Formulation and production of polymeric systems for the intestinal release of probiotics

The intestinal microbiota is composed by a large number of microorganisms that normally live in the human gastro-intestinal tract. Bacteria are the majority of these microorganisms and their total number in the gut is about 1014 cells. Most of these are located in the lower intestine (ascending colon) and play several health promoting activities, such as fermentation of undigested substrates, stimulation of the immune system, prevention of enteropathogen colonization, regulation of the development of enterocytes and intestinal mucosa, production of vitamins (K and B12) and hormones for the regulation of fat storage. Bacteria strains belonging to Bifidobacterium and Lactobacillus, dominant and subdominant groups of the intestinal microbiota, are the most widely used probiotic bacteria and are included in many functional foods and dietary supplements. Probiotics are live microorganisms which, when ingested in adequate amounts, confer a health benefit on the host by improving its intestinal balance [1]. To provide functional benefits, the minimum suggested therapeutic dose is 108- 109 viable cells per day/dose [2]. Probiotics exert their action after colonization and growth in the distal ileum and colon, which means they must survive passage through the esofagus and stomach. In recent years several microencapsulation methods and different polymers have been developed with the aim of increasing survival of different bacterial strains. However, few studies reported satisfactory results about the survival of cells after exposure to acids and during storage. The purpose of this study was to develop a new formulative and manufacturing approach to obtain microcapsules which would ensure the survival of two different bacterial strains, L. acidophilus and B. lactis after the technological processing, under simulated gastric fluid (SGF), in the gut medium (GM) containing bile salts and during storage. The microcapsules were obtained by interfacial ionic crosslinking with both the traditional extrusion method using a hypodermic syringe (Method 1) and by a technology that uses an innovative pneumatic spray nozzle for the atomization of the fluid (Method 2). In the first case relatively large (1-2 mm) microcapsules were obtained, while in the second method, the mean size was  100 m. Sodium alginate was used as main carrier, while xanthan gum (XG) was added as hydrophilic retardant polymer and cellulose acetate phthalate (CAP) was used as a gastro-resistant polymer. 9 different formulations were ontaned by means of Method 1 and only those that have reported encouraging vitality data have been then processed by Method 2. The spraying system has produced spherical and not aggregated microcapsules, despite the high viscosity of the biomass suspension. The results of viability tests showed that the microcapsules obtained by Method 2 with the incorporation of 0.5% w/v XG or 1% w/v CAP in 3% w/v sodium alginate solution has significantly increased the survival of probiotic bacteria after two hours of incubation in SGF (98%) compared with freeze-dried bacteria powder (63%) and calcium alginate microcapsules (69%). These results indicate that the microcapsules thus obtained were able to deliver probiotics to the site of action, protecting them from gastric juice bile salts. Furthermore, viability of probiotic bacteria was maintained (97%) after incubation in GM for 24 h. Finally, stability tests performed at 5 °C showed a viability of about 82% (108 CFU / g), the therapeutic dose, after 6 months.