Improved separation of conjugated fatty acid methyl esters by silver ion-high-performance liquid chromatography

Silver Ion High-Performance Liquid Chromatography-Atmospheric Pressure Chemical Ionization Mass Spectrometry: A Tool for Analyzing Cuticular Hydrocarbons

Aliphatic hydrocarbons (HCs) are usually analyzed by gas chromatography (GC) or matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. However, analyzing long-chain HCs by GC is difficult because of their low volatility and the risk of decomposition at high temperatures. MALDI cannot distinguish between isomeric HCs. An alternative approach based on silver ion high-performance liquid chromatography (Ag-HPLC) is shown here. The separation of HC standards and cuticular HCs was accomplished using two ChromSpher Lipids columns connected in series. A gradient elution of the analytes was optimized using mobile phases prepared from hexane (or isooctane) and acetonitrile, 2-propanol, or toluene. HCs were detected by atmospheric pressure chemical ionization mass spectrometry (APCI-MS). Good separation of the analytes according to the number of double bonds, cis/trans geometry, and position of double bonds was achieved. The retention times increased with the number of double bonds, and trans isomers eluted ahead of cis isomers. The mobile phase significantly affected the mass spectra of HCs. Depending on the mobile phase composition, deprotonated molecules, molecular ions, protonated molecules, and various solvent-related adducts of HCs were observed. The optimized Ag-HPLC/APCI-MS was applied for characterizing cuticular HCs from a flesh fly, Neobellieria bullata, and cockroach, Periplaneta americana. The method made it possible to detect a significantly higher number of HCs than previously reported for GC or MALDI-MS. Unsaturated HCs were frequently detected as isomers differing by double-bond position(s). Minor HCs with trans double bonds were found beside the prevailing cis isomers. Ag-HPLC/APCI-MS has great potential to become a new tool in chemical ecology for studying cuticular HCs.

Algae as Feedstuff for Ruminants: A Focus on Single-Cell Species, Opportunistic Use of Algal By-Products and On-Site Production

There is a wide range of algae species originating from a variety of freshwater and saltwater habitats. These organisms form nutritional organic products via photosynthesis from simple inorganic substances such as carbon dioxide. Ruminants can utilize the non-protein nitrogen (N) and the cell walls in algae, along with other constituents such as minerals and vitamins. Over recent decades, awareness around climate change has generated new interest into the potential of algae to suppress enteric methane emissions when consumed by ruminants and their potential to sequester atmospheric carbon dioxide. Despite the clear potential benefits, large-scale algae-livestock feedstuff value chains have not been established due to the high cost of production, processing and transport logistics, shelf-life and stability of bioactive compounds and inconsistent responses by animals under controlled experiments. It is unlikely that algal species will become viable ingredients in extensive grazing systems unless the cost of production and practical systems for the processing, transport and feeding are developed. The algae for use in ruminant nutrition may not necessarily require the same rigorous control during the production and processing as would for human consumption and they could be grown in remote areas or in marine environments, minimizing competition with cropping, whilst still generating high value biomass and capturing important amounts of atmospheric carbon. This review will focus on single-cell algal species and the opportunistic use of algal by-products and on-site production.

Temperature-programmed capillary high-performance liquid chromatography with atmospheric pressure chemical ionization mass spectrometry for analysis of fatty acid methyl esters

A new capillary high-performance liquid chromatography method with atmospheric pressure chemical ionization mass spectrometry was developed for the analysis of fatty acid methyl esters and long-chain alcohols. The chromatographic separation was achieved using a Zorbax SB-C18 HPLC column (0.3 × 150 mm, 3.5 μm) with a mobile phase composed of acetonitrile and formic acid and delivered isocratically at a flow rate of 10 μL/min. The column temperature was programmed simply, using a common column oven. Good reproducibility of the temperature profile and retention times were achieved. The temperature programming during the isocratic high-performance liquid chromatography run had a similar effect as a solvent gradient; it reduced retention times of later eluting analytes and improved their detection limits. Two atmospheric pressure chemical ionization sources of the mass spectrometry detector were compared: an enclosed conventional ion source and an in-house made ion source with a glass microchip nebulizer. The enclosed source provided better detectability of saturated fatty acid methyl esters and made it possible to determine the double bond positions using acetonitrile-related adducts, while the open chip-based source provided better analytical figures of merit for unsaturated fatty acid methyl esters. Temperature-programmed capillary high-performance liquid chromatography is a promising method for analyzing neutral lipids in lipidomics and other applications.

