Our previous studies revealed that photo-irradiation of polyphenols could exert bactericidal action via reactive oxygen species (ROS). In the present study, the photo-irradiation-induced bactericidal activity of the aqueous extract from the residue of crushed grapes from winemaking was investigated in relation to ROS formation. Staphylococcus aureus suspended in the extract was irradiated with LED light at 400 nm. This solution killed the bacteria, and a 3-4 log and a >5-log reduction of the viable counts were observed within 10 and 20 min, respectively. LED light irradiation alone also killed the bacteria, but the viable counts were 2-4 log higher than those of the photo-irradiated extract. In contrast, almost no change occurred in the suspension without LED irradiation. When hydroxyl radical scavengers were added to the suspension, the bactericidal effect of the photo-irradiated extract was attenuated. Furthermore, electron spin resonance analysis demonstrated that hydroxyl radicals were generated by the photo-irradiation of the extract. The present study suggests that polyphenolic compounds in the extract exert bactericidal activity via hydroxyl radical formation upon photo-irradiation.
Our previous study revealed that aqueous extract of grape pomace obtained from a winemaking process could exert bactericidal action upon photo-irradiation via reactive oxygen species (ROS) formation. In the present study, we focused on chemical composition and prooxidative profile of the extract. Liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) analysis showed that polyphenolic compounds including catechin monomers, dimers, trimers, and polyphenolic glucosides were contained. The polyphenol rich fraction used for the LC-ESI-MS analysis generated hydrogen peroxide (H2O2) upon photo-irradiation possibly initiated by photo-oxidation of phenolic hydroxyl group. That is, reduction of dissolved oxygen by proton-coupled electron transferred from the photo-oxidized phenolic hydroxyl group would form H2O2. The resultant H2O2 was then photolyzed to generate hydroxyl radical (•OH). The prooxidative profile of the extract in terms of •OH generation pattern upon photo-irradiation was similar to that of grape seed extract (GSE) as an authentic polyphenol product and (+)-catechin as a pure polyphenolic compound, and in all the three samples •OH generation could be retained during photo-irradiation for at least a couple of hours. The prooxidant activity of the photo-irradiated extract indicated by •OH yield was more potent than that of the photo-irradiated GSE and (+)-catechin, and this was well reflected in their bactericidal activity in which the photo-irradiated extract could kill the bacteria more efficiently than did the photo-irradiated GSE and (+)-catechin.
Wine lees, a major waste product of winemaking, is a rich source of polyphenolic compounds. LED-light irradiation at 400-nm elicited microbicidal activity of aqueous extract from wine lees (WLE) against Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans, in addition to reactive oxygen species (ROS) formation, including hydroxyl radical (ÁOH) and hydrogen peroxide (H 2 O 2 ). Although treatment for 20 min of photoirradiation alone exerted bactericidal activity with a 2-to 3-log reduction, photoirradiated WLE for 20 min achieved a 5-log or greater reduction in viable S. aureus and P. aeruginosa cells. Regarding C. albicans, a 1-log reduction (90 % reduction) of viable cells was achieved by photoirradiated WLE for 40 min, whereas photoirradiation alone did not show any fungicidal effect. ROS analyses revealed that approximately 170 lM ÁOH and 600 lM H 2 O 2 were generated in photoirradiated WLE for 20 min. Because the bactericidal activity of photoirradiated WLE was abolished by ÁOH scavengers, ROS, especially highly oxidative ÁOH, may be responsible for the microbicidal activity of photoirradiated WLE. In addition to its microbicidal activity, WLE may act as an antioxidant as it exerted radical scavenging activity against 2,2-diphenyl-1-picrylhydrazyl, a stable free radical.
The annual production of grape worldwide amounts to almost 70 million tons, and around 80% is used for winemaking. The two major wastes from winemaking process, pomace and lees account for 20 and 7% of the grapes, respectively. They have been expected as a valuable resource to be recycled because they are rich in polyphenols. Polyphenols possess prooxidatve activity as well as antioxidative one just like a two sides of a coin. A typical example of the prooxidative activity is antibacterial activity of catechins. The activity is exerted through oxidation of phenolic hydroxyl moiety coulpled with reduction of dissolved oxygen leading to hydrogen peroxide (H2O2) generation. In addition, once the oxidation of phenolic hydroxyl moiety is augmented by photoirradiation, highly reactive hydroxyl radical (·OH) is generated. Accordingly, there have been several reports showing that photoirardiation of polyphenols exerts bactericidal activity via ·OH generation. This review focuses mainly on antimicrobial intervention by photoirradiation of grape pomace extract in relation to ·OH generation analyzed by an electron spin resonance-spin trapping method.
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