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

To investigate the growth and release of Lactococcus lactis subsp. lactis in gel beads and to affect rates of cell release by changing the growth conditions.

The rate of release and the distribution of immobilized L. lactis subsp. lactis in alginate beads were studied in continuous fermentations for 48 h. A change in operating pH from 6.5 to 9.25 initially reduced the ratio of the rates of cell release to lactate production by almost a factor of 105. Compared with fermentations at pH 6.5, growth at pH 9.25 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.

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.

These data illustrate that diffusional limitations and corresponding pH gradients can be exploited in affecting the distribution of immobilized growing cells and their concomitant release.