Xanthan is a natural polysaccharide. It is produced using bacteria of the genus Xanthomonas from sugar containing substrates and is being used as food additive (E415) for thickening and gelating. Xanthan is approved for Bio-Food. Xanthan gum should be produced with Xanthomonas campestris in batch-culture. Laboratory experiments have shown that for each gram of glucose utilised by the bacteria, 0.23 g oxygen and 0.01 g ammonia are consumed, while 0.75 g gum, 0.09 g cells, 0.27 g gaseous CO2 and 0.13 g H2O are formed. Other components of the system, such as phosphate, can be neglected. Medium containing glucose and ammonia dissolved in 20,000 l of water is pumped into a stirred fermenter and inoculated with X. campestris. Air is sparged into the fermenter; the total amount of off-gas recovered during the entire batch culture is 1250 kg. Because xanthan gum solutions have high viscosity and are difficult to handle, the final gum concentration should not be allowed to exceed 3.5 % (w/w).

How much glucose and ammonia are required?

What percentage excess air is provided?