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

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Abstract
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.