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. Cassie, rose, orange, blossom more energy efficient. and violet flowers are generally treated by this process. The flowers are allowed to remain in the Extraction by Solvents melted fat from 12-48 hours and kept stirred. The It has already been pointed out that by distillation, contents of the pan are filtered and further quantities essential oils of high purity and very fine aroma can of fresh flowers are mixed with it. The process is be obtained. In a large number of cases this method repeated till the extraction media i.e., fat becomes does not produce satisfactory oils, because many fully saturated with perfume. The absolute or oil is unstable aromatic substances are destroyed by the recovered from the fat by treatment with alcohol. high temperature of the steam while in other cases, the quality of oil is poor. In view of these factors Extraction by Volatile Solvents solvent extraction method is used. The solvent used Essential oils can be extracted by using solvents may be volatile or non-volatile, the latter one again such as petroleum, ether, methanol, ethanol, sub-divided according to the conditions of benzene, hexane and is often used on fragile temperature during the process i.e. i) at normal material such as jasmine, hyacinth, narcissus and temperature – Effleurage and ii) with the application tuberose. Out of this petroleum, ether and benzene of heat- Maceration. Effleurage extraction is a very are generally used. The solvents are purified using labor-intensive way of extraction. Glass plates in a sulphuric acid. The extraction is carried out in frame (called a chassis) are covered with highly extractors, which are either stationary or mobile and purified and odorless vegetable or animal fat (about cylindrical in shape fitted with false bottoms over 12.6 mm thick) and the petals of the botanical matter which the raw materials are placed. They are (jasmine, tuberose and orange blossom) that are hermetically sealed and interconnected through being extracted are spread across it and pressed tubes. The solvent comes in direct contact of the in. The flowers are normally freshly picked before material and runs down slowly from one extractor so encased in their fatty bed. The petals remain in to another, until the flowers are exhausted and this greasy compound for a few days to allow the temperature is maintained around 50 0C. The essence to disperse into the compound, where the solvent is removed from the extractor and distilled. then depleted petals are removed and replaced with The product left behind in distillation still after a fresh harvest of petals. This process is repeated distilling the solvent is solid or nearly so and is until the greasy mix is saturated with the essence, “concrete”. The concentrated concretes are and needs to be repeated a couple of times until processed further to remove the waxy materials saturation is achieved. The resulting fat is known which dilute the pure essential oil. To prepare the as ‘pomade’. When the mix has reached saturation absolute from the concrete, the waxy concrete is point the flowers are removed and the pomade - warmed and stirred with alcohol (usually ethanol.). the fat and fragrant oil, then washed with 95% During the heating and stirring process the concrete

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breaks up into minute globules. Since the aromatic leave no harmful residue as it is an inert gas. Also molecules are more soluble in alcohol than is the high boiling components are extracted at relatively wax an efficient separation of the two takes place. low temperatures. But it requires high capital But along with the aromatic molecules a certain investment and elevated pressure. Compression of amount of wax also becomes dissolved and this solvent requires elaborate recycling measures to can only be removed by agitating and freezing the reduce energy costs. Wenqiang et al., (2007) solution at very low temperatures (around 30 examined the Supercritical fluid extraction (SFE) of

