L-lactic Acid Bacteria Species Breeding And Suspended And Immobilized Acidogenic Optimization

Lactic acid is one of the three organic acids that has the biggest market and has been used in many fields. The molecular structure of laetic acid has asymmetry carbon atom, so it has three kinds of optical isomer: L-lactic acid, D-lactic acid and DL-lactic acid racemized. In the foodstuff and medicine industry D and DL-lactic acid should be replaced by L-lactic acid because the human body can only metabolize L-lactic acid. Moreover, the potential use of L-lactic acid to produce poly-lactic acid for synthesis of biodegradeing plastic, makes it to have even greater potential market. In this paper a strain of Lactobacillus rhamnosus that can produce L-lactic acid was studied, and fermentation process for production of L-lactic acid with high productivity and efficiency was optimized, and the fermentation dynamic was studied and simulated.UV was used to mutate the strain of Lactobacillus casei subsp. rhamnosus to improve the resistance to high glucose and L-lactic acid concentrations. After the mutation and a series of selections, a mutated strain was selected with higher glucose consumption and L-lactic acid production rates under high glucose and lactic acid concentrations, and L-lactic acid production was 16.8% higher than the control.Optimum seed culture medium and culture medium conditions have been confirmed by using orthogonal experiment design theory. The optimum seed culture medium of mutant 6# used contains: Glucose 15g,Peptone 10g,Beef extract 12g, Yeast extract powder 6g,Sodium acetate 5g,Ammonium citrate 2g,Magnesium sulfate 1g,Potassium phosphate monobasic 2g, Manganese sulfate 0.05g,Tween80 1ml,pH 6.5. The optimum culture medium conditions was proved that inocula were restingly cultivated for eight to ten hours at 42°C and 10.0g of Calcium carbonate was added to the medium in one time for regulating the value of pH.Optimum shake flask fermenting culture medium and culture conditions were determined.The optimum culture medium for fermentation consists of sweet potato saccharification liquid 150g,soybean meal 15g,Yeast extract powder 3g,Magnesium sulfate 2g,Potassium phosphate dibasic 0.3g,Manganese sulfate 0.03g,Ferrou sulfate 0.03g,pH 5.5-6.0, 70.0g of Calcium carbonate(added after fermentation for eight hours) was used to regulate the pH of the fermented liquid during process of fermentation.The optimum culture conditions was that mutants were cultivated in 500ml cotton-plugged Erlenmeyer flasks containing 150ml of the optimum culture media (120rpm).Under the optimum culture media and culture conditions,L-lactic acid accumulation content of the mutant 6# in shake flask can be up to 117.07g per liter.This research investigate effect of various conditions on production of lactic acid.The results show that 2% sodium alginate is the optimal consentration for immobilization,it can be stabilized for 150h while a high yield production can be attained.In fermental medium the optimal chemical composition is that yeast extract 3.0g/L; inoculation volume 15%;diameter of gel bead 2.5-3.5mm.The optimal temperature is 42°C.Overpass experiment of 4 batch repeated fementation,the fementational time is 48h the first batch and 36h the other 3 batches,respectively.Obviously the time of last three batches is decrease.Production of lactic acid is that 40.1g/L in first batch and 45g/L in last three batches.Cell percolation appears after 4 batches fementation.