ABSTRACT
Essential oils have been widely used in antimicrobial, antiviral, antiparasitical, insecticidal, medical, and cosmetic applications (Bakkali et al. 2008). Cymbopogon species are well known as a source of commercially valuable compounds, such as geraniol, geranyl acetate, citral (neral and geranial), citronellal, piperitone, eugenol, etc. (Shahi and Tava 1993). Bioactivity of Cymbopogon species such as lemongrass (C. citratus), Indian lemongrass (C. flexuosus), Indian palmarosa (C. martinii), Java citronella (C. winterianus), and Ceylon citronella (C. nardus) has been reported. Essential oils from Cymbopogon species and their components are known for their antimicrobial (de Billerbeck et al. 2001; Pattnaik et al. 1995a; Pattnaik et al. 1995b) and antioxidant activities (Hierro et al. 2004; Ruberto and Baratta 2000; Lertsatittanakorn et al. 2006). Bioactivity of the same essential oils may be markedly different when using different strains of the same microorganism and different sources
6.1 Introduction .......................................................................................................................... 167 6.2 Factors Affecting Antimicrobial Activity of Essential Oils ................................................. 168
6.2.1 Solubilizing Agents ................................................................................................... 168 6.2.2 Type of Organism ..................................................................................................... 169
6.2.2.1 Gram-Positive Bacteria .............................................................................. 169 6.2.2.2 Gram-Negative Bacteria ............................................................................ 169 6.2.2.3 Mould and Yeast ........................................................................................ 169
6.2.3 The Correlation between Oil Components and Activity .......................................... 169 6.2.4 Methods Commonly Used for Antimicrobial Assessment of Essential Oil ............. 170
6.2.4.1 The Serial Broth Dilution Method ............................................................. 170 6.2.4.2 The Agar Diffusion Method ...................................................................... 170 6.2.4.3 Vapor Contact Assay .................................................................................. 170
6.3 In Vitro Antioxidant Activity of Some Cymbopogon Species and Their Major Components .......................................................................................................................... 178 6.3.1 Factors Affecting Antioxidant Activity .................................................................... 178
6.3.1.1 Choice of Oxidizable Substrate and End-Product Evaluation ................... 178 6.3.1.2 Media ......................................................................................................... 178 6.3.1.3 Oxidation Conditions ................................................................................. 179 6.3.1.4 Methods Commonly Used for Testing Antioxidant Activity of
Essential Oils ............................................................................................. 180 6.4 Summary .............................................................................................................................. 180 References ...................................................................................................................................... 181
of essential oils. According to Oussalah et al. (2006), the major constituents of lemongrass oil are citral (77%) and limonene (8.5%); Indian lemongrass has citral (77%); palmarosa has geraniol (80%) and gerany1 acetate (8.6%) as main constituents; Java citronella oil contains citronellal (34%), geraniol (21.5%), and citronellol (11.5%) as major components; and Ceylon citronella oil contains geraniol (19.1%), limonene (9.9%), and camphene (9.0%). Since the oils are poorly soluble in water, many factors affect the results of their activities, for example, oil solubilizers, vehicles, method of testing, etc. Therefore, this chapter reviews the common methods of testing antimicrobial and antioxidant activities of some Cymbopogon species and their major components, as well as factors affecting their activities.
