Food matrices and cell conditions influence survival of Lactobacillus rhamnosus GG under heat stresses and during storage

The present study evaluated impact of moisture content and cell conditions on survival of probiotic strain, Lactobacillus rhamnosus GG, under lethal heat stresses and during long-term storage using freeze-dried cells and oils as matrices. Viable cell counts of freeze-dried L. rhamnosus GG cells suspended in oils had only 1-log-reduction after 5 min at 80 °C and approximately 3-log-reduction after 20 min, while no or very few viable cells were recorded for freeze dried cells suspended in buffer and cultured cells in oils. Surprisingly, freeze-dried cells suspended in oils still contained 4.3 to 6.7 logCFU/ml after 5 min at 95 °C. Long-term storage study indicated that freeze-dried cells suspended in oils kept viable conditions for 4 months, and a loss of the viability was only 0.3 to 0.6 logCFU/ml. Viable cell counts of cultured cells suspended in oils were not present after 3 days to 3 months. These results clearly indicate that moisture and cell conditions have a great impact on survival of probiotics under severe heat stress in processing and during long-term storage. Combination of freeze-dried cells and oils as carrier provides beneficial options to preserve viability of probiotics in food processes and storage.