Bioconversion Of Linoleic Acid Into Conjugated Linoleic Acid And Analysis Of CLA Isomers

Conjugated linoleic acid (CLA) is a collective term for geometric and positional isomers of linoleic acid (c,c-9,12-octadecadienoic acid) with conjugated double bonds. CLA occurs naturally in fat of milk and meat from ruminants, approximately 2.5-17.7 mg total CLA per gram fat. c9,tll-CLA is the main isomer in nature, which has the anticarcinogenic activity in vivo and in vitro. CLA can be produced by chemosynthesis or bioconversion in large scale. The CLA produced by chemosynthesis method consist of many kinds of isomers. However, the products from bioconversion contain relative simple isomer, mainly are c9,tll-CLAor t10,c12-CLA.High purity of LA was prepared by urea adduction. A c9,t11-CLA producer related to lactic acid bacteria (LAB) was screened by UV scan and HPLC. A new method with CD-MEKC was established for analyzing CLA isomers. CLA products from bioconversion were confirmed by FTIR, GC-MS and NMR. Conditions of bioconversion were optimized and scale up in 5 L fermentor. The linoleate isomerase was also studied preliminarily. The main results are described as follow.1. Ratio of FA, Urea, and EtOH was the main factor affecting LA production by urea adduction. When ratio of FA, Urea, and EtOH was 1:3:6 (w./w./v.), circumfluence for 15 min and adduction for 2 h, the purity of LA was increased from 44.48% to 95.68% by the urea adduction only once at room temperature, and the yield of LA was 72.41%.2. A rapid and accurate method for screening CLA-producing LAB was developed by UV scan and HPLC. Four CLA producers, L. acidophilus (CGMCC 1.1854), L. casei subsp. casei (CGMCC 1.574), L. plantarum L1 and L. helveticus L7, were screened from 33 strains of LAB. The CLA produced by the 4 bacteria consisted of c9,t11-CLA and t9,t11-CLA. Culture medium affected yield of CLA. The highest yield of c9,t11-CLA was found in MRS medium by L. helveticus L7.3. A CD-MEKC method was established for analysis of CLA isomers. The optimized analysis conditions were 4% (w./v.) β-CD, 54 mM SDS, 80 mM borate (pH...