Microbicidal action of photoirradiated aqueous extracts from wine lees

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 (·OH) and hydrogen peroxide (H₂O₂). 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 μM ·OH and 600 μM H₂O₂ were generated in photoirradiated WLE for 20 min. Because the bactericidal activity of photoirradiated WLE was abolished by ·OH scavengers, ROS, especially highly oxidative ·OH, 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.