Quantitative determination of conjugated linoleic acid isomers in beef fat

The amounts of 14 conjugated linoleic acid (CLA) isomers (t12t14, t11t13, t10t12, t9t11, t8t10, t7t9, t6t8; 12,14 c/t, t11c13, c11t13, t10c12, 9,11 c/t, t8c10, t7c9‐18:2) in 20 beef samples were determined by triple‐column silver‐ion high‐performance liquid chromatography (Ag⁺‐HPLC). Quantitation was performed using an external CLA reference standard consisting of cis9,trans11‐18:2,trans9,trans11‐18:2 and cis9,cis11‐18: 2. Linearity was checked as being r > 0.9999 between 0.02 × 10^‐3 to 2 mg/ml. The determination limit (5‐fold signal/noise ratio) of the CLA reference was estimated to be 0.25, 0.50, 1.0 ng/injection for the cis/trans, trans,trans and cis,cis isomers, respectively. As expected, cis9,trans11‐18:2 was the predominant isomer (1.95 ± 0.54 mg/g fat) in beef, followed by trans7,cis9‐18:2 (0.19 ± 0.04 mg/g fat); cis,cis isomers were below the determination limit in most beef samples. Total CLA amounts determined by Ag⁺‐HPLC were compared to total CLAs determined by gas chromatography (GC, 100 m CPSil^TM 88 column). The amounts obtained by GC were generally higher than those determined by Ag⁺ ‐HPLC due to co‐eluting compounds.     

Preparation of conjugated linoleic acid from safflower oil

Synthetically prepared mixtures of conjugated linoleic acid (CLA) are widely used in animal and cell culture studies to investigate the potential effects of the Δ9c, 11t-18:2 isomer found in food products from ruminant animals. Alkali isomerization of linoleic acid is a common method used in the synthesis of a mixture of CLA isomers containing predominantly the Δ9c, 11t-18:2 and Δ10t, 12c-18:2 isomers. Some biological activity might also be mediated by the Δ10t, 12c-18:2 isomer. Currently few published methodologies exist describing procedures for the enrichment of these two isomers. A method is described herein to take advantage of an inexpensive oil, safflower oil, for use in synthesis of CLA and a procedure to enrich the Δ10t, 12c-18:2 isomer.     

Occurrence of conjugated linoleic acid isomers in beef

The amounts of Δ9,Δ11-conjugated linoleic acid (CLA) isomers were determined in loin-associated fat samples of bulls (n=6) and steers (n=7) by capillary gas chromatography of fatty acid methyl ester (FAME) derivatives. The main CLA-isomer—18:2 c9,t11—provided approximately 0.76 ± 0.15% and 0.86 ± 0.15% of total FAME in bulls and steers, respectively. No differences (P>0.05) were observed between the CLA isomer distribution of bulls (t9,c11, 0.026 ± 0.014%; c9,c11, 0.015 ± 0.008%; and t9,t11, 0.029 ± 0.003%) and steers (t9,c11, 0.027 ± 0.014%; c9,c11, 0.015 ± 0.005%; and t9,t11, 0.030 ± 0.007%).     

Emulsion-based pressure sensitive adhesives from conjugated linoleic acid/styrene/butyl acrylate terpolymers

Free radical emulsion terpolymerizations of conjugated linoleic acid (CLA), styrene (Sty), and butyl acrylate (BA) were performed at 80 °C. Terpolymers were characterized for composition, conversion, molecular weight and glass transition temperature, latexes were characterized for viscosity and particle size while adhesives were characterized for tack, peel strength, shear strength, storage modulus, loss modulus and tan delta. One impurity commonly found in CLA, oleic acid, was shown to influence the reaction kinetics significantly. Adhesive performance was tuned using divinylbenzene (DVB) crosslinker to keep the terpolymer molecular weight in a desired range. By using a constrained mixture design, the influence of terpolymer composition, chain transfer agent (CTA) concentration, DVB concentration, molecular weights, viscosity and particle size on tack, peel strength and shear strength was investigated. The final forms of the resulting empirical models allowed the creation of 3D response surfaces for pressure sensitive adhesive (PSA) performance optimization.     

