Preparation Of Gelatin-Xylooligosaccharides Maillard Reaction Products And Study On Microencapsulated Probiotics

Probiotics are a group of active microorganisms that colonized the human gut and beneficial to the host.However,probiotics are susceptible to various environmental factors during production,storage and digestion,such as loss of probiotic viability due to heat,acid,oxygen,bile salts and enzymatic digestion.Microencapsulation helps to reduce the environmental sensitivity of probiotics and improve the efficiency of probiotic delivery to the intestinal tract.Spray drying as one of the most widely used technologies in the production of probiotic products,with advantages such as low cost,high production efficiency and good product stability.However,the high temperature,oxidation,water evaporation and high shear involved in spray drying greatly reduce the probiotic cell viability,therefore,it is necessary to select suitable protective agents to improve the protection of probiotics.Maillard reation products（MRPs）are considered as a reliable microencapsulated wall material because of their excellent film-forming,emulsifying and antioxidant activities.However,most studies at home and abroad have focused on MRPs of proteins with monosaccharides or polysaccharides,and fewer reports on MRPs of proteins with oligosaccharides.In addition,more studies have mainly applied MRPs to the encapsulation of bioactive components such as polyphenols and vitamins,and fewer studies have been conducted for probiotic microencapsulation.Therefore,in this study,probiotic microcapsules were prepared by spray drying using gelatin-xylooligosaccharides Maillard reaction products（GA-XOS-MRPs）as a protective agent,the changes of physicochemical properties and structure of MRPs during the heating process were investigated,and the effects of different heating times of MRPs on the production,storage,and in vitro simulated gastrointestinal digestive stability of probiotic microcapsules were investigated.Finally,the physiological protection mechanism of MRPs on probiotic bacteria during spray drying process were studied.The main findings were as follows:（1）GA-XOS-MRPs were successfully prepared by wet Maillard reaction.Under the condition of 80℃,the products in the early stage of Maillard reaction decreased within 15 min,and then increased continuously.The contents of intermediate and late products increased continuously with the extension of time within 300 min.The grafting degree of GA-XOS increased continuously within 150 min and reached the maximum grafting degree of 40.05%,and then remained unchanged.Maillard reaction increased the hydrophilicity,thermal stability,pepsin resistance and antioxidant activity of GA-XOS.After heating for 300 min,the DPPH radical scavenging ability,ABTS⁺radical scavenging ability,hydroxyl radical scavenging ability and reducing capacity of MRPs reached 170.32μg Trolox/m L,4.88 m M Trolox,8224.13 U/m L and 0.82 m M Fe²⁺,respectively.The formation of MRPs was verified by SDS-PAGE gel electrophoresis,fluorescence spectrum,infrared spectrum and circular dichroism.（2）The protective effects of MRPs with different heating times on the preparation,storage and in vitro simulated gastrointestinal digestion of probiotic microcapsules were investigated.The results showed that MRPs,especially MRP60improved the thermal stability and digestive tolerance of the strain under spray drying,and enhanced the delivery and adhesion of L.fermentum.The survival rate of MRP60@LAB was 14.28%,about 1.83 times that of Mix@LAB.After 4 h of in vitro simulated gastrointestinal digestion,the bacterial activity in MRP60@LAB microcapsule was still as high as 5.27×10⁹CFU/g.After 10 weeks of storage at 4℃and 25℃,the viable counts of MRPs microencapsulated probiotics ranged from 6.80to 9.00 Log CFU/g,which were higher than the general recommended dose.MRPs used for spray drying microencapsulation of probiotics produced the products with smaller particle size and lower moisture and conducive to product storage.（3）The physiological protective mechanism of MRPs on spray-dried probiotics was studied by measuring the integrity,fluidity,fatty acid composition of membrane and intracellular metabolism-related enzyme activity of microencapsulated probiotics.The results showed that Maillard reaction contributed to the protective effects of GA-XOS on the membrane intergrity and fluidity of probiotic bacteria during spray drying.In addition,the results of intracellular metabolism-related enzyme activity assay of microencapsulated probiotics showed that MRP150@LAB cells had the highest intracellular lactate dehydrogenase and pyruvate dehydrogenase activities,which might contribute to the growth and metabolism of probiotics after drying.