Abstract
Chlorophyll and its derivatives are potential natural sensitizers frequently applied in antimicrobial photodynamic therapy. Chlorophyll derivatives are formed naturally during tea processing, but they do not contribute to the color of tea infusions and thus are presumably left in the tea dregs. The present study aimed to investigate (i) the chlorophyll remnants in the pigments recovered from dregs of green and black teas and (ii) the antibacterial activity of pigments extracted from the tea dregs upon illumination using a light-emitting diode (LED) as the light source. Pigment analysis using high-performance liquid chromatography (HPLC) revealed the presence of main degradation products of chlorophylls, such as pheophytin and its epimers, pyropheophytin, and pheophorbides. In vitro assays demonstrated significant reductions in the number of viable bacteria in the presence of the pigments after 30 min of incubation with LED light irradiation. The descending order of bacterial susceptibility was Listeria monocytogenes > Staphylococcus aureus > Escherichia coli > Salmonella typhi. At an equivalent irradiation intensity, the blue and red LEDs could stimulate a comparable inactivation effect through photodynamic reactions. These findings demonstrated the valorization potential of tea dregs as a source of chlorophyll derivatives with visible light-induced antibacterial activity.
Highlights
In the midst of escalating public health concern over the global-scale spread of infectious diseases, antibiotic resistance, and issues related to energy crises and environmental problems, the task to combat microbial contamination has become increasingly challenging
Much research effort has been focused on the development of photodynamic inactivation technology that combines physical and chemical reactions to induce the death of targeted microorganisms, antimicrobial photodynamic therapy as a promising nonthermal disinfection technology. is novel therapy has been reported to offer significant breakthroughs such as rapid inactivation of pathogenic microorganisms, effective elimination of the resistant strains, and even the biofilm-producing bacteria, which are often resistant to treatments [1,2,3]
We found that the extraction of tea dregs using acetone resulted in a pale pellet, suggesting the attainment of pigment recovery. e pigments extracted from both green and black tea dregs exhibited comparable absorption spectra, with two obvious maxima at 410 and 665 nm, with several weak absorption signals at 475, 533, and 606 nm. e typical absorption spectra of the chlorophyll groups showed along the x- and y-axis electronic transitions within the pigment molecules (Figure 3(a)), with the weak Qx band near 550 nm and strong Qy band near 660 nm, whereas the intense Soret band in the blue region indicated overlapping region [25]
Summary
In the midst of escalating public health concern over the global-scale spread of infectious diseases, antibiotic resistance, and issues related to energy crises and environmental problems, the task to combat microbial contamination has become increasingly challenging. Much research effort has been focused on the development of photodynamic inactivation technology that combines physical and chemical reactions to induce the death of targeted microorganisms, antimicrobial photodynamic therapy as a promising nonthermal disinfection technology. Is novel therapy has been reported to offer significant breakthroughs such as rapid inactivation of pathogenic microorganisms, effective elimination of the resistant strains, and even the biofilm-producing bacteria, which are often resistant to treatments [1,2,3]. E three components in a typical photodynamic reaction are a photosensitizer, light, and oxygen. Photosensitizers are substances that can capture photon energy from the light and transfer them to other surrounding molecules. Energy released from the photosensitizer causes the formation of radicals from sensitive surrounding molecules, such as proteins, lipids, and oxygen [4]. Chlorophylls ( some of their derivatives) have been reported as promising candidates for natural sensitizers owing to their
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