Several plants contain essential oils, however, parts of plants, which serve as the major source of essential oil can be different. Those include roots, peels, leaves, seeds, fruits, barks, and so on. Plant essential oils are usually the complex mixture of natural compounds, both polar and nonpolar compound. Dominant compounds in various essential oils are presented in Table. In general, the constituents in essential oils are terpenes (monoterpenes and sesquerpenes), aromatic compounds (aldehyde, alcohol, phenol, methoxy derivative, and so on), and terpenoids (isoprenoids). Compounds and aroma of essential oils can be divided into 2 major groups: terpene hydrocarbons and oxygenated compounds.
| Parts | Plants |
|---|---|
| Leaves | Basil, bay leaf, cinnamon, common sage, eucalyptus, lemon grass, citronella, melaleuca, mint, oregano, patchouli, peppermint, pine, rosemary, spearmint, tea tree, thyme, wintergreen, kaffir lime, laurel, savory, tarragon, cajuput, lantana, lemon myrtle, lemon teatree, niaouli, may chang, petitgrain, laurel, cypress |
| Seeds | Almond, anise, cardamom, caraway, carrot celery, coriander, cumin, nutmeg, parsley, fennel |
| Wood | Amyris, atlas cedarwood, himalayan cedarwood, camphor, rosewood, sandalwood, myrtle, guaiac wood |
| Bark | Cassia, cinnamon, sassafras, katrafay |
| Berries | Allspice, juniper |
| Resin | Frankincense, myrrh |
| Flowers | Blue tansy, chamomile, clary sage, clove, cumin, geranium, helichrysum hyssop, jasmine, lavender, manuka, marjoram, orange, rose, baccharises, palmarosa, patchouli, rhododendron anthopogon, rosalina, ajowan, ylang-ylang, marjoram sylvestris, tarragon, immortelle, neroli |
| Peel | Bergamot, grapefruit, kaffir lime, lemon, lime, orange, tangerine, mandarin |
| Root | Ginger, plai, turmeric, valerian, vetiver, spikenard, angelica |
| Fruits | Xanthoxylum, nutmeg, black pepper |
Essential oils can be extracted from several plants with different parts by various extraction methods. The manufacturing of essential oils, and the method used for essential oil extraction are normally dependent on botanical material used. State and form of material is another factor used for consideration. Extraction method is one of prime factors that determine the quality of essential oil. Inappropriate extraction procedure can lead to the damage or alter action of chemical signature of essential oil. This results in the loss in bioactivity and natural characteristics. For severe case, discoloration, off-odor/flavor as well as physical change such as the increased viscosity can occur. Those changes in extracted essential oil must be avoided. Extraction of essential oils can be carried out by various means
| Extraction methods | Plants | References |
|---|---|---|
| Solvent extraction – Solvent | sage (Salvia officinalis), apiaceae (Ptychotis verticillata), chasteberry (Vitexagnuscastus L.), lemon(Citrus x limon) | Durling and others (2007); Matsingou and others (2003); El Ouariachi and others (2011); Sarikurkcu and others (2009); Koshima and others (2012) |
| – Supercritical CO2 | rosemary (Rosmarinus officinalis), fennel(Foeniculum vulgare), anise (Pimpinella anisum), cumin seed (Cuminum cyminum), sage (Salvia officinalis), lemon (Citrus x limon), carrot fruit (Daucus carrota L.), marjoram (Majorana hortensis Moench), catnip (Nepeta cataria L.), oregano (Origanum vulgare L.), lavender (Lavandula angustifolia Mill), thyme (Thymus vulgaris L.), hyssop (Hyssopus officinalis L.), anise hyssop (Lophantus anisatus Benth), patchouli (Pogostemon cablin), cumin (Cuminum cyminum), clove (Eugenia caryophyllata), coriander (Coriandrum sativum L.), chamomile (Matricaria chamomilla), baccharises (Baccharis uncinella, Baccharis anomala, and Baccharis dentata) | Pereira and Meireles (2007); Reverchon and Senatore (1992); Eikani and others (1999);Djarmati and others (1991); Gironi and Maschietti (2008); Glišić and others (2007); Dapkevicius and others (1998); Donelian and others (2009); Li and others (2009); Guan and others (2007); Mhemdi and others (2011); Araus and others (2009); Xavier and others (2011) |
