by: Urip Santoso
Department of Animal Science, Faculty of Agriculture, Bengkulu University, Bengkulu, Indonesia
INTRODUCTION
Recently, there is a great demand to produce healthier animal products. Consumers tended to consume animal products with the characteristics of low fat, low contaminated pathogenic microorganisms, low drug residues. Pertaining to these demands, many investigations have been conducted with some success and other unsuccess.
It was recently proven that conjugated linoleic acid (CLA), an uncomplete biohydrogenation of linoleic acid in rumen had beneficial effect on human health. Conjugated linoleic acid is collective terms describing a mixture of positional and geometric conjugated diene isomers of linoleic acid (Dunshea et al., 2002). CLA is a general term for positional and geometrical isomers of linoleic acid, cis-9, cis-12 octadecadienoic acid, in which the deoble bonds are conjugated instead of being in the typical methylene interrupted configuration (Ham et al., 2002). Of the individual isomers of CLA, cis-9, trans-11-octadecadienoic acid (c9,t11-18:2) has been suggested to be the most important in terms of biological activity because it is the major isomer. CLA can be produced by alkaline isomerization which are not fully characterized (Nicholas et al., 1951; Sehat et al., 1998).
Limited number of bacterial spp were reported to be able to produce CLA from linoleic acid (C18:2) in vitro (Jiang et al., 1998). CLA has been shown to be produced from polyunsaturated fat by certain rumen microorganisms such as Butyrivibrio species (Forgety et al., 1988). More recently, it was reported that Propionibacterium freudenreichii commonly used as dairy starter culture, was able to produce CLA from free linoleic acid (Jiang et al., 1998). Pariza and Yang (2000) screened 45 cultures from whole intestinal tract of two conventional rats by measuring the conversion of linoleic acid to CLA with HPLC and GC, and developed the method of producing CLA with selected strain in Tris-HCl buffer. However, Ogawa et al. (2001) insisted after 4 days of reaction with washed cells of L. acidophilus transformed more than 95% of the added linoleic acid into CLA and cells themselves could be used as source of CLA. Ham et al. (2002) found CLA producing lactic acid bacteria idenfied to be Lactobacillus fermentum in feces of healthy babies. CLA producing lactic acid bacteria can be useful as a starter culture for making milk products, a source of enzyme systems in the production of CLA, or a probiotic culture. In vitro studies with mixed culture or pure strains of ruminal bacteria have shown that most bacteria are capable of hydrogenating linoleic acid (C18:2) to trans-C18:1 and related isomers, but only a few have the ability to hydrogenate C18:2 completely to stearic acid (Miles et al., 1970; Harfoot et al., 1973). Oleic acid (C18:1) was also extensively hydrogenated to stearic acid (C18:0) by ruminal bacteria in vitro (Song and Choi, 1998, Wong et al., 1999).
Ha et al. (1987) found that a lipid fraction isolated from cooked ground beef had anticarcinogenics.Other investigations (Banni and Martin, 1998; Belury, 1995; Ip et al., 1999) also found that lipid known as CLA had anticarcinogenic activity in a wide range of animal models.
Its effect on CLA content
Eggs produced by hens fed 5.0% CLA will contain 310 to 365 mg of CLA per eggs. This is far from the prediction that a 70 kg human would need to consume about 1.5 to 3.0 g of CLA daily (Draker, 1995). Although it is unlikely that people would routinely consume four to five eggs daily, eggs containing substantial CLA could be a valuable diatary CLA source in combination with foods, such as milk, cheese, and beef, that are relatively high in CLA (Chin et al., 1992). Schafer et al. (2001) found that inclusion of CLA at 29 g per kg diet transfer CLA into egg at about 400 mg CLA per eggs. The current consumption of CLA in US is estimated to be 0.5 to 1.0 g per person.
Its effect on growth
CLA has been proven to increase body weight gain and to improve feed efficiency in rat, mice and chickens (Chin et al., 1994; Park et al., 1997). Ostrowsha et al. (1999) found that CLA had no effect on growth but improved feed conversion efficiency. Dunshea et al. (2002) found that under commercial condition dietary CLA can improve growth performance of pigs.
Chamruspollert and Sell (1999) found that the inclusion of CLA had no effect on rate of egg production, body weight gain and feed intake. CLA inclusion at level of 5% significantly decreased weights of eggs and yolks. However, when feeding CLA was given at longer duration, it decreased feed intake with no effect on rate of egg production, weight of eggs, albumens or yolks or body weight.
