Citrus peel oils

The objectives of this study were to compare the yields of cold-pressed essential oil, water consumption, material balance and efficiency of the process in a typical citrus peel oil recovery plant with and without recycling system. The different emulsions and aqueous discharges from these processes were also characterized. 

Citrus peel oils are a special type of essential oil. They are isolated by pressing the peel to release the volatile substances stored in the pericarp in small oil glands. The resulting products are termed essential oils because they consist largely of highly volatile terpene hydrocarbons. However, they also contain small amounts of nonvolatile compounds, such as dyes, waxes, and furocoumarines. 

Production of Citrus Peel Oils. Apart from distilled lime oil, citrus peel oils are produced by pressing. Pressing of the peels for oil is often combined with juice production [357a]. 

Brunner et al [1, 2] investigated separations of fatty acids according to chain length, using methyl esters of different carbon chain length from C14 to Cl8, separation of tocopherols from a by-product of the edible oil production and separation of fish oil esters [3], Stahl et al [4] proposed the supercritical fractionation of orange peel oil and Reverchon et al [5,6] of an orange flower concrete. Different authors treated citrus peel oil [7,8] and citrus oil [9-12]. 

Limonene (92) is the most widely distributed terpene in nature after a-pinene [68]. The (+)-isomer is present in Citrus peel oils at a concentration of over 90% a low concentration of the (-)-isomer is found in oils from the Mentha species and conifers [26]. The first data on the microbial transformation of limonene date back to the sixties. A soil Pseudomonad was isolated by enrichment culture technique on limonene as the sole source of carbon [69]. This Pseudomonad was also capable of growing on a-pinene, / -pinene, 1-p-menthene and p-cymene. The optimal level of limonene for growth was 0.3-0.6% (v/v) although no toxicity was observed at 2% levels. Fermentation of limonene by this bacterium in a mineral-salts medium resulted in the formation of a large number of neutral and acidic products. Dihydrocarvone, carvone, carveol, 8-p-menthene-1,2-cw-diol, 8-p-menthen-1 -ol-2-one, 8-p-menthene-1,2-trans-diol and 1 -p-menthene-6,9-diol were among the neutral products isolated and identified. The acidic compounds isolated and identified were perillic acid, /Msopropenyl pimelic acid, 2-hydroxy-8-p-menthen-7-oic acid and... 

Citrus-peel oils -food toxicants m pOOD TOXICANTS, NATURALLY OCCURRING] (Vol 11)... 

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. 

The economic importance of the various citrus oils has resulted in intensive research directed toward processing methods, compositional analyses, quality, and utilization. Early work described recovery methods and some characteristics related to quality of citrus peel oils in the United States (UO, 11). More recently, citrus peel oil yield and quality has been related to processing methods (12) and cultural practices (13). 

A complete description of the oils is given in the section Flavonoids in Citrus Peel Oils , and other references are listed in the bibliography. 

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 ... 

Compositions of volatiles in different orange oils are shown in Tables 4 and 5. It is evident that most of the constituents belong to the terpene family and may be arranged into two groups, terpene hydrocarbons (terpenes and sesquiterpenes) and oxygenated terpene products (21). Aside from the volatile components, there are small amounts (2-15%) of nonvolatile residues in citrus peel oils that possess antioxidative property these include coumarins, psoralens, and polymethoxylated flavones (30-34). 

Citrus peel oils have been used widely in beverages, cosmetics, pharmaceuticals, and perfumery industry, whereas seed oils are used in cooking and for treatment of leather and textile. The quality, freshness, and uniqueness of citrus oils are major considerations pertaining to their value and applications (43). However, large amounts of volatile components, as well as unsaturated compounds, render the oils unstable and prone to change with time and storage conditions. 

These compositional changes usually negatively influence the odor and flavor of citrus peel oils by generating off-flavor products. It has been shown that nonvolatile residues of citrus peel oil contain some compounds that exhibit antioxidative activities, among which permethoxylated flavones, dehydroabietic acid (46), coumarins, and psoralens have been identified (33). In this respect, cold-pressed citrus peel oil is more stable than distilled oil and essence oil, in which most of the natural antioxidants present are left behind when the oil is distilled (1). 

The applications of citrus oils are versatile and in many domains. As a result of their freshness, lightness, and fine fruity aroma, citrus peel oils and essences are widely used in the food and beverage industries as well as in some nonfood applications (1). 

Citrus peel oils may also be used for their antioxidative, antitumor, and radicalscavenging activities. The radical-scavenging ability of citrus peel oil may help prevent free radical-induced and various chronic diseases (48, 55, 56). Monoterpenes from volatile components and polymethoxylated flavones from nonvolatile residues have been reported to be effective inhibitors of tumor cell growth, implicating that citrus peel oils may be good cancer preventive food additives (57-59). Furthermore, citrus peel oils are useful to alleviate pain from burnt skin (60). Demonstrating anxiolytic and sedative effect, they could also be used in primary medical care against insomnia, anxiety, and epilepsy (61). 

The insecticidal property and antimicrobial activity of citrus peel oils have been reported. The oil can repel moth, mosquito, cockroach, domestica, and housefly (62-66). It also inhibits the growth of microbes such as fungi and salmoneUae, with monoterpenes being the major compounds that account for pathogen fungi inhibition (46, 67, 68). 

Unlike citrus peel oil, citrus seed oil is mainly used after refining as edible oil and a source of essential fatty acids. Refined citrus seed oil is widely used in margarines, shortenings, salad dressings, and salad and cooking oils. Meanwhile, crude citrus seed oils are useful in the preparation of fatty acid derivatives, soap and detergent, and for the treatment of leather and textile (1). 

Another contamination of citrus peel oils comes from chlorine-treated water used in the oil recovery process and sanitizers used in postharvest handling and process equipment cleaning, which serve as a potential source of hypochlorous acid (HOCl) (73). HOCl can react with a variety of terpenes similar to d-limonene in structure, including hmonene, a-pinene, and a-terpineol, resulting in the formation of terpene chlorohydrins. The contamination of terpene chlorohydrins could be reduced through reduction of the chlorine levels in the treatment water (74). 

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). 

There is considerable interest in the chemical composition and properties of citrus oils and essences as well as the role they play in food and nonfood industries. Citrus peel oils and essences possess a pleasant aroma, with oxygenated compounds being the major constituents that account for their characteristic odor. Terpenes, the most abundant components in cold-pressed citms peel oil, are removed in concentrated oil production, usually by use of adsorbant and supercritical carbon dioxide, to increase the concentration of oxygenated compounds and to enhance the qualification of the oil. Meanwhile, citms seed oils are composed largely of triacylglycerols and are rich in oleic and linoleic acids. 

A simple way to obtain a clear soft drink is adding clear, water-soluble flavours, so-called essence flavours. The most popular products, usually derived from ethanol-extracted and distilled citrus peel oils, provide a subtle taste of lemon or lime. The dosage of these flavours is around 1 g per litre of final drink. Together with sweetener, acidifier and carbonation, one gets a fizzy clear and colourless drink with citrus taste. 

Limonene is widespread in essential oils. The main source for (-i-)-limonene are citrus peel oils. From this source it is obtained in large quantities as a by-product of the orange juice production. Therefore nature-identical products (e.g. from pinene) are not of great importance. The 5 C-values of natural limonene from orange peel oil has been found to range from -26.1 to -28.5%o, and the reported 5 H-values are from -215 to -264%o, in agreement with results for other natural isoprenoids. 

Derivation Citrus peel oils, especially from oranges. Made synthetically from geraniol. 

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