Gas chromatographic analysis of diels-alder adducts of geometrical and positional isomers of conjugated linoleic acid

This research demonstrates the gas chromatographic analysis of the 4-methyl-1,2,4-triazoline-3,5-dione (MTAD) adducts derived from standards of cis,trans-9,11-octadecadienoic acid, trans,trans-9,11-octadecadienoic acid, and cis,cis-9,11-octadecadienoic acid. Methyl cis,trans-9,11-octadecadienoate and methyl trans,trans-9,11-octadecadienoate formed Diels-Alder addition products with MTAD to produce adducts with similar mass spectral fragmentation patterns but different retention times determined by gas chromatography/ mass spectrometry. Methyl cis,cis-9,11-octadecadienoate reacted slowly and produced two adducts with similar fragmentation patterns and different retention times. These results were comparable to those reported for an analogous series of conjugated hexadienes. Based on hexadiene reactions, methyl cis,trans-9,11-octadecadienoate produced a trans adduct as a major product while methyl trans,trans-9,11-octadecadienoate formed a cis adduct. Methyl cis,cis-9,11-octadecadienoate reacted slowly under the conditions used leaving mostly unreacted material. Of the adducts observed from this isomer, a major trans adduct and a minor cis adduct were formed.     

Egg yolk conjugated linoleic acid alters phospholipid molecular species in chick tissues

The effects of egg conjugated linoleic acid (CLA) on chick yolk sac and liver phospholipid composition and molecular species were determined. Fertile eggs with no (control), low (CLA1) or high (CLA2) levels of CLA were incubated. Upon hatching, total lipid in the remnant yolk sac constituted 11.5, 18.9 and 15.3% in control, CLA1 and CLA2, respectively (p <0.05). Maternal CLA led to a decrease in phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdEtn) and an increase in lysophosphatidylcholine (LPtdCho) in the yolk sac and liver tissues of CLA1 and CLA2 when compared to control (p <0.05). The effect of maternal dietary CLA was very prominent in yolk sac PtdCho (34:1) where 13 and 38% reductions were observed in CLA1 and CLA2, respectively, when compared to control. Among different liver PtdCho species, the highest difference was found in 36:2, where a 41% increase was observed in CLA2 when compared with control chicks. The liver LPtdCho of CLA1 and CLA2 chicks had a 92% increase in 16:0 and 18:0 when compared to control. Over 80% increase was observed for 18:2 and 20:4 in the liver LPtdCho of CLA2 chicks compared to control. These results suggest that the yolk CLA content alters the proportions of phospholipids in the progeny during avian embryogenesis.     

Fatty acid profiles in tissues of mice fed conjugated linoleic acid

The incorporation of vaccenic acid (VA, 0.5 and 1.2%), conjugated linoleic acid (CLA, mixture of primarily c9,t11‐ and t10,c12‐CLA, 1.2%), linoleic acid (LA, 1.2%) and oleic acid (OA, 1.2%) into different tissues of mice was examined. The effects on the fatty acid composition of triacylglycerols (TAG) and phospholipids (PL) in kidney, spleen, liver and adipose tissue were investigated. VA and CLA (c9,t11‐ and t10,c12‐CLA) were primarily found in TAG, especially in kidney and adipose tissue, respectively. Conversion of VA to c9,t11‐CLA was indicated by our results, as both fatty acids were incorporated into all the analyzed tissues when a diet containing VA but not c9,t11‐CLA was fed. Most of the observed effects on the fatty acid profiles were seen in the CLA group, whereas only minor effects were observed in the VA groups compared with the OA group. Thus, CLA increased n‐3 polyunsaturated fatty acids (PUFA) in PL from kidney and spleen and lowered the ratio of n‐6/n‐3 PUFA in these tissues. Furthermore, CLA increased C₂₂ PUFA in the PL fraction of kidney, spleen and liver, but reduced the level of arachidonic acid in PL of liver and spleen and lowered the Δ⁹‐desaturation indexes in all analyzed tissue TAG.     

