Chemical Composition and Antimicrobial Activity of the Essential Oils Extracted by Microwave-Assisted Hydrodistillation from the Flowers of Two Plumeria Species

Abstract

Microwave-assisted hydrodistillation (MAHD) was applied to obtain essential oils from the fresh flowers of Plumeria rubra Linn (PRL) and Plumeria rubra Linn var. acutifolia (PRLA) cultivated in China, which were subsequently analyzed via gas chromatography with flame ionization detection and gas chromatography with mass spectrometry. The essential oils were assessed for their antimicrobial activity. A variation of the chemical composition attributed to varieties was revealed. The essential oil of PRLA was found to have a high content of carboxylic acids (59.7%) with n-hexadecanoic acid (35.8%) and n-tetradecanoic acid (11.2%) as main components. Whereas, the PRL oil was characterized by high hydrocarbon content (38.6%), in which 9-hexacosene (14.6%) was found to be the major constituent. All essential oils possessed antimicrobial activity especially against five bacteria with diameter of inhibition zone (DD) and minimum inhibitory concentrations (MIC) values in the range of 6.8 to 21.3 mm and 2.8 to 46.5 mg/mL, respectively.

Keywords:

• Antimicrobial activity
• Essential oil
• Microwave-assisted hydrodistillation
• Plumeria rubra Linn
• Plumeria rubra Linn var. acutifolia

Acknowledgments

This research was supported by Science and Technology Planning Project of Guangdong Province, China (Grant No.2011B020314011), Natural Science Foundation of Guangdong Province, China (Grant No. S2011010004004), and Science and Technology Planning Project of Zhaoqing city, Guangdong Province, China (Grant No. 2011C005).

Notes

^a RI: retention indices relative to n-alkanes (C ₈–C ₂₇) on the DB-5column.

^b MS: mass spectrum.

^c -: trace.

^d CoI, coinjection with an authentic sample.

^a diameter of zone of inhibition (mm) including disc (6 mm) impregnated with 300 µg/disk.

^b Values are given as mg/mL for essential oils and µg/mL for Gentamycin.