degrees F) In this way most of the wax precipitates essential oil from clove buds with CO2. The effect out. As a final precaution the purified solution is cold of different parameters, such as temperature (30 filtered leaving only the wax-free material (the 0C, 40 0C, 50 0C), pressure (10 M Pa, 20 M Pa, 30 absolute.) This solvent extraction actually yields M Pa) and particle size (three degree index), on three usable products; first the concrete, the the extraction yield and the content of eugenol in precious absolutes, and the floral waxes, for addition extracts was investigated. The experimental results to candles, thickening creams and lotions as a softly show that the temperature has the largest effect on floral scented alternative to beeswax. the eugenol content of the extracts, and particle size has the maximum effect on the oil yield. The Supercritical Fluid Extraction essential oil of 19.56% yield, in which the maximum The use of supercritical carbon dioxide extraction content of eugenol in extracts is 58.77%, can be is a fairly new way to extract essential oils from extracted from clove buds at pressure of 10 M Pa botanical material. The basic principle of SCF and temperature of 50 0C. Essential oil of clove buds extraction is that the solubility of a given compound obtained by SFE, hydro distillation, steam distillation (solute) in a solvent varies with both temperature and Soxhlet extractions were further analyzed by and pressure. At ambient conditions (25 0C and 1 gas chromatography/mass spectrometric detection bar) the solubility of a solute in a gas is usually to compare the extraction methods. The comparison related directly to the vapor pressure of the solute of Supercritical Fluid extraction and Steam and is generally negligible. In a SCF, however, solute Distillation is given in Table 1. solubilities of up to 10 orders of magnitude greater than those predicted by ideal gas law behavior have Table 1: Comparison of Supercritical Fluid Extraction been reported. Carbon dioxide is the most & Steam Distillation. commonly used SCF, due primarily to its low critical Material CO Extraction Steam Distillation 0 2 parameters (31.1 C, 73.8 bar), low cost and non- Time Yield Time Yield toxicity & non flammability. When CO2 (carbon (h) (%) (h) (%) dioxide) is subjected to high pressure, the gas turns Cardamom 2.5 9.4 5 9.0 into liquid. This liquid CO2 can be used as a very inert, safe, “liquid solvent.” which will extract the Parsley 2.0 9.8 5 2.7 aromatic molecules in a process similar to that used Clove Bud 2.0 20 4 14.0 to extract absolutes. The advantage is that no Ginger 2.5 3.7 6 1.6 solvent residue remains, since at normal pressure Cumin 2.0 3.5 4.0 3.0 and temperature, the CO2 simply reverts to a gas and evaporates Fennel 2.0 5.79 4.0 2.5 Sandalwood 2.5 4.86 24 3.8 The apparatus used for the extraction is the high (Khajeh et al.,2004; Mehra,2001;Tuan & Ilangtileke,1997) pressure Soxhlet apparatus. The equipment is designed for maximum pressure up to 300 bar and Microwave Extraction maximum temperature up to 200 0C and can withstand up to 1000 bars. Dissolving power of the Microwaves are electromagnetic fields in the SCF can be controlled by pressure and/or frequency range 300 MHz to 300 GHz or between temperature. SCF is also easily recoverable from wavelengths of 1 cm and 1 m (Singh & Heldman, the extract due to its volatility. Non-toxic solvents 2001). Microwave extraction is a green technology

27 Agricultural Engineering Today and appears as a good alternative for the extraction operation for microwave accelerated steam of essential oils from spice crops. By using distillation (MASD) of essential oils. The apparatus microwaves to mediate the extraction, it is possible has a cylindrical Pyrex body (12 cm inside diameter to maintain mild conditions and have superior and 12 cm long) with a Teflon grid at its lower end. extraction. Microwave energy is used in many A batch of 50 g of dry lavender flowers is packed in industrial processes since it has the advantage of the MASD with 200 mL of water. The raw material bringing about heating through kinetic effects inside forms the packed bed. At the bottom, steam is the sample thereby improving efficiency and produced by heating water with microwave controllability of the process. Although each irradiation. Steam produced in the lower part of the biomaterial responds differently to microwave apparatus passes through the lavender bed, exposure, they all heat faster and more uniformly evaporating and carrying the desired lavender in microwaves compared to other thermal essential oil, and is then directed towards the treatments. Specifically in the essential oil condenser, located on the top of the main apparatus extraction, microwave mediated processes are body. Following condensation, the mixture is highly desirable due to their small equipment size decanted to separate oil and water. The excess of (portability) and controllability through mild water is refluxed and recycled to the extraction increments of heating. The principle behind the vessel in order to restore the water used for steam microwave extraction is the internal heating of the production. The essential oil is collected, dried with in situ water within the plant material distends the anhydrous sodium sulphate and stored at 4 0C until plant cells and leads to rupture of the glands and used. Extraction of essential oils from lavender with oleiferous receptacles. This process thus frees MASD was better than steam distillation as energy essential oil, which is evaporated by the in-situ water consumption (0.13 kWh) with MASD was low as of the plant material. A cooling system outside the compared to that of Steam Distillation (1.5 kWh). microwave oven condensed the distillate The extraction time with MASD (10 min) was also continuously thus separating the essential oil. low as compared to that of Steam distillation (90 min). There are two types of microwave extraction viz. Microwave Assisted Hydro-Distillation (MAHD) and Microwave Accelerated Distillation (MAD) Microwave Accelerated Steam Distillation (MASD). Ferhat (2006) studied microwave Clevenger or Microwave assisted hydro distillation is based on microwave accelerated distillation (MAD) for the interaction between water contained in the extraction of orange essential oil using fresh orange vegetal material and microwaves generated from a peel. MAD was compared with a conventional source. This type of approach presents a series of technique, hydro-distillation (HD). Based on a characteristic features. Microwaves are the only relatively simple principle, this method involves energetic resource in the system; continuous placing orange peels in the microwave reactor, distillation is accomplished through sample without any added solvent or water. The internal microwave interactions that take place during the heating of the in-situ water within the orange peels entire process. The experiment may be carried out distends the oil glands and sacs and leads to rupture under a defined set of conditions i.e. water and of the glands and oleiferous receptacles. This essential oil are simultaneously present. Presti et process thus frees essential oil, which is evaporated al. (2005) compared the traditional hydro-distillation by the in-situ water of the plant material. A cooling (HD); supercritical fluid extraction (SFE), organic system outside the microwave oven condenses the solvent extraction (SE), and water microwave distillate continuously. In a typical MAD procedure assisted hydro-distillation (MAHD) techniques and performed at atmospheric pressure, 200 g of fresh evaluated their effectiveness in the isolation of orange peels were heated using a fix power density rosemary essential oil. The microwave assisted of 1Wg”1 for 30 min without addition of solvents or hydro-distillation technique was optimized in terms water. The extraction was continued at 100 0C until of both delivered power and time duration. no more essential oil was obtained. The extraction Chemat et al. (2006) developed a new design and of oil with MAD was found to be more efficient as

