Linoleic acid requirement of rats fedtrans fatty acids

The amount of linoleic acid required to prevent undesirable effects of C18trans fatty acids was investigated. In a first experiment, six groups of rats were fed diets with a high content oftrans fatty acids (20% of energy [en%]), and increasing amounts of linoleic acid (0.4 to 7.1 en%). In a second experiment, four groups of rats were fed diets designed to comparetrans fatty acids with saturated andcis-monounsaturated fatty acids of the same chain length at the 2 en% linoleic acid level. After 9–14 weeks, the oxygen uptake, lipid composition and ATP synthesis of heart and liver mitochondria were determined. The phospholipid composition of the mitochondria did not change, but the fatty acid compositions of the two main mitochondrial phospholipids were influenced by the dietary fats.Trans fatty acids were incorporated in all phospholipids investigated. The linoleic acid level in the phospholipids, irrespective of the dietary content of linoleic acid, increased on incorporation oftrans fatty acids. The arachidonic acid level had decreased in most phospholipids in animals fed diets containing 2 en% linoleic acid. At higher linoleic acid intakes, the effect oftrans fatty acids on the phospholipid arachidonic acid level diminished. However, in heart mitochondrial phosphatidylethanolamine,trans fatty acids significantly increased the arachidonic acid level. Despite these changes in composition, neither the amount of dietary linoleic acid nor the addition oftrans fatty acids influenced the mitochondrial function. For rats, a level of 2 en% of linoleic acid is sufficient to prevent undesirable effects of high amounts of dietary C18trans fatty acids on the mitochondrial function.     

Lipase‐mediated hydrolysis of flax seed oil for selective enrichment of α‐linolenic acid

Polyunsaturated fatty acids (PUFA) are important ingredients of human diet because of their prominent role in the function of human brain, eye and kidney. α‐Linolenic acid (ALA), a C18, n‐3 PUFA is a precursor of long chain PUFA in humans. Commercial lipases of Candida rugosa, Pseudomonas cepacea, Pseudomonas fluorescens, and Rhizomucor miehei were used for hydrolysis of flax seed oil. Reversed phase high performance liquid chromatography followed by gas chromatography showed that the purified oil contained 12 triacylglycerols (TAGs) with differences in fatty acid compositions. Flax seed oil TAGs contained α‐linolenic acid (50%) as a major fatty acid while palmitic, oleic, linoleic made up rest of the portion. Among the four commercial lipases C. rugosa has preference for ALA, and that ALA was enriched in free fatty acids. C. rugosa lipase mediated hydrolysis of the TAGs resulted in a fatty acid mixture that was enriched in α‐linolenic to about 72% yield that could be further enriched to 80% yield by selective removal of saturated fatty acids by urea complexation. Such purified ALA can be used for preparation of ALA‐enriched glycerides. Practical applications : This methodology allows purifying ALA from fatty acid mixture obtained from flax seed oil by urea complexation.     

Fatty acid and conjugated linoleic acid isomer profiles in human milk fat

The fatty acid composition of 39 mature human milk samples from four Spanish women collected between 2 and 18 weeks during lactation was studied by gas chromatography. The conjugated linoleic acid (CLA) isomer profile was also determined by silver‐ion HPLC (Ag⁺‐HPLC) with three columns in series. The major fatty acid fraction in milk lipids throughout lactation was represented by the monounsaturated fatty acids, with oleic acid being the predominant compound (36–49% of total fatty acids). The saturated fatty acid fraction represented more than 35% of the total fatty acids, and polyunsaturated fatty acids ranged on average between 10 and 13%. Mean values of total CLA varied from 0.12 to 0.15% of total fatty acids. The complex mixture of CLA isomers was separated by Ag⁺‐HPLC. Rumenic acid (RA, cis‐9 trans‐11 C18:2) was the major isomer, representing more than 60% of total CLA. Trans‐9 trans‐11 and 7‐9 (cis‐trans + trans‐cis) C18:2 were the main CLA isomers after RA. Very small amounts of 8‐10 and 10‐12 C18:2 (cis‐trans + trans‐cis) isomers were detected, as were different proportions of cis‐11 trans‐13 and trans‐11 cis‐13 C18:2. Although most of the isomers were present in all samples, their concentrations varied considerably.     

