Chemical composition and antimicrobial activity of three essential oils from Curcuma wenyujin

Curcuma wenyujin is a traditional medicinal plant in China. The non-steamed rhizomes, steamed rhizomes and steamed roots of this plant are used as herbal medicines in three clinics, namely Pian-jiang-huang (PJH), Wen-e-zhu (WEZ), and Wen-yu-jin (WYJ), and are officially listed in the Chinese Pharmacopoeia. The purpose of this study was to conduct a comparative analysis of the three essential oils extracted from the C. wenyujin rhizomes and roots using GC-MS, and in doing so thirty compounds were identified. Principal component analysis (PCA) effectively distinguished the samples taken from the three different groups. Monoterpenoids, including camphene, linalool, camphor, isoborneol, borneol and eucalyptol, were characteristic components of the PJH oil, while beta-elemene, beta-elemenone, gamma-elemene and delta-elemene were typical components of the WEZ oil, and propanenitrile, caryophyllene oxide, (-)-caryophyllene, germacrene B, pogostol and alpha-humulene were representative ingredients of the WYJ oil. The ratio of sesquiterpenoids to monoterpenoids in PJH, WEZ, and WYJ were 2:1, 5:1 and 7:1, respectively. The antimicrobial activities of the three essential oils and of the six main ingredients were tested against two bacterial and one fungal strains using agar diffusion and broth dilution methods. The essential oil of PJH was shown to present a higher antimicrobial activity than that of WEZ and WYJ. Based on the Partial Least Square Model (PLS), the correlation between the antimicrobial activity of the tested oils and the identified chemical components was discussed and potential components of the antimicrobial activity were predicted according to Variable Importance in the Project (VIP) Value. The tested monoterpenes eucalyptol and isoborneol demonstrated a higher inhibitory activity than the sesquiterpenes germacrone, curdione and beta-elemene. Therefore, the potent inhibitory effect of the PJH oil might be attributed to its higher content of monoterpenes. The MIC values for the essential oils and their ingredients ranged from 62.5 to 500 microg/mL.