Optimization Of Vacuum Freeze Drying And Low Temperature Spray Drying Of Lactiplantibacillus Plantarum P-8

Vacuum freeze drying was one of the common technical means to prepare probiotic powder,which had the advantages of retaining biological activity to the greatest extent.As an emerging drying technology,Low-temperature spray drying can be produced continuously with less energy consumption,high yield and better retention of active substances,etc.Both of them can be widely used in the field of probiotic production.In this thesis,Lactiplantibacillus plantarum P-8 was used as the object of study,and the powder was prepared by Vacuum freeze-drying and Low-temperature spray drying techniques,and the process conditions to be optimized by single-factor method and response surface method,respectively,with the survival rate as the main index.After obtaining the optimal process conditions,the morphological characteristics,storage survival rate changes and β-galactosidase activity content of the powder prepared by different drying methods were measured,and the storage stability was evaluated as follows.The results of single-factor test for the preparation of Lactiplantibacillus plantarum P-8 by Vacuum freeze-drying method showed in which the pre-freezing rate and p H of the bacterial suspension had significant effects on the survival rate of the dried powder,which was optimized by the response surface method,it was determined that the best process conditions were the pre-freezing rate of 0.6℃/min,p H of the bacterial suspension of 6.5and the thickness of the material of 0.3cm,which resulted in the survival rate of 96.14%.The results of the single-factor test for the preparation of Lactiplantibacillus plantarum P-8by Low-temperature spray drying showed that the feed rate and vacuum degree were significantly influential on the survival rate of the dried bacteria,which was optimized by the response surface method to determine the best process conditions when the feed rate was 9 m L/min,while the vacuum degree was 0.03 MPa that the survival rate reached81.5% when the spray pressure was 0.3 MPa.The morphology of the powder was observed by scanning electron microscope after Vacuum freeze-drying and Low-temperature spray drying respectively,which showed that the morphology of the powder prepared by different process conditions was significantly different,while the surface of the bacterium was smooth after Vacuum freeze-drying,which caused the leakage of the contents due to the rupture of the cell surface of very few bacterium;when the bacterium was dried by Low-temperature spray,which showed a rough and spherical surface with many folds and collapses,and part of the structure was loose.The changes in the survival rate and key enzyme activities of the strains were compared between Vacuum freeze-dried and Low-temperature spray-dried strains stored at4℃ and 25℃ for 35 d.The results were found that the increase in storage temperature affected the activity of the strains and accelerated the decrease in their survival rate.When the storage was completed,the extracellular β-galactosidase content of the strain which was prepared by Low-temperature spray drying was significantly higher than that of Vacuum freeze-drying(P<0.05),which indicated that the damage caused by spray drying to the cells was more serious.The survival rate of the Vacuum freeze-dried powder was96.45% at 4 ℃,which was significantly higher than that of 92.18% for the Low-temperature spray-dried powder(P<0.05);when stored at 25℃,the survival rate of the Low-temperature spray-dried strain was 87.49%,which was higher than that of 85.75%for the Vacuum freeze-dried strain,which indicated that the storage of the dried powder at low temperature could better maintain the survival rate of the strain.The survival rate of the strains can be maintained better by storing the dried powder at low temperature,while storage at room temperature,Low-temperature spray drying was more beneficial to maintain the survival rate of the strains.