Preparation Of Microencapsulated Lactobacillus Plantarum-Lentinan Synbiotics And Its Effect On The Growth Performance Of Broilers

At present,the global animal husbandry is in a period of vigorous and orderly development.However,because of the irrational use of antibiotics,the world is facing the challenge of the spread of drug-resistant and multi-drug resistant bacteria.To alleviate this problem,countries around the world have adopted measures to replace and reduce the use of antibiotics.China has banned the addition of antibiotics to feed since July 2020,and many researchers have actively engaged in the research of finding alternatives to antibiotics.Microecological preparations have attracted wide attention due to its characteristics of bacteriostatic,balance,protection,immunity and nutrition.Synbiotics are microecological preparations composed of probiotics and prebiotics,which not only has the function of regulating gastrointestinal function,promoting the absorption of nutrients and improving immunity,but also can be selectively utilized by host microorganisms and increase the number of beneficial microflora,thus exerting the dual role of probiotics and prebiotics.Lactobacillus plantarum is a kind of lactic acid bacteria and one of the feed additives announced by the Ministry of Agriculture and Rural Affairs of China,it has the function of maintaining intestinal microenvironment balance and enhancing gastrointestinal digestion and absorption.Lentinan is a fungal polysaccharide,its main active ingredient isβ-glucan,which has prebiotic function.In this study,synbiotics composed of Lactobacillus plantarum and lentinan were prepared,and microencapsulation technology was applied to embed synbiotics to enhance the stress resistance of probiotics.The application effect of microencapsulated synbiotics in antibiotic-free feed of broilers was studied to provide reference for antibiotic-free farming.In order to prepare microencapsulated synbiotics,the prebiotic activity of lentinan was determined firstly.Lentinan was added into culture medium at five different concentrations,and the effect of lentinan on the growth of Lactobacillus plantarum was analyzed.The results showed that lentinan added to culture medium at 20 mg/m L had the best effect.In the preparation of microencapsulated synbiotics,lentinan added to bacterial suspension at 20 mg/m L.In order to improve the stress resistance of synbiotics,sodium alginate and concentrated whey protein were selected as composite wall materials,and the internal emulsification method was used to prepare synbiotics microcapsules.First,the optimum preparation conditions of microcapsules were determined by single factor and orthogonal test.Then,the characteristics,storage stability,gastric juice tolerance and intestinal solubility of microencapsulated synbiotics were evaluated in vitro.The results showed that the optimum parameters for the preparation of microencapsulated Lactobacillus plantarum-lentinan synbiotics were as follows:the mass fraction of sodium alginate was 2.5%,the mass ratio of sodium alginate to concentrated whey protein was 1:1,the mass ratio of calcium carbonate to sodium alginate was 1:4,and the volume ratio of water to oil was 1:3.The embedding rate of microcapsules was 87.72%,the effective load was 2.53×10~9 CFU/g,and the particle size was concentrated at about 112.24μm.The morphology of wet microcapsules was round and the particle size was uniform,freeze-dried microcapsules maintained the integrity of the structure.The water content of synbiotics microcapsules was 3.76%,and after 35 days of storage at4℃and 25℃,the number of viable bacteria in microcapsules decreased by 0.30 lg CFU/g and 0.97lg CFU/g,and the number of unembedded bacteria decreased by 0.76 lg CFU/m L and 4.32 lg CFU/m L,which indicated that microencapsulation could significantly improve the storage stability.After the microencapsulated synbiotics were treated in simulated artificial gastric juice for 1 h,the survival rate of Lactobacillus plantarum could reach 60%and the number of viable bacteria in microcapsules was 1.06×10~9 CFU/g.Therefore,microencapsulation could effectively improve the tolerance of probiotics to gastric juice and protect more active probiotics from reaching intestinal tract.The synbiotics could be released completely after treated in simulated intestinal fluid for about1.5 h,and the microencapsulated synbiotics had good intestinal release performance.In order to exam the effect of microencapsulated synbiotics as feed additives in broiler feeding,synbiotics were added to the antibiotic-free diets at a dose of 1×10~9 CFU/kg,and intestinal function and growth performance of 28-day-old broilers were evaluated.The results showed that the microencapsulated Lactobacillus plantarum-lentinan synbiotics could increase the average daily gain and feed efficiency of broilers,improve immune organ index and intestinal villus morphology,enhance the activity of digestive enzymes in the small intestine,increase the number of Lactobacillus,and decrease the number of Escherichia coli in cecum.The application of microencapsulated synbiotics could promote intestinal health and improve growth performance of broilers.In conclusion,the microencapsulated Lactobacillus plantarum-lentinan synbiotics were successfully prepared in this study.In vitro experiments confirmed that microencapsulation could improve the storage stability and the tolerance of probiotics to gastric juice of synbiotics,as well as enable more active probiotics to enter the intestine and release.The in vivo experimental results showed that the synbiotics could improve the intestinal function and growth performance of broilers.