Influence of native antioxidants on the formation of fatty acid hydroperoxides in model systems

The effect of alpha‐tocopherol (alpha‐T) and quercetin on the formation of hydroperoxides of linoleic and linolenic acids during autoxidation at 60 ± 1 °C was investigated. Three isomers of hydroperoxides were detected using HPLC. Of isomers of linoleic acid hydroperoxides, 13‐hydroperoxy‐octadecadienoic acid trans‐trans (13‐HPODE t‐t), 9‐HPODE cis‐trans (9‐HPODE c‐t) and 9‐HPODE trans‐trans (9‐HPODE t‐t) were identified, constituting 64, 19 and 17% of the total amount, respectively. For linolenic acid, the components 13‐hydroperoxy‐octadecatrienoic acid trans‐trans (13‐HPOTE t‐t), 9‐HPOTE c‐t and 9‐HPOTE t‐t contributed 7, 33 and 60% to the total, respectively. The different dominant hydroperoxide isomers detected in linoleic and linolenic acids during oxidation are related to their chemical structure and the microenvironment of emulsion droplets. The ratios between specific isomers for both fatty acid hydroperoxides did not change during oxidation with or without antioxidants. Alpha‐T effectively inhibited the oxidation of fatty acids and reduced the formation of hydroperoxides. The total amount of the hydroperoxides decreased along with the increase in the concentration of alpha‐T, 1–40 µM. Quercetin inhibited the oxidation of both fatty acids at similar efficiency only at 40 µM concentration. A synergistic antioxidant effect of quercetin with alpha‐T in a binary system on both fatty acids was observed.     

Supercritical Carbon Dioxide Extraction,Fatty Acid Composition,Oxidative Stability,and Antioxidant Effect of Torreya grandis Seed Oil

Torreya grandis seed oil (TGSO) extraction with supercritical carbon dioxide was explored from the extraction conditions, fatty acid composition, its oxidative stability and antioxidant activity in a bench‐scale apparatus. An L₉(3⁴) orthogonal design was applied to optimize extraction parameters. The results demonstrated that the maximum yield of 94.57 % was obtained at 45 MPa, 4 h and 50 °C. There were 18 kinds of compounds found within TGSO; the predominant ingredient was linoleic acid (42.02 %), followed by oleic acid (32.14 %) and dihomo‐γ‐linolenic acid (9.80 %). The IC₅₀ values for 1,6‐bis(diphenylphosphino) hexane radical (DPPH), hydroxyl radical (HO?) and superoxide radical (O₂^·?) were 5.61, 3.16 and 4.20 mg/mL, respectively.     

Lack of effects oftrans fatty acids on eicosanoid biosynthesis with adequate intakes of linoleic acid

The minimum requirement of linoleic acid to prevent effects of dietary C18trans fatty acids on eicosanoid biosynthesis in rats was assessed. In a first experiment, six groups of animals were fed diets with a high content oftrans fatty acids [20% of energy (en%)], and increasing amounts of linoleic acid (0.4 to 7.1 en%). In a second experiment, four groups of rats were fed diets designed to comparetrans fatty acids with saturated andcis-monounsaturated fatty acids of the same chain length at the 2 en% linoleic acid level. After 9–14 weeks the biosynthesis of prostacyclin by pieces of aorta and the biosynthesis of hydroxy-heptadecatrienoic acid and 12-hydroxy-eicosatetraenoic acid by platelets were measured. The fatty acid compositions of aorta phospholipid and platelet lipid were also determined. Both the prostacyclin-production by aorta pieces and the production of hydroxy-heptadecatrienoic acid and 12-hydroxy-eicosatetraenoic acid by platelets appeared to be a linear function of the arachidonic acid level in aorta phospholipid and platelet lipid, irrespective of thetrans fatty acid content in the diet. This indicates thattrans fatty acids do not directly influence enzymes involved in eicosanoid biosynthesis. In a direct comparison withcis-monounsaturated or saturated fatty acids with 2 en% linoleic acid in the diet, only a moderate reduction in arachidonic acid level in aorta phospholipids in the group fedtrans fatty acids was observed. The geometry of the double bond did not influence the arachidonic acid level in platelet lipid, although the diet rich in saturated fatty acids increased arachidonic acid levels significantly compared with all other diets. Neither prostacyclin-production nor hydroxy-heptadecatrienoic acid or 12-hydroxy-eicosatetraenoic acid-production were significantly affected bytrans fatty acids when 2 en% linoleic acid was present in the diet. Our study indicates that in rats 2 en% linoleic acid is sufficient to prevent effects of dietarytrans fatty acids on eicosanoid synthesis.     

