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J. HALIM, Food Science and Technology, The Ohio State Univ., 140 West 19th Ave, Columbus, OH 43210 and S. T. Yang, Chemical and Biomolecular Engineering, The Ohio State Univ., 140 West 19th Ave, Columbus, OH 43210. Current commercial production of xanthan gum using conventional fermentation process suffers from several limitations, including energy-intensive and costly production, low product concentration and reactor productivity due to high broth viscosity, and low filterability due to cells in the broth. Cell immobilization in a novel, centrifugal, packed-bed reactor (CPBR) has been developed to overcome these limitations by producing cell-free xanthan broth. In the CPBR, Xanthomonas campestris cells are immobilized in a rotating fibrous matrix and the medium broth is continuously circulated through the fibrous matrix, providing intimate contact of gas and liquid with the immobilized cells and thus circumventing mixing and aeration problems occurring to viscous xanthan fermentation. Conventional free-cell batch fermentation in a stirred-tank reactor usually has a low cell density of less than 2 g/L, low xanthan productivity of ~0.5 g/L∙h, and low final xanthan concentration of ~25 g/L. To study the feasibility and performance of long-term xanthan production in the CPBR, the fermentation was operated in a repeated-batch mode. High cell density (~7 g/L), high xanthan productivity (3 g/L∙h based on fibrous bed volume and 1 g/L∙h based on total liquid volume), and high final xanthan concentration (up to 75 g/L) were achieved in the CPBR. The fermentation process was stable for continuous operation for one month, with an average ~85% xanthan yield from glucose. Ultrafiltration was used as an energy-efficient method to concentrate the cell-free xanthan broth to ~150 g/L before further purification with alcohol precipitation. The permeate or filtrate can be recycled and reused in the fermentation, saving the raw material costs and reducing the amount of spent medium. The CPBR and ultrafiltration process can be used in large scale production of high quality, low cost xanthan gum, broadening it's already multitude applications in food, pharmaceutical and oil recovery industries.
Session 17, Biotechnology: General
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |