Mutation Breeding Of L. Plantarum With High Yield Of Conjugated Linoleic Acid And Its Application In Yogurt

Conjugated linoleic acid (CLA) has proved to be a functional fatty acid which provided a series of physiological function such as anticancer, reducing body fat, improving body immunity and so on. CLA can be recognized as a conjugated formation of linoleic acid (LA), which is produced mainly through the chemical synthesis methods in the industry. High convert ratio is the positive characteristic of the chemical synthesis methods; however the product is impurity that limits the application of CLA in the food service industry. Besides, high temperature and high pressure operations are involved in the CLA processing cycle, which make high energy-consuming, serious pollution, more dangerous and high cost of investments. It has been discovered that CLA isomers are much simper, less pollution, no high temperature and high pressure and no strong acid and alkali by use of biology isomerization methods that has attracted much attention in the scientific community.The main research contents in the paper include four parts that are :improving the CLA producing ability by use of induced mutation, optimizing fermentation process,CLA conversion experiments under the supercritical CO2 conditions and improving the CLA contents in the yoghurts. The main results are as the follows:1. An original L. plantarum strain A6-1F was induced by N~+ implantation and NTG, then a mutation strain L. plantarum M-66 was screened out, by which the average CLA production could increase 47%,which reached to 197μg/mL.2. Based on the single-factor experiments, the fermentation process was optimized by use of response surface analysis methods (5 factors and 3 levels). The optimal fermentation conditions for CLA were: reaction time 30h, temperature 34℃, pH 7.0, inoculum concentration 3%, LA concentration 1.2mg/mL. CLA fermentation was carried out under this condition, and the average yield of CLA was 224.1μg/mL, and 18.68% CLA was converted from LA.3. L. plantarum M-66 cell was used as the catalyst to convert LA to CLA under Supercritical CO2 conditions in this part. The optimal conditions were: pH 7, temperature 37℃, LA concentration 1mg/mL, cell concentration 25%, and pressure 15MPa. The CLA yield was 600μg/mL and conversion ratio was 60% under the above conditions.4. Improving the content of CLA in the yoghurts was researched in this part. Two kinds of starter cultures (YO-MIX 495 and L. plantarum M-66) were employed, and we choose acidity, CLA and sensory evaluation as the evaluating indicator to identify the optimizing fermentation conditions that were: L. plantarum M-66: YO-MIX 495=1:3, temperature 42℃, and inoculum concentration 3%. The color of yoghurt was milkiness, good solidifiability, well-closed formation, and better flavor. CLA contents were 150.8μg/mL that accounts for 4.48% of the total fatty acid by use of GC analysis, and the proportion of c9, t11-CLA and t10, c12-CLA was 1.3:1.