Tea extract render probiotic Lactobacillus helveticus more resistant to oxygen exposure through lipid modification mechanism
Résumé
Exposure to oxygen can cause a decrease in growth rates or a complete inhibition of growth of oxygen-sensitive probiotic bacteria. A recent study in our laboratory demonstrated that the growth of an oxygen-sensitive strain, Lactobacillus helveticus, was stimulated, under aerobic conditions, when the culture medium was enriched with green tea extracts (GTE). However, information on the mechanism by which GTE influenced the growth, in the presence of oxygen, of that strain is limited. In the present work, the effects of GTE concentrations (0 to 2000μg/mL) and exposure to oxygen on maximal populations of L. helveticus R0052 cells and bacterial lipids were evaluated using viable counts, infrared spectroscopy and gas chromatography analyses. Supplementation of the culture medium with 0 to 500μg/mL GTE did not have an effect on the populations reached under microaerophilic conditions and on bacterial lipid structure and composition. However, at 2000μg/mL GTE, high population levels were reached under microaerophilic conditions concomitant with an increase in lipid order and with important changes in fatty acid composition of the bacterial lipids. Interactions between GTE components and bacterial lipids were shown by spectroscopic results. Moreover, bacterial cells have adapted to the presence of 2000μg/mL GTE in the growth medium by changing their lipid composition. To the best of our knowledge, this work is the first to establish a relationship between the effects of GTE at 2000μg/mL on bacterial cell's lipids and a stimulation of growth under microaerophilic conditions of an oxygen-sensitive strain.