| – Subcritical water | fructus amomi, marjoram (Origanum majorana), olive (Olea europaea), coriander seeds (Coriandrum sativum L.) | Deng and others (2005); Jimenez-Carmona and others (1999); Amarni and Kadi (2010); Eikani and others (2007) |
| Distillation - Steam | rose-scented geranium (Pelargonium sp.), thyme (Thymus kotschyanus), germander (Teucrium orientale), rosemary (Rosmarinus officinalis), fennel (Foeniculum vulgare), anise (Pimpinella anisum), eucalyptus (Eucalyptus citriodora), basil (Ocimum basilicum L.), lavender (Lavandula dentata L.), patchouli (Pogostemon cablin), clove (Eugenia caryophyllata), orange (Citrus sinensis) | Babu and Kaul (2005); Sefidkon and others (1999); Yildirim and others (2004); Pereira and Meireles (2007); Rajeswara Rao and others (2003); Cassel and others (2009); Donelian and others (2009); Guan and others (2007); Farhat and others (2011) |
| – Hydrodistillation | rose-scented geranium (Pelargonium sp.), germander (Teucrium orientale), rosemary (Rosmarinus officinalis), lemon (Citrus x limon), oregano (Origanum vulgare L.), marjoram (Majorana hortensis Moench), catnip (Nepeta cataria L), lavender (Lavandula angustifolia Mill), hyssop (Hyssopus officinalis L.), anise hyssop (Lophantus anisatus Benth), sage (Salvia officinalis L), cumin (Cuminum cyminum), clove (Eugenia caryophyllata), caraway (Carum carvi), thyme (Thymus vulgaris L.), basil (Ocimum basilicum L.), garden mint (Mentha crispa L.) | Babu and Kaul (2005); Yildirim and others (2004); Reverchon and Senatore (1992); Ferhat and others (2007); Bayramoglu and others (2008); Dapkevicius and others (1998); Li and others (2009); Guan and others (2007); Farhat and others (2010); Gavahian and others (2012) |
| – Hydrodiffusion | orange (Citrus sinensis), rosemary leaves (Rosmarinus officinalis) | Farhat and others (2011); Bousbia and others (2009) |
| Solvent-free microwave | oregano (Origanum vulgare L.), fragrant fern (Dryopteris fragrans), rosemary (Rosmarinus officinalis), caraway (Carum carvi), 5 flavor berry (Schisandra chinensis), cumin (Cuminum cyminum L.), cardamom (Elletaria cardamomum L.), basil (Ocimum basilicum L.), garden mint (Mentha crispa L.), thyme (Thymus vulgaris L.), sea buckthorn (Hippophae rhamnoides L.), spearmint (Mentha spicata L.), pennyroyal (Mentha pulegium L.) | Bayramoglu and others (2008); Li and others (2012); Okoh and others (2010); Farhat and others (2010); Ma and others (2012); Wang and others (2006); Lucchesi and others (2007); Lucchesi and others (2004); Michel and others (2011); Vian and others (2008) |
| Combination methods - Solvent + Steam | cumin (Cuminum cyminum), tobacco (Nicotiana tabacum) | Li and others (2009), Zhang and others (2012) |
Essential oils from plants have been known to act as natural additives, for example, antimicrobial agents, antioxidant, and so on. Their activities vary with source of plants, chemical composition, extraction methods, and so on. Due to the unique smell associated with the volatiles, this may limit the use of essential oil in some foods since it may alter the typical smell/flavor of foods.
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