Trans-10 18:1 in ruminant meats: A review

Trans (t) fatty acids (TFA) from partially hydrogenated vegetable oils (i.e., industrial trans) have been phased out of foods in many countries due to their promotion of cardiovascular disease. This leaves ruminant-derived foods as the main source of TFA. Unlike industrial TFA where catalytic hydrogenation yields a broad distribution of isomers, ruminant TFA are enzymatically derived and can result in enrichment of specific isomers. Comparisons between industrial and ruminant TFA have often exonerated ruminant TFA due to their lack or at times positive effects on health. At extremes, however, ruminant-sourced foods can have either high levels of t10- or t11-18:1, and when considering enriched sources, t10-18:1 has properties similar to industrial TFA, whereas t11-18:1 can be converted to an isomer of conjugated linoleic acid (cis(c)9,t11-conjugated linoleic acid), both of which have potential positive health effects. Increased t10-18:1 in meat-producing ruminants has not been associated with negative effects on live animal production or meat quality. As such, reducing t10-18:1 has not been of immediate concern to ruminant meat producers, as there have been no economic consequences for its enrichment; nevertheless at high levels, it can compromise the nutritional quality of beef and lamb. In anticipation that regulations regarding TFA may focus more on t10-18:1 in beef and lamb, the present review will cover its production, analysis, biological effects, strategies for manipulation, and regulatory policy.     

Individual trans 18:1 Isomers are Metabolised Differently and Have Distinct Effects on Lipogenesis in 3T3‐L1 Adipocytes

The objective of this research was to study the metabolism of individual trans fatty acids (FAs) that can be found in ruminant fat or partially hydrogenated vegetable oils (PHVO) and determine their effects on FA composition and lipogenic gene expression in adipocytes. Differentiated 3T3‐L1 adipocytes were treated with 200 µM of either trans‐9‐18:1, trans‐11‐18:1, trans‐13‐18:1, cis‐9‐18:1 or BSA vehicle control for 120 h. Trans‐9‐18:1 increased total cell FA content (µmole/well) compared to other FA treatments, which was mainly related to the accumulation of trans‐9‐18:1 in the cells. Adipocytes were able to desaturate a significant proportion of absorbed trans‐11‐18:1 and trans‐13‐18:1 (~20 and 30 % respectively) to cis‐9,trans‐11‐18:2 and cis‐9,trans‐13‐18:2, whereas trans‐9‐18:1 was mostly incorporated intact resulting in a greater lipophilic index (i.e. decreased mean FA fluidity) of adipocytes. Trans‐9‐18:1 up‐regulated (P < 0.05) the expression of lipogenic genes including acetyl‐CoA carboxylase (1.65 fold), FA synthase (1.45 fold), FA elongase‐5 (1.52 fold) and stearoyl‐CoA desaturase‐1 (1.49 fold), compared to the control, whereas trans‐11‐18:1 and trans‐13‐18:1 did not affect the expression of these genes compared to control. Our results suggest that the metabolism and lipogenic properties of trans‐11‐18:1 and trans‐13‐18:1, typically the most abundant trans FA in beef from cattle fed forage‐based diets, are similar and are different from those of trans‐9‐18:1, the predominant trans FA in PHVO.     

The labile lipid fraction of meat: from perceived disease and waste to health and opportunity

The fatty acid composition of beef and pork has been stigmatized due to their relationships with several diseases from cardiovascular disease to cancer. Meat lipids are, however, one of the few components of meat that can be modified in content and composition, and can present opportunities for value added production and health promotion. Until regulations and policies are in place to define requirements for fatty acid enrichment, however, the process remains relatively academic. Once practical goals are in place for fatty acid enrichment in meat, both theory and practice need to converge for successful production of fatty acid enriched meat. The present review covers aspects of policy in Canada, and requirements for research networks to respond to theoretical and practical challenges associated with production of fatty acid enriched meat. Finally, needs for education and marketing are outlined which must be in place to truly realize a transition of meat lipids from perceived disease and waste to health and opportunity.     

Predicting fat quality from pigs fed reduced-oil corn dried distillers grains with solubles by near infrared reflectance spectroscopy: Fatty acid composition and iodine value

This study tested the ability of near infrared reflectance spectroscopy (NIRS) to estimate the fatty acid (FA) composition and iodine value (IV) of backfat from carcasses of pigs fed reduced-oil corn dried distillers grains with solubles. NIRS was suitable for screening purposes for the proportions of total saturated, monounsaturated, polyunsaturated, n − 3 and n − 6 FAs and some individual FAs such as C16:0, C18:1, C18:2n − 6 and C18:3n − 3 (R² = 0.80–0.89; RMSECVs, root mean square errors of cross-validation = 0.21–1.37% total FA) in both cold and warm intact backfat samples. This technology also met the requirements for a quick screening for the backfat IV in both cold and warm intact samples (R² = 0.90 and 0.87; RMSECVs = 1.66 and 1.80% total FA, respectively), which would help provide differential feed-back to pig producers and the feed industry and may provide the opportunity for breeding pigs for a desirable fat quality.     

