A kinetic model of the production of bacteriocins on MRS medium by Lactococcus lactis subsp. lactis CECT 539 and Pediococcus acidilactici NRRL B-5627 has been developed. The model is a modification of the Luedeking and Piret expression, including a term for the influence of pH on both nisin and pediocin production. With this model it was demonstrated that these bacteriocins are produced as primary metabolites depending on the pH. By modeling the effects of temperature and pH on their activities. the high heat stability of both bacteriocins was demonstrated, with optimum values at acidic pH and short incubation times. The initial activity of both nisin and nisaplin was drastically reduced by treatment with trypsin, subtilisin and pepsin, but 50% activity was retained when both antibacterial substances were treated with papain. The inhibitory activity of pediocin almost totally disappeared after 15 min of treatment with these four proteases. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.