The present study provides valuable data that the herbal water byproduct of Japanese peppermint, produced during the steam distillation extraction of an essential oil, can be utilized as an antibacterial agent. The major ingredient in the herbal water from Japanese peppermint 'Hokuto' was menthol, with a concentration close to its water solubility. The herbal water produced showed excellent antibacterial efficacy against typical gram-negative and gram-positive bacterial strains of Escherichia coli and Staphylococcus aureus, respectively, and the antibacterial efficacy was maintained even when the herbal water was diluted up to an appropriate concentration of 50%. The efficacy of the herbal water against E. coli was higher than that against S. aureus, which is likely because of the difference in the efficacy of menthol against these two different bacterial strains. The excellent antibacterial efficacy of the herbal water is mainly attributed to the function of menthol, while other trace ingredients also contributed to the antibacterial efficacy. The Japanese peppermint herbal water byproduct, generally treated as industrial waste and disposed, can be easily commercialized as an antibacterial agent if efforts are made to maintain a constant menthol concentration throughout the steam distillation essential oil extraction process.
Keywords: Japanese peppermint; antibacterial agent; herbal water; hito.