Dietary influence on the m. longissimus dorsi fatty acid composition of lambs in relation to protein source

Dietary lipid effect, as a consequence of protein supplement, on lamb m. longissimus dorsi fatty acid composition was investigated, with emphasis on biohydrogenation intermediates. Crossbred lambs (White Swedish Landrace × Texel) were fed a barley-based diet without (CON) or with protein supplements including peas (PEA), rapeseed cake (RC) or hempseed cake (HC). The HC diet resulted in the highest muscle 22:6n-3 proportion, with the RC diet being similar (P<0.05). Protein supplement did not affect the c9,t11 conjugated linoleic acid (CLA) proportion, however the HC diet increased some minor CLA isomers, including t10,c12 CLA (P<0.05). The t10-18:1 and total trans-18:1 were lowest for the RC diet (P<0.05), likely relating to rumen conditions and precursor availability. The saturated, monounsaturated and branched-chain fatty acids were largely unaffected by protein supplement. In conclusion, feeding the RC diet lowered the t10-18:1 and total trans-18:1 in meat, and modestly increased 22:6n-3 content. The direction of these changes would be beneficial, making the RC diet the preferred protein supplement; however the magnitude of the changes in the present experiment may not be sufficient to have an impact on human health.     

Types of Oilseed and Adipose Tissue Influence the Composition and Relationships of Polyunsaturated Fatty Acid Biohydrogenation Products in Steers Fed a Grass Hay Diet

The current study evaluated the composition and relationships of polyunsaturated fatty acid biohydrogenation products (PUFA-BHP) from the perirenal (PRF) and subcutaneous fat (SCF) of yearling steers fed a 70 % grass hay diet with concentrates containing either sunflower-seed (SS) or flaxseed (FS). Analysis of variance indicated several groups or families of structurally related FA, and individual FA within these were affected by a number of novel oilseed by fat depot interactions (P < 0.05). Feeding diets containing SS increased the proportions of non-conjugated 18:2 BHP (i.e., atypical dienes, AD) and conjugated linoleic acids (CLA) with the first double bond from carbon 7 to 9, trans-18:1 isomers with double bonds from carbon 6 to 12, and these PUFA-BHP had greater proportions in SCF compared to PRF (P < 0.05). Enrichment of conjugated linolenic acids, AD and CLA isomers with the first double bond in position 11 or 12, and t-18:1 isomers with double bonds from carbon 13 to 16 were achieved by feeding diets containing FS, with PRF having greater proportions than SCF (P < 0.05). Principal component analysis visually confirmed interaction effects on these groups/families of FA, and further confirmed or suggested a number of relationships between PUFA-BHP. Feeding SS or FS in a grass hay diet and exploiting adipose tissue differences, therefore, present unique opportunities to differentially enrich a number of PUFA-BHP which seem to have positive health potential in humans (i.e., t11-18:1, c9,t11-18:2 and c9,t11,c15-18:3).     

Double Bond Position Plays an Important Role in Delta-9 Desaturation and Lipogenic Properties of Trans 18:1 Isomers in Mouse Adipocytes

The objective of this research was to study the delta‐9 desaturation of individual trans (t) fatty acids that can be found in ruminant fat or partially hydrogenated vegetable oils (PHVO) and determine their effects on lipogenic gene expression in adipocytes. It was hypothesized that delta‐9 desaturation and lipogenic properties of t‐18:1 isomers depend on the position of double bond. Differentiated 3T3‐L1 adipocytes were treated with 200 µM of t6–18:1, t9–18:1, t11–18:1, t13–18:1 or t16–18:1, cis (c)‐9 18:1 or bovine serum albumin (BSA) vehicle control for 48 h. Cells were then harvested for fatty acid and gene expression analyses using gas chromatography and quantitative PCR respectively. Among t‐18:1 isomers, t13–18:1 and t11–8:1 had the greatest percent delta‐9 desaturation (44 and 41 % respectively) followed by t16–18:1 and t6–18:1 (32 and 17 % respectively), while c9–18:1 and t9–18:1 did not undergo delta‐9 desaturation. Trans9–18:1 up‐regulated (P < 0.05) the expression of lipogenic genes including fatty acid synthase and stearoyl‐CoA desaturase‐1 (P < 0.05), whereas the expression of these genes were not affected with other t‐18:1 isomers (P > 0.05). Consistent with gene expression results, t9–18:1 increased the de novo lipogenic index (16:0/18:2n‐6) compared with control cells and increased delta‐9 desaturation index (c9–16:1/18:0) compared to other t‐18:1 isomers (P < 0.05). The current study provides further evidence that the predominant trans fatty acid in PHVO (t9–18:1) has isomer specific lipogenic properties.     

