in solutions of a wide range of fatty acid methyl esters and glyceride-type fats and oils. Compounds which reduced the disorder were: methyl laurate, methyl palmitate, methyl stearate, methyl oleate, methyl linoleate, methyl linolenate, palm oil, sunflower oil, safflower oil, coconut oil, lard and lecithin.     

Autoxidation of methyl linolenate. The effect of antioxidants on product distribution

Studies on autoxidation of polyunsaturated fatty acids in the presence of antioxidants have shown that there can be significant differences in the proportions and types of products produced in ‘inhibited’ autoxidations, as compared with control autoxidations, in the absence of an antioxidant. The autoxidation of methyl linolenate has been used as a model system with which to study the effects of different concentrations of both natural and synthetic antioxidants on the proportions of the various types of oxidation product formed. The antioxidants studied included α-, γ-, and δ-tocopherol, α-tocotrienol, 2,2,5,7,8-pentamethylhydroxychroman (PMHC), 2,6-di-tert-butyl-4-methylphenol (BHT), 3-tert-butyl-4-hydroxyanisole (BHA), and mono-tert-butylhydroquinone (TBHQ). In order to investigate the effect of the antioxidants, the oxidation products were analysed for the proportions of diperoxides and monohy-droperoxides present, and the monohydroperoxide class was further analysed for the proportions of cis, trans and trans, trans dienes and ‘inner’ and ‘outer’ hydroperoxides. In all cases where any significant oxidation occurred the extent of the change in product distribution caused by the antioxidant increased as the antioxidant concentration increased. In many cases the extent of methyl linolenate oxidation occurring under standard conditions (after 100 h at 40°C) also increased as the antioxidant concentration increased, but this was not so for δ-tocopherol, BHT and TBHQ. The importance of these findings in relation to food systems and to the understanding of antioxidant behaviour is discussed.     

Autoxidation of methyl linolenate and methyl linoleate: The effect of α-tocopherol

α-Tocopherol substantially affects the distribution of peroxidic compounds formed during the autoxidation of methyl linolenate and methyl linoleate. In the autoxidation of both these unsaturated fatty acid esters the proportion of monohydroperoxides with conjugated double bonds in the trans, trans configuration is reduced until at high concentrations of α-tocopherol (5%) only cis, trans isomers are formed. In the autoxidation of methyl linolenate the proportion of hydroperoxy-epidioxides is reduced and only monohydroperoxides are formed when 5% α-tocopherol is present. The results are discussed in terms of recent findings concerning the mechanism of the autoxidation of unsaturated lipids.     

THE QUALITY OF VEGETABLE OIL FROM THREE VARIETIES OF SUNFLOWER SEEDS (HELIANTHUS ANNUUS)

ABSTRACT

Vegetable oils become susceptible to oxidation during their processing. The appropriate extraction and refining conditions of oil from two experimental cultivars (Madero‐91 and Cianoc‐2) of sunflower seeds and a commercial one (Victoria) as a control, were studied. Isopropyl alcohol was used in the extraction and refining, and compared with hexane. The refining was performed by the miscella method at 40, 50, 60 and 70%. Free fatty acids (FFA) and malonaldehyde analysis of crude oils afforded no significant differences among solvents and sunflower varieties. In refined oils, differences found with the miscella concentration, the malonaldehyde content and FFA content were not significant. Cianoc‐2 was the best source for oil production because of its lower values in FFA and malonaldehyde content.

PRACTICAL APPLICATIONS

The use of hexano in refining vegetable oil in Mexico is common, lack of knowledge about the use of new solvents and their impact on the processing conditions with sunflower seed cultivars is lack. The present work describes at lab scale, the work conditions, advantages and posibilities and limitations of the use on isopropyl alcohol in comparison with hexane and the use of three Mexican cultivar with this approach, with emphasize in oxidation conditions of refined vegetable oil.

