Morphology of Etlingera species The genus Etlingera belonging to Zingiberaceae family consists of more than 100 species. They are perennial herbs mainly grown in perhumid forest (Poulsen, 2007). The leafy shoots of some of the Etlingera species can be up to eight m tall and the bases of these shoots are so stout as to seem almost woody. Many of the Etlingera species grow as clumps of leafy shoots, while others have such long creeping rhizomes that each of their leafy shoots can be more than a meter apart. True, Etlingera is characterized by its unique and distinctive flowers which have exceptional ornamental value. The inflorescence shoots are found short and do not emerge from the ground. The flowers are characterized with prominent bright red petal-like structures (labella) radiating outward, with the flower tubes and ovaries being below ground level. The brightly colored flowers are thought to be pollinated by insects. Fruits ripen below ground, and the seeds are thought to be dispersed by wild pigs. These plants are very aromatic because of the high content of essential oil in its leaves, stems, flower, fruit and rhizomes.
Traditional application Plants of Etlingera have been used since ancient times as spice and vegetable as well as for medicinal purposes. More specialized uses of few species include perfume (rhizome of Etlingera baramensis), shampoo (fruit of Etlingera elatior and Etlingera pyramidosphaera) and spice (rhizome of Etlingera punica) (Chan et al., 2013). Several other species of Etlingera also have been used as medicine in the prevention and therapy of diseases (e.g. rheumatism: Etlingera foetens; jaundice, fever, urinary ailments: E. belalongensis; stomach-ache: E. pyramidosphaera; snake bite: Etlingera sessilanthera, diarrhea: E. pyramidosphaera).
ESSENTIAL OILS IN COMMERCIAL PREPARATIONS Several European countries have developed some essential oil-based industry in last few decades. Carvon, the principal constituent of the dill and caraway seeds EO, is currently marketed as Talent® in the Netherlands. The preparation is used to inhibit the growth of storage pathogens and to suppress sprouting of potatoes in the warehouse (Hartmans et al., 1995). Soil Technologies Corporation (USA) has developed two natural products named Fungastop™ and Armorex™ which are commercially available for the control of various plant diseases in agriculture. Eugenol based formulations (eugenol-Tween®; eugenolethoxylate) showed potent inhibitory effect against four apple pathogens (Phlyctema vagabunda, Penicillium expansum, Botrytis cinerea and Monilinia fructigena) and thus used in post-harvest disease management of apple fruit (Amiri et al., 2008). Cinnamite™ (cinnamon), Valero™ (rosemary), Promax™ (thymus) and several other essential oil based pesticides are already commercially available (Prakash et al., 2015). EOs or their components (α-bisabolol, geraniol, elemene, d-limonene, diallyl trisulfide (DATS) and Eucalyptol) have been shown to exhibit cancer suppressive activity against glioma, colon cancer, gastric cancer, human liver tumor, pulmonary tumors, breast cancer, leukemia and others (De Angelis, 2001). Essential oils rich in terpinolene and/or eugenol have shown antioxidative activity against low density lipoprotein (LDL) oxidation thereby reducing the chance of atherosclerosis (Edris, 2007). Essential oils and their components are exploited for antibacterial properties in diverse commercial products as dental root canal sealers, antiseptics and feed supplements for lactating sows and weaned piglets (Burt, 2004). A few preservatives containing EOs are already available in the market, such as DMC Natural base, which comprises 50% essential oils (Speranza and Corbo, 2010). Beside these, essential oil and their individual constituents exhibited antiviral, antimycotic, antiparasitic and insecticidal properties.
EXTRACTION PROCEDURES OF ESSENTIAL OIL Extraction of essential oils can be achieved by various methods such as distillation, solvent extraction, effleurage, aqueous infusion, cold or hot pressing, supercritical fluid extraction, solvent free microwave extraction (SFME) and phytonic process. The method of extraction is normally dependent on what type of botanical material is being used. It is the key step that determines the quality of the oil as wrongly executed extraction method can damage the oil and alter the chemical signature of the essential oil. Today, hydrodistillation (with a collecting solvent that is then removed under vacuum) and steam distillation are widely used for extracting essential oils from plants. Volatile components in these methods can be distilled at temperatures lower than their individual boiling points and are easily separated from condensed water. Losses of some volatile compounds, low extraction efficiency, degradation of unsaturated or ester compounds of these widely used conventional methods have led to the consideration of the use of new "green" technique in essential oil extraction, which typically use less solvent and energy, such as supercritical fluids, ultrasound and microwave extraction. Berka-Zougali et al. (2012) describes a new innovative method, solvent free microwave extraction (SFME), which yields an essential oil with higher amounts of more valuable oxygenated compounds and allows substantial savings of costs, in terms of time, energy and plant material. However, essential oils obtained by SFME were quantitatively (yield) and qualitatively (aromatic profile) similar to those obtained by conventional method (hydro-distillation), while SFME is highly effective for reducing extraction time (30 min for SFME against 180 min for hydro-distillation) (Périno-Issartier et al., 2013). In Etlingera species, hydro-distillation technique is extensively used for extracting essential oils except from the flower of E. elatior, where steam distillation is used.