Study On The Damage Mechanism And Protection Methods Of Bifidobacterium Lactis Probio-M8 Spray Freeze-Drying

Spray freeze-drying is an emerging drying technology,which has the advantages of low energy consumption,low cost,short-term production,and good retention of active substances.It has the potential to replace freeze-drying technology in the field of probiotic production.In this paper,the spray freeze-drying technology is used to prepare Bifidobacterium lactis Probio-M8 bacterial powder particles,to optimize the spray freeze-drying process conditions as the preliminary test,and the single factor metho d and response surface method are used to optimize the process conditions.On the basis of improving the technological conditions,the damage mechanism of Bifidobacterium lactis Probio-M8 by spray freeze drying was studied,at the same time,the Bifidobacterium lactis Probio-M8 spray freeze-drying at the transcription level was analyzed by measuring cell composition,cell structure,cell membrane integrity,cell morphology,and membrane fatty acid content.To analysis of damage mechanism of Bifidobacterium lactis Probio-M8 spray freeze drying at transcriptional level,taking corresponding protective measures to reduce physiological damage and provide help for spray freeze drying technology in the preparation of probiotic powder.The analysis results are as follows:The single factor test results showed that the drying temperature and nozzle diameter have a significant effect on the drying survival rate of Bifidobacterium lactis Probio-M8 powder particles,and the feed rate has no significant effect on the survival rate.After optimization by response surface methodology,the best process is determined When the conditional feed rate is 15 m L/min and the nozzle diameter is 1.5mm,the predicted survival rate is 73.79%.Scanning electron microscopy was used to observe the morphology of the bacterial powder prepared at different process conditions.The results showed that the shapes produced by the process conditions were different,and the overall morphology showed approximately spherical or irregular-shaped particles and aggregated particles.Through Fourier Transform Infrared Spectroscopy to study the changes in bacterial composition before and after spray freeze-drying,the study shows that after drying,the absorption peak of the alpha helix in the bacterial protein structure disappears,indicating that the structure of the cell wall S-protein layer is damaged,the cell wall to be affected first.At the same time,according to the FTIR wavelength change,the cell membrane has changed,but there is no phase change.After drying,the integrity of the cell membrane is damaged,the cell membrane is damaged,and the permeability increases,which leads to damage or death of the bacteria.After drying,DNA no damage occurred,but according to the results of the differential medium,the repair function of the cell wall and cell membrane was affected,the morphology of the bacteria changed after drying,and some of the bacteria appeared to shrink,break and collapse.According to the results of the changes of membrane fatty acids,the proportion of unsaturated fatty acids increased,indicating that the bacteria made adaptive changes to maintain the stability of the cell membrane.Transcriptomics technology was used to study the effect of spray freeze-drying on the physiological damage of Bifidobacterium lactis Probio-M8.Through analysis methods such as GO and KEGG functional gene annotation,functional enrichment analysis and metabolic pathways of differentially expressed genes,it was found that the differential genes after drying are mainly concentrated in metabolic pathways such as cell membrane structure,membrane transport,and fatty acid synthesis.Among them,the control of unsaturated fatty acids,the gene was significantly up-regulated(P?0.05).Because of trehalose,whey protein and L-cysteine hydrochloride show good effects in freeze-dried protective agents,the response surface method has been optimized to formulate trehalose at 7.5% and whey protein at 11%,L-cysteine hydrochloride is1.25g/L.After differential scanning calorimeter analysis,the glass transition temperature of the compound protective carrier is increased,and it has a better storage and preservation effect;after drying,the compound protective carrier has a better pro tective effect on bacterial metabolic enzymes.