Total and Free Fatty Acids Analysis in Milk and Dairy Fat

Dairy fat is one of the most complex natural fats because of its fatty acid (FA) composition. Ruminant dairy fat contains more than 400 different FA varying in carbon chain length, and degree, position and configuration of unsaturation. The following article reviews the different methods available to analyze FA (both total and free) in milk and dairy products. The most widely used methodology for separating and analyzing dairy FA is gas chromatography, coupled to a flame ionization detector (CG-FID). Alternatively, gas chromatography coupled to a mass spectrometer (GC-MS) is also used. After lipid extraction, total FA (TFA) are commonly converted into their methyl esters (fatty acid methyl esters, FAME) prior to chromatographic analysis. In contrast, free FA (FFA) can be analyzed after conversion to FAME or directly as FFA after extraction from the product. One of the key questions when analyzing FAME from TFA is the selection of a proper column for separating them, which depends mainly on the objective of the analysis. Quantification is best achieved by the internal standard method. Recently, near-infrared spectroscopy (NIRS), Raman spectroscopy (RS) and nuclear magnetic resonance (NMR) have been reported as promising techniques to analyze FA in milk and dairy products.

Fatty Acid Desaturase 3 (FADS3) Is a Specific ∆13-Desaturase of Ruminant trans-Vaccenic Acid

In mammalian species, the Fatty Acid Desaturase (FADS) gene cluster includes FADS1 (∆5-desaturase), FADS2 (∆6-desaturase), and a third gene member, named FADS3. According to its high degree of nucleotide sequence homology with both FADS1and FADS2, FADS3 was promptly suspected by researchers in the field to code for a new mammalian membrane-bound fatty acid desaturase. However, no catalytic activity was attributed to the FADS3 protein for a decade, until the rat FADS3 protein was shown in vitro to be able to catalyze the unexpected ∆13-desaturation of trans-vaccenic acid, producing the trans11,cis13-conjugated linoleic acid isomer. This review summarizes the recent investigations establishing the FADS3 enzyme as a reliable mammalian trans-vaccenate ∆13-desaturase in vivo and tries to identify further unresolved issues that need to be addressed.

Synthesis of the suspected trans-11,cis-13 conjugated linoleic acid isomer in ruminant mammary tissue by FADS3-catalyzed Δ13-desaturation of vaccenic acid

The octadecadienoic conjugated linoleic acid (CLA) isomer with trans-11 and cis-13 double bonds (trans-11,cis-13 CLA) has been described in ruminant milk. For now, this specific CLA is suspected to derive exclusively from ruminal biohydrogenation of dietary α-linolenic acid. However, in rodents, the fatty acid desaturase 3 (FADS3) gene was recently shown to code for an enzyme able to catalyze the unexpected Δ13-desaturation of vaccenic acid, producing a Δ11,13-CLA with all the structural characteristics of the trans-11,cis-13 isomer, although no commercial standard exists for complete conclusive identification. Because the FADS3 gene has already been reported in bovine animals, we hypothesized in the present study that an alternative direct FADS3-catalyzed Δ13-desaturation of vaccenic acid in mammary tissue may therefore co-exist with α-linolenic acid biohydrogenation to explain the final ruminant milk trans-11,cis-13 CLA presence. Here, we first confirm that the FADS3 gene is present in ruminant mammal genomic sequence databases. Second, we demonstrate that the Δ11,13-CLA found in milk fat and the highly probable trans-11,cis-13 CLA isomer produced by rodent FADS3 possess exactly the same structural characteristics. Then, we show that bovine mammary MAC-T and BME-UV epithelial cells express both FADS3 and stearoyl-CoA desaturase 1 (SCD1) mRNA and are able to synthesize both the suspected trans-11,cis-13 CLA and cis-9,trans-11CLA (rumenic acid) isomers when incubated with vaccenic acid. Finally, the concomitant presence of the suspected trans-11,cis-13 CLA isomer with FADS3 mRNA was shown in goat mammary tissue, whereas both were conversely very low or even absent in goat liver. Therefore, this study provides several lines of evidence that, by analogy with rumenic acid, trans-11,cis-13 CLA may originate both from ruminal biohydrogenation and from direct FADS3-catalyzed Δ13-desaturation of vaccenic acid in mammary tissue.