Effects of feeding flaxseed or sunflower-seed in high-forage diets on beef production,quality and fatty acid composition

Yearling steers were fed 70:30 forage:concentrate diets for 205 d, with either grass hay (GH) or red clover silage (RC) as the forage source, and concentrates containing either sunflower-seed (SS) or flaxseed (FS), each providing 5.4% oil to diets. Feeding diets containing SS versus FS significantly improved growth and carcass attributes (P < 0.05), significantly reduced meat off-flavor intensity (P < 0.05), and significantly increased intramuscular proportions of vaccenic (t11-18:1), rumenic (c9,t11-CLA) and n − 6 fatty acids (FA, P < 0.05). Feeding diets containing FS versus SS produced significantly darker and redder meat with greater proportions of atypical dienes (P < 0.05). A significant forage × oilseed type interaction (P < 0.05) was found for n − 3 FA, α-linolenic acid, and conjugated linolenic acid, with their greatest intramuscular proportions found when feeding the RC-FS diet. Feeding GH versus RC also significantly improved growth and carcass attributes, sensory tenderness (P < 0.05) and significantly influenced intramuscular FA composition (P < 0.05), but overall, forage effects on FA profiles were limited compared to effects of oilseed.     

Beef Fat Enriched with Polyunsaturated Fatty Acid Biohydrogenation Products Improves Insulin Sensitivity Without Altering Dyslipidemia in Insulin Resistant JCR:LA-cp Rats

The main dietary sources of trans fatty acids are partially hydrogenated vegetable oils (PHVO), and products derived from polyunsaturated fatty acid biohydrogenation (PUFA‐BHP) in ruminants. Trans fatty acid intake has historically been associated with negative effects on health, generating an anti‐trans fat campaign to reduce their consumption. The profiles and effects on health of PHVO and PUFA‐BHP can, however, be quite different. Dairy products naturally enriched with vaccenic and rumenic acids have many purported health benefits, but the putative benefits of beef fat naturally enriched with PUFA‐BHP have not been investigated. The objective of the present experiment was to determine the effects of beef peri‐renal fat (PRF) with differing enrichments of PUFA‐BHP on lipid and insulin metabolism in a rodent model of dyslipidemia and insulin resistance (JCR:LA‐cp rat). The results showed that 6 weeks of diet supplementation with beef PRF naturally enriched due to flaxseed (FS‐PRF) or sunflower‐seed (SS‐PRF) feeding to cattle significantly improved plasma fasting insulin levels and insulin sensitivity, postprandial insulin levels (only in the FS‐PRF) without altering dyslipidemia. Moreover, FS‐PRF but not SS‐PRF attenuated adipose tissue accumulation. Therefore, enhancing levels of PUFA‐BHP in beef PRF with FS feeding may be a useful approach to maximize the health‐conferring value of beef‐derived fats.     

Meat quality of Nguni steers supplemented with Acaciakarroo leaf-meal

The objective of the study was to determine the meat quality of Nguni steers supplemented with Acaciakarroo leaf-meal. Thirty 19-month old steers were randomly assigned to A.karroo leaf-meal (AK), sunflower cake (SF) and a control (CN) diets. Steers on the AK and SF diets were given an additional 150 g of protein per day for 60 days. The steers were slaughtered at 21 months and the m.longissimusthoracisetlumborum was sampled for meat quality measurements. Steers that received SF diet had lighter-coloured (L*) (P < 0.05) meat than those on AK and CN diets. The highest redness (a*) (17.3 ± 0.29) values were recorded in steers supplemented with AK compared to those that received SF and CN diets. Diet had no effect on pH, drip loss, water holding capacity, sarcomere length, muscle bundle areas, myofibrillar fragment length, Warner–Bratzler shear force and cholesterol values. Steers supplemented with AK (22.4 ± 0.08%) and SF (22.5 ± 0.08%) had higher (P < 0.05) meat protein content than those on the CN (20.2 ± 0.08%) diet. Highest muscle fibre area (3472.6 ± 119.51 μm²), fat content (1.2 ± 0.11%) and cooking loss (25.2 ± 0.73%) of meat aged for 2 days were recorded in steers given the SF diet compared to those on the AK and CN diets. Supplementing Nguni cattle with A.karroo leaf-meal produced beef of comparable quality to natural pasture alone but with a fresher appearance and higher protein content.