INHIBITORY EFFECT OF DIHYDROXYACETONE ON GLUCONOBACTER-OXYDANS - KINETIC ASPECTS AND EXPRESSION BY MATHEMATICAL EQUATIONS

Microbial conversion of glycerol into dihydroxyacetone (DHA) by Gluconobacter oxydans was subjected to inhibition by excess substrate. Comparison of cultures containing increasing initial DHA contents (0 to 100 g l-1) demonstrated that DHA also inhibited this fermentation process. The first effect was on bacterial growth (cellular development stopped when DHA concentration reached 67 g l-1), and then on oxidation of glycerol (DHA synthesis only occurred when the DHA concentration in the culture medium was lower than 85 g l-1). Productivity, specific rates and, to a lesser extent, conversion yields decreased as initial concentrations of DHA increased. The changes in the specific parameters according to increasing initial DHA contents were described by general equations. These formulae satisfactorily express the concave aspect of the curves and the reduction in biological activity when the cells were in contact with DHA concentrations of up to 96 g l-1.