Directed sequential synthesis of conjugated linoleic acid isomers from Δ7, 9 to Δ12, 14

Position and configuration isomers of conjugated linoleic acid (CLA), from 7, 9‐ through 12, 14‐C18:2, were synthesized by directed sequential isomerizations of a mixture of rumenic (cis‐9, trans‐11 C18:2) and trans‐10, cis‐12 C18:2 acids. Indeed, the synthesized conjugated fatty acids cover the range of unsaturated systems as found in milk fat CLA. The two‐step sequence consisted in initial sigmatropic rearrangement of cis/trans CLA isomers at 200 °C for 13 h under inert atmosphere (Helium, He), followed by selenium‐catalyzed geometrical isomerization of double bonds at 120 °C for 20 h under He. Product analysis was achieved by gas‐liquid chromatography using a 120 m polar capillary column coated with 70% cyanoalkylpolysiloxane equivalent polymer. Migration of conjugated systems was geometrically controlled as follows: the cis‐C_n, trans‐C_n+2 double bond system was rearranged through a pericyclic [1, 5] sigmatropic mechanism into a trans‐C_n‐1, cis‐C_n+1 unsaturated system, while the trans‐C_n, cis‐C_n+2 double bond system was rearranged through a similar pericyclic mechanism into a cis‐C_n+1, trans‐C_n+3 unsaturated system. Selenium‐catalyzed geometrical isomerization under mild conditions then allowed cis/trans double bond configuration transitions, resulting in the formation of all cis, all trans, cis‐trans and trans‐cis isomers. A sequential combination of the two reactions resulted in a facile controlled synthesis of CLA isomers, useful for the chromatographic identification of milk fat CLA, as well as for the preparation of CLA standard mixture.     

Geometrical isomerization of polyunsaturated fatty acids in physically refined rapeseed oil during plant‐scale deodorization

The effect of the operating temperature (between 220 and 270 °C) on the formation of trans isomers of linoleic and linolenic acids in physically refined rapeseed oil during deodorization in a plant‐scale semicontinuous tray‐type deodorizer (capacity 10 t/h) was investigated. The industrial procedures of physical refining consisted of a two‐step bleaching and deodorization process. The degree of isomerization of linoleic acid ranged from 0.33 to 4.77% and that of linolenic acid from 4.43 to 45.22% between 220 and 270 °C, respectively. A relation between the logarithm of the degree of isomerization and the deodorization temperature can be approximated by statistically highly significant linear functions for both linoleic and linolenic acids. Oleic acid was resistant to the heat‐induced geometrical isomerization. The values found for the ratio between the degrees of isomerization of linolenic and linoleic acids, slightly decreasing with increasing temperature, were equal to 13.6 and 12.9 at 230 and 240 °C, respectively. Two trans isomers of linoleic acid, exclusively with one double bond isomerized into trans configuration, and four trans isomers of linolenic acid, mostly with one double bond isomerized into trans configuration, were determined in deodorized rapeseed oils. Linolenic acid was observed to be the main source responsible for the formation of nearly all trans fatty acids in physically refined rapeseed oil. At 235 °C, a deodorization temperature considered as a reasonable technological compromise, the content of trans fatty acids in plant‐scale physically refined rapeseed oil was less than 1% of total fatty acids, which would be acceptable for further application.     

