| As a kind of novel functional fatty acids, conjugated linoleic acid (CLA) has attracted much attention. CLA is widely used in medicine, food additives and health products industry because of its anticarcinogenic activity,antiatherosclerosis activity, and the role of body fat regulation, treatment of obesity, immune regulation and antioxidant.At present, chemical synthesis is the major way of preparing CLA during the process of industrial production.CLA produced by this way is difficult to meet the demand on standard that high purity without harmful components which is required by medicine industry, food industry and other areas. Many microbes are able to use their enzymes to transform LA into CLA. Compared with chemical synthesis, the advantages of microbial synthesis are high specificity and mild conditions. CLA synthesised by mircrobes has high content of active CLA isomers which is similar to natural CLA and hasn't toxicity. CLA production prepared by microbes is conducive to the development and application of products.This thesis includes the results of a series of studies on producing CLA by lactic acid bacteria. First of all, the lactic acid bacteria which has the highest CLA-producing ability was screened from homemade pickle juice and was identified after being screended; Secondly, the composition of fermentation medium of the screened strain, fermentation conditions and the amount of substrate added were optimized; Finally, the screened strain was irradiated with UV and a mutant strain which has high CLA-producing ability was bred by UV mutagenesis for three times. The results are as follows:(1) A strain named QL2 which has the highest CLA-producing ability was screened from homemade pickle juice.3.88%of linoleic acid was conversed to conjugated linoleic acid by the strain and the amount of conjugated linoleic acid reached 23.263μg/mL. The strain was identified as Leuconostoc based on its morphological, physiological and biochemical character.(2) The medium components of Leuconostoc sp QL2 was optimized such as carbon source, nitrosource, inorganic salt. Finally, the optimum medium was obtained, which has the formulation of:lactose 2%, yeast extract 3%, sodium acetate anhydrous 0.2%, MgSO4-7H2O 0.08%, K2HPO4·3H2O 0.3%, MnSO4-H2O 0.015%. The amount of conjugated linoleic acid rised from 23.263μg/mL to 37.831μg/mL and percent conversion of linoleic acid rised from 3.88%to 6.31%.These were found to be 1.63 times than those values without optimization.(3) The fermentation condition of Leuconostoc sp QL2 was optimized. Finally, the optimum fermentation condition was obtained.The amount of conjugated linoleic acid rised from 37.831μg/mL to 40.953μg/ml and percent conversion of linoleic acid rised from 6.31%to 6.83%under the conditions of initial pH6.5, incubation temperature 37℃, incubation time 28h. The amount of conjugated linoleic acid and percent conversion of linoleic acid were found to be 1.08 times than those values without optimization.The addition of substrate LA of Leuconostoc sp QL2 was optimized.The suitable addition of substrate LA was 0.4%(v/v). The yield of CLA was up to 288.74μg/ml and percent conversion of linoleic acid was up to 7.21%.The percent conversion of linoleic acid was found to be 1.06 times than the value without optimization.(4) Leuconostoc sp QL2 was irradiated with UV as initial strain and a mutant strain named as UV39 which has high CLA-producing ability was bred by UV mutagenesis for three times. The yield of CLA produced by UV39 was up to 28.478μg/mL. Compared to the amount of CLA produced by Leuconostoc sp QL2, the yield of CLA produced by UV39 increased 22.4%and percent conversion of linoleic acid increased 0.87%. The tolerance on concentration of substrate LA was tested. The suitable addition of substrate LA of UV39 was 0.4%(v/v) the same as the suitable addition of substrate LA of Leuconostoc sp QL2·... |
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