CONTINUOUS MIXED STRAIN MESOPHILIC LACTIC STARTER PRODUCTION IN SUPPLEMENTED WHEY PERMEATE MEDIUM USING IMMOBILIZED CELL TECHNOLOGY

The aim of this work was to study a new process for the continuous pro duction of mixed-strain lactic acid bacteria starters using immobilize d cells. Three strains of Lactococcus (two Lactococcus lactis subsp. l actis: KB and KBP, and one Lactococcus lactis subsp, lactis biovar dia cetylactis: MD) were immobilized separately in kappa-carrageenan-locus t bean gum gel beads. Continuous fermentations were carried out in a 1 L pH-controlled stirred tank reactor with a 30% (v/v) bead inoculum ( strain ratio 1:1:1), continuously fed with a whey UF permeate medium, supplemented with 1.5% yeast extract and 0.1 M KCI. The effects of thr ee parameters-pH, temperature (T), dilution rate (D), and their intera ctions on the composition and activity of the culture in the effluent at pseudosteady state were studied according to a rotatable central co mposite design, during a 53-day fermentation. The process showed a hig h biological stability and no strain became dominant, or was eliminate d from the bioreactor. The statistical analysis showed that the three strains were differently affected by the studied parameters, and that a large range of effluent starter composition can be achieved by varyi ng D, pH, and T. However, the acidifying characteristics were not affe cted by the culture conditions. A cross-contamination from other strai ns of the mixed culture was observed in gel beads entrapping a pure cu lture at the fermentation onset, and led to a biomass redistribution w ithin the beads. However, the strain ratio (KB:KBP:MD) observed after the 53-day experiment (1:2:2) was close to the initial bead ratio (1:1 :1). The beads demonstrated a high mechanical stability throughout the 53-day continuous fermentation. (C) 1997 John Wiley & Sons, Inc.