Incorporation of conjugated linoleic acid and vaccenic acid into lipids from rat tissues and plasma

The objective of this study was to determine the incorporation of conjugated linoleic acid (CLA) into triacylglycerols (TAG) and phospholipids (PL) of tissues and plasma, and to interpret the role of dietary‐derived vaccenic acid (VA) in increasing the tissue content of CLA (c9,t11) and the influence on the fatty acid profile. We fed five groups of rats semi‐purified diets with varying levels of CLA and VA: control butter with low CLA (c9,t11) and VA; control butter added 5% CLA (c9,t11); control butter added 5% Tonalin [equal amount of CLA (c9,t11) and CLA (t10,c12)]; control butter added 5% VA; butter with high CLA (c9,t11) and VA (H‐CLA), for 3 weeks. The highest incorporation of CLA (c9,t11) was found in adipose tissue, and the lowest was observed in liver. Low intake of CLA (c9,t11) combined with high intake of VA resulted in a higher incorporation of CLA (c9,t11) in tissues due to the conversion of VA to CLA (c9,t11), compared to feeding CLA (c9,t11) without VA. However, in enterocytes, the proportion of CLA (c9,t11) was low after feeding VA, indicating no or only a minor conversion of VA to CLA (c9,t11) in the intestine. The incorporation of CLA (t10,c12) into TAG from plasma and tissues was generally much lower than that of the CLA (c9,t11) isomer, except in the enterocyte TAG, which had similar proportions of the two isomers.     

Thermally induced formation of conjugated isomers of linoleic acid

Chemical pathways responsible of the conjugation of linoleic acid during heat treatments such as refining (deodorization), frying or cooking processes have been investigated. For this purpose, methyl linoleate was submitted to oxidative and non‐oxidative thermal conditions. The resulting degradation products were mainly composed of geometrical and conjugated fatty acid isomers. Oxidative conditions were obtained using tert‐butyl hydroperoxide under inert atmosphere, and air. The obtained results from both thermal oxidative conditions were compared to non‐oxidative thermal treatment. Higher levels of conjugated linoleic acid were found when linoleate was heated under oxidative conditions. Two distinct mechanisms responsible for the formation of CLA isomers are proposed and discussed. Evidence of formation of 9,11‐C18:2 and 10,12‐C18:2 acids from 9,12‐C18:2 by a free‐radical chain reaction is provided. The first step consists in the formation of a free radical by abstraction of an active bis‐allylic hydrogen. By delocalization of the initial free radical, two allylic free radicals were stabilized and converted into the corresponding CLA isomers via the abstraction of a hydrogen radical from other linoleic acid or oxygenated species. Kinetic observations confirmed the significance of the bimolecular mechanism. Moreover, the proposed mechanism is supported by several pieces of information from the literature on peroxidation of linoleic acid. Under pure thermal conditions and/or for diluted samples, a second pathway to the formation of CLA from heat‐treated linoleic acid is proposed via an intramolecular rearrangement of the pentadienyl structure. This thermal [1,3]‐sigmatropic rearrangement results in a mixture of 9,11 and 10,12 CLA isomers. The formed cis/trans CLA isomers were readily rearranged by a [1,5]‐sigmatropic shift to yield trans‐8,cis‐10 and cis‐11,trans‐13 CLA isomers, respectively.     

Properties and biotechnological methods to produce lipids containing conjugated linoleic acid

In this review, the occurrence, properties, nutritional importance and especially biotechnological methods for the production of conjugated linoleic acids (CLA) and CLA‐rich lipids are summarized. Beside information from medical and nutritional studies on the biological activity of CLA, the focus is on the enzymatic synthesis of structured lipids containing CLA and the microbial synthesis of CLA.     