Triacylglycerols from viper bugloss (Echium vulgare L.) seed bio‐oil

Triacylglycerols (TAG) in viper bugloss oil were isolated from raw pressed oil by silicic acid column chromatography. The obtained blend of TAG was separated by silver ion thin‐layer chromatography (TLC Ag⁺) into nine fractions, varying in terms of unsaturation level and molecular polarity. The composition of TAG in viper bugloss oil was determined by HPLC coupled with a diode‐array detector and an evaporative light‐scattering detector. The results showed that the first three fractions were combinations of TAG containing palmitic, oleic and linoleic acids. Fractions 4 and 6 contained TAG of a similar acid composition as above, but with the addition of γ‐linolenic acid. The remaining fractions (7–9) were the most varied in acid composition. They were found to contain 26–39% palmitic acid, 12–15% oleic acid, 13–41% linoleic acid 8–24% γ‐linolenic acid, 1.5–5.5% α‐linolenic acid and 1–5% stearidonic acid. The analysis of fatty acid allocation in TAG of viper bugloss lipids revealed that linoleic acid (ranging from 2 to 100%) was the only acid found in all isolated fractions. In the investigated oil, the predominant TAG included: LnLnG (11.38%), LnLnSt (11.17%), LnGSt (7.71%), LnStSt (6.19%) and LnLnLn (5.44%). Almost 86% of the TAG contained α‐linolenic acid, while γ‐linolenic and stearidonic acids amounted to 49 and 38%, respectively.     

Effects of conjugated linolenic acid and conjugated linoleic acid on lipid metabolism in mice

The effects of two isomers of conjugated linolenic acid (CLnA), α‐eleostearic acid (α‐ESA) and punicic acid (PA), on body fat and lipid metabolism were investigated, compared with a conjugated linoleic acid (CLA) mixture (primarily cis9,trans11‐ and trans10,cis12‐18:2) and α‐linolenic acid (ALA), a non‐conjugated octadecatrienoic acid, in the present study. ICR mice were fed either a control diet or one of four experimental diets supplemented with 1% α‐ESA, 1% PA, 1% CLA mixture and 1% ALA in the form of triacylglycerols (TAG) for 6 weeks. The weights of perirenal and epididymal adipose tissues were significantly decreased while the liver weight was significantly increased in mice fed CLA, compared with the control. In contrast to CLA, the tissue weights in α—ESA‐, PA‐ and ALA‐fed mice were not affected. No significant differences were observed in TAG, total cholesterol, high‐density lipoprotein and low‐density lipoprotein cholesterol levels among the five groups. The liver TAG level was significantly decreased in mice fed α‐ESA and PA while it was significantly increased in mice fed the CLA mixture. These results indicate that CLnA and CLA have differential effects on body fat mass and liver TAG levels in mice.     

N‐3 fatty acids for human nutrition: stability considerations

Currently there is great interest in dietary n‐3 fatty acids to promote health. The food industry aims to produce food products enriched in α‐linolenic acid (Ln), eicosapentaenoic acid (EPA) and/or docosahexaenoic acid (DHA) to reduce some of the physiological effects of linoleic acid (L), the major polyunsaturated fatty acid in our diet. However, the goal is hampered by the susceptibility of the n‐3 fatty acids to oxidation. As a result the sensory and nutritional quality of such foods deteriorates. Lipid scientists therefore have to find a way to stabilise these fatty acids. Innovative technologies to protect n‐3 polyunsaturates using antioxidants, adequate preparation, refining and packaging of the oil are needed. In this paper we review the inherent stability and the stabilisation of these nutritionally valuable polyunsaturated fatty acids.     

Deodorization of vegetable oils: Prediction of trans polyunsaturated fatty acid content

Kinetics of the formation of trans linoleic acid and trans linolenic acid were compared. Pilot plant-scale tests on canola oils were carried out to validate the laboratory-scale kinetic model of geometrical isomerization of polyunsaturated fatty acids described in our earlier publication. The reliability of the model was confirmed by statistical calculations. Formation of the individual trans linoleic and linolenic acids was studied, as well as the effect of the degree of isomerization on the distribution of the trans fatty acid isomers. Oil samples were deodorized at temperatures from 204 to 230°C from 2 to 86 h. Results showed an increase in the relative percentage of isomerized linolenic and linoleic acid with an increase in either the deodorization time or the temperature. The percentage of trans linoleic acid (compared to the total) after deodorization ranged from <1 to nearly 6%, whereas the percentage of trans linolenic acid ranged from <1 to >65%. Applying this model, the researchers determined the conditions required to produce a specially isomerized oil for a nutritional study. The practical applications of these trials are as follows: (i) the trans fatty acid level of refined oils can be predicted for given deodorization conditions, (ii) the conditions to meet increasingly strict consumer demands concerning the trans isomer content can be calculated, and (iii) the deodorizer design can be characterized by the deviation from the theoretical trans fatty acid content of the deodorized oil.     

