Antibacterial Compounds from Rose Bengal‐Sensitized Photooxidation of β‐Caryophyllene

  The bactericidal activity of β‐caryophyllene photooxidized in acetonitrile was examined for 5 Gram‐positive and 4 Gram‐negative foodborne bacteria. The β‐caryophyllene (5 × 10 −3 M) was photooxidized in acetonitrile containing Rose Bengal (6.25 × 10 −4 M) for 24 h under fluorescent light. The antimicrobial activities of samples were determined by the agar‐disc diffusion method. Active compounds from the photooxidized β‐caryophyllene were isolated by silica gel open‐column chromatography in conjunction with recyclic high‐performance liquid chromatography (HPLC), and were identified by infrared spectroscopy, mass spectrometry, and nuclear magnetic resonance spectroscopy. The antimicrobial activity of the photooxidized β‐caryophyllene was strongly enhanced against Streptococcus aureus and Vibrio parahaemolyticus , relative to that of β‐caryophyllene, but was weakly enhanced against other tested bacteria. The photooxidized β‐caryophyllene contained 3 active compounds specific for these 2 bacteria, and the compounds were identified as 5‐α‐hydroxycaryophylla‐4(12),8(13)‐diene, 5‐α‐hydroxycaryophylla‐3(4),8(13)‐diene, and 5‐β‐hydroxycaryophylla‐3(4),8(13)‐diene. The efficacies of these compounds were similar, but the efficacy of 5‐β‐hydroxycaryophylla‐3(4),8(13)‐diene was slightly higher than that of the other 2 compounds. The results suggest that the antibacterial activities of β‐caryophyllene for S. aureus and V. parahaemolyticus could be enhanced by dye‐sensitized photooxidation, and the photooxidized β‐caryophyllene and the isolated individual compounds could be useful antimicrobial agents to control the growth of S. aureus and V. parahaemolyticus in certain food systems.