Effect of aeration and dilution rate on nisin Z production during continuous fermentation with free and immobilized Lactococcus lactis UL719 in supplemented whey permeate

The influence of dilution rate (D) and aeration on soluble and cell-bound nisin Z production was investigated during continuous free (FC) and immobilized cell (IC) cultures with Lactococcus lactis subsp. lactis biovar diacetylactis UL719 in supplemented whey permeate. Maximum total bacteriocin titres during non-aerated continuous FC and IC cultures were obtained for low D, with 1490 and 1090IU mL(-1) for 0.15h(-1) or 0.25 and 0.5h(-1), respectively. For both systems, aeration increased nisin total production with maximum titres of 2560 and 2430IU mL(-1) for low D, respectively, as well as specific production. Volumetric productivity was the highest for an intermediate D of 0.4 h(-1) during FC cultures (460IU mL(-1) h(-1) for both aerated and non-aerated cultures), while it increased continuously with D during IC cultures, reaching high values of 1090 and 1760IU ml(-1) h(-1) at 2.0 h(-1) without and with aeration, respectively. In comparison with previous data for FC batch cultures, data from this study may indicate that during continuous fermentations at steady state, some steps in nisin biosynthesis are limiting. In these conditions, nisin production by immobilized cells is reduced. (C) 2002 Elsevier Science Ltd. All rights reserved.