Soybean Dregs Cellulose–Chitosan Microcapsules Enhance Lacticaseibacillus rhamnosus 6151 Delivery and Mitigate Loperamide-Induced Constipation in Mice

Free probiotic cells are vulnerable to environmental and gastrointestinal stresses, which limits their functional efficacy and highlights the need for effective food-grade delivery systems. In this study, cellulose–chitosan microcapsules containing Lacticaseibacillus rhamnosus CICC 6151 ( L. rhamnosus 6151) were prepared using cellulose extracted from soybean dregs, Pueraria residue, Astragalus residue, and pomegranate peel. Among the four formulations, the soybean dregs cellulose-based formulation showed the highest encapsulation efficiency (51.3%), compared with 44.0%, 45.8%, and 42.3% for the other formulations, and was selected for in vivo evaluation. Free L. rhamnosus 6151 reached the stationary phase at approximately 12 h, whereas the encapsulated formulations reached the stationary phase after 19 h. In a loperamide-induced constipation mouse model, the selected microcapsule restored body weight and food intake to 92.22% and 93.94% of the blank control level, respectively, compared with 89.76% and 88.13% in the free-bacteria group and 88.47% and 86.98% in the carrier group. The microcapsule also improved constipation-related phenotypes, alleviated intestinal and liver histopathological injury, modulated colonic inflammatory mediators and serum neuropeptide-related indicators, and was associated with altered gut microbiota profiles. These findings suggest that soybean dregs-derived cellulose is a promising food-grade carrier and that the corresponding cellulose–chitosan microcapsule holds great potential to support the in vivo physiological efficacy of L. rhamnosus 6151 in alleviating constipation-associated symptoms.