Effects Of Lactobacillus Plantarum LIP-1 Activity During Storage In Different Drying Methods

Lactobacillus plantarum LIP-1 was used as the research object to compare the changes of the survival rate of the strain that was stored in different storage temperatures(-20℃,4℃,25℃ and 37℃)and different gas environments(nitrogen,oxygen and vacuum)with two different drying methods(spray drying and freeze-drying).The fatty acid composition of the cell membrane and the changes of key enzyme activities(β-galactosidase,lactate dehydrogenase and Na+K+-ATPase)were measured,which was to explore the effects of different drying methods and different storage environments on the survival rate of the strain and its mechanism.The results showed that the survival rate of the freeze-dried strains was significantly higher than the spray-dried strains(P<0.05).The survival rate of the strains decreased with the increase of storage temperature in the same storage gas environment,In the-20℃ vacuum environment,the survival rate of the freeze-dried strain can reach 61.7%,which was significantly higher than the survival rate of the spray-dried strain group stored in the same storage environment 53.7%(P<0.05);The survival rate of the dried strains of both methods was less than 1%and the storage effect was poor in the 37℃ storage temperature;In the same storage temperature,Different gas environments had significant effects on the survival rate of the strain during storage(P<0.05),The survival rate of the vacuum environment storage strain was the highest,nitrogen was second,and the aerobic environment was the worst.The relative content of the fatty acid composition of the cell membrane indicated that there was no significant difference in the relative content of unsaturated fatty acids in the cell membrane(P>0.05)after spray drying and freeze-drying;the relative content of unsaturated fatty acids decreased significantly(P<0.05)with the increase of storage temperature in the same storage gas environment.In the same storage temperature,the influence of different gas environments was significant(P<0.05).The relative content of unsaturated fatty acids remained relatively stable in vacuum and nitrogen environment.The relative content of unsaturated fatty acids was significant decrease(P<0.05)in aerobic environment.By measuring the key enzyme activities such as β-galactosidase,lactate dehydrogenase(LDH)and Na+K+-ATPase,the β-galactosidase leakage of the spray drying method was significantly higher than that of freeze drying.(P<0.05),combined with transmission electron microscopy to observe the integrity of the cell membrane of the strain,compared with the freeze-drying,the damage of the cell membrane integrity during the storage of the strain was more serious.The strains lactate dehydrogenase and Na+K+-ATPase were found to have significant effects on the lactate dehydrogenase and Na+K+-ATPase in the same storage gas environment(P<0.05).The enzyme activity significantly decreased when the storage temperature was increased.The enzyme activity was best in the vacuum environment of-20℃.The enzyme activity remained poor in the aerobic environment at 37℃;The gas environment has a significant effect on the maintenance of key enzyme activities of the strain in the same storage temperature.The vacuum environment was superior to nitrogen,and nitrogen was superior to aerobic.Based on the correlation analysis,the main mechanism of the different drying methods and different storage environments on the survival rate of the strains was revealed;There was a positive correlation between the survival rate of the strains and the relative content of unsaturated fatty acids in the cell membrane during the storage of the strain,through the 30th day and the 60th day,the principal component analysis of the cell membrane fatty acids showed that the first major components affecting the survival rate of the strain mainly include:unsaturated fatty acids such as C16:1,C18:0,C18:2 and C19cyc11,and the storage time pro longed,C 16:1,C18:2,C1 9cyc 11,etc.all have different degrees of oxidation,Which resulted in decreased relative content of unsaturated fatty acid and increased mortality of the strain;simultaneous survival rate and lactate dehydrogenase activity.The Na+K+-ATPase activity was positive correlation between the maintenance of activity and negative correlation with the amount of beta-galactosidase leakage.The correlation between the survival rate of the strain and the storage environment showed that the storage temperature of the strain was negatively correlated with the survival rate of the strain and the growth vigor of the strain during the storage period.The results showed that the survival rate of the freeze-dried strains was significantly higher than that of the spray-dried strains during the 60-day storage period in the same storage environment;Low temperature and vacuum environment helped maintain strain survival and key enzyme activities;During the storage period,the possible mechanism of action leading to a decrease in the survival rate of the strain includes:In high temperature and aerobic environment,the unsaturated fatty acid in the cell membrane of the strain was oxidized,the fluidity of the cell membrane was lowered to cause the death of the strain,On the other hand,the decrease of key enzyme activity during the storage of the strain,Which affected the energy metabolism and growth rate of the strain and resulted the decrease of the survival rate of the strain.