Adaptive control of a G. xylinus fed-batch fermentation using in situ mid-IR spectroscopy

Bacterial exopolysaccharides (EPS) have unique rheol. properties due to their high purity and regular structure. Thus, the food industry frequently uses EPS as thickening, gelling or stabilizing agents. The strain Gluconacetobacter xylinus I 2281 is capable of producing with a very high yield a new sol. EPS named gluconacetan, which is composed of rhamnose, glucose, mannose and glucuronic acid. Growth of these bacteria presents many features that represent a real challenge for both monitoring and control. High EPS concns. in the culture broth cannot be filtered and thus, classical online monitoring tools, such as "Flow Injection Anal." or chromatog. methods, are no longer suitable to follow the fermn. Another problem is related to the ethanol concn. in the reactor. This compd. is the main substrate for biomass prodn. Cells convert it to acetate and metabolize this last to form biomass. When ethanol concn. is above a certain threshold, the enzymic system that digests acetate is inhibited. As a result, biomass growth is stopped and acetate accumulates in the reactor. It is thus necessary to maintain the ethanol concn. in the reactor at a very low concn. In this work fed-batch fermn. of G. xylinus was performed. A concd. ethanol soln. was used as the feed soln. A very simple and novel adaptive control strategy was used to maintain the acetate concn. in the reactor const. Consequently ethanol concn. was forced to remain very low. In situ MIR spectroscopy, a non-invasive optical sensor system that is insensitive to the viscosity changes in the broth was used to monitor simultaneously ethanol, acetate, ammonium, phosphates and fructose concns. Both the control strategy and the exptl. results will be presented. [on SciFinder (R)]