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.
