| Probiotics play a role in regulating human intestinal health only when the number of viable bacteria reaches 10~6～10~7 CFU/m L or CFU/g.However,the activity of probiotics is easy to decline or even loss during food processing,storage or through the human gastrointestinal tract.Microencapsulation is considered to be one of the effective approaches to protect probiotics,improve their survival rate and colonize them in human gut.Traditional microencapsulation technologies,such as spray drying and high-energy emulsification,need to encapsulate probiotics in the process of high temperature,high shear stress or high pressure,which seriously reduce the encapsulation efficiency of probiotics.However,high-efficiency vibration technology can effectively overcome these problems,and can prepare microcapsules quickly on a large scale under the condition of zero shear stress and room temperature.At present,there are few studies on utilization of high-efficiency vibration technology to encapsulate probiotics,and no studies have systematically discussed the digestion and release mechanism of microencapsulated probiotics by this technology,which have been done in this study.In order to further improve the loading and release efficiency of microcapsules for probiotics,this paper also investigated the impact of antacid and co-encapsulation of prebiotics on the vitality of probiotics.In addition,isothermal microcalorimetry was used for the first time to systematically investigate the thermal kinetic parameters of microencapsulated probiotics before and after in vitro digestion,and the regulation of gut microflora in mice by L.GG and microcapsules as supplements was investigated.The main research contents of this paper are as follows:1.Lactobacillus rhamnosus GG(L.GG)was successfully encapsulated into microcapsules stabilized by sodium alginate/pectin composite wall materials using high-efficiency vibration technology.In order to further improve the activity of microcapsules,calcium carbonate,an antacid agent,was added into microcapsules,and the quantity of live L.GG in microcapsules of different formulations during a storage of up to 56 days and simulated in vitro digestion was counted.The morphology and structure of the microcapsules were characterized by SEM,XRD,DSC and TG.In the optimal ratio of sodium alginate/pectin,the maximum number of surviving cells after encapsulation reached 10.32 Log CFU/g.The addition of antacid kept the bacterial count at 8.49 Log CFU/g after gastric digestion.The results showed that the existence of calcium carbonate crystals and the"egg-box cross-linking"induced by calcium ions released during gastric digestion could significantly improve the survival rate of L.GG,while the addition of pectin improved the thermal stability.After 56 days of storage,the number of viable bacteria in microcapsules was still more than 5.52 Log CFU/g.The above study indicates that the optimized formulation prepared by this technology is promising to be utilized as a high-value probiotic product for food industry.This study also confirmed the important role of antacid in this pectin/alginate microcapsule formulation for controlled-release purpose.2.In order to further improve the delivery performance of microcapsules,inulin was added into the optimized formula obtained in the above chapter at different ratios.The results showed that the encapsulation efficiency of inulin was positively correlated with that of probiotics,and in sodium alginate/pectin(9:1,w/w)formula,the maximum encapsulation efficiency of inulin was 8.6%.The addition of the prebiotics did not significantly affect the microcapsule’s size,but significantly improved its thermal stability.When the dosage of inulin was 1.5%(w/v),the viability of microcapsules was the highest(63℃,5.58 Log CFU/g;72℃,7.85 Log CFU/g).After 60 days of storage at 4℃,the viability of L.GG in microcapsules hardly decreased,indicating that low temperature environment was more suitable for long-term storage of the microcapsules.Inulin-encapsulated probiotic microcapsules showed better gastrointestinal tolerance.In this chapter,a microcalorimeter was applied to monitor the heat produced by the growth of microencapsulated probiotics before and after gastric digestion and the resultant thermodynamic parameters.The results showed that the addition of inulin could accelerate the growth rate of L.GG in the logarithmic growth stage,making it reach the plateau in a shorter time,but had no significant effect on the overall heat generated during the whole period.3.To further verify the targeted release of L.GG microcapsules in the colon,Balb/c mice were fed with the microcapsules as supplements.The results showed that there were no significant changes in body weight gain and liver tissue morphology in mice with different dietary conditions.Feeding mice with empty microcapsules significantly reduced the contents of CAT and GSH in liver tissue,while microcapsules loaded with bacteria increased the contents of CAT and GSH in liver tissue to the original levels.L.GG-loaded microcapsules significantly changed the composition and diversity of intestinal flora in mice.At the phylum level,it increased the relative abundance of Firmicutes and Bacteroidetes.At the genus level,it increased the relative abundance of Lactobacillus,and decreased the relative abundance of Bacteroides.In conclusion,this study provides a theoretical basis and feasible scheme for probiotics-encapsulated system with high encapsulation efficiency,stability and colon-targeted delivery based on high efficiency vibration technology,which will help to promote the application of this technology and the formula developed in this study in functional foods. |
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