     

气相色谱内标法测定油脂中脂肪酸绝对含量

以十七酸甲酯为内标物,求取了十七酸甲酯相对于棕榈酸甲酯、硬脂酸甲酯、油酸甲酯、亚油酸甲酯和亚麻酸甲酯的校正因子。通过气相色谱面积归一化法对油脂中脂肪酸绝对含量进行了测定,所得结果准确,具有较强的实用价值。     

Properties of Broad Bean Lipoxygenase

An improved method of assay of lipoxygenase (E.C.1·13·1·13) was introduced by initiating and following the reaction in the spectrophotometric cell. The enzyme was extracted from broad bean (View faba) and purified fifty folds. It oxidized linoleate but not oleate and the rate of linoleate and linolenate oxidation were found to be practically the same. The enzyme had an optimum pH of 6.0 and an optimum temp of 30°C. The activation energy was found to be 7.1 KCal/mole and the Km for linoleate 2.8 × 10^a-3M.     

Antioxidant activity and characterization of volatile constituents of beechwood creosote

Volatile constituents of beechwood creosote were determined using gas chromatography (GC) and gas chromatography–mass spectrometry (GC‐MS). The major volatile constituents of creosote were 2‐methoxyphenol (guaiacol; 25.2%) 2‐methoxy‐4‐methylphenol (4‐methylguaiacol; 21.4%), 3‐methylphenol (m‐cresol; 8.3%) 4‐methylphenol (p‐cresol; 7.9%) 2‐methylphenol (o‐cresol; 4.6%) and phenol (2.8%). The antioxidant activity of creosote was evaluated by three different chemical assays. Beechwood creosote exhibited potent inhibitory effects on the formation of conjugated diene hydroperoxides (from methyl linoleate) at concentrations of 500, 750 and 1000 µg ml^?1. Creosote had a potent inhibitory effect on the oxidation of hexanal for 40 days at a level of 5 µg ml^?1 and also inhibited malonaldehyde (MA) formation from ethyl arachidonate by 92% at a level of 50 µg ml^?1. The antioxidative activity of creosote was comparable with that of the well‐known antioxidants α‐tocopherol and BHT in the hexanal assay. However, creosote displayed comparatively lower antioxidant activity in the other two assays. Copyright © 2005 Society of Chemical Industry     

Changes in wheat lipids during mixing and resting of flour-water doughs

Lipids extracted with water-saturated n-butanol from flour and flour-water doughs were examined to determine the extent of oxidations and other changes which occurred in mixing and resting dough. Extracted lipids were converted to fatty acid methyl esters (FAME) and quantified by gas-liquid chromatography (g.l.c.) using heptadecanoic acid (17 : 0) as internal standard. The original flour or dough and the corresponding solvent-extracted residues were acid hydrolysed, and the hydrolysate lipids converted to FAME for g.l.c. determination of the total lipid and residual unextracted lipid contents. The total flour or dough lipids equalled the extracted lipids + unextracted lipids, except where there were unavoidable autoxidative losses of linoleate (18 : 2) and linolenate (18 : 3). The unextracted flour lipids (13% of total lipids) were not oxidised during dough mixing. There were no changes in any of the extracted lipid classes other than free fatty acids (FFA) and monoglycerides (MG) which showed losses of 18 : 2 and 18 : 3 after aerobic dough mixing. Losses of FFA and MG are attributed to lipoxygenase activity during dough mixing and the period immediately after. The small amount of 18 : 2 in the “free” petroleum ether-extracted FFA appeared to be unaffected by lipoxygenase. Recoveries of FFA other than 18 : 2 or 18 : 3 were constant, indicating no lipolysis of glycerolipids and no general oxidation or degradation of FFA. Experiments with [U-¹⁴C]palmitic acid confirmed that there was no oxidation, degradation or re-esterification of FFA. Much of the non-polar lipids (steryl ester, triglyceride, diglyceride, FFA, MG) and almost all of the polar lipids were bound on dough mixing. Binding was non-selective with regard to fatty acid composition. Triglyceride was the only lipid class bound to a greater extent in anaerobic dough than in aerobic dough. Some selectivity of binding between lipid classes was indicated.     

Studies on dimerisation of tocopherols under the influence of methyl linoleate peroxides

The stability of plant oils is related to the level of polyunsaturated fatty acids and the presence of native antioxidants--especially tocopherols. During storage, lipids or the fat products undergo oxidation and tocopherol dimers and trimers are formed. These compounds possess reducing and antioxidant properties and participate in oxidation clearly inhibiting this process. In the present study, the correlation between levels of peroxides formed during autoxidation of methyl linoleate and simultaneous decomposition of tocopherols was examined. The peroxide value was investigated. Quantities of decomposed tocopherols and formation of their dimers were determined by high-performance liquid chromatography (HPLC). Mass spectrum analysis confirmed thatthe analysed compounds were dimes. Dimerisation of gamma-T begins at the smaller quantity of the methyl linoleate peroxides than dimerisation of delta-T. At the beginning of methyl linoleate autoxidation dimerisation of gamma-T in relation to its loss was smaller. The quantity of gamma-T dimers with ether bonds in total dimers pointed to faster binding of phenoxy radicals than transformation into the phenyl ones. delta-T dimers with phenyl bonds constitute about 65% of the total. The quantity of peroxides in methyl linoleate, necessary for quantitative and qualitative changes of homologous tocopherols, decreased from delta-T to alpha-T.     

Comparative study of the essential oil composition of Salvia urmiensis and its enzyme inhibitory activities linked to diabetes mellitus and Alzheimer’s disease

The genus Salvia has economic importance due to its broad uses in traditional medicine, perfume, food, and pharmaceutical industries. In the present work, various extracts and essential oils of Salvia urmiensis Bunge., were screened for their inhibitory activity against acetylcholinesterase and butyrylcholinesterase, the enzymes linked to neurodegeneration, and against α-amylase and α-glucosidase (involved in diabetes mellitus; DM). Chemical compositions of the essential oils of leaves and flowers of the plant were also determined. The tested samples exhibited moderate to high anti-diabetic potential (IC₅₀ = 8–145 µg/mL) and moderate anticholinesterase activity (IC₅₀ = 44–892 µg/mL). Essential oil of leaves was rich in ester compounds such as ethyl linoleate (19%), methyl hexadecanoate (17%), and methyl linoleate (7.5%). The major compound of essential oil of flowers was 6,10,14-trimethyl-2-pentadecanone (55.7%). This is the first report on the enzyme inhibitory activity of S. urmiensis and also the chemical composition of its leaves and flowers in essential oils. The results indicated that S. urmiensis could be considered a valuable source for functional foods and pharmaceuticals.     

4-Oxo-2-nonenal as a pro-oxidant during the autoxidation of methyl linoleate in bulk phase

The effect of aldehydic lipid peroxidation products on the autoxidation of methyl linoleate (MeL) was studied at 60 °C in bulk phase. Addition of 4-oxo-2-nonenal (ONE) to MeL accelerated the formation of MeL hydroperoxides. Other tested aldehydes showed no effect on the rate of MeL autoxidation. The pro-oxidative effect of ONE disappeared when pre-existing peroxides and transition metals were removed from MeL. Further addition of ferric ion to the peroxide- and metal-free MeL recovered its pro-oxidative effect. ONE reduced ferric ion to ferrous ion effectively. Furthermore, it had a chelating ability with ferrous ion. The results suggest that the pro-oxidative effect of ONE is due to its ability to reduce transition metals and to chelate the reduced form of metal ions. Thus, ONE could accelerate the metal-dependent lipid peroxidation.     

