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Application of Sub-Critical Water Extraction in Pharmaceutical Industry

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Application of Sub-Critical Water Extraction in Pharmaceutical Industry Journal of Materials Science and Chemical Engineering, 2013, 1, 1-6 http://dx.doi.org/10.4236/msce.2013.15001 Published Online October 2013 (http://www.scirp.org/journal/msce) Application of Sub-Critical Water Extraction in Pharmaceutical Industry Xiaoxia Liang, Qiaojia Fan Department of Pharmacy, College of Veterinary, Sichuan Agricultural University, Ya’an, Sichuan, China Email: [email protected] Received June 2013 ABSTRACT Sub-critical water extraction is a brand-new separation technology. This paper mainly discussed the principle, advan- tages of sub-critical water extraction, and its applications ranging from the medicinal plants traditionally used in Europe and Asia to produce pharmaceutical extracts (such as volatile oil, tannins, flavonoids, anthraquinone, lactone, etc.). Meanwhile, the prospect of sub-critical water extraction in plant extractives is also explored. It will be widely used in the field of medical plants, bringing huge economic benefits, environmental benefits and social benefits. Keywords: Sub-Critical Water Extraction; Pharmaceutical Extracts; Application 1. Introduction one or more of their desirable physical, chemical and biological properties. At present, plant medicine, which mainly comes from In recent years, many new technologies and methods, plant extraction, has occupied nearly 30 percent to 40 such as ultrasonic extraction, microwave extraction, percent among the thousands of worldwide used phar- membrane separation technology, molecular distillation, maceutical products. As a natural healthy protection macroporous resin adsorption and supercritical CO ex- product, it has incomparable natural advantages, com- 2 traction technology, are introduced to the extraction pared with the relative chemical drugs. Extraction and and separation of effective components in medicinal separation of effective pharmaceuticals, looking for plants, promoting the development of plant extracts in- leading compounds, is the first and most important step dustry. Among those new technologies, supercritical flu- in the new drug development. However, chemical com- id extraction (referred to as SFE) [1,2], is the most com- position of various medicinal plants is very complex, pelling one, which is especially feasible for heat-sensi- usually containing many kinds of effective ingredients. tive material with its own unique advantages, including Numerous methods, including conventional solvent ex- non-toxic, no solvent residue, high extraction rate, and traction, steam distillation, and sublimation, etc., are free of environmental pollution. However, as every coin known for extracting phytochemicals from plant materi- has two sides, SFE has less capacity, mainly for the ex- als, most based on sequential extraction processes incor- traction of high value-added products. Its application has porating one or more organic solvents in combination been limited [3,4], due to the high extraction pressure with washing steps. Phytochemical extracts produced by and equipment costs. Finally, with the development of such methods must be further processed to remove all SFE, a new extraction technique, “subcritical water ex- trace of the organic solvents, to remove impurities, and to traction”, emerged. Its principle, advantages, and appli- separate and purify individual phytochemicals. While cations of the extraction to a range of medicinal plants, such methods are useful for extraction and purification of traditionally used in Europe or Asia to produce pharma- small quantities of phytochemicals for research purposes, ceutical extracts (such as volatile oil, tannins, flavonoids, they are difficult to scale to commercial through-put vo- anthraquinone, lactone, etc.), will be introduced in this lumes because of the problems associated with cost-ef- article. fectively, safely and completely removing and recov- ering the organic solvents from the extracts and spent 2. Principle of Sub-Critical Water plant materials. Furthermore, the types and concentra- Extraction tions of organic solvents must be carefully selected in order to avoid structural changes to the target phyto- Water, an inexpensive and environmentally friendly sol- chemicals during extraction that may adversely affect vent is an ideal solvent for the industrial extraction of Copyright © 2013 SciRes. MSCE 2 X. X. LIANG, Q. J. FAN medical plants, but its use is limited due to poor extrac- with no waste produced at the same extraction efficiency. tion efficiency for most organic compounds such as po- The technique could achieve selectively extraction of lychlorinated biphenyls (PCBs), polycyclic aromatic hy- polar, moderately polar, and nonpolar organics by alter- drocarbons (PAHs) and most pesticides at ambient tem- ing extraction parameter, such as temperature, pressure perature. However, it has gained an increasing amount of and co-solvent. Meanwhile, compared with supercritical attention due to its unique solvation properties, which extraction (SFE) (CO2 used particularly), SBW can be can be altered by changing the temperature [5]. It is used in the extraction of substances from moderately known that the physical and chemical properties of water polar to heavy molecular weight in medical plants. This within sealed systems can be manipulated by concur- just compensates for the drawback of SFE (CO2 used rently controlling the temperature and pressure, where by particularly, which can just extract nonpolar or light mo- the water remains in a liquid state even though its tem- lecular weight substance and will not extract the com- perature is significantly increased above its atmospheric pounds most readily soluble in methanol or aqueous boiling point of 100˚C. The polarity, viscosity, surface ethanol, including the important classes of flavonoids, tension, and disassociation constant of sub-critical water lignans and other related polyphenolic compounds.) Re- are significantly lowered compared to water at ambient cently, SBEW has been applied largely abroad. Most of temperature and pressure conditions, thereby signifi- these reports focused on the determination of organic cantly altering its chemical properties to approximate pollutants [12-14] in soils, sludges and sediments, and those of organic solvents. Consequently, pressurized low- the extraction of spice components from plants. Its ap- polarity water under sub-critical conditions can easily plication in the field of pharmaceutical industry is also solubilize organic compounds from polar (at lower tem- encouraging [15]. peratures) to nonpolar (at higher temperatures), such as phytochemicals which are normally insoluble in ambient 4. Application in Pharmaceutical Industry water [6]. In this condition, it is known as “sub-critical” Sub-critical water extraction has been extracted the most or “hot/liquid” water. Sub-critical water can be main- active compounds from herbs, such as Rosmarinus offi- tained in the liquid form until a temperature of 374˚C and cinalis (rosemary), Matricaria recutita (German chamo- a pressure of 221 bars are reached after which, it be- mile), Cassia angustifolia (senna), Valeriana officinalis comes supercritical water [7,8]. Sub-critical Water Ex- (valerian), Scutellaria baicalensis (Baikal skullcap), traction (SBWE), also known as hot water extraction, Schisandra chinensis (Wuweizu), Zingiber officinale pressurized (hot) water extraction, pressurized low polar- (ginger), Astragalus Membranaceus, etc. [16]. Those ex- ity water extraction, high-temperature water extraction, tracts were demonstrated to exhibit a composition es- superheated water extraction or hot liquid water extrac- sentially similar to that of the corresponding methanol or tion, is such a promising “green” technique based on the aqueous alcohol, which would show comparable phar- use of water at a sub-critical state as the sole extraction macological activities. solvent [6,9]. A further advantage of sub-critical water extraction is that the high temperature and pressure pro- 4.1. Extraction of Volatile Oils duce high diffusion rates which promote very efficient Volatile oil, also known as essential oil, is present in a extraction of the raw material. In addition, that rates vary class of plants with aromatic smell, which is water in- according to different chemical structures [10,11] of or- soluble and can be distilled with steam. As an important ganic compounds. Therefore, extraction with subcritical class of active ingredients, essential oils are volatile oil- water can be both selective and rapid. like components of the general, with a variety of phar- 3. Advantages of Sub-Critical Water macological activities and applications in medicine and Extraction food industry. Traditional methods include steam distil- lation and organic solvent extract, indicating much more As we mentioned above, from water-solubility to lipo- shortcomings, such as volatile components loss, low ex- soluble substances were successively extracted with traction efficiency, heating for a long time, organic sol- SBW. Its ability to dissolve nonpolar organics is similar vent residual and so on. In 1998, Basile et al [17] first to that of organic solvents, which are expensive, poten- confirmed that the sub-critical water extraction was a tially harmful to the operator, and need to be disposed of. practical method for the essential oil. In their research, Using SBWE instead is highly desirable from environ- the extracts from rosemary was compared with that from mental and health perspectives. It shows lower handling steam distillation, the former showed pleasantly
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