Study On The Prebiotic Performance And Preparation Technology Of Lactobacillus Paracasei XLK401

With the wider application of antibiotics,the increasing problems of endogenous infections and bacterial resistance have become more severe.With the comprehensive "ban on antibiotics" in China,the development of antibiotic substitutes to eliminate or alleviate the impact of banned antibiotics has become urgent.Lactic acid bacteria(LAB)can improve the balance of the animal gut microbiota and enhance the host’s immunity.Their safety and environmental friendliness have received increasing attention.However,most LAB are anaerobic and susceptible to environmental stress,making them difficult to store and transport.Moreover,in order to exert their corresponding probiotic effects,a sufficient number of viable bacteria must be colonized in the intestine.Lactobacillus paracasei belongs to genus Lactobacillus and has been approved in China for use in probiotic preparations.In this study,we selected a strain of L.paracasei from the laboratory for in vivo and in vitro probiotic characteristics,genomic and microencapsulation studies.The L.paracasei XLK401,selected from fermented products(enzymes),has good tolerance to gastric acid,strong antibacterial ability,and extremely low drug resistance.Through analysis of the whole genome,the genome size is 3.1 Mb with an average GC content of 46.35%.The highest number of annotated coding genes is related to carbohydrate transport and metabolism;at the same time,it also had beneficial genes such as adhesion,colonization,and regulation of host immunity.To evaluate the in vivo probiotic characteristics of L.paracasei XLK401,a study was conducted on 1-day-old Nandan Yao chickens.After being fed for 21 days,the average weight of the two groups of Nandan Yao chickens fed with L.paracasei XLK401 was significantly higher than the groups fed with aureomycin and the control group(P<0.05).Compared with different treatment of samples and blank contrasts,the differences between antioxidants,digestive enzymes,and MDA MDA,adding aureomycin and L.paracasei XLK401 to the diet improved the digestion ability of Nandan Yao chickens and had a good effect in alleviating oxidative stress.Compared to the differences in the levels of immune activity factors in the plasma samples of different treatments and the control,adding L.paracasei XLK401 to the diet significantly improved the immune activity factor effect of Nandan Yao chickens,while adding aureomycin had no significant effect.After sequencing,the dominant bacterial phyla were Firmicutes,Actinobacteria,Bacteroidetes,Verrucomicrobia,and Proteobacteria.At the genus level,low-concentration L.paracasei group(FGL6)significantly increased the relative abundance of Bacteroides,Lactobacillus,and Parabacteroides(P<0.05),while high-concentration L.paracasei group(FGL7)significantly increased the relative abundance of Subdoligranulum(P<0.05),improving the microecological health of the intestinal microbiota.Based on the emulsion gelation method,this article studied a production process for preparing L.paracasei microcapsules using a fermenter.The tangential flow filtration system was used for the separation and purification of L.paracasei bacterial fluid,and a closed operation was achieved.The process conditions for the 5 L fermenter were as follows: tangential flow velocity of 1000 min/L,water-oil ratio of1:2,sodium alginate concentration of 1.8%,calcium carbonate concentration of 1.8%,filtration with 2 times the volume of the tank per minute of clean air,Span-85 concentration of 0.3%,rotation speed of 400 rpm,emulsification time of 5 min,and10% glacial acetic acid and 0.3 mol/L calcium chloride.The embedding rate reaches72.49%,and the highest viable count was 9.89 log CFU/g.The microcapsules were mainly spherical with a diameter ranging from 100-600 μm,and they were uniform in size.The addition of four times the volume of diatomaceous earth was used to adsorb and dry the microcapsules,reducing the water content from 90% to 16.17%.After 35 days of storage at 25℃,the viable count decreased by 0.619 log CFU/g.The heat resistance,bile tolerance,and gastric acid tolerance of the microencapsulated L.paracasei were improved,which increased its survival rate in the digestive tract.At the same time,it has relatively excellent enteric solubility,which makes it have a certain slow-release property and better play the role of probiotics.In conclusion,this study on the preparation of L.paracasei XLK401 as a new green additive to replace antibiotics has great application prospects.The evaluation of biological characteristics,in vivo probiotic characteristics,safety and microencapsulation characteristics of L.paracasei XLK401 can provide safe and effective antibiotic substitutes,which provides important theoretical value and practical guidance for realizing ecological aquaculture and green health food processing.