Flow cytometric assessment of Lactococcus lactis isolates viability after lyophilization

Lactococcus lactis strains tolerance to the lyophilization process is one of the criteria used during the selection of starter cultures in cheese production. The viability of L. lactis strains isolated from silage and milk after the lyophilization process was evaluated in the present study by flow cytometry and cell plate counting. The LIVE/DEAD BacLight TM kit, which contains the dyes SYTO 9 and propidium iodide, was used to stain the cells for flow cytometry analysis. The dried cells were also plated on M17 agar and incubated at 30 °C for 24 hours. The strain L. lactis LBU.1, isolated from buffalo milk, showed the highest tolerance to the lyophilization process, according to flow cytometry and cell plate counting. Although the strains of L. lactis isolated from silage were not the most resistant to the lyophilization process, it is noteworthy that, compared to strains isolated from conventional sources such as cow and goat milk, L. lactis strains from silage showed higher tolerance to the lyophilization process.