Protective effect of crop by-products on Lactobacillus gasseri H87 during freeze-drying and storage

Appropriate cryoprotectants are critical components of effective probiotic preparations. Beneficial lactic acid bacteria can prevent or treat genitourinary tract infections. Here, we aimed to determine a suitable cryoprotectant combined with crop by-products to ensure the viability and pathogen suppression activity of Lactobacillus gasseri H87 for vaginal capsules that can help maintain the balance of vaginal microecology. Among the five selected cryoprotectants, 15% skim milk (SM) makes L. gasseri H87 survival rate of reaches 56.5%, effectively guaranteeing maximum bacteriocin production by minimizing bacterial cell damage. On the basis of 15% SM, further addition of 1% pomegranate peel extract (PPE) optimized the production of bacteriocin, resulting in the best bacteriostatic effect. After six months of lyophilized storage, L. gasseri H87 from vaginal capsules preserved with 15% SM + 1% PPE had an inhibitory zone of 16.45 mm against the indicator strain Lactobacillus iners. Both lyophilization and storage reduced the adhesion of L. gasseri H87, but the first subculture after 6 months fully restored adhesion under all conditions. These results suggest that skim milk combined with PPE can serve as a suitable cryoprotectant. Lyophilized L. gasseri H87 vaginal capsules have the potential for use in the pharmaceutical industry.