Influence of tea extract supplementation on bifidobacteria during soymilk fermentation

In this study, the influence of tea extract (TE) supplementation on the viability and membrane lipid compositions of Bifidobacterium was investigated. Fermented soymilk-tea (SMT) was produced by culturing selected bifidobacteria in soymilk supplemented with green or black TE. Culturability of four bacteria in the presence of various concentrations of TE was examined by plate count method. Bifidobacterium longum CSCC 5089 (BL5089) and B. longum CSCC 5022 (BL5022) were selected for further study based on their sensitivity to TE. The effect of TE supplementation on bacterial cell viability and integrity was assessed by flow cytometry in combination with fluorescence probes. Total lipids of bacterial cell were extracted using an enzyme-assistant extraction method. Fatty acids (FAs) were determined and quantified by GC–MS. Phospholipids (PLs) were separated by high performance thin-layer chromatography (HPTLC) and their relative abundances were determined by densitometry. Total tea phenolic content (TTP) in SMTs with varying concentrations of TE was quantified by HPLC. Among the four Bifidobacterium monitored, TE only significantly inhibited BL5089 (p < 0.01) in a dose-dependent manner, with minimum inhibition concentrations (MICs) determined to be 15.45 mg/mL TTP for green TE and 7.34 mg/mL TTP for black TE. Flow cytometric analysis revealed different staining patterns of cell populations and compromise in cell integrity upon exposure to high concentrations of TE. Results from GC–MS showed that unsaturated to saturated FA ratios significantly decreased (p < 0.01) in the membrane of BL5089 cells upon TE exposure. Separation of PLs by HPTLC showed dramatic alterations in phosphatidylcholine and phosphatidylglycerol contents due to TE treatment.