共轭亚油酸锌的合成工艺研究

通过利用共轭亚油酸的弱酸性质,将共轭亚油酸制成盐,以期生理功能的改变,本文利用具有生物功能活性的共轭亚油酸,先与氢氧化钠反应得到共轭亚油酸的钠盐溶液,再加入氯化锌溶液得到共轭亚油酸锌盐,平均收率为67%。为共轭亚油酸锌制成制剂的进一步研究提供了原料。     

Analysis of conjugated linoleic acid isomers and content in french cheeses

Conjugated linoleic acid (CLA) occurs in food as a result of microbial enzymatic reactions, free radical-type oxidation, and heat treatment. CLA is found in animal products, such as meat and dairy products, especially in cheeses. The CLA composition of 12 different French cheeses was determined by a combination of different analytical methods: reversed-phase high-performance liquid chromatography (RP-HPLC), gas chromatography-mass spectrometry (GC-MS), GC-Fourier transform infrared (GC-FTIR), and silver nitrate thin-layer chromatography (AgNO₃-TLC). New isomers (Δ8,10- and Δ11,13-octadecadienoic acids with all possible cis and trans configurations) that co-eluted with previously identified isomers (Δ9c,11t-; Δ9t,11c-; Δ10c,12t-; Δ10t,12c-; Δ11c,13c-; Δ9c,11c-; Δ10c,12c-; Δ9t,11t-; Δ10t12t-octadecadienoic acids) were detected. Δ9c,11t-Octadecadienoic acid was the major CLA isomer in these cheeses. All isomers were present in each product, whatever the production process. However, CLA content in the cheeses varied from 5.3 to 15.80 mg/g of cheese fat, which depended primarily on the origin of the milk (season, geography) and somewhat on the production process.     

Safety of conjugated linoleic acid (CLA) in overweight or obese human volunteers

The main objective of the study was to investigate the safety of conjugated linoleic acid (CLA) in healthy volunteers. The effect of CLA on body composition was also investigated. The trial design was a randomized, double‐blind placebo controlled study including 60 overweight or obese volunteers (body mass index (BMI) 27.5—39.0 kg/m²). The subjects were divided into two groups receiving 3.4 g CLA or placebo (4.5 g olive oil) daily for 12 weeks. The safety was evaluated by analysis of blood parameters and by clinical examinations at baseline and week 12. Vital signs and adverse events were registered at baseline, week 6, and week 12. Bio Impedance Assessment was applied for body composition measurements. 55 subjects completed the study. Adverse events occurred in 10% of the subjects. No difference in adverse events or other safety parameters was found between the treatment groups. Small changes in the laboratory safety data were not regarded as clinically significant. Moreover, no clinically significant changes in vital signs were observed in any of the groups. In the CLA group, mean weight was reduced by 1.1 kg (paired t‐test p = 0.005), while mean BMI was reduced by 0.4 kg/m²(p = 0.007). However, the overall treatment effect of CLA on body weight and BMI was not significant. There were no differences found between the groups with regard to efficacy parameters. The results indicate that CLA in the given dose is a safe substance in healthy populations with regard to the safety parameters investigated.     

Bioconversion of linoleic acid to conjugated linoleic acid by Lactobacillus reuteri under different growth conditions

