Agricultural Engineering Today Extraction of Essential Oils - Need of the Hour Md. Shafiq Alam (LM-9341) and Sandhya (LM-10052) Department of Processing and Food Engineering, Punjab Agricultural University, Ludhiana, Punjab, INDIA E-mail: [email protected] ABSTRACT Essential oils are composed of a wide range of bioactive chemical compounds. These are volatile oils distilled from aromatic plant materials. The Indian essential oil industry manufactures rose, kewda, lemon grass oil, peppermint oil, oil of champa, citrus oil, palmarosa, mentha and celery oils. The extraction of highly delicate essential oils from plants remains a crucial step in all these applications. Different methods can be used for that purpose, e.g. hydro-distillation (HD), steam distillation and Solvent extraction. Losses of some volatile compounds, low extraction efficiency, degradation of unsaturated or ester compounds through thermal or hydrolytic effects and toxic solvent residue in the extract may be encountered using these extraction methods. These shortcomings have led to the consideration of the use of new innovative technique in essential oil extraction, which typically use less solvent and energy, such as supercritical fluids and microwave assisted extraction. Super critical fluid extraction has become a valid alternative, mainly, because the dissolving power of the extracting medium can be adjusted by regulating the pressure and temperature conditions. Solvent-free microwave extraction (SFME), a combination of microwave heating and dry distillation, is a newly developed technique. Key words: Aromatic plant, essential oil, extraction, SFME INTRODUCTION Rs. 386.48 crores in 2000-01(Singhal, 2003). Essential oils are the volatile oils distilled from Essential oils are extracted from different parts of aromatic plant material. Essential oils are contained plants. For instance, sweet marjoram oil comes from in the glands, sacs, veins and glandular hairs the flowering tops of the herb; ylang oil is extracted concentrated in different part of the plant. Essential from flowers. While cinnamon oil is obtained from oils are considered a secondary plant product—a leaves or bark, citrus oils such as orange, lime and compound that occurs in plants but is not critical lemon are squeezed from the peel of the fruits, and for the plant’s basic metabolic function. Any class vetiver is extracted from the roots; black pepper, of volatile odoriferous oils derived from raw materials celery oil is extracted from the seeds. The term of plant origin that impart the plant odour and other essential suggest that the oils contain the healing characteristics properties and found by processes essence of the plants. Also essential oils are volatile such as distillation, extraction, expression, and non-greasy unlike the vegetable oils. All the maceration etc is called essential oil (Anonymous, oils are antiseptic but some oil may be more than 2002). The Indian essential oil industry others. Just to name a few properties analgesic, manufactures rose, kewda, lemon grass oil, antibiotic, antiviral, aphrodisiac, diuretic, peppermint oil, oil of champa, citrus oil, palmarosa, expectorant, laxative, sedative, tonic, stimulant and mentha and celery oils. The major cities which have more. This paper discusses the different methods essential oil plants in India are Mumbai, Mysore and of oil extraction. Chennai. In last decade there has been considerable rise in essential oils. In 1990-91 the METHODS OF EXTRACTION export was 892 metric tonnes worth Rs. 31.99 The extraction of essential oils from plant material crores which increased to 4,400 metric tonnes worth can be achieved by a number of different methods. 24 Vol. 36(1), 2012 For each method there may be many variations and of the still and charring. Distillation is less labour refinements and the extraction may be conducted intensive and has a lower labour skill requirement under reduced pressure (vacuum), ambient than solvent extraction. Water distillation is probably pressure or excess pressure. The choice of the simplest and cheapest method of extracting extraction method will depend on the nature of the essential oils, but the quality of the oil has the material, the stability of the chemical components greatest potential to be modified due to the effects and the specification of the targeted product. of direct heating and the water contact (Weiss, 1997). The water distilled oils are commonly darker Expression: Expression is used exclusively for the in colour and have stronger still ‘off-note’ odours extraction of citrus oil from the fruit peel, because than oils produced by the other methods, and the chemical components of the oil are easily therefore tend to be of the lowest value. Some damaged by heat. Citrus oil production is now a components of the oil are more susceptible to major by-product process of the juice industry. Plant chemical change and oxygenated