A Study On Microencapsulation And Freeze-drying Preservation Characteristics Of Streptococcus Pentose 10a1 Adsorbed With Heavy Metal Lead

The treatment of heavy metal pollution is imminent.Lactic acid bacteria(LAB)has become a new method for adsorption of heavy metals due to its safety and efficiency.However,LAB is susceptible to adverse environment,which reduces its probiotic effects.In this study,in order to improve the freeze-dried survival rate of the strain,the culture conditions of P.pentosaceus 10a1,the cell protection agent in the endogenous emulsification method and the preparation process of double-layer microcapsules were optimized.The embedding rate,freeze-drying survival rate,morphological observation and particle size distribution of the microcapsules were investigated.Further,the survival rate in the simulated digestive tract and disintegration time were investigated,as well as the lead adsorption capacity and the storage stability at different temperatures.The results were as followed:The optimum culture condition for P.pentosaceus 10a1 was glutathione(GSH)concentration of 4.8 mmol/L,culture time of 16 hours and propagated 1 generation.The freeze-dring survival rate was 81.23%.The optimal ratio of protective agent for sodium alginate microcapsules was 10% skim milk.Under this condition,freeze-dring survival rate and embedding rate of microcapsules were 87.53% and 78.27%,respectively.The optimal process conditions of double-layer microcapsules were obtained by orthogonal test.The results showed the concentration of chitosan solution at 1.25%,the embedding time at 15 min,and the p H of the chitosan solution at 6.0 resulted in the freeze-dried survival rate reached 82.24%.The characteristics of the prepared microcapsules were investigated.The particle size of the double-layer microcapsules were increased 83.68?m.The bacteria cells were effectively protected by microencapsulation in the digestive tract system.The results showed that the sodium alginate-chitosan microcapsules had better protective effect,and the viable count could reach 7.36 log CFU/g;Both microcapsules could release the P.pentosaceus 10a1 completely in the intestine during digestion of the intestinal simulant solution.In gastrointestinal fluid environment the adsorption capacity of lead by sodium alginate-chitosan microcapsules was better.The lead adsorption rate and adsorption capacity of sodium alginate-chitosan microcapsules were 75.92% and 7.52 mg/g,respectively.The adsorption capacity of lead in freeze-dried microcapsules was lower than that in non-freeze-dried microcapsules.The storage stability were improved by microencapsulation.After 28 days storage at-20 ?,the viable count of alginatechitosan double-layer microcapsules decreased only 0.78 logarithms,while that in freeze-dried double-layer microcapsules decreased only 0.55 logarithms.