Peel Oil

Orange peel oil is the major oil produced worldwide and is used extensively in the food industry, primarily as a flavouring in beverages and sweets. It possesses a light, sweet, fresh top note with fruity and aldehydic character. Many household and personal-care products employ orange oil owing to its pleasing 

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In one extractor (FMC Inc.), the fmit is located between two cups having sharp-edged metal tubes at their base. The upper cup descends and the many fingers on each cup mesh to express the juice as the tubes cut holes in the top and bottom of the fmit. On further compression, the rag, seeds, and juice sacs are compressed into the bottom tube between the two plugs of peel. A piston moves up inside the bottom tube forcing the juice through perforations in the tube wall. A simultaneous water spray washes the peel oil expressed during extraction away from the peel as an oil—water emulsion the peel oil is recovered separately from the emulsion. 

Portugaldl, Portugallool, n. Portugal (or por-tugallo) oil, orange-peel oil. 

Enzymatic treatment in the extraction of cold-pressed lemon peel oils... 

Cold-pressed essential oils from the peel are some of the most important by-products recovered during the processing of Citrus fruits. The presence of limonene in the aqueous discharges, with its antimicrobial activity [1], decreases the effectiveness of the waste treatment system and increases the time necessary for the biological breakdown of the organic matter produced in the peel oil recovery system [2,3]. Additional recovery of essential oils from waste water would increase industry s returns and reduce the pollution problems associated with the disposal of waste water [4,5]. Several methods for reducing the levels of residual essential oils in the aqueous effluent have been developed over the years [6-11]. 

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. 

In the non-recycling system, the pectic substance content of the different samples were very stable (Figure 2a). At the end of the assay the oil-in-water emulsion from the finisher and both aqueous discharges had very similar values of around 0.2 g AGA/L, similar to that reported by Parish e( al. [5] for the aqueous discharge fi"om an orange peel oil recovery system. However, the oil-rich emulsion had higher values (around 4.0 g AGA/L). 

Table 1. Material balance in the non-recycling and recycling lemon peel oil recovery systems...

Both recycled and non-recycled essential oils met the standards for specific gravity, angular rotation and refractive index of the Food Chemicals Codex [22] and United States Pharmacopeia [23] for cold-pressed lemon peel oil. Results of gas chromatography analysis show the same compounds and levels in both systems, specially for the oxygenated compounds as citral (neral and geranial). Therefore, recycling the aqueous discharges to the extractor does not cause undesirable modifications. 

Earl Grey tea is flavored with the peel oil of bergamot, a citrus fruit, which is added by spraying onto black tea before final packaging. Other flavors may also be applied to black tea by spraying onto the leaves, incorporation of flowers into the blend, or by addition of encapsulated flavor crystals. Other common flavored teas include Rose Congou and Lychee. 

Chen, J., Montanari, A.M., and Widmer, W.W., Two new pol5nnethoxylated flavones, a class of compounds with potential anticancer activity, isolated from cold pressed dancy tangerine peel oil solids, J. Agric. Food Chem., 45, 364, 1997. 

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]. 

Production of Citrus Essence Oils. Distillative concentration of citrus juices yields essence oils, which separate from the aqueous phase in the receiver when the distillate condenses. The composition of essence oils is similar to that of peel oils, but the essence oils usually contain larger quantities of aliphatic ethyl esters (e.g., ethyl butyrate in orange essence oil). Thus, their aroma resembles that of a particular juice more than that of peel oils. 

Worldwide production of bitter orange oil is much lower than that of other pressed peel oils. Bitter orange oil is predominantly used for flavoring alcoholic beverages (liquers). FCT 1974 (12) 735 [68916-04-1], [72968-50-4]. 

Some of the more thorough studies of orange juice volatile composition were carried out by Schreier et al. [20], Duerr and Schobinger [21] and Nisperos-Carriedo and Shaw [22]. For example, Schreier et al. peeled the oranges before extraction in methanol to inactivate enzymes and prevent contamination from peel oil. Volatiles were separated from the aqueous juice using solvent extraction and were subsequently concentrated. Internal standards were employed to compensate for changes in concentration due to extraction/concentration or variation in sample introduction. Few subsequent studies prepared and analysed juice samples as thoroughly. 

Sweet orange peel oil composition has been reviewed in [1,4]. 

Fruit maturity has a major impact on peel oil composition. Terpenes are almost exclusively present in the oil from unripe fruit. As fruit mature, concentrations of aliphatic aldehydes and oxygen-containing terpenes and sesquiterpenes increase [30]. For example, nootkatone and a-selinenone were not detected in the peel oils from fully developed immature fruit, but the oil from ripe fruits contained up to 0.15% of these oxygenated sesquiterpenes. 

Lemon peel oil is much more valuable than its juice therefore, extensive research efforts have been expended to determine its natural composition as a way to detect adulteration as well as to determine quality factors [6, 31, 32]. However, a few studies on lemon juice volatiles can be found [33-35]. Lemon oils are notable for possessing relatively low levels of limonene (more than 70%) and relatively high levels of a-pinene (1-2%), -pinene (6-13%), sabinene (1-2%) and y-terpinene (8-10%) [32]. The relatively high concentration of -pinene is thought to instil the green peely odour of lemon oil. The concentrations of aliphatic and monoterpenic aldehydes, (especially citral) as well as those of esters and alcohols are critical components in the perceived quality of the oil. As lemon oil is unstable, quality can deteriorate with improper storage, resulting in... 

Mandarin peel oil volatiles contain many of the same volatiles as orange peel oil however, there are a few differences such as elevated levels of dimethyl an-thranilate and thymol. It has been reported [54] that the characteristic mandarin peel oil aroma was due to a combination of dimethyl anthranilate, thymol, a-terpinene and /1-pinene. 

The major volatile components in mandarin peel oil have been separated and quantified using capillary GC with flame ionisation detection/MS detection [7, 55, 56]. The identities and relative composition of 17-85 volatiles were reported. 

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. 

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