Effect of carbon dioxide on exopolysaccharide production and survival of Bifidobacterium bifidum after freeze-drying

Introduction: Bifidobacteria are particularly sensitive to oxygen [1], there are well-documented in studies on their protection against to oxygen toxicity in fermentation process. However the deoxygenation by inert gas (i.e., nitrogen, carbon dioxide and hydrogen) caused decreases in oxido-reduction potential and improved survival ability of B. bifidum after drying and in storage [2]. It is noted that carbon dioxide can not only maintain the anaerobic growth conditions of Bifidobacterium longum JBL05 but also enhance the cell concentrations and the exopolysaccharide (EPS) secretion [1]. Moreover, EPS was known as a factor in the B. bifidum protection in freeze-drying [3].
Objectives: The deoxygenation by inert gas (i.e., CO2 and N2) to reduce the redox potential in B. bifidum THT0101 culture aimed at (i) improving the survival of cells during freeze-drying and (ii) increasing the EPS secretion during the fermentation.
Methods and Results: ?B. bifidum THT0101 were cultured in untreated, as controls, and in the modified using gas treatments prior to the onset of culture. After culturing and freeze-drying, the concentration of exopolysaccharide and the viability of B.bifidum THT0101 were evaluated.
The results showed that the increase of viability (5.06-15.6 folds compared to controls) was associated with the duration of degassing by CO2. Besides, the CO2 treatments led to decreased redox potential. The concentration of exopolysaccharide increased related to the rate of used CO2 and B. bifidum THT 0101 survival.
Conclusions: ?The rate of CO2 treatment in culture led to the increase of exopolysaccharide concentration and B.bifidum THT0101 survival.