| Lactobacillus kefiranofaciens, which was isolated from kefir grains, produces an exopolysaccharides called Kefiran. Not only can Kefiran be used as thickener, stabilizer, emulsifier or gelling agent, but it also has an antitumor activity. Because of this, the procedure for the mass production of Kefiran from this bacterium is currently being extensively studied.In this paper, Lactobacillus kefiranofaciens JCM6985T, a strain could accumulate high concentration of exopolysaccharide(Kefiran) was selected for Kefiran production. Optimize the L. kefiranofaciens cultivation processes to achieve high product concentration, high yield and high productivity of Kefiran. Main results of this dissertation include following aspects:(1)The required carbon and nitrogen sources for Kefiran production by L. kefiranofaciens in shaking flasks were investigated. The optimal concentrations of the carbon and nitrogen sources were gained as following: sucrose 100 g/L, yeast extract 100 g/L.(2)The mode of pH control is an important factor for batch Kefiran fermentation. It was shown that pH 5.0 was the optimum condition to improve the Kefiran production by comparing the parameters of five batch processes controlled at the pH ranging from 4.0 to 5.5 and without pH control.(3)The effect of temperature, varied from 25oC to 33oC, on the batch fermentation of Kefiran was investigated. Owing to the difference occurred in the optimal temperature for cell growth and Kefiran production by thoroughly analyzing the kinetics of batch Kefiran production under different temperatures, a two-stage temperature control strategy, in which the temperature was kept at 33oC during the first 10 hours of cultivation, followed by a shift from 33oC to 28oC, then maintained at 28oC until the end of the cultivation, was developed in order to enhance the production of Kefiran. The result indicated that, the Kefiran production was 4.65 g/L,which was respectively increased by 12% and 46% compared with that at 28oC and 33oC, and Kefiran productivity was increased by 36% and 33% compared with that at above two temperature respectively.(4)Five initial sucrose concentrations were studied to determine their effects on microbial growth and substrate consumption. It was concluded that high concentration, high yield and high productivity of both cell and Kefiran could not be consolidated in a batch process. The effects of different cultivation modes such as batch feeding, constant-rate feeding, exponential rate feeding on Kefiran production were also studied. High production of cell and Kefiran were all realized in these cultivation modes of sucrose feeding. As a whole, fed-batch culture with constant feeding rate at 4 g/(L·h) was the most suitable approach to attain not only high concentrations but also high yields and high productivities of cell and Kefiran in the cultivation of L. kefiranofaciens under which the maximum dry cell weight and Kefiran reached 63.6 g/L and 4.95 g/L respectively.(5)The high concentration of lactic acid produced during the course of L. kefiranofaciens fermentation inhibits kefiran production. Yeast was cocultured with L. kefiranofaciens to improve kefiran production by consuming lactic acid to decrease the inhibition effect.The productivity of the coculture of L. kefiranofaciens and S. cerevisiae under aerobic condition reached 94.19 mg/(L·h), 53.7% higher than which of the pure culture. And the productivity of the coculture of L. kefiranofaciens and C. utilis under aerobic condition reached 86.44 mg/(L·h), 41.1% higher than which of the pure culture, another product of glutathione also reached 250 mg/L.
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