Citrus peel oils components

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. 

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). 

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. 

Studies into the method of action of essential oils as insect repellents are currently underway that may further help in the development of new products. Recently, the results of an investigation were reported on the method of action of the acaricidal properties of Lavandula angustifolia Miller essential oil and of linalool (60), one of its main components, against Psoroptes cuniculi [195]. The study confirms the anti-mite properties of lavender essential oil and of linalool (60) by inhalation, indicating an additional route for possible use of these substances both for prophylactic and therapeutic purposes. Also, the method of action of the toxicity of citrus peel oils to several insect species has recently been investigated [196]. The results indicated that an efficient way to use citrus peel essential oils to control insects would be as a fumigant in relatively enclosed or air-tight systems. 

The main constituent of all citrus peel oils is limonene - a monoterpene hydrocarbon. Antimicrobial activity of hydrocarbons is lower than that of oxygenated essential oil components. Despite of this fact, entirely good antibacterial and antifungal properties were observed for citrus oils mainly due to oxygenated monoterpenes. It is worth to mention that pressed citrus peel oils contain 1-15% non-volatile components. 

The main renewable resource for L-carvone is spearmint oil (Mentha spicata), which contains up to 75% of this flavour chemical. There also exists a synthetic process for the manufacturing of L-carvone, which is based on (-t)-limonene, which is available as a by-product of the citrus juice industry as a major component of orange peel oil (Scheme 13.4). The synthesis was developed in the nineteenth century and starts with the reaction of (-t)-limonene and nitrosyl chloride, which ensures the asymmetry of the ring. Treatment with base of the nitrosyl chloride adduct results in elimination of hydrogen chloride and rearrangement of the nitrosyl function to an oxime. Acid treatment of the oxime finally results in l-carvone. 

Juice Cloud. Mechanical extraction of citrus fruits yields a turbid suspension of wall fragments and cellular organelles in a serum composed primarily of cell vacuolar fluids. In most citrus juice products, such a suspension of fragments and organelles is a desirable component, since it provides most of the characteristic color and flavor (28). Essence and peel oils suspended in juice contribute desirable citrus notes to flavor, and these oils are rapidly adsorbed by juice particulate material shortly after extraction (29). 

The flavor of most citrus cultivars is complex, and compounding citrus flavors requires the blending of several components in specific proportions to obtain the unique flavor of each citrus cultivar (3). Studies on Sicilian mandarin oil suggest the distinct flavor and aroma of mandarins is mainly due to 2 compounds, thymol and methyl-N-methyl anthranilate (dimethyl anthranilate) but no evidence to support this claim has been presented (42). Thymol has been identified in Dancy tangerine peel oil, and both thymol and dimethyl anthranilate have been identified in Sicilian mandarin oil (3). The reported quantities of thymol in mandarin oil varied from 0.04-0.2% of the oil, whereas only one value (0.9%) was reported for dimethyl anthranilate. 

Olsen et al. (51) assumed that cardboard off-flavor was due to oxidation of components in the concentrated juice. They proposed calling this "citrus oxidized flavor" or COF and concluded that COF could be avoided by maintaining the peel oil content above a certain level, based on the observation that 10 of 16 commercial samples which exhibited COF had very low peel oil levels. It was also recommended that care be taken to avoid the incorporation of air during the manufacture of concentrate. The exact nature of the substances oxidized and the mechanism of oxidation remain to be determined. 

Cyclohexane monoterpenes are a chemically diverse group of monoterpenoids that occur in the plant kingdom mainly as hydrocarbons, alcohols, ketones, aromatic hydrocarbons, and phenols (Fig. 5). The saturated hydrocarbon trans-p-menthme (El) is a constituent of the oil of turpentine and the resin of pine (Pinaceae) trees. Its unsaturated analogs, namely (i )-(- -)-limonene (E2) [present in oil of orange (Citrus aurantium) and mandarin (Citrus reticulata, Rutaceae) peel oil] a-terpinene (E3) and terpinolene (E4) in some Citrus, Juniperus, Mentha and Pinus species (i )-(-)-a-phellandrene (E5) in Eucalyptus phellandra (Myrtaceae) and (5)-(- -)-3-phellandrene (E6) in water feimel (Phel-landrium aquaticum, Umbelliferae), are components of many plant volatile oils. The rich chemical diversity of cyclohexane monoterpene alcohols is apparent from the natural occurrence of all four pairs of / -menthan-3-ol enantiomers, for... 

Distillation of citrus juices yields two volatile fractions, namely, aqueous essences and essence oils that are separated from each other by condensation of the distillate (7). Aqueous essence, the bottom layer of the condensate is comprised of organic acids, alcohols, aldehydes, esters, hydrocarbons, ketones, hydrogen sulfide, and oxides (10). Considering many components found in both cold-pressed peel oil and aqueous essence, essence oil has a flavor similar to that of the combined peel oil and aqueous essence (10). However, essence oil usually contains a larger amount of... 

The monoterpene o-limonene is a naturally occurring chemical which is the major component in oil of orange and other natural oils including lemon, grapefruit, berry, leaf, caraway, dill, bergamot, peppermint, and spearmint oils. o-Limonene may be obtained by steam distillation of citrus peels, from pulp resulting... 

D-Limonene Another class of low-temperature HTF is based on naturally derived terpenes such as D-limonene. U.S. Patent 3,597,355 describes o-limo-nene as being particularly preferred among all the monocycloterpenes because of its characteristic properties such as low viscosity at low temperatures. D-Limonene is the major component in the oil of citrus fruit and is present in trace quantities in orange juice. It is recovered in commercial quantities by distilling orange oil obtained from citrus peels. Being derived from the citrus industry, o-limonene is considered a safe and environmentally friendly HTF, and hence it is preferred in many food and pharmaceutical processes. However, the melting point of D-limonene is about —78°C. Below this temperature, it becomes a thick white gel like substance that is impossible to pump. Therefore, the use of o-limonene is limited to... 

A tliird byproduct from citrus processing is citrus molasses (CM). CM is obtained from tlie spent citrus peel after the juice and peel oils are extracted The peels are furtlier processed to squeeze out residual juice sugars and peel oils. This mixture is concentrated by distillation wliich removes water and many of the volatile oil components present. A sample of 33 Brix orange molasses was analyzed for PMF content to compare with our other results. The HPLC spectrum (Figure 6) shows a very different absorption spectrum from the typical juice sample. A large (unidentified) peak is seen eluting before 2.5 minutes with the PMF peaks eluting later. The total PMF content in this... 

Song, H.S., H. Ukeda, and M. Sawamura, 2001. Antioxidative activities of citrus peel essential oils and their components against hnoleic acid oxidation. FoodScl Technol Res., 7(1) 50-56. 

The most important compounds are menthadienes, derived from p-menthane, which differ in the positions of the double bonds (8-5). A common hydrocarbon is limonene (p-mentha-1,8-diene), which typically occurs in many essential oils (such as essential oils of citruses, mints and conifers) and turpentine. For example, the (-1-)-limonene isomer is the major component (>90%) ofessentialoilsof citrus peels, (-)-Kmonene is a component of essential oils of different types of mint Mentha spp., Lamiaceae) and conifers. Racemate, which is trivially known as dipentene, occurs in many essential oils. Other important menthadienes include a-terpinene (p-mentha-1,3-diene), y-terpinene (p-mentha-1,4-diene), a-phellandrene... 

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