Intracellular osmoprotectant concentrations determine Propionibacterium freudenreichii survival during drying

Abstract

Propionibacterium freudenreichii is a beneficial bacterium widely used in food as a probiotic and as a cheese-ripening starter. In these different applications, it is produced, dried, and stored before being used. Both freeze-drying and spray-drying were considered for this purpose. Freeze-drying is a discontinuous process that is energy-consuming but that allows high cell survival. Spray-drying is a continuous process that is more energy-efficient but that can lead to massive bacterial death related to heat, osmotic, and oxidative stresses. We have shown that P. freudenreichii cultivated in hyperconcentrated rich media can be spraydried with limited bacterial death. However, the general stress tolerance conferred by this hyperosmotic constraint remained a black box. In this study, we modulated P. freudenreichii growth conditions and monitored both osmoprotectant accumulation and stress tolerance acquisition. Changing the ratio between the carbohydrates provided and non-protein nitrogen during growth under osmotic constraint modulated osmoprotectant accumulation. This, in turn, was correlated with P. freudenreichii tolerance towards different stresses, on the one hand, and towards freeze-drying and spray-drying, on the other. Surprisingly, trehalose accumulation correlated with spray-drying survival and glycine betaine accumulation with freeze-drying. This first report showing the ability to modulate the trehalose/GB ratio in osmoprotectants accumulated by a probiotic bacterium opens new perspectives for the optimization of probiotics production.

Effect of culturing lactic acid bacteria with varying skim milk concentration on bacteria survival during heat treatment

“…A recent study showed that supplementing Ca 2+ to the growth medium of LAB can increase the thermotolerance of cells as well as their survival after spray drying (Wang et al, 2020). Similar effects have been reported for Propionibacterium freudenreichii by adding lactose and NaCl during the cultivation of cells (Gaucher et al, 2020). Huang et al (2016a) utilized concentrated sweet whey as a 2-in-1 medium for both growth and spray drying of Lactobacillus casei BL23 and Propionibacterium freudenreichii ITG P20, and the results showed that bacterial population after growth and residual viability in spray-dried powder were both increased with the increase of the total solids of sweet whey from 5 wt% to 20 or 30 wt%.…”

“…The intrinsic stress tolerance of LAB is significantly affected by culture conditions used, including the composition of culture medium, temperature, pH, and oxygenation conditions (Dijkstra et al, 2014;Gaucher et al, 2020). A variety of modifications on culture medium have been attempted in the literature to improve the robustness of LAB towards environmental stresses.…”

Environmental Conditions Modulate the Protein Content and Immunomodulatory Activity of Extracellular Vesicles Produced by the Probiotic Propionibacterium freudenreichii

“…11 time), the pH of the extracellular medium at the end of stationary phase and cell viability after stress challenges (63,64).…”

Propionibacterium freudenreichii: General Characteristics and Probiotic Traits

“…A wide range of genetic and environmental optimizations have been conducted to improve these properties [6,29]. Moreover, some optimizations of the growth and processing conditions allowed the improvement of resistance towards storage and towards several industrial processes, such as freeze-drying and spray-drying [30][31][32][33].…”