Improving the survival of probiotics via in situ re-culture in calcium alginate gel beads

Despite the fact that probiotics have several health benefits for the host, low-pH gastric acid and bile salts threaten their survival. Here, a simple in situ re-culture approach using calcium alginate gel beads to improve the survival of probiotics was reported. After re-culture, Lacticaseibacillus rhamnosus GG (LGG) in both liquid and solid core gel beads (LCGB and SCGB) exhibited 100% gastric acid resistance, while the bile salt resistance varied from 59.38% to 92.39%. LGG in LCGB generally showed higher bile salt resistance than SCGB, and the resistance would be further improved with high initial bacterial concentration due to more extracellular polymer secretion. Besides, the re-cultured LGG in beads exhibited survival of 95.02%–96.05% in calcium-supplemented MRS broth within 6 weeks at 4 °C. Importantly, this storage did not threaten the aforementioned resistance of re-cultured LGG. The mechanism of LGG damage by gastric acid in LCGB includes 8 pathways, among which, 2 pathways including propanoate metabolism, phenylalanine, tyrosine and tryptophan biosynthesis are responsible for the improved resistance of re-cultured LGG. The unique re-culture strategy provides a powerful platform for microbial agents to smoothly enter the gut to serve host health.