Its effects on fat deposition
CLA inclusion decreased carcass fat content in mice (West et al., 1998) and reduced fat deposition in pig (Ostrowsha et al., 1999). It was also demonstrated that CLA inclusion also reduced back fat thickness (Thiel et al., 1998) and reduced the fat content of commercial meat cuts (Dugan et al., 1999). Recently, Dunshea et al. (2002) found that CLA inclusion at level of 4 g/kg diet reduced backfat thickness of commercial pigs housed under industry conditions. At the highest dose of CLA used (10g/kg of CLA-55) there was a 25% (6 mm) reduction in backfat and fat deposition. Other studies have indicated that dietary CLA supplementation of growing pigs results in less fat at slaughter as estimated by dissection of wholesale loin cuts (Dugan et al., 1999). On back fat thickness (Thiel et al., 1998). For example, at 5 times the anticipated dose of CLA investigated in this study (20 g/kg of CLA-55), Dugan et al. (1997) reported a 27% reduction in subcutaneous fat per kg of total cuts in gilts Huang et al. found CLA inclusion reduced cholesterol.
Park et al. (1997) found that CLA inclusion reduced body fat but increased body protein, water and ash contents. A reduced in body fat might be correlated with increased b-oxidation as indicated by increased in carnitine palmitoyltransferase activity, - a rate-limiting enzyme in b-oxidation, in fat pad and muscle. Another key enzyme in lipid metabolism is adipocyte LPL, which hydrolyzes free fatty acids from circulating triacylglyceride; the fatty acids are then taken up by the adipocytes and re-esterified. It was found by Park et al. (1997) that CLA inhibits LPL activity in 3T3-L1 adipocytes, while apparently enhancing lipolysis. West et al. (1998) however found that CLA reduced adipocyte depot weight, carcass lipid and protein in mouse. Bouthegourd et al. (2002) found that CLA mixture prevents body triglyceride accumulation. Futhermore they found that CLA mixture had no effect on adipose weight or energy expenditure in despite a theoretically higher capacity of red muscle to oxideze lipids
Cantwll e al. (1999) found that incubation of rat hepatocytes with 20 ppm CLA for 3 hours did not affect the specific activity of 3-hydroxy-3-methylglutaryl conenzyme A reductase, protein synthesis in hepatocytes was elevated in the present of 5 and 10 ppm CLA. Gluconeogenesis was decreased at > 10 ppm. Glutathione peroxidase activity was significantly decreased in the presence of 10 ppm CLA..
Park e al. (1999b) CLA inclusion increased body protein, water and ash, and reduced body fat were associaed with feeding the rans-10 cis 12 CLA isomer. In cultured 3T3-L1 adipocytes, the trans 10 cis 12 isomer educed lipoprotein lipase activity, intramuscular triacylglycerol and glycerol, and enhanced glycerol release into the medium. By contrast, the cis-9, rans-11 and trans 9, trans 11 CLA isomers did not affect those biochemical activities.
Park et al. (1999a) also found hat feeding CLA increased protein, water but reduced body fat. Tissue CLA levels declined following the withdrawal of CLA from the die.
Azain et al. (2000) found that the reducion in fat mass in rats fed CLA can be aaounted for by a reduction in cell size rather han a change in cell number. Blankson et al. (2000) found that CLA reduced body fat mass in humans and hat no additional effect on body fat mass is achieved with doses >3.4 g CLA/d.
Jones et al. (2000) found tha birds fed 0.5 and 1.0 g CLA/kg feed had significantly more CLA in he egg yolk lipid vs control and 0.01 g CLA/kg diet groups after 7 d. Incorporation of CLA into egg lipid was highest on d 24 and 36. CLA enrichment in egg lipid in the 1.0 g CLA/kg diet group was similar to that in ruminant animal food product, 3 mgCLA/g fat.
Stangl (2000) found that CLA inclusion reduce serum VLDL lipids wih no effect on serum LDL and HDL, reduced hepatic cholesterol. Gravino et al. (2000) found hat isomeric mixture of CLA reduced plasma triglyceride, total cholesterol. HDL-c did not different. The CLA group had significantly lower weight gain but greater feed intake. They concluded hat short-term feeding, c911, thought to be the active compound in CLA, does not produce the same effect as the isomer mixure.
Egg production
Jones et al. (2000) found that high and medium CLA fed groups had lower egg production raes than those fed 0 and 0.1 mg CLA/kg, indicating hat CLA affect reproductive efficiency of the hens.
Fatty acid profiles
Chamruspollert and Sell (1999) found that CLA inclusion decreased the concentration of C18:1, C18:2, C18:3, C20:4 and C22:6, whereas saturated fatty acid was increased. Change in SFA and MUFA may be due to the inhibition of D 9 desaturase enzyme system in the liver caused by CLA.
Aminal product quality
Cherion et al. (2002) found irradiation leads to high ion counts volatiles in cooked eggs. However, no specific volatile compounds unique to irradiation were observed in hard-boiled-irradiated eggs with high CLA content.
CONCLUSION
From the current review, it was shown that CLA inclusion to diet would reduce fat deposition in animals such as rat, mice and poultry. The mechanism following the reduction of fat in the body was unclear. CLA also increased body protein although the mechanism of it was unclear. CLA also change fatty acid composition by increased saturated fatty acid and reduced monounsaturated fatty acid and polyunsaturated fatty acid. CLA also affected the quality of egg and meat. It is needed to investigate by which mechanism CLA could reduce fat deposition in rat, mice and poultry in the future.
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