Preparation And Application Of Lactobacillus Casei Microcapsules

Probiotics benefit the human health by improving intestinal microbial balance of the host.However,probiotics are vulnerable to the adverse environment such as gastric acid and bile salts of stomach,resulting in few probiotics survive during their passage through the upper gastro-intestinal tract,which affects the survivability and effective delivery of probiotics to their target sites in the intestine.Microencapsulation could confer protection to probiotic against harsh environment effectively.Selection of the suitable wall material is crucial to the preparation of probiotic microcapsules.The protective effect of probiotic microcapsules prepared by single wall material is limited.Incorporation other polymers could serve as a potential strategy in reinforcing its protection properties.In this paper,polyelectrolyte hydrogels formed by positive charges carried by chitosan(CS)negative charges carried by gellan gum(GG)could be used to prepare Lactobacillus casei L61 microcapsules.The preparation process was optimized to improve the encapsulation effect.On the above basis,the tolerance of L.casei L61 microcapsules to acid,heat and bile salts and the storage stability were studied.In addition,L.casei L61 microcapsules were characterized by scanning electron microscopy(SEM)? X-ray diffraction(XRD)? fourier transform infrared spectroscopy(FTIR)and differential scanning calorimetry(DSC).Finally,L.casei L61 microcapsules were incorporated in pomegranate juice,orange juice,yoghurt and milk beverage to study storage stability.The results were shown as follows:1.With viable counts and encapsulation yield as response value,the single factor test and response surface method were employed to optimize the preparation process of L.casei L61 microcapsules.The optimum conditions were: chitosan concentration 0.51%,pH 4.5,gellan gum concentration 1.52%,cell suspension/GG 1:6,L.casei-GG mixture)/CS 1:4,stirring time 40 min,corresponding to a high viable count 9.90 log CFU/g,and encapsulation yield 89.20%,respectively.The GG was used to encapsulate CS-GG microcapsules,the viable count of of the GG-CS-GG L.casei L61 microcapsules was 9.89 log CFU/g.2.The tolerance of single and double-layer L.casei L61 microcapsules to gastric juice(pH 1.2 and 2.0),bile salts(1% and 2%)and heat(55 °C,60 °C,65 °C)were studied.And storage stability of single and double-layer L.casei L61 microcapsules at room temperature,4°C and-18°C were evaluated.The results demonstrated that encapsulation system improved the tolerance of L.casei L61 to simulated gastric juice,bile salts and heat significantly.The double-layer microcapsules showed a better protection effect than the singlelayer microcapsules.The storage test results showed that the single and doublelayer L.casei L61 microcapsules showed good stability during storage at-18 °C for 28 days,the viable counts of them only decreased by 0.26 log and 0.16 log CFU/g,respectively.After treated with SGF and SIF for 2 hours,the survival of L.casei L61 encapsulated in single and double-layer microcapsules increased by 31.2% and 43.5% compared to that of the control group,respectively,indicating that GG-CS and GG-CS-GG beads have a significant protective effect on L.casei L61.The release of L.casei L61 encapsulated in single and double-layer microcapsules reached the maximum level after exposure to SIF for 90 min.3.The structure of L.casei L61 microcapsules was characterized by SEM,XRD,FTIR and TG.The surface of wet CS-GG gel beads prepared were spherical and smooth.After vacuum drying,all formulated beads appeared “crumpled” and irregular in shape.It was observed by SEM that L.casei L61 trapped within the polymeric matrix homogeneously.More compact morphology was observed in GG-CS-GG beads compared to single-layer one.It was found by FTIR,XRD and TG that the hydrogen bond formed between CS and GG was the main binding force of L.casei L61 microcapsules,and the microcapsules formed enhanced thermal stability.4.The application study of L.casei L61 microcapsules showed that the viable counts of free and encapsulated L.casei L61 in pomegranate juice,orange juice,milk beverage and yogurt decreased at 4°C and room temperature.There was a maximum drop in the number of free viable cells,while minimal decline was observed in double-layer L.casei L61 microcapsules.The effective encapsulation system could significantly protect probiotic activity and prolong storage period of food.The preparation process of L.casei L61 microcapsules was optimized,and the microscopic morphology and structure were characterized.Its tolerance and stability to adverse environment were improved,which provided a technical reference for the preparation and application of probiotic microcapsules.