58-10 Characterization and scale-up considerations of a centrifugal, packed-bed bioreactor for xanthan gum production

Y. M. Lo and C. H. HSU. Dept. of Nutrition & Food Science, Univ. of Maryland, Food Bioprocess Engineering Lab., 3102 Marie Mount Hall, College Park, MD 20742

Xanthan gum is widely used as a suspending/thickening agent in the food, chemical, and pharmaceutical industries. To improve the energy-intensive, low-yield fermentation process caused by limited aeration, our research group has developed a novel, centrifugal, packed-bed reactor (CPBR) that produces cell-free broth with elevated productivity at the laboratory scale. However, process scale-up remains challenging due in part to the unique design of the packed bed (PB) as well as the recirculation loop (RL). Therefore, it is critical that, to identify optimal strategies for process scale-up, respective contributions of PB and RL in the performance of CPBR need to be characterized.

The objective was to characterize the roles of PB and RL in xanthan fermentation in order to strategize scale-up considerations of CPBR.

Xanthan biosynthesis by Xanthomonas campestris immobilized in PB was characterized using metabolic flux analysis (MFA). The metabolic fluxes through the carbon pathways for xanthan gum production were calculated using a flux-based stoichiometric model. The role of RL in broth aeration was characterized by comparing its effects on the maximum volumetric transfer coefficient (k_La) in xanthan broth.

Results from MFA indicate that use of 5.0% instead of 2.5% glucose enhanced glucose uptake rates (n_s) in PB. Both n_s and the assembling rate (n₁)of sugar nucleotides transformed from Glc-6-P were significantly higher than those in suspending cultures, indicating that most glucose was utilized for xanthan synthesis with the minimum maintenance requirements in CPBR. Furthermore, the aeration efficiency (k_La) of CPBR was significantly increased by the installation of RL. A scale-up model integrating parameters associated with PB and RL in addition to those governing the geometric aspects was developed accordingly.

Characterization of X. campestris metabolism and understanding of CPBR aeration capacity is vital for the development of scale-up strategies that can lead to industrial improvement of xanthan gum production.