Analysis of fatty acid profile in plasma phospholipids by solid‐phase extraction in combination with GC

Phospholipids are recognised as an important source and transport form for metabolically active fatty acids. Therefore, detailed analysis of fatty acid profiles in plasma phospholipids as marker for dietary habits or interventions gains more and more importance. Appropriate analytical methods described so far are either expensive or susceptible to handling errors. We developed a method to separate plasma phospholipids by acetone fractionation combined with SPE in order to analyse the fatty acid compositions in phospholipid fractions of human plasma by GC analysis. The method has been validated in order to be applied to the routinely performed analysis of the samples of patients who will be participating in a dietary supplement study. The method presented here was successfully validated and is stable, efficient and reproducible. It can be used in a routine fashion to deliver the fatty acid profile [palmitic acid (16:0), heptadecanoic acid (17:0), stearic acid (18:0), oleic acid (18:1n‐9), linoleic acid (18:2n‐6), linolenic acid (18:3n‐3), arachidonic acid (20:4n‐6), eicosapentaenoic acid (20:5n‐3) and docosahexaenoic acid (22:6n‐3)] in plasma phospholipid samples. Using a sample volume of 500 µL, recovery of plasma phospholipids is 92 ± 11%; LOQ is 2.2 µg fatty acid/mL. A set of samples from cancer patients and healthy individuals was analysed and confirmed the applicability of the described method.     

Determination of the fatty acid profile by 1H‐NMR spectroscopy

The common unsaturated fatty acids present in many vegetable oils (oleic, linoleic and linolenic acids) can be quantitated by ¹H‐nuclear magnetic resonance spectroscopy (¹H‐NMR). A key feature is that the signals of the terminal methyl group of linolenic acid are shifted downfield from the corresponding signals in the other fatty acids, permitting their separate integration and quantitation of linolenic acid. Then, using the integration values of the signals of the allylic and bis‐allylic protons, oleic and linoleic acids can be quantitated. The procedure was verified for mixtures of triacylglycerols (vegetable oils) and methyl esters of oleic, linoleic and linolenic acids as well as palmitic and stearic acids. Generally, the NMR (400 MHz) results were in good agreement with gas chromatographic (GC) analyses. As the present ¹H‐NMR‐based procedure can be applied to neat vegetable oils, the preparation of derivatives for GC would be unnecessary. The present method is extended to quantitating saturated (palmitic and stearic) acids, although in this case the results deviate more strongly from actual values and GC analyses. Alternatives to the iodine value (allylic position equivalents and bis‐allylic position equivalents) can be derived directly from the integration values of the allylic and bis‐allylic protons.     

Influence of different fats in pig feed on fatty acid composition of phospholipids and physical meat quality characteristics

Two feeding experiments (i, ii) were conducted to investigate the influence of different dietary fats on the fatty acid (FA) composition of phospholipids as well as meat quality in pigs. In each experiment 12�4 siblings of Swiss Landrace or Large White breed were allocated to one of four feeding treatments according to sex, breed, and litter and fattened from about 25 to 105 kg liveweight. Pigs were fed a control diet (barley, wheat, soybean meal) or the control diet supplemented with 7% pork fat, 4.95% olive oil or 3.17% soybean oil (i) or 5% of olein or stearin fraction of pork fat or hydrogenated fat (ii). The dietary FA composition was reflected in the FA composition of phospholipids in M. long. dorsi and triceps brachii. However, the unsaturated to saturated ratio was not affected by the dietary intake of polyunsaturated FAs and was only slightly increased by the olive oil supplementation. Trans FAs including conjugated linoleic acid were incorporated into phospholipids only to a small extent. The dietary altered fatty acid composition of phospholipids did not cause any effect on pH, cooking loss, texture, or colour of pork, but meat quality as well as the proportion of saturated FA, arachidonic acid, and n‐3 fatty acids were significantly influenced by genetic effects.     

