Effect of pH on the morphology OFLactobacillus helveticusin free‐cell batch and immobilized‐cell continuous fermentation

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Abstract
The effect of pH control set point in the 4.3–6.3 range on the morphology of Lactobacillus helveticus was studied in free‐cell batch and immobilized‐cell continuous fermentations using a supplemented whey permeate medium. The mean chain length of L. helveticus was measured by microscopic observation in both free and entrapped phase. In free‐cell batch fermentation, chain elongation of L. helveticus occurred progressively when pH set point was in the 5.1–6.3 range. During immobilized‐cell continuous fermentations, morphology was much less pH‐dependent. This phenomenon could be due to the long response time of entrapped cells to daily random changes in pH set point. Bacterial counts, dry weight and optical density measurements were compared in order to develop a methodology to ensure accurate biomass measurement in the different phases of the immobilized‐cell bioreactor.