Influence of dietary conjugated linoleic acid (CLA) and age at slaughtering on performance, slaughter- and meat quality, lipoproteins, and tissue deposition of CLA in barrows

To assess the effects of dietary conjugated linoleic acid (CLA) on performance, slaughter and meat quality, 100 Danish barrows were fed diets containing 0.5% sunflower oil (control) and 0.5% CLA from 40 kg live weight until slaughter at either 100 or 130 kg live weight. Plasma total cholesterol (P=0.006) and HDL-cholesterol (P=0.021) was reduced, and plasma FFA-concentration increased (P=0.06) in pigs fed CLA. CLA supplementation improved (P=0.01) the feed utilisation by 4.7% and 4.3% for pigs slaughtered at 100 and 130 kg, respectively. Daily gain tended (P=0.06) to increase with the CLA-treatment (1.236 versus 1.194 kg for CLA- and control, respectively). Dietary treatments had no effects on slaughter- (meat percentage and backfat thickness) and meat quality responses (pH, temperature and water holding capacity). CLA tended (P=0.09) to reduce the intramuscular cholesterol, but had no influence on the total content of intramuscular fat.     

Influence of dietary conjugated linoleic acids and vitamin E on meat quality, and adipose tissue in rabbits

Eighty New Zealand White rabbits, age 55 days, half male and half female, were randomly assigned to one of four diets in a 2×2×2 factorial arrangement. The diets contained 0% or 0.5% CLA, and 60 or 240mg/kg α-Tocopheryl acetate. Forty-eight rabbits were slaughtered at age 92 days. Growth performances and carcass weight were higher (P<0.05) in 240mg/kg of α-tocopheryl acetate-fed rabbits. Fat and CLA isomers content of Longissimus Lumborum (LL) muscle was higher (P<0.05) in CLA-fed rabbits than control. Fatty acid composition of LL muscle was modified (P<0.05) and oxidative stability was increased (P<0.001) by both dietary treatments. CLA increased (P<0.05) triglyceride, total cholesterol and glucose levels in plasma. Adipocytes in interscapular and perirenal fat in the 240mg/kg α-tocopheryl acetate and 0.5% CLA groups were larger in size but lesser in number than in 60mg/kg α-tocopheryl acetate and no CLA rabbit (P<0.01).     

Effects of dietary conjugated linoleic acid (CLA) on spontaneously hypertensive rats

Conjugated linoleic acid (CLA) has a number of beneficial biological effects, including reducing cancer incidence and development, reducing severity of atherosclerosis, modulating immune responses, reducing body fat, and enhancing lean mass. Recently CLA has been reported to have a beneficial effect on blood pressure. Thus the effects of CLA supplementation on blood pressure and its associated adverse health effects using spontaneously hypertensive rats were investigated. Results indicated that CLA had no effect on blood pressure in this animal model. However, feeding CLA significantly reduced the incidence and number of animals with stroke-like symptoms. Although the reason CLA reduced stroke-like symptoms is not clear at this moment, there is great potential that CLA may be useful in reducing stroke incidence in humans.     

Influences of dietary conjugated linoleic acid (CLA) and total lysine content on growth, carcass characteristics and meat quality of heavy pigs

To assess the effects of dietary CLA, lysine and sex on performance, blood metabolites, carcass characteristics, meat quality and skeletal development, seventy-two pigs (initially 105.3 ± 6.6 kg live weight) barrows and gilts, were assigned to one of four diets in a 2 × 2 × 2 factorial arrangement. The diets contained 0% or 0.75% CLA, and 0% or 0.16% of l-lysine–HCl. All pigs were slaughtered at an average weight of 153.4 ± 11.0 kg. Neither CLA nor lysine supplementation influenced growth, blood metabolites or carcass characteristics. CLA reduced (P < 0.05) pH₂₄ and increased (P < 0.01) yellowness (b^*) of the Longissimus muscle. Lysine increased (P < 0.01) pH₂₄ and reduced (P < 0.01) muscle ash content. CLA reduced (P < 0.05) collagen synthesis, and lysine increased (P < 0.05) collagen synthesis in Longissimus muscle, but no influence on intramuscular collagen maturity or muscle hydroxylysylpyridinoline crosslink concentration were observed. In addition, metacarpal bone diameter was reduced (P < 0.05) by CLA. Barrows had higher ADG, final weight (P < 0.01), carcass weight, lean percentage (P < 0.05), serum cholesterol (P < 0.05) and triacylglycerol (P < 0.001) than gilts. Metatarsal diameter was larger in gilts than barrows (P < 0.05).     

