Construction And Environmental Tolerance Of Protein-based Probiotics Microcapsules

Probiotics are a kind of active microorganisms,which can have beneficial effects on the health and physiology of the host by promoting the ecological balance of the intestinal flora of the host.In order to exert its effect,the number of viable bacteria of the probiotics taken by consumers is at least 6 Log CFU/g,but the tolerance of probiotics is poor.High temperature,pressure,oxygen,stomach acid,bile salt,etc.are affected in the process of processing,storage and digestion,resulting in greatly reduced activity.A large number of experiments have proved that microencapsulated probiotics can improve the survival rate of probiotics in harsh environment.Currently,more studies on microencapsulated probiotics are aimed at improving the ability of probiotics to tolerate stomach acid and bile salt.In order to achieve that the probiotics in microcapsules can release an effective amount of probiotics in the intestine,but there are few studies on the heat resistance of probiotics after microencapsulation.This paper aims to explore the protective effects of four proteins(WPI,SPI,NC,CWP)as wall materials on probiotics,and then select a protein with strong stress resistance and Shellac to explore the effects of different mix ratios on the encapsulation efficiency,storage properties,in vitro digestion properties,heat resistance and other properties of probiotic microcapsules.The microcapsules were prepared by emulsification and freeze-drying by adding alginate and trehalose in the optimal compound ratio,and the physicochemical properties of microcapsules and the survival of probiotics were analyzed.The main experimental contents and results are as follows:(1)Compared with nude bacteria,microencapsulation significantly improved the neutralization activities of probiotics in spray drying,in vitro digestion,storage and humid and hot environment,indicating that protein-based microcapsules effectively improved the vitality of probiotics.WPI and CWP had higher glass transition temperature and lower viscosity,which reduced the damage during spray drying of probiotics and showed good storage stability.The activity of probiotics after 8 weeks storage at 4 ℃ decreased by 0.32 Log CFU/g and 0.44 Log CFU/g,respectively.However,WPI and CWP samples had high solubility,low p H buffer capacity and low structural density,and had weak protective effects on probiotics in vitro digestion and thermal stability experiments.SPI and NC have lower glass transition temperature and higher viscosity,which is not conducive to spray drying,and have poor storage stability,but the SP and NC samples have poor solubility,strong p H buffer capacity,high structural density,which makes SPI and NC samples have higher stress resistance in harsh environment.In the in vitro simulation experiment,the decrease was 0.81 and 1.02 Log CFU/g,respectively,and the decrease was 5.40 and 5.74 Log CFU/g,respectively,during the 16 min humid heat treatment at 75 ℃.(2)Embedding Bacillus coagulans BC01 in a substrate of different proportions of SPI-Shellac significantly improved the survival rate of probiotics compared to free probiotics during spray drying.However,with the increase of shellac proportion,the spray drying yield and storage stability of probiotics decreased gradually.When the shellac proportion increased from 0% to 33.3%,the survival rate of probiotics during spray drying decreased from 23.34% to 0.38%.The decrease of probiotic activity increased from 0.69 Log CFU/g to 1.25 Log CFU/g.(3)Compared with simple SPI microcapsules,SPI:Shellac(8:1,4:1)Microcapsules were increased by 0.33 and 0.15 Log CFU/g in the gastrointestinal simulation experiment and 0.69 and 0.47 Log CFU/g in the humid heat experiment at75℃,respectively,because the addition of shellac reduced the solubility of probiotics,and low solubility prevented the premature release of probiotics from the microcapsules.This can provide better physical barrier protection for probiotics in the gastrointestinal tract and humid and hot environment.However,when the proportion of shellac increased to 33.3%,this protective effect decreased,mainly because the excessive shellac resulted in a sharp increase in the viscosity of spray drying liquid,difficult misting process,prolonged drying time,and increased thermal damage of probiotics,In vitro digestion and hot water,the stress resistance of probiotics with impaired vitality can be greatly reduced.(4)Four kinds of alginate based probiotic microcapsules(ALG,ALG/Shellac,ALG/SPI,ALG/SPI/Shellac)were prepared by freeze-drying to explore the protective effects of different formulations of microcapsules on probiotics in freeze-drying,gastrointestinal digestion,storage stability,thermal stability,etc.The results showed that all the microcapsule samples obtained by freeze-drying had more than 7 Log CFU/g viable bacteria and less than 7% moisture content,and the powder quality was good.In vitro tests of gastrointestinal digestion,storage stability,heat resistance and other in vitro stress resistance,it was found that compared with free probiotics,the survival rate of microencapsulated probiotics was significantly improved,indicating that microcapsules can effectively protect probiotics from harmful environmental factors.Among them,ALG/SPI/Shellac provided the best protection for probiotics in harsh environment.Probiotics lost 0.35 Log CFU/g and 2.79 Log CFU/g after gastrointestinal digestion and hot and wet environment,which was mainly attributed to the synergistic action of SPI and ALG.The microcapsules are endowed with a more dense structure with complete shape rules and high mechanical strength,showing good physical barrier effect,and significantly improving the protective effect of probiotics.