Extraction citrus oils

Polyterpenes. Polyterpenes is one of the first classes of non-polar tack-ifiers to be developed. Terpene monomers are a by-product in the extraction of rosin from wood stumps or tree sap, and from the extraction of oils from citrus fruits. The latter is the dominant source. As such, polyterpene prices generally mirror those of citrus fruits, which fluctuate substantially from one growing season to the next. Terpenes like rosin are cyclic, see Fig. 6, which is partly responsible for their excellent solvent properties. 

A 10-g representative sample (5-g sample for citrus oil or cotton substrates) was extracted by adding 150 mL of acetonitrile-water (4 1, v/v) to the sample in an 8-oz bottle and homogenized with a Polytron at high speed for 2 min. The extract was filtered through a Whatman No. 1 filter-paper into a 500-mL side-arm flask. The extraction bottle was rinsed with 50 mL of acetonitrile-water (4 1, v/v) for citms and cottonseed oil (for molasses use lOmL of water followed by 40 mL of acetonitrile for rinsing). The extract was transferred to a 500-mL separatory funnel and partitioned twice, each time with 50 mL of hexane for 1 min. The hexane fractions... 

The three main platform molecules employed in terpene chemistry are a-pinene and / -pinene, which are extracted from turpentine oil (350000 t a-1) a co-product of paper pulp industry, and limonene extracted from citrus oil (30000 t a-1). 

Citrus oils - pOOD ADDITIVES] (Volll) - [OILS, ESSENTIAL] (Vol 17) -extraction using SCFs [SUPERCRITICAL FLUIDS] (Vol 23)... 

TERPENELESS OIL. An essential oil from which the teqoene components have been removed by extraction and fractionation, either alone or in combination. The optical activity of the oil is thus reduced. The terpene-less grades are much more highly concentrated than the original oil (15—30 times). Removal of terpenes is necessary to inhibit spoilage, particularly of oils derived from citrus sources. O11 atmospheric oxidation the specific terpenes form compounds that impair the value of the oil for example, d-limonene oxidazes to carvone and y-terpinene to p-cymene. Terpeneless grades of citrus oils are commercially available. 

For flavones in citrus peel oils, separations were accomplished with isocratic mobile phases of 38% and 40% acetonitrile in H20 (1). The extracts of peel and cold-pressed peel oils were diluted in ethanol and analyzed by reversed-phase on various C18 columns with good results. For the dilute citrus oils, gradient elution was preferred, to prevent the accumulation of terpenes on the column. With normal-phase chromatography, the elution order is reversed terpenes elute with the solvent front and are not a problem. 

A flavouring essence is a traditional flavouring product prepared by washing a selected oil blend (predominately citrus oils) with an aqueous alcoholic solvent mixture (e.g. 60% ethanol/40% water). It is an extraction process in which the aqueous extract phase becomes the flavouring. The process is earned out under cool temperatures, for example, 5-10°C, either batch-wise or by counter-current extraction. The soluble oxygenated flavouring constituents present in the essential oil blend (e.g. citral in lemon oil) are effectively partitioned between the two phases of the mixture. The low temperatures employed ensure that the transfer of any oil into the hydro-alcoholic phase is minimised as a poorly processed essence will tend to cloud when used in the drink formulation. 

Processing effects. Citrus oil quality may be affected by certain processing parameters. Some which have been studied include effects of yield from the fruit, the amount of water used during recovery and extraction, storage of fruit prior to processing, blending of fruit varieties, and handling the emulsion or finished oils (12). 

Data by Waters et al. (26) have demonstrated that the type of commercial extraction had a significant influence on the tocopherol content and the evaporation residue of citrus oils. 

Brose, D.J., Chidlaw, M.B., Friesen, D.T., Lachapelle, E.D. and Vaneikeren, P. (1995) Fractionation of citrus oils using a membrane-based extraction process. Biotechnology Progress, 11, 214. 

Many other processes can be applied to concretes, absolutes, resinoids, and essential oils to obtain products with special characteristics. For example, decolorized products may be obtained by extraction with appropriate solvents to eliminate highly colored components. Colorless products may be obtained by fractional molecular distillation under vacuum. Yet another type of product is obtained by vacuum codistillation using a suitable solvent. Many essential oils, particularly citrus oils, contain high levels of insoluble terpene hydrocarbons, which can be removed by fractional distillation or by countercurrent extraction to produce concentrated or terpeneless oils. 

SUMMARY In essential oils, most constituents are terpenes and terpenoid molecules. The method of extraction can influence the terpene content. In citrus oils extracted by expression (squeezing or pressing the plant material), the terpenes present are similar to those found in the living plant tissue for example, orange, lemon, mandarin and grapefruit essential oils may be made up of up to 90% of the monoterpene limonene. When extraction is by steam distillation the action of the hot water and steam on thermolabile (heat-sensitive) molecules present in the plant is responsible for the formation of the bulk of the terpene content. Solvent extraction often produces absolutes that are very low in terpenes or do not contain them at all, when compared to a distillation of the same material, for example as found in lavender and rose products. 