Potential use of extra virgin olive oil in bakery products rich in fats: a comparative study with refined oils

The lipid fraction of bakery products undergoes a significant degradation during baking, with an increase in undesirable oxidised substances, that can act as catalysts for further oxidative reactions during storage reducing the product shelf life. The use of extra virgin olive oil in bakery products rich in fat in place of refined oils was studied, assessing the evolution of the oxidative and hydrolytic degradation during storage. Two‐way analysis of variance, followed by Tukey's HSD test for multiple comparisons, covariance and principal component analyses were carried out to compare the effect of the type of oils. The data obtained showed that the evolution of the oxidation levels in the analysed samples during storage was related to the type of oil used in the production process. Particularly, the use of extra virgin olive oil led to significantly lower values of hydroperoxides, ultraviolet absorption constants, triacylglycerol oligopolymers and oxidised triacylglycerols.     

基于主成分分析法的安溪铁观音香气质量评价模型的构建

从4个季节(每个季节两个等级)共8个安溪铁观音茶样中提取并分离出74种香气组分。通过主成分分析法鉴定出安溪铁观音中的主要特征香气成分,它们分别是：橙花叔醇、法呢烯、吲哚、苯乙醇、反-2-己烯醛、壬醛、苯乙醛、亚油酸甲酯、亚麻酸甲酯、棕榈酸甲酯、顺-己酸-3-己烯酯、苯甲酸-3-己烯-1-醇酯、辛酸-2-苯乙酯、5-正丁基-δ-戊内酯、顺式茉莉酮、法尼基丙酮、棕榈酸、香叶基芳樟醇异构体。利用主成分分析法,基于综合评价函数F＝β1F1＋β2F2＋…＋βkFk构建了安溪铁观音香气质量的评价模型,以不同特征值的方差贡献率βi(i＝1,2,…,k)为加权系数,利用所建立的模型计算各样本得分,然后进行排序评价各个茶样的香气质量。通过感官评价法进一步对模型评价结果进行了检验,结果显示两种方法具有很好的一致性,表明所建立的方法是可行的。     

3种生物柴油氧化降解特性研究

利用Rancimat试验法氧化降解菜籽油生物柴油、大豆油生物柴油、小桐子油生物柴油,采用GC-MS测定不同氧化时间下的生物柴油中主要脂肪酸甲酯含量变化,进而通过半衰期法计算动力学参数(反应级数、速率常数),同时研究生物柴油氧化深度与热值的关系,并对氧化前后生物柴油样品进行FTIR分析。研究表明:除大豆油生物柴油中的硬脂酸甲酯外,3种生物柴油中主要脂肪酸甲酯氧化降解反应级数都为1;氧化降解反应速率从小到大依次为棕榈酸甲酯、硬脂酸甲酯、油酸甲酯、亚油酸甲酯、亚麻酸甲酯;氧化降解时间与热值为一元三次函数关系;另外,FTIR分析表明在1 740 cm~(-1)处的吸光度随着氧化降解时间延长不断增加,说明氧化程度不断加深。     

Triglyceride species compositions of common edible vegetable oils and methods used for their identification and quantification

The chromatographic, spectrophotometric, and spectroscopic methods used for detection, identification, and quantification of the triglyceride (TG) species present in common edible vegetable oils are reviewed. The TG species identified in each kind of oil and their percentage distributions reported in literature are presented in tabular form. Data on oils from the following 10 sources are reviewed: corn, cottonseed, grapeseed, linseed, olive, palm, peanut, rapeseed, soybean, and sunflower. The number of TG species identified in these vegetable oils ranged from 20 (grapeseed oil (GR)) to 79 (peanut oil (PN)), with six (GR) to 13 (PN) different fatty acyl moieties contributing to their molecular structures. The quantitative levels reported ranged from traces (below 0.1%) to 49.7% (trilinolenin in linseed oil) and 54.6% (triolein in olive oil), respectively. The highest mean values (30-35%) correspond to four predominant TG species (dipalmitoylolein, trilinolein, trilinolenin, and triolein).