Studies On Preparation And Properties Of Microencapsules Containing Streptoccus Thermophilus By Emulsification/Internal Gelation

The intestinal flora plays an important role in human health, the main function of which is to prevent colonization of potential pathogenic microorganisms, exert health benefits of inherent basic nutrition and improve intestinal microbial balance of the host. Microencapsulation can be used to detach probiotics from outside environment and prevent the damage, which will advantage the storage and conveyance. The damage of gastric acid can be avoided with the enteric dissolved materials so that a larger number of live cells can get to intestines and make a true function in health care.Using Streptoccus thermophilus as the mode bacteria, the paper studied the preparation of chitosan/alginate microcapsules by emulsification/internal gelation, and further investigated the release and survival properties of the bacteria in the gastrointestinal tract. Based on the experimental results, main conclusions can be drawn as follows:(1) The optimal conditions for the preparation of alginate microcapsules are: alginate concentration 1.5%(w/v), emulsifier Span80 concentration 0.7%(v/v), the ratio of water to oil 1:8 (v/v) and the ratio of CaCO3 to NaALG 1:5(w/w) , under the optimal conditions, the content of the microcapsules with the aimed diameter of 40～60μm is 80.2%. Microcapsules will improve their chemical and mechanical stability with a chitosan membrance by the encapsulation and releasing of casein, and the optimal conditions of the chitosan are observed when chitosan concentration is 4mg/ml, chitosan initial pH value is 6, and reacting time is 10min.(2)The enrichment culture formula of Streptoccus thermophilus is determined. Experiments shows that the best addition of carbon source is sucrose 0.56%, and the best addition of nitrogen source is soyer peptone 2.0%. The equal amount of yeast extract, Tween80, ammonium citrate sodium, sodium acetate and MgSO 4·7H2O can promote the growth of Streptoccus thermophilus, the best additions of which are 0.5%, 0.1%, 0.2%, 0.3%and 0.02% respectively, but excessive additions can restrain the growth.Further research is done by SAS software combined with the Plackett-Burman design and response surface analysis method, which provides the most prominent influential factors for the growth of thalli and the best additions with sucrose 0.56%, soyer peptone 2.12% and yeast extract 0.54%. Moreover, the OD value can reach up to 1.223.The optimal enrichment culture conditions of Streptoccus thermophilus can also obtained, namely, initial pH value at 7.7, suitable temperature 39℃, and inoculate amounts 5%. By adopting the optimal conditions, the arrearage phrase of Streptoccus thermophilus is shortened and OD value is enhanced to 1.412. Furthermore, Streptoccus thermophilus incubated in 5L fermentor is analyzed giving the best culture time of 6h. Results show that the density of the bacteria gets to the best at this time, and OD600 could reach up to 1.71.(3) The optimal conditions for the preparation of alginate microcapsules containing Streptoccus thermophilus are: the ratio of bacteria and alginate 1:1, Span80 concentration 0.7%, emulsification time 10min, and alginate concentration 1.5%. The trapping efficiency will reach up to 75.6%.The survival rate of Streptoccus thermophilus is advanced by 65.74% when the alginate microcapsules are coated with chitosan. The experiment shows that the release of chitosan/alginate microcapsule is slower than before in the artifical intestinal juice. In order to exert positive health effects, Streptoccus thermophilus should resistthe stressful conditions of stomach upper intestine that contain bile.The chitosan/alginate microcapsule has a high survival rate in the gastic juice and bile solution when it is in the gastric juice for about 2h and in the bile acid for 6h with its viability reaching up to 8.2×107cfu/mL and 1.99×109cfu/mL respectively.The chitosan/alginate microcapsule proves to have strong fermentation activity. Its survival rate still keeps in 94.8% when it has been storaged for 2 months under 4℃in the refrigeratory. And its storage period of validity is 94.54 days calculated according to the demand of our country for the health care production.In summary, the production of microcapsules containing Streptoccus thermophilus by emulsification/internal gelation is feasible, which can resist the bad circumstance and improve the survival rate in the low temperature and intestinal tract so that the probiotics can exert health benefits more effectively. Under the aimed diameter of 40～60μm, the microcapsule can be appended to drinks and foods, which will provide the foundation for further research and development of new-type microbioecologics.