Developing probiotic bread using Lactobacillus reuteri part 1: Evaluation of fluidized bed microencapsulation on viability of Lactobacillus reuteri in simulated gastrointestinal conditions

Intoduction: Probiotics are defined as essential live microorganisms that, when administered in adequate amounts, confer a health benefit on the host. The range of beneficial properties reaches from lowering cholesterol to preventing cancer. The most important probiotic microorganisms belong to the group of lactic acid bacteria. Lactobacillus reuteri which naturally occurs in the human intestine possess probiotic properties with good colonization potential. The development of probiotic foods presents many challenges, particularly with respect to the stability of the bioactive compounds during processing, storage and passage through acidic gastric environment. Therefore, it is a great challenge to bring the probiotics into a stable form, which guarantees, that the microorganisms reach their target location, the human intestine, in an adequate amount. Microencapsulation helps improve survival probiotic bacteria from environmental stresses. In most studies, probiotic bacteria are entrapped in a gel matrix of natural biological materials such as alginate, or gellan. The core and wall solutions are turned into drops of the desired size by employing an emulsion method. The main problem in the probiotic entrapment approach is that gel bead entrapment technologies generally stabilize the bacteria in liquid products and are difficult to scale up. In order to extend the shelf life of encapsulated probiotics, a glassy state form of the embedding matrix is required. This can be achieved by employing such as air-suspension fluidized-bed coating. In the present research, an air-suspension fluidized-bed technique for generation of core and shell microcapsules containing probiotic Lactobacillus reuteri cells and the efficacy of shellac and sodium alginate at different concentrations on viability of capsules in simulated gastrointestinal conditions was evaluated.
Pure freeze-dried Lactobacillus reuteri PT-1655 were obtained from Persian Type Culture Collection (Tehran, Iran) and were activated by inoculation in the MRS broth at 37°C for 36-48 h. The air-suspension process was performed in a Wurster coater system with a bottomspraying atomizer. The growth curve of lactobacillus reuteri were determined by measuring the optical density (turbidity) at 600 nm to estimate the time when the growth curve enters a stationary phase in which bacteria develop a general stress resistance and are thus more resistant to various types of stresses. In various pretests the fluidization pressure, the atomization pressure and the spraying rate of the microencapsulation process were varied to examine their influence on process conditions, especially on the particle development. Several different solutions of Lactobacillus reuteri were prepared and evaluated for percentage survival during the coating. The solution containing Lactobacillus reuteri (6–12 g/100 g solution), maltodextrin (4–7 g/100 g solution) and sorbitol (4–7 g/100 g solution) concentrations was spray-coated at three inlet temperatures: 37, 47 and 62°C onto and absorbed by the inert carrier microcrystalline cellulose to produce nonagglomerating dry coated. For the coating processes an aqueous shellac solution at 3 concentrations (16, 17 and 18% (w/v)), containing plasticizers in the ratios of 95 5 and an aqueous sodium alginate solution at 3 concentrations (0.5, 1 and 1.5% (w/v)), were used. Simulated gastric juice was prepared fresh daily containing 3.2 mg of pepsin, 1 ml of NaCl solution (0.5%) and acidified with HCl (1.2 M) to pH 1.5 ± 0.5. Tolerance to gastric juice was examined by placing freshly prepared cells in a tube containing sterile simulated gastric juice for 1 h and incubated at 37°C for 2 h. To characterize the morphology of the MCC particles coated with the different matrix formulations, SEM images were taken. Experimental data have been represented as the mean with standard deviation (SD) of different independent determinations. The significance of differences was evaluated by analysis of variance (ANOVA). Differences were considered statistically significant at p