Photostability Study of New Photosensitizer from Dregs of Green Tea and its Antibacterial Adjustment against Escherichia coli ATCC 8739

The dregs of green teas have recently been investigated as a potential source of pigments which exhibits antibacterial effects via the photodynamic mechanism. The dregs contain chlorophyll derivatives and trace carotenoids, which can absorb visible lights and produce cytotoxic radicals. The present research was aimed to perform: (i) the photostability study of pigments extract from dregs of green teaunder the illumination of red LED (light-emitting diode) lamp, and (ii) the evaluation of photodynamic antibacterial activity against Escherichia coli ATCC 8739 upon the adjustment of either illumination time or sensitizer concentration. The pigments extract from the dregs was irradiated under a red LED lamp at 300 Pmol/m²s for 40 minutes while being periodically observed using UV-Visible spectrophotometer and high-performance liquid chromatography. The microbial assay was performed by positioning the mixture of photosensitizer and liquid culture of bacteria under the illumination of a red LED lampwith a series of incubation times (10, 20, 30, and 40 minutes) as well as sensitizer concentration (25, 50, 100, and 150 Pg/mL). The result showed that irradiation treatment with red LED altered pigments composition, in which the fractions of chlorophyll derivatives exhibited desirable photostability, while the carotenoids residue rapidly degraded. Thirty minutes illumination of bacterial culture with photosensitizer at 150 Pg/mL caused up to 0.79 log reduction of E. coli.