Growth performances ofLactobacillus hilgardii immobilized in dextran gel and in continuous fermentation

A variant ofLactobacillus hilgardii was immobilized by its own production of dextran gel, forming grains. The best rate of weight increase of the gel in continuous fermentation was 16.3±3.3%/h, at pH 4.8±0.1 and with a dilution rate of 0.22 to 0.26/h. Observation by scanning electron microscopy located most of the bacteria as microcolonies on the surface. A similar arrangement appeared in calcium alginate beads. The best population density (10¹⁰ cells/g) was obtained in grains at pH 5.8, after 30h. At a similar pH value, 4.8, the growth rate was higher in alginate beads than in dextran gel but the final population density was approximately the same. Acidification rate increased faster with mixed gel at pH 5.2 than with dextran at pH 5.8.