A critical review of methods used to estimate linoleic acid Δ6‐desaturation ex vivo and in vivo

Δ6‐desaturase is located in a pivotal position in the metabolism of essential fatty acids (EFA). Various methods have been used to estimate Δ6‐desaturase activity, including the assessment of: (i) tissue fatty acid compositions (and associated product/precursor ratios), (ii) Δ6‐desaturase activities ex vivo, and (iii) isotopically labelled linoleic acid metabolism in vivo. This review critically examines these methods and considers their appropriateness and reliability in assessing linoleic acid metabolism in diabetes and cardiovascular disease. In general, there was a good agreement between the three methods and the effect of experimental diabetes on linoleic acid metabolism. In humans, however, the effect of diabetes on tissue fatty acid composition was inconsistent, and there was a paucity of data on linoleic acid metabolism ex vivo and in vivo. The inconsistency in human fatty acid compositional data may relate to variable and uncontrolled intakes of linoleic acid and its n‐6 metabolites, but also to a less extreme insulin deficiency as studied in animals. Risk markers for cardiovascular disease generally reduced rat liver Δ6‐desaturase activity ex vivo. This was not, however, reflected in tissue fatty acid compositions in these controlled studies. Linoleic acid metabolism, as determined by tissue fatty acid composition in humans, is reduced in cardiovascular disease; however, the omnivorous dietary patterns and decreased linoleic acid intakes make this conclusion potentially unreliable. Few stable‐isotope studies have been conducted on the effect of cardiovascular risk markers on linoleic acid metabolism, and there is a requirement for this type of work to be standardised to facilitate inter‐study comparisons. These studies may eventually help optimise EFA intake in health and disease conditions.     

Geometrical isomerisation of eicosapentaenoic and docosahexaenoic acid at high temperatures

Concentrates of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were heated at 140–240 °C for 2–8 h under nitrogen. The trans isomers were analysed by gas chromatography‐mass spectrometry on a BPX‐70 cyanopropyl column. All geometrical isomers of EPA and DHA with one trans double bond were observed. The rate constants (k) for the isomerisation of the all‐cis isomers were calculated and found to be higher than previously reported for linoleic acid and α‐linolenic acid. Arrhenius plots showed a linear relationship between ln k and the reciprocal absolute temperature above 180 °C. The distribution patterns of isomers with one trans double bond are approximately constant up to a degree of isomerisation of 25%. The degree of isomerisation can therefore be estimated from selected trans peaks.     

Analysis of genetic effects and heritabilities for linoleic and α‐linolenic acid content of Brassica napus L. across Chinese environments

A genetic model for quantitative traits of seed in diploid plant was applied to analyze the main genetic effects and genotype × environment (GE) interaction effects for linoleic and α‐linolenic acid content of rapeseed (Brassica napus L.) by using two year experimental data with 8 parents and their F₁ and F₂. Results indicated that the performance of linoleic (C18:2) and α‐linolenic acid content (C18:3) of rapeseed were simultaneously controlled by diploid embryo nuclear genes, cytoplasmic genes and diploid maternal plant nuclear genes, and the GE interaction effects for these two seed quality traits were more important than the genetic main effects. The total narrow‐sense heritability was 69.5% and 41.8% for C18:2 and C18:3, respectively, and the GE interaction heritabilities were found to be larger than the general heritabilities for both quality traits. It was suggested by the predicted genetic effects that Huashuang 3 was better than other parents for improving offspring of C18:2 and Youcai 601, Zhongyou 821, Eyouchangjia and Zhong R‐888 for decreasing C18:3.     

Lipids and human milk

To support the growth and development of the breast‐fed infant, human milk provides the dietary essential fatty acids, linoleic acid (LA; 18:2n‐6), α‐linolenic acid (ALA, 18:3n‐3), as well as longer‐chain polyunsaturated fatty acids including arachidonic acid (20:4n‐6) and docosahexanoic (DHA 22:6n‐3). The linoleic acid, alpha‐linolenic acid, DHA and arachidonic acid concentration of pasteurized and unpasteurized human milk remains stable during the first month of storage at –20°C and –80°C. However after the first month, a slow decrease in concentration progresses until the end of 6 months of storage at both temperatures. The levels of n‐6 and n‐3 fatty acids, particularly linoleic acid, alpha‐linolenic acid and DHA, in human milk vary widely within and among different populations, and are readily changed by maternal dietary intake of the respective fatty acid. The present paper reviews recent understanding from key researchers of maternal diet and human milk fat composition and form our work the effect of milk fat composition on storage conditions. It is important to understand that maternal diet can affect human milk fat composition and subsequently infant development and growth.