牛乳中共轭亚油酸（CLA）的研究

共轭亚油酸（CLA）是亚油酸的同分异构体的混合物,主要来源于牛乳、乳制品及反刍物食品的天然成分。本文就CLA的抑癌和降血脂等多种生理功能及其作用机理,阐述了CAL作为一种新型营养物质的潜力。     

Cosupplementation of dietary calcium and conjugated linoleic acid (CLA) improves bone mass in mice

Conjugated linoleic acid (CLA) has shown a variety of biologically beneficial effects, such as anticancer, antiatherosclerosis, antidiabetic, immunomodulating, and antiobesity effects. Its effects on reduction of body fat occur with enhancement of lean body mass and body ash; the effects of CLA on bone mass are inconsistent in mice and human studies. We hypothesized that the inconsistency of CLA's effect on ash may be linked to interaction between CLA and dietary calcium levels. We reanalyzed our previous studies, which used mice fed 0.5% CLA-containing diet with regular calcium content (0.5%) or enhanced calcium level (0.66%). Extra calcium in the diet improved CLA's effects on bone mass, particularly in male mice (P= 0.0194); without extra dietary calcium there was no effect of CLA on bone mass. This finding may help improve the efficacy of CLA to be used as a dietary supplement to be used as part of an osteoporosis prevention strategy. Further studies are needed to confirm this observation.     

Chemoenzymatic synthesis of structured triacylglycerols with conjugated linoleic acids (CLA) in central position

A chemoenzymatic process for the production of structured triacylglycerols (TAG) containing CLA at sn2 position and lauric acid at external ones is proposed. First, castor bean oil was chemically dehydrated and isomerised to obtain a new modified oil with very high proportion of CLA (>95%). Then, this new oil was used for enzymatic transesterification allowing the grafting of lauric acid at external positions of the TAG backbone by using 1,3 regioselective enzymes. Among these, Aspergillus niger lipase was not satisfactory giving very low lauroyl incorporation (<5%) On the contrary, lipases from Thermomyces lanuginosa (Lipozyme TL IM) and from Carica papaya latex allowed good reaction yields. The effect of the type of acyl donor was studied. With alkyl esters T. lanuginosa lipase provided a final incorporation of 58.9% after 72 h corresponding to 88.4% transesterification yield. Concerning C. papaya lipase, incorporation of lauroyl residues was lower than Lipozyme TL IM. This lipase exhibited higher performance with lauric acid accounting for 44.7% lauroyl incorporation at the end of reaction for a 67.1% transesterification yield. The effect of the substrates mole ratio was also evaluated. It was observed that a 1:3 TAG/acyl donor mole ratio was the most efficient for both lipases. Finally, fatty acids regiodistribution of the newly formed structured TAG was determined. With Lipozyme TL IM, the proportion of lauric acid incorporated at the sn2 position did not exceed 5.4% after 72 h while with C. papaya lipase a more pronounced incorporation of lauroyl residues at the central position (8.8%) was observed.     

Implication of conjugated linoleic acid (CLA) in human health

Conjugated linoleic acid (CLA) has drawn significant attention in the last two decades for its variety of biologically beneficial effects. CLA reduces body fat, cardiovascular diseases and cancer, and modulates immune and inflammatory responses as well as improves bone mass. It has been suggested that the overall effects of CLA are the results of interactions between two major isomers, cis-9,trans-11 and trans-10,cis-12. This review will primarily focus on current CLA publications involving humans, which are also summarized in the tables. Along with a number of beneficial effects of CLA, there are safety considerations for CLA supplementation in humans, which include effects on liver functions, milk fat depression, glucose metabolism, and oxidative stresses.     

