Preparation Of Probiotic Microcapsules From Milk Proteins Degraded By Different Proteases

To improve the resistance of probiotics to unfavourable environments and reduce losses in extreme conditions such as the digestive tract,Lactiplantibacillus plantarum LIP-1 was selected as the encapsulated strain in these.The fermented skim milk was degraded using rennet,papain and pineapple protease respectively,and then prepared by calcium ion-induced gelation of Lactiplantibacillus plantarum The LIP-1 microcapsules of Lactiplantibacillus plantarum were prepared by calcium-induced gelation.On this basis,the morphological structure,particle size distribution,acid resistance,intestinal solubility and storage properties of the microcapsules prepared by the three proteases were compared;the protein content and changes of the different samples were analysed by gel electrophoresis to explore and analyse the intrinsic mechanism of the proteases affecting the performance of the microcapsules.The main experimental results are as follows.(1)The encapsulation rate of probiotic microcapsules prepared from rennet was(86.46±2.31)%,which was significantly higher than that of pineapple protease microcapsules was(78.51±2.45)% and papain microcapsules was(80.26±2.18)%(P<0.05);and the average particle size of rennet microcapsules was 180.17 μm,with the particle size distribution ranging from 150 μm to The mean particle size of rennet microcapsules was 180 μm and the distribution range was between 150 μm and 200 μm,which was relatively narrow,while the mean particle size of papain microcapsules and pineapple protease microcapsules was 190.42 μm and the distribution range was between160 μm and 220 μm,which was wider;therefore,the particle size of rennet microcapsules was smaller and better dispersed.(2)All three groups of protease microcapsules had good intestinal solubility and basically completed disintegration and release within 60 min in the intestinal fluid.120 min after digestion with artificial gastric juice at p H 2.0,the survival rate of Lactiplantibacillus plantarum LIP-1 in the unembedded group was less than 10%,while the survival rate of all three protease microcapsules was more than 70%,indicating that the protease microcapsules can provide protection for Lactiplantibacillus plantarum LIP-1 in a low acid environment.protection for subsequent Lactiplantibacillus plantarum LIP-1 colonisation of the intestine.The gastric survival rate of Lactase microcapsules was(84.05±2.08)%,papain microcapsules was(75.65±2.16)% and pineapple protease microcapsules was(70.48±2.06)%,with a significant difference(P<0.05)in the gastric survival rate.microcapsules.(3)The survival rate of all three groups of protease microcapsules at 4℃ was higher than that at 37℃,indicating that low temperature storage was more beneficial for the probiotic microcapsules to maintain their activity.The survival rate of rennet microcapsules was(92.41±2.13)%,papain microcapsules was(86.71±2.19)% and pineapple protease microcapsules was(81.35±2.11)% after 28 days of storage at 4℃,so the storage performance of rennet microcapsules was better than papain microcapsules and pineapple protease microcapsules.(4)The observation of the ultrastructure of the microcapsules by scanning electron microscopy and the analysis of the gel electrophoresis of the protein composition of the wall materials showed that the better overall spherical shape,smaller and denser surface pore size,higher number of embedded viable bacteria and better protection of the bacterium in the microcapsules prepared by rennet compared to papain and pineapple protease treatment of fermented skim milk could be attributed to the adequate degradation of fermented skim milk by rennet,which produced more abundant protein fragments.The overall structure of the microcapsules was poorly spherical and the surface structure was loose and porous,with fewer and less protective organisms.These results suggest that the use of rennet,papain and pineapple protease for the preparation of probiotic microcapsules was feasible and all significantly improved the resistance of Lactiplantibacillus plantarum LIP-1 to adverse conditions(P<0.05).Compared to the three,rennet performed better than papain and pineapple protease microcapsules in improving the resistance of Lactiplantibacillus plantarum LIP-1 to adverse environments.This experiment provides a new idea for developing the preparation of food-derived probiotic microcapsules and lays a certain theoretical foundation for the industrial production of probiotic microcapsules.