Essential oils of Zingiber officinale var. rubrum Theilade and their antibacterial activities
Introduction
The genus Zingiber comprises about 85 species of herbs mostly distributed in East Asia and tropical Australia. Many of these are used as food and for traditional treatment of a variety of ailments (Sabulal et al., 2006). The essential oil composition of many of these herbs and their biological activities has been the subject of numerous previous studies (Bordoloi et al., 1999, Kami et al., 1972, Prakash et al., 2006, Sabulal et al., 2006, Sacchetti et al., 2005, Srivastava et al., 2002, Vahirua-Lechat et al., 1996, Zhannan et al., 2009). Phytochemical investigation of the rhizomes of several Zingiber sp. has revealed the presence of bioactive compounds, such as gingerols, which are antibacterial agents and shogaols (Kim et al., 2008, Park et al., 2008), diarylheptanoids (Zhou et al., 2007), phenylbutenoids (Jitoe, Masuda, & Nakatani, 1993), flavanoids (Dae, Han, Park, Jhon, & Seo, 2004), diterpenoids (Akiyama et al., 2006), and sesquiterpenoids (Dae & Seo, 2005).
Zingiber officinale var. rubrum Theilade is distributed mainly in Peninsular Malaysia, where it is known as halia bara. This herb is cultivated for its medicinal value. Its rhizome is a common ingredient in folk medicine (jamu) for treating stomach discomfort, tumours, relieving rheumatic pains, and as a post partum medicine (Ibrahim et al., 2008). Halia bara is morphologically similar to the common ginger (halia), but the rhizomes of this variant are smaller and more pungent, red on the outside with a yellow to pinkish cross-section, while the base of its leaf shoot is red. Unlike the common ginger, the petiole of halia bara is reddish when young, and the lip is scarlet red mottled with cream (Ibrahim et al., 2008). Little is known about the chemical constituents of this variety apart from a paper which reported the composition of the rhizome oil, which comprised mainly geranial, neral and geranyl acetate (Malek et al., 2005).
Infectious diseases are the leading cause of death worldwide. The emergence of multidrug resistant pathogens threatened the clinical efficacy of many existing antibiotics. This situation fuels the ongoing research to discover antimicrobial agents from natural origins (Eldeen, Van Heerden, & Van Staden, 2010). The methanol extract of Zingiber officinale rhizomes was reported to possess significant antibacterial activities against Escherichia coli, Salmonella enteriditis and Staphylococcus aureus during an in vitro investigation (Anbu Jeba Sunilson, Suraj, Rejitha, & Anandarajagopa, 2009). Hence, in continuation of our investigation on the essential oils of the Zingiberaceae family and their antimicrobial activities (Wong et al., 2006a, Wong et al., 2006b, Wong et al., 2006c, Ibrahim et al., 2009a, Ibrahim et al., 2009b), this prompted us to investigate the chemical composition of the leaf and rhizome oils of halia bara in detail, and utilise these oils in an attempt to explore alternative sources of antibacterial agents to treat multidrug resistant pathogens that cause infections and food poisoning, which to the knowledge of the authors have not been previously reported.
Section snippets
Plant material
Fresh leaves and rhizomes of halia bara were purchased from a market in Negeri Sembilan in September, 2009, and a voucher specimen (KU 0107) has been deposited with the herbarium of University of Malaya.
Solvents and chemicals
Pentane (GC–MS grade) and ethanol (analytical grade) were purchased from Merck (Germany) and Systerm (Malaysia), respectively. The homologous series of n-alkanes (C6–C30) was purchased from Dr. Ehrenstorfer Gmbh (Germany). Reference compounds were obtained from Sigma–Aldrich (USA).
Composition of the essential oils
Table 1 lists the oil constituents identified in the leaves and rhizomes of halia bara, the relative GC peak areas of these constituents, and their experimental retention indices on the HP-5 MS UI column.
Forty-six compounds, constituting 91.7% of the leaf oil of halia bara, were identified. Sesquiterpenoids (47.1%) and monoterpenoids (42.6%) were dominant, although these figures were largely due to β-caryophyllene (31.7%), geranial (13.1%), neral (9.8%) and caryophyllene oxide (6.3%). Other
Conclusions
The leaf oil and the oil from the rhizomes of halia bara differed in chemical composition, the former comprising mainly sesquiterpenoids and monoterpenoids in approximately equal amounts, while the latter was dominated by monoterpenoids. Antimicrobial assays of these oils have demonstrated that the Gram-positive bacteria in this study were more sensitive to both the oils compared to the Gram-negative bacteria. Toward the leaf oil, B. licheniformis and S. aureus were the most sensitive strains,
Acknowledgements
The authors acknowledge the research grant 5702031007 (Science Fund) provided by the French Government that has resulted in this article. The authors wish to thank Mr. Teo, Mr. Rafly and Mr. Din in assisting with the preparation of the voucher specimen, and Ms. Saripah in assisting with the GC–MS analysis.
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