components tend material used is orange, lemon, grapefruit and to dissolve in the still water so their complete mandarin rind. The oils extracted using this method extraction is not possible. The water present in the have a relatively short shelf life. still must always be more than enough to last the Sponge extraction process: This method was duration of the distillation, other wise the plant developed in France and is still used for extraction material can over-heat and char. of Italian lemon and orange peel oil. Most citrus Steam distillation is the most common method of essences are extracted by means of expression. extracting essential oils. Steam distillation uses an The emulsion ejected from the oil sacs is soaked outside source of steam which pipes the steam into up by sponge which must be kept clean. After some the distillation unit, sometimes at high pressure. The time the contents of the sponge (oil + water) are steam passes through the aromatic material and squeezed into a pot and oil is decanted after some exits into the condenser. Steam distillation is done time (Bhatia, 2001). Oil recovery in this method is in a still. Fresh or sometimes dried, botanical around 50-75% but oil obtained has less shelf life material is placed in the plant chamber of the still, as conditions under which this process takes place and pressurized steam is generated in a separate are unhygienic. Also this method is labour intensive chamber and circulated through the plant material. and quality produced is not reproducible because The heat of the steam forces the tiny intercellular of the physical condition of the peel, ability of the pockets that hold the essential oils to open and operator and ambient temperature. release them. The temperature of the steam must Distillation: The vast majority of true essential oils be high enough to open the pouches, yet not so are produced by distillation. Distillation is still the high that it destroys the plants or burns the essential most economical method of extracting essential oil oils. As they are released, the tiny droplets of from spices and aromatic plant material. In this, essential oil evaporate and, together with the steam water is heated to produce steam, which carries molecules, travel through a tube into the still’s the most volatile chemical of the aromatic material condensation chamber. As the steam cools, it with it. The steam is then chilled (in a condenser) condenses into water. The essential oil forms a film and the resulting distillate is collected. The essential on the surface of the water. To separate the oil will normally float on top of the Hydrosol (the essential oil from the water, the film is then decanted distilled water component) and may be separated or skimmed off the top. The remaining water, a off. Hydro distillation is the simplest of the three byproduct of distillation, is called floral water, distillation methods. It achieves component isolation distillate, or hydrosol. It retains many of the according to the hydro solubility. The plant material therapeutic properties of the plant, making it is mixed directly with water in a still pot. A perforated valuable in skin care for facial mists and toners. The grid may be inserted above the base of the still pot main advantage of this process is that the amount to prevent the plant material settling on the bottom of steam and quality of steam can be controlled. and coming in direct contact with the heated base For flavour and fragrance industry, this is the 25 Agricultural Engineering Today standard method and cost effective compared to alcohol to separate the extract from the remaining supercritical fluid extraction. But it requires higher fat, which is then used to make soap. The fat mostly capital investment and higher level of technical skill used is lard and suet or a mixture of these (Kumar for fabrication, repair and maintenance. et al, 2001). The advantage of this process is that the extraction occurs at or below ambient Water and steam distillation is the best method for temperatures; hence there is no thermal distilling leafy materials, but doesn’t work well for degradation of the products. The extraction process woods, roots, seeds, etc. The plant material is utilizes the selectivity of the solvent and produces packed into the still pot sitting on a grill or perforated free flowing clear oil free of waxes. plate above the boiling water. The capacity of the still pot volume is reduced but it may be possible to Maceration is the process in which a certain quantity achieve a high packing density because the plant of purified beef suet mixed with purified lard, is put material is not suspended in the water. Higher oil into a clean metal or porcelain pan. This being yield can be obtained by this and also the effect of melted over a water bath with a temperature of 60- refluxing is minimized. It is a faster process so it is 70 OC maintained.