Preparation Of Lactobacillus Plantarum Microcapsules And Its Application In Yogurt

Probiotics are active microorganisms that are beneficial to the host^[1],It refers to the general name of active beneficial microorganisms that can be colonized in the intestinal tract and reproductive system of the body,and can play a positive role in improving the host's microecological balance and exerting beneficial effects on the intestine^[2].Probiotics mainly have various physiological functions such as inhibiting the growth of pathogenic bacteria,promoting the absorption of nutrients,immunoregulation,reducing serum cholesterol content,preventing cardiovascular diseases,and inhibiting the formation of tumor cells^[3,4].With the improvement of living standards,its superior functional properties,probiotics have attracted more and more attention from scholars and consumers^[5].At the same time,it was found that the probiotics'activity during storage and gastrointestinal digestion were extremely vulnerable,which would cause the probiotics'activity to be reduced or lost^[6,7].In order to make full use of the functions of developing probiotics and open up the market of probiotic products,the protection and improvement of probiotic activity has become an urgent problem to be studied and solved.This study mainly explored the protective effects of different embedded wall materials and two preparation methods for the preparation of probiotic microcapsules.Whey protein isolate and inulin were selected as the raw materials of the embedded wall materials,and Lactobacillus plantarum was used as the template bacteria.The first part,the Maillard reaction product of whey protein isolate and inulin was used as the embedding wall material,and the inlet air temperature,wall material concentration,and material flow rate of spray drying conditions were optimized.Then the Maillard reaction products of protein and inulin,whey protein isolate and inulin,denatured whey protein isolate and inulin are used as embedding wall materials,respectively.Spray and dry preparation methods are used to prepare Lactobacillus plantarum microbes.Capsules,and the performance of the microcapsules was measured,and the embedding effect and the protective effect of the microcapsules were compared and analyzed.In the last part,microcapsules were used in yogurt,and sensory evaluation,physical and chemical properties of the yogurt were measured.The main experimental results are as follows:?1?Spray drying conditions optimization experiment results:The optimum concentration of wall material is 10%,the optimum concentration range is 8-12%;the optimum material flow rate is 11 mL/min,and the optimum material flow rate is 6mL/min-12 mL/min.The final optimized microcapsule preparation conditions for response surface are:inlet air temperature is 130?,wall material concentration is 10%?w/v?,and material flow rate is 9 mL/min.?2?Comparative analysis of the performance of microcapsules with different preparation methods and wall materials.Spray-dried microcapsules are spherical,and freeze-dried microcapsules are irregularly fragmented.The particle size of the microcapsules prepared by spray drying is 10?m-40?m,which is smaller than that of the microcapsules prepared by freeze-drying?80?m-400?m?.The water content of spray-dried microcapsules was significantly higher than that of freeze-dried microcapsules,and the water content of spray-dried microcapsules with MRPs as wall material was significantly lower than the other two microcapsules.The degree of damage to bacterial cells during spray drying preparation was significantly higher than freeze drying.The embedding rate of freeze-drying is significantly higher than the embedding rate of spray-drying.Among the different wall material microcapsules prepared by spray drying,WPI+INU and DWPI+INU as the embedding wall material have no obvious difference in embedding rate,All were significantly higher than the embedding rate of microcapsules with MRPs as wall material?p>0.05?.After in vitro simulated gastric juice digestion for 1 h and intestinal fluid digestion for 6 h,the viable count of spray-dried microcapsules was still higher than 10⁷ cfu/g,and the viable count of freeze-dried microcapsules was about 10⁶ cfu/g,of which MRPs was used as The microcapsules of the wall material have a smaller reduction of live bacteria,and the microcapsules have a better protection effect on Lactobacillus plantarum during the digestion process.The results of storage experiments showed that the effects of different preparation methods on the activity of Lactobacillus plantarum were relatively small.The number of Lactobacillus plantarum at 25?showed an increasing trend in the first three weeks and then decreased,but the degree of decline was greater than that at 4?.Comparing different wall materials,it was found that microcapsules with WPI+INU and DWPI+INU as wall materials have the ability to improve the activity of Lactobacillus plantarum.?3?The prepared microcapsules are used in yogurt,and the optimal amount of microcapsules selected based on the effect of the amount of microcapsules on the sensory score is 3%.The addition of microcapsules has a small effect on the sensory perception of yogurt,and the color of microcapsules with only MRPs as the wall material becomes slightly yellow.The addition of microcapsules reduced the value of pH and viscosity of yogurt.The protein content,acidity and water holding capacity of the emulsion increased.In vitro simulated gastrointestinal digestion experiments and storage experiments showed that the gastrointestinal fluid and storage environment had little effect on the activity of Lactobacillus plantarum after being embedded,and the microcapsule shell had a protective effect on probiotics.