BACKGROUND: Lactobacillus reuteri was grown in De Man/Rogosa/Sharpe (MRS) broth (initial pH 6.5) supplemented with free linoleic acid (LA) at different concentrations (5, 10, 20 and 30 mg mL^?1) and incubated aerobically at different temperatures (4, 10, 16, 22 and 30 °C) in order to test its ability to accomplish the bioconversion of LA to conjugated linoleic acid (CLA). Temperatures and LA concentrations producing the highest conversion of LA to CLA in the initial trials were tested further using micro‐anaerobic conditions and a lower initial pH (5.5). RESULTS: Data showed that production of CLA exhibited variations with regard to the fermentation conditions used. The highest production of CLA (0.108 mg mL^?1) was measured in a broth containing 20 mg mL^?1 free LA that was incubated aerobically at 10 °C for 30 h. When the initial pH of the reaction medium was reduced from 6.5 to 5.5, CLA production decreased. Micro‐aerobic conditions reduced the ability of Lb. reuteri to produce CLA, since production of CLA under aerobic conditions was at least 1.4 times greater. CONCLUSION: Production of CLA by Lb. reuteri at low temperatures and relatively high substrate concentrations provides novel opportunities for the development of functional foods with the benefits of enrichment in CLA and probiotic bacteria. Copyright © 2008 Society of Chemical Industry     

Effects of tocopherols and tocotrienols on the inhibition of autoxidation of conjugated linoleic acid

The effect of eight vitamin E homologues, i.e. α‐, β‐, γ‐, and δ‐tocopherol and α‐, β‐, γ, and δ‐tocotrienol, on the inhibition of autoxidation of conjugated linoleic acid (CLA) were investigated. The oxidation was carried out in the dark for 21 days at 50 °C and monitored by peroxide values (PV) and TBA values. The levels of the individual vitamin E homologues in CLA during storage were determined by HPLC. γ‐Tocopherol exhibited the highest antioxidant activity among the homologues tested in this study when the antioxidant activities of the individual homologues in CLA were compared by PV. The order of antioxidant activity of eight homologues was γ‐tocopherol > δ‐tocopherol = δ‐tocotrienol ≥ γ‐tocotrienol > β‐tocopherol = β‐tocotrienol > α‐tocopherol = α‐tocotrienol. The degradation rates of α‐tocopherol and α‐tocotrienol were faster than those of the other homologues, whereas δ‐tocopherol had the highest stability in CLA during storage. All homologues exhibited an antioxidant activity by inhibiting the formation of secondary oxidation products. It appears that α‐tocotrienol and β‐tocotrienol have significantly higher antioxidant activities for secondary oxidation in CLA than α‐tocopherol and β‐tocopherol. Meanwhile, the other homologues, namely γ‐tocopherol, γ‐tocotrienol, δ‐tocopherol, and δ‐tocotrienol, exhibited similar antioxidant activity for secondary oxidation in CLA.     

共轭亚油酸粉末化微胶囊的制备

研究了喷雾干燥法制备共轭亚油酸微胶囊的工艺参数及配比条件。结果表明,最佳的工艺参数及配比条件为:乳液80℃热处理60 m in,乳化剂蔗糖酯加入量为水液的1%~1.5%,大豆分离蛋白与麦芽糊精质量比为1∶4,壁材中玉米糖浆含量38.5%,固形物含量16.7%,共轭亚油酸理论含量16%左右,进风温度130~150℃,进料流量(2.5~3.5)×150 mL/h,进料温度35℃,进风流量1.1 m3/m in左右,喷嘴压力180 kPa。制备出的共轭亚油酸微胶囊有较好的产品质量。     

Enzymatic interesterification of structured lipids containing conjugated linoleic acid with palm stearin for possible margarine production

Structured lipids containing conjugated linoleic acid as a functional ingredient were blended with palm stearin in the ratios of 30 : 70, 40 : 60, 50 : 50, 60 : 40 and 70 : 30 (wt/wt). The blends were subjected to enzymatic interesterification by Candida antarctica lipase. After interesterification of the blends, changes in the physical properties of the products, including lower melting points and solid fat contents along with different melting behaviors, were evidenced. Analysis of triacylglycerols (TAG) of the interesterified blends showed a decrease in the concentration of high‐melting TAG. X‐ray diffraction analysis revealed, that all the reacted blends were predominantly in the β' crystal form. The mixture could be used for the formulation of margarines or other, similar products.