The fractionation of citrus oil is an important subject in perfume industry. Citrus oil consists of terpenes (over 95 %), oxygenated compounds (less than 5 %), waxes, and pigments. Terpenes must be removed to stabilize the products and to dissolve it in aqueous solution. Terpenes are conventionally removed by distillation or solvent extraction, which involves higher temperature process resulting in thermal degradation of essential oil. Furthermore, nonvolatils such as waxes and pigments must be eliminated because of turbidity in the oil and phototoxic activity [1-2]. 

Supercritical fluid extraction has been focused for the deterpenation of citrus oil as a lower temperature process [1-6]. Coppella and Barton [4], Stahl and Gerard [5], and Temelli et al. [6] studied the extraction process for the removal of terpenes in citrus oil. However, the simple extraction process does not give sufficient selectivity and yield A continuous countercurrent extraction process is one of the method to achieve higher selectivity between terpenes and oxygenated compounds. Perre et al. [7] and Sato et al. [8] succesfully developed the continuous extraction process. 

Introducing adsorbents into a supercritical fluid extraction system is an alternative attractive method to improve the selectivity for the citrus oil processing. Several applications using silica gel as adsorbent have been reported in the last decade [1-3]. Yamauchi and Saito [3] fractionated lemon peel oil into 3 fractions with gradual increase in pressure by supercritical fluid chromatography, where terpene rich fraction, ester rich, and alcohol and aldehyde rich fraction were obtained at 10 MPa, 20 MPa, and 20 MPa with ethanol as a cosolvent,... 

Usually, the terpenes are removed from the cold-pressed oils (deterpenation) to concentrate the flavour fraction, thus resulting in a more stable product with improved solubility in the alcoholic solvents used in food and perfume processing. Supercritical carbon dioxide extraction appears as a promising and alternative technique to refine cold-pressed citrus oils [1,2, 3). Potentially, it has the advantages that it can be carried out at mild temperatures, provides better yields and leaves no solvent residues. 

Citrus oil dominates this class of essential oil. It is obtained by the cold press method with the exception of lime oil, which is also prepared by steam distillation of essential oil separated during the production of juice.106,107 Aside from bergamot, these oils are primarily monoterpene hydrocarbon mixtures of which (if)-limonene (3) is usually the dominant compound. Since odor contribution of this monoterpene compound is low, it is often removed by distillation or repeated solvent extraction. The resulting oil rich in odor-active compounds is called terpeneless oil and is used extensively. In the case of bergamot and lemon oils, psoralen derivates like bergaptene (64) causing photosensitivity are problematic, and those for fragrance use are rectified to remove it (Table 8). 

Table 8 Aroma extract from peel (citrus oil)...

Citrus peel oils of very complex composition are contained in oval, balloon-shaped oil sacs, or vesicles, located in the outer rind, or flavedo, of the fmit (3). The oil is usually extracted by mechanical separation or hydrodistUlation. The five main types of citrus from which peel oils are recovered are orange, grapefruit, tangerine, lemon, and lime (4). Mechanical separation, known as cold-pressing of peel oils, does not use heat in order to avoid loss of volatile components. Swisher and Swisher (1) described three general commercial methods that are widely used in citrus industry to extract crude oils from fruit peels ... 

Pesticide residues may contaminate citrus peel oils as well. Cultivation of citrus crops commonly involves the use of chemicals such as fertilizers and pesticides. Regulations are increasingly stricter in terms of residual levels of pesticides because of the application of citrus oils in food, pharmaceutical, and cosmetic industries (75). Citrus peel oils, extracted from citms peels, contain a higher concentration of pesticide residues than the fruits, due to the direct contact of the peels with pesticides. Organophosphorus and organochlorine pesticide residues in citrus peel oils have shown a steady decrease in recent years (76). 

In comparison with essential oils from conifers the enantiomeric ratio of monoterpenic hydrocarbons is more stable in citrus oils and thus it can give information about their origin, extraction techniques and genuineness of the oils. The main component of monoterpenes in those types of oils is (+)-limonene of a high enantiomeric purity for most of the citrus oils. 

Hooser, S.B. (1990). D-Limonene, linalool, and crude citrus oil extracts. Veterinary Clinics of North America Small Animal Practice, 20(2), 383-385. 

Cats are susceptible to poisoning by ingestion of insecticidal products containing d-limonene, linalool and crude citrus oil extracts. Signs of toxicosis include hypersalivation, muscle tremors, ataxia, depression and hypothermia (Hooser, 1990). 

While the droplets are falling down in the continuous dense gas phase, which is moving in countercurrent mode from the bottom to the top, some components are dissolved and carried out as extract into the separator whereas the insoluble part is collected and withdrawn from the bottom of the column as raffinate. This is illustrated in Fig. 2.28 as trickle flow mode. Examples are the deterpenation of citrus oils, the deacidification of vegetable oils, the separation of alcohol and water and the enrichment of carotenes or of EPA- and DHA-fatty acid esters from fish oils. 

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