Effects of aeration and pH gradient on nisin production.: A mathematical model

A study on the effects of aeration and pH on nisin production by Lactococcus lactis showed significant increases as either aeration or pH drop gradient were risen. Nisin production at the maximum biomass point quadrupled when the oxygen saturation percentage increased from 50 to 100%. This suggests the association of this bioproduction with an oxidative metabolic pathway. A procedure based on successive re-alkalizations of the culture with feeding with glucose at regular intervals was proposed. It was shown that pH drop gradient (VpH) enhances nisin production, which increased approximately four-fold, and increases the efficiency of nutrient consumption. By using conventional equations of microbial kinetics, with the only additional assumption that VpH has some effect on the growth rate of the microorganism, a model that describes the results successfully is proposed. This model enables nisin to be typified as a primary metabolite, which tends to acquire secondary nature when the productive period of the culture is prolonged by imposing a stepwise-pH profile. (C) 2001 Elsevier Science Inc. All rights reserved.