BACKGROUND: Lactobacillus reuteri is unable to grow on glycerol as sole carbon and energy source hence, glycerol is used as an alternative hydrogen acceptor during growth on available carbohydrates. Thus, glycerol is converted to reuterin and 1,3-propanediol (1,3-PDL), both products with interesting industrial applications. These compounds are commonly produced by using resting cells in two-step fermentation processes. RESULTS: The glycerol/glucose cofermentation by L. reuteri yields reuterin and 1,3-PDL at a glycerol concentration higher than 100 mmol L-1. An increase of glycerol concentration from 200 to 400 mmol L-1 showed no additional stimulatory effect on ethanol and acetate production but consistently reduced the lactate concentration. It was also found that reuterin concentration reached a maximum value and subsequently decreased due to its conversion to 1,3-PDL. An unstructured kinetic model was proposed to describe simultaneously microbial growth, substrates consumption and products formation. A multi-response nonlinear regression analysis based on Marquardt algorithm combined with a Runge-Kutta integration method was used to obtain the values of the fitting parameters. CONCLUSIONS: The optimum concentration of glycerol for maximum reuterin and 1,3-PDL production was 200 mmol L-1. The complete process was satisfactorily described by the kinetic model proposed. (C) 2008 Society of Chemical Industry