Effect of dietary conjugated linoleic acid (CLA) supplementation on CLA isomers content and fatty acid composition of dry-cured Parma ham

To evaluate the effects of dietary conjugated linoleic acid (CLA) supplementation on cis-9, trans-11 and trans-10, cis-12 isomer content and on the fatty acid composition of subcutaneous adipose tissue and intramuscular lipids of biceps femoris, the lipids of 24 dry cured Parma hams, obtained from Large White pigs fed isoenergetic diets supplemented with either 0 (CON) or 0.25% (T1) CLA from 97 to 172kg live weight, were analysed by Ag(+)-HPLC and capillary GLC. The dietary treatment had no influence on lipid content of BF and subcutaneous adipose tissue but increased (P<0.01) the content of both isomers, more markedly in the latter tissue. CLA supplementation increased (P<0.01) myristic, palmitic, palmitoleic and total saturated fatty acids, and decreased oleic and eicosenoic acids in both tissues. In adipose tissue, an increase (P<0.05) in stearic acid content was observed. Supplementing the finishing diet of heavy pigs with CLA has thus shown to be an effective tool for increasing the CLA content in cured ham and, also, the saturated:unsaturated ratio of the lipids, a positive effect from a technological point of view. From a human nutritional standpoint, the changes occurring in fatty acid composition negatively affect the atherogenic and thrombogenic indexes, but probably these changes are of no particular concern, as they would only partly offset the progressive increase in the degree of unsaturation of heavy pig lipids that has occurred in recent years, as a consequence of reduced adipose depots in carcasses.     

Effect of dietary conjugated linoleic acid in combination with monounsaturated fatty acids on the meat composition and quality traits of dry-cured loin

Three levels (0%, 1% and 2%) of an enriched conjugated linoleic acid oil (CLA) were combined with two levels of monounsaturated fatty acids (MUFA) (low −19% average and high −39% average) for pig feeding. Composition, weight losses, lipid oxidation (thiobarbituric acid test, TBARs), change in the fatty acid content of the lipid fractions and sensory analysis of dry-cured loin as affected by dietary CLA, MUFA and CLA × MUFA interaction were studied. CLA and CLA × MUFA did not affect moisture and intramuscular fat content of dry-cured loin, weight losses during the processing, changes in the content of most fatty acids from lipid fractions and sensory traits. CLA and MUFA supplementation led to lower TBARs values (1.3 mg MDA/kg sample for 0% CLA and 0.9 mg MDA/kg sample for 2% CLA; 1.2 mg MDA/kg sample for low MUFA diets and 0.9 mg MDA/kg sample for high MUFA diets), the highest TBARs values being detected for 0% CLA-low MUFA diets [1.5 mg MDA/kg sample]. The combination of dietary CLA with different MUFA levels in pig diets did not affect most composition and quality traits of dry-cured loin. Dietary CLA and MUFA seemed to lead to lower lipid oxidation in this product.     

混菌固定化对生物合成共轭亚油酸的影响

海藻酸钠为固定材料,研究了嗜酸乳杆菌和嗜热链球菌先混菌后固定化对生物合成共轭亚油酸的影响.试验结果表明,最佳固定化条件为:海藻酸钠3.5%,氯化钙2.5%,菌种(嗜酸乳杆菌∶嗜热链球菌=1∶1,La:St=1∶1)包埋量40%,胶粒直径3mm,固定化时间1h;最佳发酵条件:培养温度37℃,发酵时间24h.在此条件下CLA积累量可达118.91μg/mL.固定化后菌种活力得到保持持久且可重复利用.     

