BATCH FERMENTATIONS WITH A MIXED CULTURE OF LACTIC-ACID BACTERIA IMMOBILIZED SEPARATELY IN KAPPA-CARRAGEENAN LOCUST BEAN GUM GEL BEADS

Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp. Bulgaricus were immobilized separately in κ-carrageenan-locust bean gum gel beads. The beads were prepared by a dispersion process in a two-phase system (water in oil) and two ranges of bead diameter selected by sieving (0.5-1.0 mm and 1.0-2.0 mm). Fermentations with the two strains were conducted in bench bioreactors in a supplemented whey permeate medium. Free and entrapped cells (two ranges of bead diameter and two levels of initial bead cell load) were grown in mixed culture, and carbohydrate utilization, acid production and cell growth or cell release rate measured. Fermentation rates were influenced by bead diameter and initial cell load of the beads. Beads with high initial cell density increased fermentation rates compared to low cell density beads or free cells. Smaller diameter beads (0.5-1.0 mm) showed a stable tendency (not statistically significant pa > 0.05) towards higher cell release rates, lactose utilization, galactose accumulation and lactic acid production than did larger diameter beads (1.0-2.0 mm). Immobilization of S. salivarius subsp. thermophilus and L. delbrueckii subsp. bulgaricus in separate beads did not seem to affect protocooperation during batch fermentation, and allowed for high cell release rates into the medium. © 1990 Springer-Verlag.