Characterization of the fatty acid composition of lamb commercially available in northern Spain: Emphasis on the trans-18:1 and CLA content and profile

A survey of commercially available lamb meat was performed in northern Spain in order to evaluate their fatty acid (FA) composition with emphasis on trans fatty acid (TFA) and conjugated linoleic acid (CLA) isomers. Samples were collected in spring (n=24) and winter (n=24) of 2013, and were obtained in about equal numbers from grocery stores and butcher-shops. Subcutaneous fat, known to be a sensitive indicator of TFA content in ruminants, was analyzed by GC-FID. In general, very few differences were observed between collection periods and type of stores because of the high variability within the groups that was believed to be associated with differences in genetics and feeding strategies. However, the 10t/11t ratio of all samples showed two clearly identifiable groups irrespective of the source: 1) when 10t/11t was >1, 10t-shifted samples; 2) when 10t/11t was ≤1, non-shifted samples where 11t-18:1 was the predominant isomer. These two groups were clearly identified and associated with distinct FAs using principal component analysis.

Impact of calving seasons and feeding systems in western Canada. II. Meat composition and organoleptic quality of steaks

Durunna, O. N., Block, H. C., Iwaasa, A. D., Scott, S. L., Robins, C., Khakbazan, M., Dugan, M. E. R., Aalhus, J. L., Aliani, M. and Lardner, H. A. 2014. Impact of calving seasons and feeding systems in western Canada. II. Meat composition and organoleptic quality of steaks. Can. J. Anim. Sci. 94: 583–593. Fatty acid profiling, meat and organoleptic quality assessments were conducted on 160 carcasses of crossbred steers born into one of two calving systems and later assigned to one of two postweaning feeding systems. The steers were weaned from either an early calving or late calving system and later assigned to either a rapid-gain feeding (RF) or a slow-gain feeding (SF) system. The RF steers received a silage–hay diet during the backgrounding period prior to finishing, while the SF steers received a hay diet at backgrounding and then grazed alfalfa–meadow bromegrass pasture and annual cereal swaths prior to finishing. All treatment groups received a conventional diet during finishing until the steers attained a target backfat thickness or body weight. Fatty acid analyses were conducted on longissimus dorsi muscle (LDM) and subcutaneous fat samples. Other analyses included LDM composition, tenderness and taste panel evaluations. Total saturated fatty acid was greater (P<0.02) in samples from RF steers, while total monounsaturated fatty acid was greater (P<0.01) in SF steers. The SF steers had greater (P<0.01) conjugated linoleic acid concentration. There was no main or interaction effect (P>0.05) on beef aroma, flavour and tenderness but the SF steaks had lower (P=0.02) cooking losses than RF steaks. The SF strategy has the potential to create a value chain that would lead to finished steers with higher backfat omega-3, conjugated linoleic acid and trans vaccenic acid and less cooking moisture losses.

Short Communication: Rapid separation of cis9, trans11- and trans7,cis9-18:2 (CLA) isomers from ruminant tissue using a 30 m SLB-IL111 ionic column

Turner, T., Rolland, D. C., Aldai, N. and Dugan, M. E. R. 2011. Short Communication: Rapid separation of cis 9, trans 11- and trans 7,c is 9-18:2 (CLA) isomers from ruminant tissue using a 30 m SLB-IL111 ionic column. Can. J. Anim. Sci. 91: 711–713. Rumenic acid (cis9,trans11-18:2) is the main natural isomer of conjugated linoleic acid (CLA). Rumenic acid has many purported health benefits, but effects of most other CLA isomers are unknown. Typically trans7,cis9-18:2 is the second most abundant CLA isomer, but it co-elutes with rumenic acid on conventional polar gas chromatography (GC) columns, requiring complimentary analysis with silver-ion high performance liquid chromatography (Ag+-HPLC). Herein we report a rapid method for analyzing rumenic acid and trans7,cis9-18:2 using a 30 m ionic-liquid GC column. Optimal resolution of the two CLA isomers was at 145°C and analysis of backfat from barley-fed cattle compared well with GC/Ag+-HPLC (y=0.978x – 0.031, r=0.985, P<0.001).

