Viability of Lactobacillus plantarum encapsulated with poly-γ-glutamic acid produced by Bacillus sp. SJ-10 during freeze-drying and in an in vitro gastrointestinal model

In the present study, the probiotic Lactobacillus plantarum was encapsulated with 0.1%, 0.25%, or 0.5% 400-kDa poly-gamma-glutamic acid (gamma-PGA(400)) produced by Bacillus sp. SJ-10. The viability of the encapsulated cells was assessed under various stress conditions that are common to the processing and ingestion of probiotics, such as freeze-drying, exposure to simulated gastric juice (SGJ), and exposure to bile salt. During freeze-drying to make powder, L. plantarum levels decreased by 1.50 log colony forming units (CFU)/ml without encapsulation. When encapsulated with 0.5% gamma-PGA(400) under the same conditions, L. plantarum levels decreased by 0.19 log CFU/ml. In the SGJ condition (pH 2), all L. plantarum bacteria died within 1 h without encapsulation but exhibited the highest viability (decrease of 0.30 log CFU/ml) when encapsulated with 0.5% gamma-PGA(400). All groups had a high survival rate in the bile salt condition (pH 5.9). In the intestinal adhesion test with Caco-2 cells, the highest rate of adherence was 35.9% when the cells were encapsulated with 0.25% gamma-PGA(400). The present findings suggest that gamma-PGA(400) as an encapsulating material increases the viability of L. plantarum under various stress conditions.