SPECTROPHOTOMETRIC QUANTIFICATION OF LACTIC BACTERIA IN ALGINATE AND CONTROL OF CELL RELEASE WITH CHITOSAN COATING

Lactococcus lactis ssp. cremoris was entrapped within a Ca-alginate ma trix, and an in situ spectrophotometric method for monitoring cell pop ulation in calcium alginate beads described, The intracapsular cell po pulation can be estimated by measuring the optical density of beads co ntaining cells, using cell-free beads as reference, or by measuring ab sorbance of a liquified bead suspension, Alginate beads, and beads coa ted with chitosan type I, II, and I and II mixtures, were examined for cell release, Lower viscosity chitosan (type I) coatings reduced cell release by a factor of 100 from 10(5) cfu ml(-1) to 10(3) cfu ml(-1) after 6 h of fermentation, Reuse of chitosan I coated alginate beads a lso showed a reduction in cell release by a factor of 100. Cell loadin g and initial cell growth within the beads greatly affected cell relea se, Reducing the initial cell release would lower the overall levels o f cell release throughout the fermentation. Compared to non-immobilize d cultures, a 20-40% reduction in the lactic acid production rate was observed for alginate beads and chitosan I coated alginate beads, resp ectively. This reduction can be compensated for by increasing the intr acapsular cell loading during immobilization, or before the onset of f ermentation.