Dietary conjugated linoleic Acid and hepatic steatosis: species-specific effects on liver and adipose lipid metabolism and gene expression

Objective. To summarize the recent studies on effect of conjugated linoleic acid (CLA) on hepatic steatosis and hepatic and adipose lipid metabolism highlighting the potential regulatory mechanisms. Methods. Sixty-four published experiments were summarized in which trans-10, cis-12 CLA was fed either alone or in combination with other CLA isomers to mice, rats, hamsters, and humans were compared. Summary and Conclusions. Dietary trans-10, cis-12 CLA induces a severe hepatic steatosis in mice with a more muted response in other species. Regardless of species, when hepatic steatosis was present, a concurrent decrease in body adiposity was observed, suggesting that hepatic lipid accumulation is a result of uptake of mobilized fatty acids (FA) from adipose tissue and the liver's inability to sufficiently increase FA oxidation and export of synthesized triglycerides. The potential role of liver FA composition, insulin secretion and sensitivity, adipokine, and inflammatory responses are discussed as potential mechanisms behind CLA-induced hepatic steatosis.

Monocarboxylate transporter 1 and CD147 are up-regulated by natural and synthetic peroxisome proliferator-activated receptor alpha agonists in livers of rodents and pigs

Monocarboxylate transporter (MCT)-1 mediates the transport of ketone bodies and other monocarboxylic acids across the plasma membrane. MCT1 is up-regulated by peroxisome proliferator-activated receptor (PPAR)-alpha, a transcription factor that mediates the adaptive response to fasting by up-regulation of genes involved in fatty acid oxidation and ketogenesis. Here, we show for the first time that MCT1 is up-regulated by dietary natural PPAR-alpha agonists. Both, an oxidized fat and conjugated linoleic acids increased MCT1 mRNA concentration in the liver of rats. Also, in the liver of pigs as non-proliferating species MCT1 was up-regulated upon PPAR-alpha activation by clofibrate, oxidized fat and fasting. Concomitant with up-regulation of MCT1, mRNA level of CD147 was increased in livers of rats and pigs. CD147 is a plasma membrane glycoprotein that is required for translocation and transport activity of MCT1. CD147 mRNA increase upon PPAR-alpha activation could not be observed in mice lacking PPAR-alpha, which also fail in up-regulation of MCT1 indicating a co-regulation of MCT1 and CD147. Analysis of the 5'-flanking region of mouse MCT1 gene by reporter gene assay revealed that promoter activity of mouse MCT1 was not induced by PPAR-alpha, indicating that the 5'-flanking region is not involved in MCT1 regulation by PPAR-alpha.

A review of fatty acid profiles and antioxidant content in grass-fed and grain-fed beef

Growing consumer interest in grass-fed beef products has raised a number of questions with regard to the perceived differences in nutritional quality between grass-fed and grain-fed cattle. Research spanning three decades suggests that grass-based diets can significantly improve the fatty acid (FA) composition and antioxidant content of beef, albeit with variable impacts on overall palatability. Grass-based diets have been shown to enhance total conjugated linoleic acid (CLA) (C18:2) isomers, trans vaccenic acid (TVA) (C18:1 t11), a precursor to CLA, and omega-3 (n-3) FAs on a g/g fat basis. While the overall concentration of total SFAs is not different between feeding regimens, grass-finished beef tends toward a higher proportion of cholesterol neutral stearic FA (C18:0), and less cholesterol-elevating SFAs such as myristic (C14:0) and palmitic (C16:0) FAs. Several studies suggest that grass-based diets elevate precursors for Vitamin A and E, as well as cancer fighting antioxidants such as glutathione (GT) and superoxide dismutase (SOD) activity as compared to grain-fed contemporaries. Fat conscious consumers will also prefer the overall lower fat content of a grass-fed beef product. However, consumers should be aware that the differences in FA content will also give grass-fed beef a distinct grass flavor and unique cooking qualities that should be considered when making the transition from grain-fed beef. In addition, the fat from grass-finished beef may have a yellowish appearance from the elevated carotenoid content (precursor to Vitamin A). It is also noted that grain-fed beef consumers may achieve similar intakes of both n-3 and CLA through the consumption of higher fat grain-fed portions.

