| As a natural microflora from dairy products, lactic acid bacteria always encounters sever-al stressful conditions which will greatly affect its viability, productivity and flavor. In these cases, we have to improve the shelf life of the product, meanwhile guarantee a better general survive and propagate of lactic acid bacteria in adverse environment of human being. Howev-er, traditional research on starter and oral lactobacillus products limited to be used in produc-tion. In this study, we investigated the impacts of various protective agents on their physio-logical changes of Lactobacillus casei (L. casei) during freeze-drying. In additional, we found that GSH as a novel protective agents plays a significant role in the process of freeze-drying. In another hand, we investigated the microencapsulation containing L. casei by extru-sion and spray-congealing to enhance probiotic functions in the human body. These results indicated that the survival of L. casei can be increased significantly with optimum cryopro-tectants, especially with GSH as a novel ingredient and demonstrated the novel way that mi-croencapsulation by spray-congealing with protective agent such as resistant starch can sig-nificantly improve the survival of L.casei during extreme conditions such as the human ga-stro-intestinal tract, thus enlighten us to exploit its industrial application in the future. The main research results are as follows:1. We compared the survival rate of L. casei under varying cryoprotectant conditions. A 5.56-folds increase of survival was observed respectively when skimmed milk was added as a cryoprotective agent. In addition, the survival rates of L. casei increased 14%-27% by com-bining skimmed milk with other materials such as glucose, lactose and trehalose. Furthermore, the optimal compositions of cryoprotective agent were found with increased survival of 54.5% in L. casei, which exhibited a overall survive of 6.16×108cfu/mL.2. Further study revealed that L.casei Zhang with GSH exhibited higher U/S ratio and decreasing length of saturated fatty acids as well as increased content of cyclopropane fatty acid C19:0-cyc, which may benefit to increase the membrane fluidity during freeze-drying, thus maintained the intact cell wall and membrane tissue during freeze-drying process., which contributed to cell integrity.3. In microcapsulation, extrusion was used as a preliminary experiment, explore Lac-tobacillus optic embedding rate, gastrointestinal release etc. In different concentrations of so-dium alginate solution and CaCl2 solution as the material of wall, the study found that al-though the microcapsule showed a high encapsulation efficiencies of 97.32%, the particle size was too large to swallow. Therefore, we improved the character of microencapsulation by spray-congealing. The optimal concentrations of sodium alginate and CaCl2 obtained by comparing the encapsulation efficiencies and particle size distributions of microcapsule, were 2% and 3%, respectively. Meanwhile, the encapsulation efficiency reached up to 95.80%.In comparing encapsulation efficiencies and particle size distributions of microcapsule under different concentrations of sodium alginate solution and CaCl2 solution, we selected the con-centration of sodium alginate and CaCl2 of 2% and 3%, respectively, which means the encap- sulated rate up to 95.80%. Furthermore, the microcapsules with 109 cfu/mL were digested in simulated human gastric juice for 3 h, and only about 24.17% of cells escaped from micro-capsule, suggesting that the microencapsulation may protect the cells against low pH and pep-sin. Subsequently, microcapsules were transferred into the simulated human intestinal juice, and 84.22% of the cells in microcapsules released after treating for 60 min. These results in-dicated the advantages of spray-congealed microcapsules with proper releasing area and health-promoting effects. Resistant starch was then added as prebiotic based on this formula, and large amounts of viable cells were obtained after 60 min in simulated human intestinal juice in this case. |
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