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 matrix, and an in situ spectrophotometric method for monitoring cell population in calcium alginate beads described. The intracapsular cell population can be estimated by measuring the optical density of beads containing cells, using cell-free beads as reference, or by measuring absorbance of a liquified bead suspension. Alginate beads, and beads coated 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 from10⁵ cfu ml^?1 to 10³ cfu ml^?1 after 6 h of fermentation. Reuse of chitosan I coated alginate beads also showed a reduction in cell release by a factor of 100. Cell loading and initial cell growth within the beads greatly affected cell release. Reducing the initial cell release would lower the overall levels of cell release throughout the fermentation. Compared to non-immobilized cultures, a 20–40% reduction in the lactic acid production rate was observed for alginate beads and chitosan I coated alginate beads, respectively. This reduction can be compensated for by increasing the intracapsular cell loading during immobilization, or before the onset of fermentation.