The effect of the immobilisation of Lactobacillus acidophilus and Bifidobacterium lactis in alginate on their tolerance to gastrointestinal secretions

This research aimed at evaluating the "in vitro" tolerance of Bifidobacterium lactis and Lactobacillus acidophilus, both free and immobilised in calcium alginate, to pH and bile levels similar to those encountered in the human stomach and intestine, respectively. Free and immobilised cultures were inoculated, at the level of 10%, into HCl solutions with pH values of 1 and 2, and then incubated anaerobically at 37 degrees C, being subsequently plated out at intervals of 0, 1 and 2 h after incubation. The bile concentrations tested were 0, 2 and 4%. Counts were made by the pour plate method using MRS broth after 0 and 12h of anaerobic incubation. Morphological observations of the cells immobilised in alginate gel were made using a scanning electron microscope. The cell counts of samples containing alginate drops were effected after solubilisation in 2% sodium citrate using a Stomacher homogeniser. A pH value of 2 promoted a slight decline in the number of viable microorganisms and pH 1 was extremely deleterious for both B. lactis and L. acidophilus, the same effect being shown for the cells immobilised in alginate. inoculation into bile did not affect the stability of B, lactis and L. acidophilus. Thus B. lactis and L. acidophilus showed intolerance to pH 1 and immobilisation in alginate was not effective in protecting their cells.55949649