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

Hybrid coating of alginate microbeads based on protein-biopolymer multilayers for encapsulation of probiotics

A hybrid coating based on multilayers of proteins and biopolymers was developed to enhance the protection performance of alginate microbeads against acidic conditions for delivery of probiotics (Lactobacillus rhamnosus GG). Zeta potential measurements and quartz crystal microbalance with dissipation confirmed layer-by-layer deposition of protein-polymer layers. The stability of protein-based coatings during simulated gastric fluid (SGF) treatment was monitored by microscopy. Protein-coated microbeads were partially dismantled, whereas polymer-coated microbeads were intact after a sequential treatment in simulated gastric and intestinal fluids. This suggests that hybrid formulation offers an advantage over the coatings based on biopolymer multilayers in terms of better release of bacteria. Uncoated alginate microbeads completely dissolved and could not protect bacteria after SGF treatment whereas microbeads with hybrid coating showed increased physical stability and a modest decrease of culturability of 3.8 log units. Therefore, this work provides a concept for future protein-based hybrid coatings for bacterial delivery systems