Determination by fourier transform Raman spectroscopy of conjugated linoleic acid in I2-photoisomerized soybean oil

The potential of Fourier transform (FT)-Raman spectroscopy to quantify the total conjugated linoleic acid (CLA) content was evaluated to find a technique for the routine control of CLA synthesis by chemical procedures. The calibration and validation samples were obtained by photoisomerization of linoleic acid contained in soybean oil. The catalyst was iodine (I(2)), and the light source was the green line (514.5 nm) of an argon ion laser. The criteria to select the best partial least-squares (PLS) calibration model were a low standard error of prediction (SEP), a high correlation coefficient (R), and the selection of relevant variables of the Raman spectrum to reduce spectral interferences. The total CLA content of the 22 samples ranged from 0.05 to 3.28% of total lipids. The best PLS calibration model was obtained with three optimal factors, a SEP of 0.22, and a R of 0.97. This calibration model was obtained after baseline correction of the CC stretching region (1642-1680 cm(-1)), which contained sufficient spectral information for reliable CLA quantification.

Recent trends in the advanced analysis of bioactive fatty acids

The consumption of dietary fats have been long associated to chronic diseases such as obesity, diabetes, cancer, arthritis, asthma, and cardiovascular disease; although some controversy still exists in the role of dietary fats in human health, certain fats have demonstrated their positive effect in the modulation of abnormal fatty acid and eicosanoid metabolism, both of them associated to chronic diseases. Among the different fats, some fatty acids can be used as functional ingredients such as alpha-linolenic acid (ALA), arachidonic acid (AA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), gamma-linolenic acid (GLA), stearidonic acid (STA) and conjugated linoleic acid (CLA), among others. The present review is focused on recent developments in FAs analysis, covering sample preparation methods such as extraction, fractionation and derivatization as well as new advances in chromatographic methods such as GC and HPLC. Special attention is paid to trans fatty acids due its increasing interest for the food industry.

Conjugated linoleic acid (CLA) and fatty acid composition of milk, curd and Grana Padano cheese in conventional and organic farming systems

CLA levels and fatty acid composition were measured to compare the fat composition in organic bulk milk, destined to the production of Grana Padano cheese, with those produced by conventional system. The curds and Grana Padano cheeses were also analysed to evaluate the effects of the production technology on the CLA content. All analysed organic samples were characterized by higher annual means of CLA, vaccenic acid (TVA) and linolenic acid (LNA) in comparison with conventional samples (with P<0·05). Nevertheless, no particular effect of the production technology was seen on the CLA content. The animal diet appears to be the factor which has the highest effect on the CLA concentration in milk and milk products and an organic diet based on fresh or dried forage, that is rich in CLA precursory fatty acids, may improve the yield of fatty acids with beneficial effects on health.

Conjugated linoleic acid prevents growth attenuation induced by corticosteroid administration and increases bone mineral content in young rats

Corticosteroids are a common therapy in many disease states, despite frequent and potentially serious side effects. Nutritional supplementation with conjugated linoleic acid (CLA) has been shown to increase fat-free mass, whereas supplementation with n-3 and n-6 fatty acids has been shown to increase bone mineral density (BMD). To determine whether CLA can attenuate the side effects of 8 weeks of corticosteroid administration, we randomized twenty-four 5-week-old male Sprague-Dawley rats into 1 of 4 groups: control; control + methylprednisolone (7 mg.kg-1.week-1); CLA diet (1% CLA w/w); or CLA plus methylprednisolone. Body composition, bone mineral content (BMC), and BMD were assessed with dual-energy X-ray absorptiometry at the onset and at the end of the 8-week intervention. The mechanical properties of bone were determined using 3-point femur bending at the end of the intervention. Methylprednisolone resulted in an attenuation of the increase in body mass and lean mass over the 8 weeks (p < 0.05). CLA prevented the methylprednisolone-induced attenuation of body mass and lean mass accumulation. CLA also resulted in a greater increase in BMC (p < 0.05) in the lumbar spine. The energy at failure of the isolated femurs was increased with CLA (p < 0.05). Dietary CLA prevents many of the growth- and bone-related side effects arising from 8 weeks of corticosteroid administration, results in greater increases in BMC and BMD, and can contribute to an improvement in some of the mechanical properties of bone.

