Assessing the viability of three Lactobacillus bacterial species protected in the cryoprotectants containing whey and maltodextrin during freeze-drying process.

Abstract

Freeze-drying of bacteria associates with different stresses such as osmotic pressure, temperature and oxidation, and decreases bacterial viability, which seem to reduce by applying cryoprotectants. The present study evaluated the effect of four cryoprotectants on decreasing the stress caused by freeze-drying process among three Lactobacillus species. Additionally, it highlighted the use of whey and maltodextrin as a substitute for peptone and sucrose in cryoprotectants respectively. The viability of lactobacilli was measured after freeze-drying, 1 month of storage at 25 and 4°C. Based on the results, the viability rate of bacteria in protectants during freeze-drying stage was dependent on their strains. The best viability of Lacticaseibacillus rhamnosus GG and Ligilactobacillus salivarius 20687 was, respectively, observed in the protectants containing sucrose and whey, while Lactiplantibacillus plantarum NRRL B-14768 viability was equal in all protectants. The number of live bacteria reduced significantly by storing bacteria for 1 month at 25°C compared to the 4°C storage. During the storage period, the viability of L. salivarius improved by adding sucrose in protectant. Due to the positive effect of whey and sucrose in the drying and storage stage, on bacterial viability, the protectant consisting of whey and sucrose is suggested for all of the species under study.