pH-controlled cell release and biomass distribution of alginate-immobilized Lactococcus lactis subsp lactis

Aims: To investigate the growth and release of Lactococcus lactis subsp. la ctis in gel beads and to affect rates of cell release by changing the growt h conditions. Methods and Results: The rate of release and the distribution of immobilize d L. lactis subsp. lactis in alginate beads were studied in continuous ferm entations for 48 h. A change in operating pH from 6.5 to 9.25 initially red uced the ratio of the rates of cell release to lactate production by almost a factor of 10(5). Compared with fermentations at pH 6.5, growth at pH 9.2 5 also increased the final internal bead biomass concentration by a factor of 5 and increased the final rate of lactate production by 25%. After 48 h, the ratio of the rates of cell release to lactate production was still 10 times lower than in fermentations at pH 6.5. Conclusions: A change in the operating pH from 6.5 to 9.25 reduced rates of cell release throughout 48 h of fermentation and increased the final rates of lactate production and internal bead biomass concentration. Significance and Impact of the Study: These data illustrate that diffusiona l limitations and corresponding pH gradients can be exploited in affecting the distribution of immobilized growing cells and their concomitant release .