Study On The Technology Of High-Density Culture And The Fermentation Agent’s Producing Of Lactobacillus Plantarum NCU166

Lactobacillus is the main producing strain of fermented food.In the process of producing,the technology of high-density culture is the key of the stable quality and strain’s quick producing.Freeze-drying is the key step of production of agents.The improvement of high-density culture and freeze-drying can shorten the time of producing,reduce costs and investment in equipment,improve the efficiency of agent’s producing,and make the fermentation agent’s producing efficient,safe,standardized.Main contents discussed in this thesis are as follows:(1)Studies on the optimization of the conditions for temperature-shift cultivation of L,plantarum NCU166.The condition of culture was determined by measuring viable cells count,pH,acidity.The influence of temperature-shift culture on the viable cells count and activity was studied by the batch fermentation at four different temperatures(37℃,40～32℃,40～34℃,42～32℃,42～34℃).At 40～32℃,the viable cells count in the fermentation broth reached the maximum at 6.31×109cfu/mL and the activity of fermentation also reached the maximum.The fermentation broth was inoculated in MRS medium,fermenting at 37℃ for 24h.The pH of medium decreased to 4.24.The result showed L.plantarum which cultured at 40～32℃ have the best activity.(2)Studies on the low-cost culture of NCU166,use the single-factor test to finalize that the simplified MRS media do not join buffer salt,sodium hydroxide solution instead of ammonia.In the actual producing,using low purity peptone and yeast extract to make seed media and liquid media.(3)Studies on L.plantarum NCU166 frozen preservation.After the fermenttaion,mixed bacteria mud with protective agent,preserved in the set temperature.Under-70℃,glycerol’s cell viability is better than skim milk and trehalose.Under-20℃,the bacteria preserved in the skim milk,trehalose has a higher cell viability.(4)Studies on the optimization of the conditions for two-step vacuum freeze-drying method of L.plantarum NCU166.Through single-factor test,optimizing the conditions of two-step vacuum method.The concentration of protective agent(skim milk,trehalose)is 12%,6%.The drying sample’s thickness is between 3-4mm.Vacuum drying’s time and temperature is 2h and 34℃.After optimizing the two-step vacuum drying method,compare two-step vacuum drying method with vacumm freeze-drying method,vacuum freeze-drying method’s cell viability was 86.12%,two-step vacuum drying method’s cell survival rate was 92.14%.