Produce xanthan gum from glucose in cell-free xanthan broth.

The current commercial production of xanthan gum, which involves the use of conventional fermentation processes, suffers from several limitations, including energy-intensive and costly production, low product concentration and poor reactor productivity. These issues are often caused by the high viscosity of the broth, and poor filterability caused by the cells in the broth.

To overcome these limitations, researchers at The Ohio State University have developed a cell immobilization technique in a novel, centrifugal, packed-bed reactor (CPBR). The approach is able to produce a cell-free xanthan broth. The CPBR, combined with ultrafiltration, can be used in the large-scale production of high-quality, low-cost xanthan gum, broadening its applications in the food, pharmaceutical and oil recovery industries.

By using the CPBR, the researchers estimate cost savings at more than 50%, as the reactor productivity is doubled and xanthan gum can be produced at two to three times concentration. This can reduce the recovery cost by 50% to 67%. The scientists have two U.S. patents on this technology, which is available for licensing.

In the CPBR, cells of Xanthomonas campestris are immobilized in a rotating fibrous matrix. The medium broth is continuously circulated through the fibrous matrix, enabling gas and liquid to closely contact the immobilized cells. This approach avoids the mixing and aeration problems that are caused by viscous xanthan fermentation.

Conventional free-cell batch fermentation in a stirred-tank reactor usually has a low cell density of less than 2 g per L, low xanthan productivity and a low final xanthan concentration of about 25 g per L. To study the feasibility and performance of long-term xanthan production in the CPBR, the scientists operated the fermentation in a repeated-batch mode. The reactor achieved high cell density (about 7 g per L), high xanthan productivity and a high final xanthan concentration of up to 75 g per L.

The fermentation process was stable enough to be continuously operated 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 about 150 g per L before the broth was purified 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.

Patents. 6033896--S.T. Yang, Process of Separation of Cells from Liquid by Adsorption onto Fiber, Issued March 7, 2000. 6787340--S.T. Yang, Apparatus for Separating Cells and Producing Microbial Polysaccharides, issued Sept. 7, 2004.

Further information. S. T. Yang, Department of Chemical and Biomolecular Engineering, The Ohio State University, 140 West 19th Ave., Columbus, OH 43210; phone: [phone]; fax: [phone]; email: [e-mail].