| Summary: | 碩士 === 國立中興大學 === 食品暨應用生物科技學系所 === 105 === Lactic acid bacteria (LAB) are typical probiotics which provide a wide variety of health benefits. While the probiotic effect(s) of LAB can vary with different types, Lactobacillus johnsonii appears to be a type with high potential in expressing the characteristics of anti-Helicobacter pylori. Nonetheless, probiotics must survive in the extreme environment of the gastrointestinal tract if they are to reach the intestines so that their benefits can be imparted. To protect the bacteria strain, extrusion technique for microencapsulation of L. johnsonii was applied. To enhance the resistance of bacteria strains against adverse conditions, formulas of the culture media were adjusted by adding different concentrations of selected fatty acid, namely oleic acid, linoleic acid, and linolenic acid. Moreover, investigation of the optimum operating conditions based on maximum survival rate of L. johnsonii was carried out, and the assessment of health effects was also made. Results showed that L. johnsonii cultivated in the media containing 8 μg/ml unsaturated fatty acid appears to have high survival rate in the process of microencapsulation, while the microencapsulation rates were decreased with increasing addition concentrations. Since the process of extrusion did not cause serious damage of cells, this technique was applied in the subsequent validation tests. Results of the tests indicated that L. johnsonii incubated in the media added with oleic acid (namely the oleic acid group) could survive most after treatment with simulated digestive juice. In addition, the oleic acid group not only showed higher cell integrity in the determination of β-galactosidase activity, acidification power test, and protein analysis, but also had little cell deformation in the scanning electron microscopy (SEM). The linolenic acid group, on the contrary, appeared to be seriously deformed and had lower cell activity. In conclusion, L. johnsonii incubated in the modified medium with 8 μg/ml oleic acid had higher activity and survival rate in the simulated gastrointestinal tract, as well as higher bacteria resistance to adverse environmental conditions.
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