Biofilm-like Lactobacillus rhamnosus probiotics encapsulated in alginate and carrageenan microcapsules exhibiting enhanced thermotolerance and freeze-drying resistance

Microcapsules containing high-density biofilm-like Lactobacillus rhamnosus probiotics, in place of planktonic cells, are developed in order to enhance the cell viability upon exposures to stresses commonly encountered during food lifecycle (i.e., heating, freeze-drying, refrigerated storage, and acid). The high-density (HD) capsules are prepared by in situ cultivation of the planktonic cells in the confined space of polysaccharide-based capsules (i.e., chitosan-coated alginate and carrageenan capsules). Compared to their planktonic counterparts, the HD capsules exhibit higher freeze-drying resistance (∼40×) and higher thermotolerance upon prolonged wet heat exposures at 60 and 70 C (∼12-8000×), but not at higher temperatures even for short exposures (i.e., 80 and 100 C). The enhanced viability of the HD capsules, however, is not observed during the refrigerated storage and exposure to the simulated gastric juice. The alginate capsules are superior to carrageenan owed to their better cell release profile in the simulated intestinal juice and storage viability.