EFFECTS OF GLYCEROL ON ALCOHOL FERMENTATION - INHIBITION-MECHANISM AND DIFFUSION LIMITATIONS

Batch alcohol fermentations have been carried out varying the starting level of glycerol in the broth and keeping constant all the other fer mentation parameters, in order to study the effect of the accumulation of this metabolite on the fermentation kinetics. A linear slow decrea se of the maximum specific ethanol productivity with increasing glycer ol level has been followed by a sharp fall of this parameter over a gl ycerol concentration threshold. A kinetic study through unstructured i ntegrated models demonstrates that, at low concentrations, glycerol be haves as a non competitive inhibitor of fermentation, while, over a co ncentration threshold (105 kg/m(3)), an additional effect takes place, likely ascribable to diffusion limitations provoked by excess viscosi ty of the broth.