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Identification of stressful conditions during fermentation and preservation for improving the stability of freeze-dried Lactobacillus salivarius BT621
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International audience. Lactobacillus salivarius has been gaining attention in recent years as a promising probiotic bacteria. L. salivarius BT621 has demonstrated its probiotic property, antimicrobial activity against bacterial species responsible of some common gastrointestinal infections, in both in vivo and in vitro studies. Despite these promising benefits, a high viability and long term stability of this bacteria are mandatory for being commercialized. The main goal of our work was to identify the fermentation conditions to be applied to improve survival and stability of L. salivarius BT621. We also aimed at selecting protective agents and storage conditions allowing a significant stability improvement.Fermentations were conducted in 2L fermenters in batch mode with control of pH, temperature and stirring rate. Stressful conditions were defined and compared to the standard production conditions (MRS type medium, 37°C, pH 5). We studied a large range of fermentation parameters (temperature, pH, neutralizing solution, harvest time) and medium compositions (carbon and nitrogen sources and concentrations, growth factors and reducing agents). The impact of fermentation conditions was evaluated on bacterial viability (plate counts method) before and after freeze-drying with different protective agents and during storage at variable water activities.Mild heat stress as well as the nature of the protective agents were main factors that enabled a 1 log improvement of L. salivarius BT621 viability after freeze-drying, a 3 log improvement after 4 week storage of the dried samples and a gain of stability of more than 50 %. Ongoing work on cells biophysical properties would help unravelling the markers of resistance.
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