conjugated linoleic acid (CLA) has multiple applications in medicine, pharmacy and food industry. Nowadays, CLA as a food supplement is usually produced chemically by alkaline isomerization of similar fatty acids (e.g linoleic acid) which leads to the production of some unwanted isomers, too. As this functional lipid is only found in tiny quantities in dairy products and the meat of ruminator animals, it is necessary to develope a safe and healthy method for producing this compound. To achieve this goal recognition and introducing the biological ways would be helpful. This reaserch aims were to produce CLA using two indiginous speicies of Lactobacillus ( L. plantarum A7 and L. acidophilus Sh4) already isolated from the native sources in this labratory and a feasibility study of its production in the semi-pilot plant scale. For these purposes, the above mentioned bacteria were cultured and activated at first. They were then adapted to the medium containing Linoleic acid as the substrate and eventually, reaction mixture were provided. Every milliliter of this reaction mixture contained 0.12 g washed cells and 30 mg Castor oil which the latter was made in Triton X-114 in ratio 5 to 1. At last 100 units of lipase enzyme (M Amano 10) were added to the reaction mixture. The 1 M sodium citrate buffer with pH 6 was used to reach the final volum of the raction mixture to one milliliter. The reaction mixtures were incubated at 37° C in the shaking incubator with 120 rpm for 99 hours. The cultures were then centrifigued at 6000 g for 10 min. The lipid cantents of both supernatants and the pellets were extracted using Bligh and Dyer method. The isolated lipids were analyzed using gas choromatography. The results of the analysis showed that both bacterial strains were able to produce CLA, but L. plantarum A7 could produce 6.26 mg/mL CLA with the yeild rate of 24.60 % whereas L. acidophilus Sh4 produced 1.69 mg/mL CLA with the 6.66% yeild rate. Furthermore both microorganisms only produced the isomers of cis-9,trans-11 and trans-9,trans-11 that the amount of trans-9,trans-11 isomer was higher than that cis-9,trans-11. In addition the amount of the CLA produced in the pelletes was much more than that in the supernatants. Considering all the results together it was decided to use L. plantarum A7 to produce CLA in the next step. The effect of lipase enzyme and Castor oil, both in five different concentrations on the amount of the CLA production were monitored during five different trials. Fanally, 30 mg of Castor oil along with 100 units of lipase enzyme were selected as the optimum quantities for producing of CLA in laboratory conditions. Conclusively it could be said that firstly:
