Studies Of Screening Of Propionibacterium Freucenreichii Starain Producing Conjugrated Linoleic Acid And Optimization Of The Fermentation Conditions

Linoleic acid(LA) is one of the three essential unsaturated fatty acids, the conjugated linoleic acid(CLA) which is the isomer of linoleic acid, has recently attracted much attention because of its important variety of physiological functions. Currently, the mainly method to producing CLA is by chemical approaches, and the biological transformation method to producing CLA is becoming a research hotspot.In this thesis, we screened Propionibacterium strains with high CLA producing capacity from food, then optimized the fermentation medium and fermentation conditions based on the fast determination method of CLA, the main contents and results of this paper are as follows:1. There are 13 strains which producing CLA were screened from cheese. Strain PF-3, has the relatively highest CLA producing ability, the CLA productivity is up to 38.41μg·mL-1. The fermentation products were detected by Gas Chromatography-Mass Spectrometry(GC-MS), and the strain PF-3 has the ability to produce CLA by futher confirmed. According to the analysis of the cell and colony morphology and physio-biochemical characteristics, the bacterium strain PF-3 was identified as Propionibacterium freudenreichii finally.2. The different fermentation mediums were optimized preliminary, and the MRS medium was defined as culture medium. Fermentation conditions to produce CLA of strain PF-3 were studied by using response surface analytic method and orthogonal experiment. The optimum medium consisted of peptone 2%, beef extract 1%, yeast extract 0.5%, glucose 2.5%, sodium acetate 0.5%, ammonium Citrate 0.3%, dipotassium hydrogen phosphate 0.2%, manganese sulfate 0.02%, magnesium sulfate 0.02%; The optimum fermentation conditions to produce CLA were:cell inoculum 10.2%, LA 0.075%, pH 6.75, temperature 31℃, and Tween-80 as emulsifier(LA/Tween-801:20), the best fermentation time was 36h under anaerobic shaking condition. In the optimized conditions, the CLA productivity of the strain PF-3 is up to 63.58μg·mL-1.