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compared to HD. The yield, extraction time and Free Microwave Extraction (SFME), in which a energy consumption data was 0.42 g of oil/100 g of microwave absorption solid medium, such as fruit, 30 min and 0.25 kWh respectively for oil carbonyl iron powders (CIP), was added and mixed extracted with MAD as compared to 0.39 g of oil/ with the sample, were applied to extraction of 100 g of fruit, 180 min and 4.33 kWh respectively essential oil from the dried plant materials without for oil extracted with HD. any pretreatment. Improved SFME was compared with conventional SFME, microwave-assisted Solvent Free Microwave Extraction (SFME) hydro-distillation (MAHD) and conventional hydro- Lucchesi et al. (2004) developed a solvent-free distillation (HD) for the extraction of essential oil microwave extraction (SFME) and compared it with from dried Cuminum cyminum L. and Zanthoxylum a conventional technique, hydro-distillation (HD), for bungeanum Maxim. The time of extraction in the extraction of essential oil from three aromatic Improved SFME, Conventional SFME (85W), herbs: basil (Ocimum basilicum L.), garden mint Microwave assisted hydro-distillation, Hydro (Mentha crispa L.), and thyme (Thymus vulgaris L.). distillation was 30 min, 50 min, 90 min and 180 min In a typical SFME procedure performed at respectively. atmospheric pressure, 250 g of fresh plant material Thus there is a huge research potential in the field was heated using a fixed power of 500 W for 30 of essential oils, its effective extraction and min without added any solvent or water. A cooling application due to its wide application i.e. air system outside the microwave cavity condensed the refreshing, bathing, compresses, hair care, distillate continuously. Condensed water was massage, saunas, steam care, steam inhalations, refluxed to the extraction vessel in order to provide vaporizations etc. Some work has been initialized uniform conditions of temperature and humidity for at various R&D centres but much more efforts are extraction. The extraction was continued at 100 0C needed. Some of the crops which need immediate until no more essential oil was obtained. The attention for essential oil extraction are aniseed, essential oils extracted by SFME for 30 min were basil, black pepper, carrot seed, spearmint, clove, quantitatively (yield) and qualitatively (aromatic coriander, fennel, eucalyptus, ginger, lemon, profile) similar to those obtained by conventional orange, jasmine, etc. hydro-distillation for 4.5 h. The SFME method yields an essential oil with higher amounts of more CONCLUSIONS valuable oxygenated compounds and allows substantial savings of costs, in terms of time, energy There are various isolation procedures for essential and plant material. oils based on distinct principles. The use of low boiling solvents has advantage of low operating Improved Solvent Free Microwave Extraction temperatures, thus thermally linked components (SFME) degradation is avoided. Recently, super critical fluid extraction has become a valid alternative, mainly, When dried herbs are to be used for extraction, because the dissolving power of the extracting adding some microwave absorption solid medium medium can be adjusted by regulating the pressure to the sample can be a feasible way. The types of and temperature conditions. An innovative isolation material must have good microwave absorption technique called microwave assisted extraction is capacity and good chemical stability. Carbonyl iron based on the interaction between water in the powders (CIP) are among the most popular vegetal material and microwaves generated by the conventional magnetic absorption materials that energy source. It has various advantages over the have a good microwave absorption capacity. By conventional methods: high extraction rates, no absorbing microwave energy, the calefaction speed toxic residue in the extract, reduced energy of CIP is much higher than that of water. So using consumption and more environments friendly. CIP as a microwave absorption solid medium in SFME is justifiably believed to be a feasible way to REFERENCES make the process more simple, rapid and economic. Wang et al. (2006) developed an improved Solvent Anonymous. 2002. The complete technology book

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