Super gastro-resistant microcapsules based on CaCO₃ nanocrystal buffered alginate/pectin composites for colon-targeted probiotic delivery: in vitro and in vivo evaluation

Encapsulation of probiotics using a polysaccharide-based formulation is becoming a common strategy to enhance the viability of probiotics. However, the hydrophilic nature of polysaccharide-based encapsulants may still cause the loss of probiotic activity during harsh processing and gastric digestion. In this study, Lactobacillus rhamnosus GG was successfully encapsulated into alginate/pectin composite hydrogel beads using the high-efficiency vibration technology (HEVT), which were further reinforced by CaCO₃ nanocrystals as antacid and freeze-dried into microcapsules. The structure, the physicochemical, encapsulation, and digestion properties of the beads were observed. The sample composed of a mass ratio of 9:1 alginate/pectin with CaCO₃ nanocrystals showed a significantly higher viability of 10.32 Log CFU/g. A maximum of 8.49 Log CFU/g of probiotics survived after harsh gastric digestion and were control-released in the colonic fluid. The formulation with CaCO₃ nanocrystals significantly improved the survival number compared to the alginate/pectin formulation. This can be attributed to the buffering properties of CaCO₃ on the gradual dissolution process and the simultaneous dication-induced egg-box crosslinking. Additionally, after being stored for 56 days, the viable numbers of encapsulated probiotics were more than 5.52 Log CFU/g. The results of animal tests indicated that feeding encapsulated probiotics significantly altered the composition of gut microbiota in mice. Overall, the optimized formulation and fabrication route show promise for direct utilization by the food industry. This study also confirmed the significance of antacid nanocrystals in the design of polysaccharide-based oral delivery system for probiotics.