High nisin-Z production during repeated-cycle batch cultures in supplemented whey permeate using immobilized Lactococcus lactis UL719

摘要

Nisin-Z production was studied during repeated-cycle pH-controlled batch (RCB) cultures using Lactococcus lactis subsp. lactic biovar. diacetylactis UL719 immobilized in kappa-carrageenan/locust bean gum gel beads in supplemented whey permeate. After an initial colonization of gel beads during the first two cycles, nisin-Z production in bulk medium and gel beads was very similar for 1-h and 2-h cycle RCB cultures. A very high nisin-Z production (8200IUmL(-1)) was measured in the broth after the 1-h cycles, with a corresponding volumetric productivity of 5730IUmL(-1) h(-1). This productivity is much higher than maximum nisin productivities reported in literature or maximum productivities obtained previously for free-cell batch cultures (850IUmL(-1)h(-1)), and free-cell (460IUmL(-1) h(-1)) or immobilized-cell (1760IU mL(-1) h(-1)) continuous cultures, using the same strain and fermentation conditions. The stability of RCB cultures was demonstrated for 24 and 36 1-h cycles carried out over 3 and 6-day periods, respectively. Changing environmental conditions during batch cultures resulted high nisin production.