Effect of high or low protein ration combined or not with rumen protected conjugated linoleic acid (CLA) on meat CLA content and quality traits of double-muscled Piemontese bulls

A trial was carried out on double-muscled Piemontese bulls to evaluate the effects of two rations differing in crude protein density (HP=14.5% DM and LP=10.8% DM) and top dressed or not with 80 g/d of rumen protected CLA (rpCLA) for a long period (336 d) on meat quality traits and CLA content. Forty-eight bulls were fed one of the four experimental diets based on corn silage and cereals and were slaughtered at an average age and body weight (BW) of 562 ± 18 d and 668 ± 56 kg, respectively. After slaughter the 5th rib cut was dissected into Longissimus thoracis (LT), other muscles (OM), inter-muscular fat (IF), cover fat (CF), and bones. Muscles and fatty tissues were analyzed for proximate composition and fatty acid (FA) profiles. Rib was composed by 81.1, 3.7, 1.6 and 13.6% of muscles, IF, FC and bone, respectively; LT and OM contained only 0.8 and 1.4% of lipid, respectively. The treatments did not influence these values, but rpCLA increased, compared to control, both c9,t11-CLA and t10,c12-CLA concentrations in all the tissues (P<0.01); t10,c12-CLA concentration was increased much more in muscles (+20 times) than in fatty tissues (from +0.2 to +0.9 times). This suggests that in the muscle this isomer is preferentially stored and/or less combusted with respect to other fatty acids. Low protein rations did not exert any influence on carcass and meat quality, as on growth performance, but reduced nitrogen excretion, their use for improving the environmental impact (process quality) of this meat production system is recommended.     

共轭亚油酸对畜禽肌肉品质影响的研究进展

共轭亚油酸(Conjugated linoleic acid,CLA)是亚油酸的一组构象和位置异构体。它作为一种新型功能性脂肪酸,具有许多重要的生理功能,其中调节机体脂肪代谢,降低脂质沉积的功效尤为显著。目前国内外研究人员利用此生物活性在动物饲养方面的研究也日益广泛。文章简要介绍了共轭亚油酸的结构、活性及降脂机制。重点结合近年来国内外在共轭亚油酸和畜禽饲养方面的相关研究报道,从畜禽肌肉品质的主要影响因素展开,综述了共轭亚油酸对畜禽肌肉品质和风味的影响。     

Mechanisms of body fat modulation by conjugated linoleic acid (CLA)

Since its discovery as an anticancer principal from ground beef extract in the 1980s, conjugated linoleic acid (CLA) has drawn much attention due to its variety of biological activities. One of the most interesting aspects of CLA is its ability to reduce body fat while enhancing lean body mass. One explanation for the variety of biological activities of CLA is that CLA is a mixture of geometric and positional isomers, although the primary research focus is on the two main isomers, cis-9,trans-11 and trans-10,cis-12. The involvement of eicosanoid metabolism has been suggested as one mechanism for CLAs wide range of biological activities. Incorporation of CLA in the sn-2 position of phospholipid fractions, and the negative correlation between tissue levels of CLA and arachidonic acid support this. Other possible mechanisms of CLA with regard to body fat reduction will be discussed, as well as differences between human and animal studies. Safety concerns regarding the use of CLA in humans are not conclusive and need further investigation.     

共轭亚油酸的抗氧化活性及其抗氧化剂筛选

目的:考查共轭亚油酸的抗氧化活性并筛选对其活性有保护作用的抗氧化剂。方法:采用连苯三酚体系考察共轭亚油酸及其乙酯的抗氧化性;运用气相色谱—质谱联用技术考察影响共轭亚油酸稳定性的因素,筛选保存共轭亚油酸适宜添加的抗氧化剂并考察合适的加入量。结果:共轭亚油酸及其乙酯在连苯三酚体系实验体系中均表现出良好的抗氧化作用,在筛选的抗氧化剂中,TBHQ、茶多酚、BHA、BHT效果理想。结论:共轭亚油酸具有明显的抗氧化性,建议使用抗氧化剂TBHQ与茶多酚保护其免于氧化分解。     

Effect of cooking methods on fatty acids,conjugated isomers of linoleic acid and nutritional quality of beef intramuscular fat

