Study On High-density Cultivation And Concentrated Ctarters Of Lactic Acid Bacteria

Lactic acid bacteria are one kind of Gram-positive bacteria being able to metabolize carbohydrates into lactic acid, and used generally in food process and functional food products. Their starter is being researched and developed in the world, which has many advantages including of convenience in using and transporting, high viability and safety, low in volume, and so on. In this paper the lactobacillus sp. was used to culture in high cell density and to develop the starter for pickling vegetables. The conditions were optimum in medium composition and environment factors, and continues fermentation bioreactor was designed based on the half-continues culture experiments. The results were showed as following: The optimum medium for seed culture was got with the composition of glucose 2%, peptone 1%, beef extract 0.5%, yeast extract 0.5%, tomato juice 10%, pH 6.5.The optimum environment conditions were obtained as culture temperature 37℃, original pH 6.5 of medium for 18-21 hours in stillness style using common incubators. And the optimum medium for high cell density culture was obtained as glucose:lactose (1:1) 2%, beef extract 1.0%, sodium citrate 0.5%, toween 80 0.05%, NaCl 0.25%, MgSO4 0.1%, tomato juice 10%, pH 6. The amount of lactobacillus sp. was up to 1.05×1011cfu/ml based on the above conditions.Then half-continues culture style was experimented by replacing fresh medium after centrifugating the culture by three times. The result showed the highest cell density was 9.3×1012cfu/ml after three times culture. Moreover, the culture-separation bioreactor were designed and its parameters calculated to realize high cell density culture with high productivity for large-scale product based on the half-continues results.On the other hand, the starter was prepared by the lyophilization. The different protector for lactobacillus sp. was selected including of L-cystein, milk without fat, sodium glutamine and chitin. Using RSA experiment, the combined protector was optimum as L-cystein 0.03M, milk without fat 9.7%, sodium glutamine 3.2%. The survival rate of lactobacillus sp was kept to 89.5% using this combined protector. Experiment results showed that the media for rehydrating the starter were not notablely different for viability rate of lactobacillus sp.. And the survival rate of the starter was up to 66.4% stored at 4℃ for five months.