Saccharomyces cerevisiae as a probiotic has been prescribed for prophylaxis and treatment of gut infected diseases. This study was designed to assess the effects of encapsulated S. cerevisiae on gastrointestinal tract properties in the animal model. In rats, after 8-week feeding by encapsulated and unencapsulated S. cerevisiae, the mount of the IgA protein was determined by ELISA. Rats were euthanized, and the liver, kidney, and intestinal tract were collected for histological analysis. The

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... umption of S. cerevisiae could increase IgA levels in comparison with the control group. This increase was significant in the lower parts of the small intestine (p<0.05). In histopathological evaluations; Liver microscopic examination showed fatty change and margination of Kupffer cells as well as their hyperplasia and hypertrophy, which is a mark for liver regeneration in both groups that received microencapsulated and free probiotic. In spleen structure, in both groups, mild inflammation of the spleen tissue in the form of accumulation of red pulp of erythrocytes, hypercellular of this tissue was observed due to hyperplasia of lymphoid follicles and hyperplasia and hepaticophyta of retinal cells and macrophages. The lymphatic structure of the spleen showed relatively intense hyperplasia. In the colon structure, in both groups, hyperplasia of goblet calls along with slight infiltration of inflammatory cells was noted. Calcium alginate encapsulation considerably improves the yeast viability in simulated gastric juice and simulated intestine juice situations. Also, S. cerevisiae has positive profits in suitable food absorption and then decreasing diarrhea and other similar gastrointestinal disorders.