| Probiotics play an important role in anti-cancer,anti-inflammatory,regulating intestinal transit,competing with pathogens,enhancing the host immune system,and synthesizing a variety of bioactive components.However,due to the sensitivity of probiotics to the environments,the probiotic loss during the processing and gastrointestinal digestion limits the application of probiotics in the food and pharmaceutical fields.Encapsulation technology is wildly used to deliver active substances and resist the adverse effect of external environment.Thus,the encapsulation system directly influences the survival of probiotics during subsequent processing and digestion.In this study,in order to improve the survival rate of probiotics in the process of storage and digestion,a stable and edible W/W Pickering emulsion was constructed.The emulsion system was composed of hydroxypropyl methylcellulose（HPMC）and dextran（DEX）,and it was applied as the encapsulation system of probiotics.Microcrystalline cellulose（CNCs）was used as the stabilizer of the water-in-water（W/W）emulsion.The feasibility of W/W emulsion system as an encapsulation system for probiotics was proved,and the performance of microcapsules was regulated by adding proteins or inorganic nanoparticles.Probiotic microcapsules were prepared by spray drying.Moreover,the physical properties,storage performance,and digestion resistance of the microcapsules were investigated.The main research contents and results were indicated as follows:1.Stable W/W emulsion systems for delivering active substances are generally difficult to be constructed,due to their indistinct interfacial layer and low interfacial tension.The phase diagram was used to select a suitable two-phase concentration interval to derive an emulsion concentration that was relatively stable and suitable for subsequent processing.The effects of CNCs concentration,p H,and ionic strength on the microscopic morphology and macroscopic stability of the emulsion.Moreover,the physical properties,storage stability,and digestive characteristics of the probiotic microcapsules obtained by spray drying were investigated.The results showed that the W/W Pickering emulsions stabilized with 0.05 wt%CNCs,at the concentration of 4.0 wt%HPMC and 1.5 wt%DEX,exhibited good environmental stability and storage stability.The CNCs improved the stability of the emulsions under different p H and ionic strength conditions.The active probiotic of the microcapsules after spray drying was 2.08×1010 CFU/g.The protective effect of the emulsions on Lactobacillus plantarum reduced the loss of probiotics during the spray drying.The obtained microcapsules had good storage stability and gastrointestinal digestive stability.These results provided a theoretical basis for the application of W/W Pickering emulsion as a probiotic encapsulation carrier.2.Due to the pores on the surface of the microcapsule,small molecules and ions in the environment are easily diffused into the microcapsules,thereby affecting the active of probiotics encapsulated in the microcapsules.Thus,the addition of inorganic nanoparticles can fill the pores.In this study,the effect of hydrophobic silica nanoparticles（Si O2）on the stability of emulsions was investigated.The effect of Si O2 content on the physical properties,gastrointestinal digestive stability,and storage stability of microcapsules was further explored,the microcapsules were prepared by spray drying the W/W Pickering emulsions.It could be observed by the optical microscope that Si O2 particles aggregated together while the content of Si O2 above 0.10 wt%.The macroscope of the emulsion showed the Si O2 migrated rapidly to the upper layers of the emulsions,due to the hydrophobic properties of Si O2 particles.The physical properties,gastrointestinal digestion stability,and storage stability of microcapsules prepared by spray drying were further investigated.The results showed that the addition of Si O2 improved the fluidity and reduced the water content of the microcapsules.Moreover,the heat loss of Lactobacillus plantarum during spray drying was also decreased.When the Si O2 content of the spray-dried sample increased from 0 to 0.20 wt%,the survival rate of Lactobacillus plantarum microcapsules increased from 66.11±0.03%to 67.18±0.04%.At the same time,the activity of Lactobacillus plantarum in microcapsules with different contents of Si O2 under gastrointestinal environment and long-term storage conditions was explored.With the increase of Si O2 content in microcapsules,the activity of Lactobacillus plantarum increased from 3.9×106 CFU/g to 1.41×108 CFU/g after gastric digestion.After intestinal digestion,the activity of Lactobacillus plantarum in microcapsules increased from 1.02×106 CFU/g to 9.67×107 CFU/g,which was mainly caused by trypsin and bile salts.Si O2not only improved the physical propertied of probiotic microcapsules,but also significantly reduced the loss of Lactobacillus plantarum in the gastrointestinal digestion stage and long-term storage stage.3.In order to reduce the probiotic loss caused by heat during spray drying and the hydrogen ion during gastrointestinal digestion.Protein was added to microcapsules as buffers to improve the survival of probiotics.This experiment was conducted to investigate the regulation of SPI microgels on the interface of W/W Pickering emulsion and its effect on microcapsule performance.The protein distribution could be adjusted by the p H value of the emulsions.With the decrease of p H,SPI microgels aggregated and gradually migrated from the internal phase to the water-water interface.The addition of SPI microcapsules also increased the survival rate of probiotics during spray drying.When 0.25wt%SPI microgels were added to the spray-dried emulsions,the survival rate of the obtained probiotics microcapsules increased from 65.24±0.03%to 70.50±0.03%,the moisture content and density of the microcapsules also increased,while the fluidity of the microcapsules decreased.Although the addition of SPI microgels was not conducive to the long-term storage of microcapsules,the increase of SPI microgels improved the ability of probiotics resisting gastrointestinal digestion environment.After digestion,the probiotics activity of microcapsules without SPI microgels and with 0.50 wt%SPI microgels was 4.21×106 CFU/g and 1.57×107 CFU/g,respectively.When the p H of emulsions with 0.25 wt%SPI microgels were adjusted from 6.0 to 4.0,the survival rate of Lactobacillus plantarum decreased from 75.95±0.04%to 63.28±0.04%after spray drying.However,the decrease of p H reduced the loss of Lactobacillus plantarum in microcapsules during gastrointestinal digestion.The number of viable probiotics in microcapsules after gastrointestinal digestion increased from 9.63×105 CFU/g to 4.61×106 CFU/g with the decrease of p H value.The results confirmed that SPI microgels could regulate the water-water interface of the emulsion and improve the storage and digestion resistance of probiotic microcapsules,which were beneficial for the further application in functional food. |
