Cell release from alginate immobilized Lactococcus lactis ssp lactis in chitosan and alginate coated beads

The effects of chitosan and alginate coatings of alginate beads with entrap ped Lactococcus lactis ssp. lactis were studied in batch and continuous fer mentations. Chitosan coating reduced the final concentrations of free cells , the initial release of free cells and the rate of lactate production in m ilk fermented batch-wise to a final pH of 4.7 in five consecutive batch fer mentations. An alternative experimental system based on continuous fermenta tion with controlled pH and a high dilution rate was developed to better st udy the phenomenon of cell release. To estimate the effects of different be ad coatings on cell release, alginate beads were coated with chitosan or al ginate, or sequentially with chitosan/alginate or chitosan/alginate/chitosa n. Chitosan coating alone seemed to reduce the rate of cell release only in the early stages of the fermentation, while sequential coatings with chito san and alginate showed significant reduction throughout the whole test per iod. To examine whether the observed effects of bead coating could be expla ined only by a decrease in cell activity, the ratios between the rate of ce ll release and the rate of lactate production were examined during the ferm entations for the different beads. This ratio showed qualitatively the same behavior as direct results of volumetric cell release.