Preparative argentation reversed-phase high performance liquid chromatography

In this study, a preparative chromatography method named preparative argentation reversed-phase high performance liquid chromatography (Ag-RP-HPLC) was developed by adding silver ion to the mobile phase of preparative HPLC. Firstly, an analytical Ag-RP-HPLC method was developed, and the effects of silver content and acid content in the mobile phase on the column efficiency were studied. Based on the method of linear amplification, a preparative Ag-RP-HPLC technique with optimized separation conditions was developed. The new technique was applied successfully to the separation of the unsaturated aliphatic acid amide isomers contained in Asarum forbesii Maxim. Compared with the commonly used technique of argentation normal phase chromatography, this method with little solvent consumption is simple, fast, efficient, and flexible for the isolation and purification of the unsaturated compounds.

The potential benefits of creatine and conjugated linoleic acid as adjuncts to resistance training in older adults

Human aging is associated with a significant reduction in muscle mass (sarcopenia) resulting in muscle weakness and functional limitations in the elderly. Sarcopenia has been associated with mitochondrial dysfunction and the accumulation of mtDNA deletions. Resistance training increases muscle strength and size and can increase mitochondrial capacity and decrease oxidative stress in older adults. Creatine monohydrate (CrM) and conjugated linoleic acid (CLA) have biological effects that could enhance some of the beneficial effects of resistance training in older adults (i.e., up arrow fat-free mass, down arrow total body fat). We have completed two resistance-training studies with CrM alone and CrM+CLA supplementation in older adults to evaluate the independent effects of exercise and dietary supplements, as well as their interactive effects. Our studies, and several others, have found that CrM enhanced the resistance exercise mediated gains in fat-free mass and strength. More recently, we found that the addition of CLA also lead to a significant reduction of body fat after six months of resistance training in older adults. Older adults have fewer wild-type mtDNA copies and higher amounts of mtDNA deletions as compared with younger adults in mature skeletal muscle; however, these deletions are not seen in the satellite cell-derived myoblast cultures. These findings, and the fact that mtDNA deletions are lower and wild-type mtDNA copy number is higher after resistance training in older adults, suggests that activation of satellite cells secondary to resistance exercise-induced muscle damage can dilute or "shift" the proportion of mtDNA genotype towards that of a younger adult. Recent evidence suggests that CrM supplementation in combination with strength training can enhance satellite cell activation and total myonuclei number per muscle fiber in young men. Future studies are required to determine whether the mitochondrial adaptations to resistance exercise in older adults are further enhanced with CrM supplementation and whether this is due to increased recruitment of satellite cells. It will also be important to determine whether these changes are maintained over a longer time period.

Effects of fish oil and conjugated linoleic acids on expression of target genes of PPAR alpha and sterol regulatory element-binding proteins in the liver of laying hens

In mammals, (n-3) PUFA and conjugated linoleic acids (CLA) act as activators of PPAR alpha and alter nuclear concentrations of sterol regulatory element-binding proteins (SREBP) in the liver, and thereby influence hepatic lipid catabolism and synthesis. In this study, we investigated the hypothesis that (n-3) PUFA and CLA exert similar effects in the liver of laying hens. Thirty hens (64 weeks old) were fed diets containing 30 g/kg of sunflower oil (control), fish oil (salmon oil) or CLA in TAG form (containing predominantly cis-9, trans-11 CLA and trans-10, cis-12 CLA) for 5 weeks. Hens fed fish oil had a higher expression of some PPAR alpha target genes and a lower nuclear concentration of SREBP-2 in the liver and lower concentrations of cholesterol and TAG in plasma than control hens. Nuclear concentration of SREBP-1 and its target genes involved in lipogenesis were not altered in hens fed fish oil. Hens fed CLA had increased concentrations of TAG and cholesterol in the liver. However, their mRNA levels of PPAR alpha target genes and nuclear concentrations of SREBP-1 and SREBP-2 as well as mRNA levels of their target genes in the liver were largely unchanged compared to control hens. The results of this study suggest that (n-3) PUFA cause a moderate activation of PPAR alpha and lower cholesterol synthesis but do not impair fatty acid synthesis in the liver of laying hens. CLA lead to an accumulation of TAG and cholesterol in the liver of hens by mechanisms to be elucidated in further studies.

