91C-31

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, during process scale up, the immobilization capacity of CPB was reduced, as indicated by cells suspending in the broth.  We hypothesize that, by introducing crosslinking agents such as polyethylenimine (PEI), the immobilization capacity of CPBR can be enhanced.

The objective was to evaluate the effects of PEI on the immobilization of Xanthomonas campestris during the scale up operation of CPBR.

A variety of supporting matrices, including cotton, silk, polyester, and viscose fibers, were treated with PEI (0-5%).  The optimal PEI concentration for immobilizing X. campestris was determined using the response surface methodology (RSM) with a quadratic model.  The ratio of immobilized-to-suspending cells (I/S) was determined by measuring the dry cell weight in both portions and confirmed by viewing the fibers in question under SEM.  The productivity of xanthan gum was also monitored.

Among all fibers investigated, cotton fiber adsorbed the most cells without PEI treatment.  However, cell retention was significantly higher on all fibers treated with up to 3% PEI than those untreated.  Viscose fiber treated with 1% PEI showed the highest adsorption of cells, whereas PEI > 4% diminished cell growth.  The I/S ratio was enhanced by at least 50% by using viscose fibers treated with 1% PEI without noticeable reduction in xanthan gum productivity.  The operation parameters of CPBR can then be better optimized accordingly.

Successful immobilization of X. campestris without sacrificing product yield and productivity is vital for the development of integral strategies that can lead to industrial improvement of xanthan gum production.