The effect of boiling, microwaving and grilling on the composition and nutritional quality of beef intramuscular fat from cattle fed with two diets was investigated. Longissimus lumborum muscle from 15 Alentejano young bulls fed on concentrate or pasture was analyzed. Cooking losses and, consequently, total lipids, increased directly with the cooking time and internal temperature reached by meat (microwaving > boiling > grilling). The major changes in fatty acid composition, which implicated 16 out of 34 fatty acids, resulted in higher percentages in cooked beef of SFA and MUFA and lower proportions of PUFA, relative to raw meat, while conjugated linoleic acid (CLA) isomers revealed a great stability to thermal processes. Heating decreased the PUFA/SFA ratio of meat but did not change its n−6/n−3 index. Thermal procedures induced only slight oxidative changes in meat immediately after treatment but hardly affected the true retention values of its individual fatty acids (72–168%), including CLA isomers (81–128%).     

Influence of dietary conjugated linoleic acid on volatile profiles, color and lipid oxidation of irradiated raw chicken meat

Forty-eight, 27-week-old White Leghorn hens were fed a diet containing 0, 1.25, 2.5 or 5.0% conjugated linoleic acid (CLA) for 12 weeks. At the end of the 12-week feeding trial, hens were slaughtered, and boneless, skinless breast and leg meats were separated from carcasses. Meats were ground through 9 and 3-mm plates, and patties were prepared. Patties prepared from each dietary treatment were divided into two groups and either vacuum- or aerobic-packaged. Patties were irradiated at 0 or 3.0 kGy using a linear accelerator and stored at 4°C. Samples were analyzed for thiobarbituric acid reactive substances, volatile profiles, color and odor characteristics at 0 and 7 days of storage. Dietary CLA reduced the degree of lipid oxidation in raw chicken meat during storage. The content of hexanal and pentanal in raw chicken meat significantly decreased as dietary CLA level increased. Irradiation accelerated lipid oxidation in meat with aerobic packaging, but irradiation effect was not as significant as that of the packaging. Dietary CLA treatment improved the color stability of chicken patties. Color a*-value of irradiated raw chicken meat was higher than that of the nonirradiated meat. Dietary CLA decreased the content of polyunsaturated fatty acid and increased CLA in chicken muscles, which improved lipid and color stability and reduced volatile production in irradiated and nonirradiated raw chicken meat during storage.     

Amounts of conjugated linoleic acid (CLA) in German foods and evaluation of daily intake

 The quantities of the biologically active isomer of conjugated linoleic acid (CLA) – C18:2 c9t11 – in 139 German foods were analysed by capillary gas chromatography (results are given as a % of all identified fatty acid methyl esters). The CLA content ranged from 0.40% (Gouda) to 1.70% (Jurassic cheese, Old Emmentaler) in dairy products, from 0.11% (rabbit) to 1.20% (lamb) in meat, and from 0.01% (pike-perch) to 0.09% (carp) in fish. CLA could be detected in neither vegetable fats or oils nor in margarines (CLA <0.01%). Crisps, chocolates, cakes and pastries, and other foods have only a negligible CLA content. The average estimated CLA intake in Germany was calculated to be 0.35g CLA/day for women and 0.43g CLA/day for men. Received: 22 July 1997     

Amounts of conjugated linoleic acid (CLA) in German foods and evaluation of daily intake

 The quantities of the biologically active isomer of conjugated linoleic acid (CLA) – C18:2 c9t11 – in 139 German foods were analysed by capillary gas chromatography (results are given as a % of all identified fatty acid methyl esters). The CLA content ranged from 0.40% (Gouda) to 1.70% (Jurassic cheese, Old Emmentaler) in dairy products, from 0.11% (rabbit) to 1.20% (lamb) in meat, and from 0.01% (pike-perch) to 0.09% (carp) in fish. CLA could be detected in neither vegetable fats or oils nor in margarines (CLA <0.01%). Crisps, chocolates, cakes and pastries, and other foods have only a negligible CLA content. The average estimated CLA intake in Germany was calculated to be 0.35g CLA/day for women and 0.43g CLA/day for men. Received: 22 July 1997