Rhodomyrtone, an Antimicrobial Acylphloroglucinol, in the Peel of Myrciaria dubia (Camu-camu)

Abstract

　Camu-camu (Myrciaria dubia) grows in the upstream Amazon, and has fruit with particularly high vitamin C content. Camu-camu fruit juice is used industrially in various processed foods; however, large amounts of residual peel and seed are discarded during juice production. We have been investigating functional constituents in the residual peel and seed as a potential resource of functional foods and food additives. We previously reported that the n-hexane extract of camu-camu peel has strong antimicrobial activity against Staphylococcus aureus. Our further investigation resulted in the isolation of rhodomyrtone, an acylphloroglucinol, and its structure was characterized by spectral data such as ¹H- and ¹³C-nuclear magnetic resonance (NMR). As reported previously, rhodomyrtone showed strong antimicrobial activities, and its minimum inhibitory concentration (MIC) values against six Gram-positive bacteria (0.78-1.56μg/mℓ for all bacteria) were lower than that of kanamycin (1.56-6.25μg/mℓ) used as a positive standard. Rhodomyrtone has attracted particular attention because it showed remarkable antimicrobial activities against methicillin-resistant S. aureus. The presence of rhodomyrtone in camu-camu peel may be significant for the camu-camu fruit industry.