Thesis (M.Sc.)--Chulalongkorn University, 2011

Probiotic is a dietary supplement that has been used in tilapia culture. In this study the microencapsulation technique was applied to improve the viability of probiotic during storage and unflavored condition. The probiotic, Saccharomyces cerevisiae were mixed with Peptone dilution saline (group A) or 10% skim milk (group B), encapsulated with alginate via extrusion method and freeze-dried. The viability of group B after being freeze-dried was significantly higher than group A. At 7 and 14 days after being kept in room temperature, the viability of group B was higher than group A. The morphologies of the two groups of microencapsules were round to oval in shape. Group A had rough with concave polygonal ridges surface while group B had rough surface. The survival percent of both groups were higher than the control group after being exposed to NSS pH 1.5 for 1, 2, 3, and 4 h and group B was higher than group A. The survival percent of group B after being exposed to 10% tilapia bile salts was significantly higher than the control group and group A in 1, 2 and 3h. The survival percent of group A was lower than group B, but higher than the control group in every hour of exposer to 10% tilapia bile salts. Free S. cerevisiae, group A and group B had similar antimicrobial activity to 17 from 25 strains of Streptococcus agalactiae. All the results have suggested that the encapsulation of S. cerevisiae with alginate can improve the viability during freeze-drying and storage. Moreover, it can also confer the effect of protection in acid and bile environment.