| Lactobacillus plantarum LT2-6 was screened as a bacterium having high catalysis to isomerize Linoleic Acid (LA) into Conjugated Linoleic Acid (CLA). After cultivated in MRS medium for 24 h, LT2-6 was harvested by centrifugation, washed with 0.85% NaCl2 or the right buffer, centrifugated again, and then used as washed cells in the following reaction. The whole cells (or the washed cellls) of LT2-6 were selected as a potent CLA producer from LA in the reaction.In this paper, the catalysis ability of the cells and the conditions for CLA production from LA and soybean oil were investigated using washed cells of LT2-6, and fatty acid analysis of the final product was also carried out by gas chromatography.The study clarified that washed cells of LT2-6 showed effective bioconversion with the free acid form of LA under optimal reaction conditions (0.1M sodium phosphate buffer , pH7.0, 30℃, 120r/min), 4.628 mg/mL CLA was produced from 6 mg/mL LA in 48 h by the catalyst of 10% (w/v) washed cells with a 77.1% yield as to LA; 7.861 mg/mL CLA was produced from 15 mg/mL LA in 64 h by the catalyst of 20% (w/v) cells with a 52.4% yield as to LA; the majority of resultants were cis-,trans-9,ll-CLA. Then the research of cooperation effect of porcine pancreatic lipase and washed cells on CLA production from soybean oil was carried out. The result showed that with the aid of porcine pancreatic lipase, under the optimal conditions (0.1M sodium citrate buffer, pH6.0, 30℃, 120r/min), with 15 mg/mL soybean oil as the substrate and 15% (wet cell, w/v) washed cells as the catalyst, the production of CLA reached a maximum (4.39 mg/mL) at 72 h with a 54% yield as to linoleic acid contained in the soybean oil.Research of different cell immobilizing technologies and bioconversion activities of the immobilized cells was measured in this paper. The experiment results showed that the immobilized cells entrapped by embedding medium of sodium alginate gel under the optimum embedding condition kept the satisfying catalysis and efficient bioconversion; the optimized conditions were 0.6g of cells/(g of carrier), 50 mM Tris-HCl buffer system (pH 8.0) and 37℃, respectively. Under the optimal conditions, the immobilized cells produced 0.271 mg/mL CLA from 1 mg/mL LA in 24 h with a yield of 27.1%. The CLA-producing ability of reused cells was investigated over five reused reactions and was maximal at pH 7.5 and 25℃. The pilot study of CLA production in organic media showed that the biocatalysis of washed cell was related to the water content in this special system. |
