Quality control of essential oil in Nepal

Essential oils are complex mixtures, constituted by terpenoid hydrocarbons, oxygenated terpenes and sesquiterpenes. They originate from the plant secondary metabolism and are responsible for their characteristic aroma. The various applications of essential oils account for the great interest in their study. Such applications may be found in the cosmetic industry, as ingredients of fragrances, decorative cosmetic, fine fragrances and flavouring, in the food industry, as aromas and flavours, in the pharmaceutical industry etc.

Essential oils are natural products that plants produce for their own needs other than nutrition (i.e. protection or attraction). In general, they are complex mixtures of organic compounds that give characteristic odour and flavour to the plants. They are mainly made up by monoterpenes and sesquiterpenes whose main metabolic pathway is through mevalonate leading to sesquiterpenes and from methyl-erythritol leading to monoterpenes. They are located in different parts of the plant. They can be found in the root such as that of the vetiver grass (Vetiveria zizanioides), in stems like that of peteribi wood (Cordia trichotoma) and incense, in leaves like in eucalyptus trees (Eucalyptus citriodora), citronella (Cymbopogon nardus), chinchilla (Tagetes minuta) and lemon grass (Cymbopogon citratus), in flowers like lavenders (Lavandula officinalis), in fruit like lemon, orange (Citrus spp.) and even in seeds as in the case of anise (Pimpinella Anisum), coriander (Coriandrum sativum) and pepper (Piper nigrum), among others (Baser, 2010). They can work as internal messengers, like defense substances or plant volatiles aimed at natural enemies but also to attract pollinating insects to their host.

Quality Control of Oil There are so many techniques use for quality control of essential oil. The main steps involved in control of essential oil contain size reduction, sieving, column chromatography, spray drying, standardization and crystallization. It seems to be reacting by heat, by the presence of air (oxygen) or moisture, catalyzed by exposure to light or by metals. For removal of these drawback. Each essential oil firstly remove metallic impurities, dry from moisture and clarified and then it can be stored in well-filled, tightly closed containers, at low temperature and protected from light. The oil can be dehydrated quite readily by the addition of anhydrous sodium sulphate, by thoroughly shaking, standing for overnight or 6-8 hours and filtration. Each oil of a compound or group of compounds has unique medicinal or specific property. They are also used as fragrance and flavoring compound in food, pan masala or synthetic juices. So it is necessary requirement to control the quality of product. The percentage of these constituents in the oil plays an important part in determining its quality. The quality and price of some oils are based on the percentage content of a single chemical component, so separation and measurement of individual components is very important. Analytical analysis has been widely done by gas chromatography (GC) and mass spectroscopy (MS). The apparatus by which the fractions and their percentage are determined is Gas Liquid Chromatographic unit (GLC). It is most widely used techniques. The analysis requires 1–5 g of plant essential oil in 80-90 minutes, including distillation.

For food or medicinal extracts TLC (Thin Layer Chromatography), HPLC (High Pressure Liquid Chromatography) and HPTLC (High Pressure Thin Layer Chromatography) techniques are being used. Identification of compounds employs a form of spectroscopy (mass, UV, IR, NMR) to indicate the molecular structure. Some property of compound like optical rotation, enantiomer, specific gravity and polarization are also play important role for the identification of compounds.