Evaluating the conjugated linoleic acid and trans 18:1 isomers in milk fat of dairy cows fed increasing amounts of sunflower oil and a constant level of fish oil

The objective was to evaluate different levels of sun-flower oil (SFO) in dairy rations to increase vaccenic (trans-11-18:1) and rumenic acids (cis-9,trans-11-18:2) in milk fat, and assess the content and composition of other trans-octadecenoic (trans-18:1) and conjugated linoleic acids (CLA) isomers. Eighty lactating Holstein cows were fed control diets for 4 wk and then placed on 4 diets for 38 d; milk fat was analyzed after 10 and 38 d. The treatments were: control, 1.5% SFO plus 0.5% fish oil (FO), 3% SFO plus 0.5% FO, and 4.5% SFO plus 0.5% FO. The forage-to-concentrate ratio was 50:50 and consisted of barley/alfalfa/hay silage and corn/barley grain concentrate. There were no differences in milk production. Supplementation of SFO/FO reduced milk fat compared with respective pretreatment periods, but milk protein and lactose levels were not affected. There was a linear decrease in all short- and medium-chain saturated fatty acids (SFA) in milk fat after 10 d (25.5, 24.1, 20.2, and 16.7%) and a corresponding linear increase in total trans-18:1 (5.2, 9.1, 14.1, and 21.3%) and total CLA (0.7, 1.9, 2.4, and 3.9%). The other FA in milk fat were not affected. Separation of trans-18:1 isomers was achieved by combination of gas chromatography (GC; 100-m highly polar capillary column) and prior separation of trans FA by silver ion-thin layer chromatography followed by GC. The CLA isomers were resolved by a combination of GC and silver ion-HPLC. The trans-11- and trans-10-18:1 isomers accounted for approximately 50% of the total trans-18:1 increase when SFO/FO diets were fed. On continued feeding to 38 d, trans-11-18:1 increased with 1.5% SFO/FO, stayed the same with 3%, and declined with 4.5% SFO/FO. Rumenic acid showed a similar pattern on continued feeding as trans-11-18:2; levels increased to 0.43, 1.5, 1.9, and 3.4% at 10 d and to 0.42, 2.15, 2.09, and 2.78% at 38 d. Rumenic acid was the major CLA isomer in all 4 diets: 66, 77, 78 and 85%. The CLA isomers trans-7,cis-9-, trans-9,cis-11-, trans-10,cis-12-, trans-11,trans-13-, and trans-9,trans-11-/trans-10,trans-12-18:2 also increased from 0.18 (control) to 0.52% (4.5% SFO/FO). Milk fat produced from 3% SFO/FO appeared most promising: trans-11-18:1 and cis-9,trans-11-18:2 increased 4.5-fold, total SFA reduced 18%, and moderate levels of trans-10-18:1 (3.2%), other trans-18:1 (6.6%) and CLA isomers (0.5%) were observed, and that composition remained unchanged to 38 d. The 4.5% SFO/FO diet produced higher levels of trans-11-18:1 and cis-9,trans-11-18:2, a 28% reduction in SFA, and similar levels of other trans-18:1 (9.2%) and CLA isomers (0.52%), but the higher levels of trans-11-18:1 and cis-9,trans-11-18:2 were not sustained. A stable milk fat quality was achieved by feeding moderate amounts of SFO (3% of DM) in the presence of 0.5% FO that had 4% vaccenic and 2% rumenic acids.