Citrus oxygenated compounds

Certain values have been reported for the concentrations of oxygenated compounds in citrus oils using chemical methods, rather than GLC. Naves (22) reported 31% octanal, 27% decanal,... 

A cyclic adsorption process for citrus oil processing in supercritical carbon dioxide (SC-C02) was studied with silica gel adsorbent. Based on the adsorption equilibrium properties, where adsorbed amounts decreased with the increase in the solvent density and oxygenated compounds were selectively adsorbed on silica gel, a continuous cyclic operation between the adsorption step at 8.8 MPa and 313 K, and the desorption step at 19.4 MPa and 313 K was demonstrated Highly concentrated fraction of oxygenated com pounds was continuously obtained for the desorption and blowdown step. The proposed system showed the feasibility of the continuous operation for citrus oil processing. 

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. 

Citrus essential oils are widely used as a raw material of flavour in food and perfumery industries. They are also called "cold-pressed oils" and contain more than 200 compounds which can be grouped in three fractions the hydrocarbon terpenes (unsaturated compounds) that constitute the major amount (from 60 to 98% by weight) but have undesirable off-flavours characteristics the oxygenated compounds (flavour fraction) that are directly responsible for the characteristic citrus flavour and the non-volatile residues. 

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. 

Citrus, like many other essential oils, consists of mixtures of hydrocarbons of the terpene and sesquiterpene groups, oxygenated compounds and nonvolatile residues. Terpenes make up approximately 95% by weight of orange oils while the oxygenated compounds constitute the remaining 5%. The compositions of citrus oils have been studied extensively by different researchers (5-9). Citrus terpenes (C QH g) are mostly unsaturated acyclic and cyclic compounds derived from the condensation of two 5-carbon isoprene units. Sesquiterpenes have the general formula Advances in... 

Apart from citrus oils, other essential oils have also been analyzed by means of LC, such as the blackcurrant bud essential oil [100]. The latter was fractionated into hydrocarbons and oxygenated compounds, and the two fractions were submitted for RP-HPLC analysis. Volatile carbonyls consist of some of the most important compounds for the blackcurrant avor and, hence, were analyzed in detail. The carbonyls were converted into 2,4-dinitrophenylhydrazones and the mixture of 2,4-dini-trophenylhydrazones was separated into derivatives of keto acids and monocarbonyl and dicarbonyl compounds. Each fraction was submitted to chromatographic investigation. 

Such a system has been used for the comprehensive 2D chromatography of proteins [9,14], synthetic polymers [16], oxygen heterocyclic fraction of cold-pressed citrus oils [22,29], carotenoids [39], triglycerides in fats and oils [18-21], pharmaceuticals [29], and acidic and phenolic compounds [27,28]. 

The oils have a high terpene hydrocarbon content (>90%, mainly (+)-limonene), but their content of oxygen-containing compounds differs and affects their quality. Important for aroma are aldehydes, mainly decanal and citral, and aliphatic and terpenoid esters. The sesquiterpene aldehydes a-sinensal [17909-77-2] and/3-sinensal [6066-88-8], which contribute particularly to the special sweet orange aroma, also occur in other citrus oils, although in lower concentration [369-370a, 370d, 394,421, 430-438]. 

P. Dugo, L. Mondello, E. Sebastiani, R. Ottana, G. Errante and G. Dugo, Identification of minor oxygen heterocyclic compounds of citrus essential oils by hquid chromatography-atmospheric pressure chemical ionisation mass spectrometry , J. Fiq. Chromatogr. 22 2991-3005(1999). 

Dugo, P., Mondello, L., Dugo, L., Gugo, L., Stancanelli, R., and Dugo, G. (2000). LC-MS for the identification of oxygen heterocyclic compounds in citrus essential oils. J. Pharm. Biomed. Anal. 24,... 

Most perfume compounds containing essential oils will deteriorate when exposed to the air, and a number of different reactions can be involved, all of which come under the general heading of oxidation, brought about by the presence of oxygen. Many of the unsaturated monoterpenes, which occur widely in citrus, coniferous, and seed oils,... 

Essential o Is like Citrus limon (lemon) and Pinus sylvestris (Scotch pine), which aie f i in terpenes such as limonene and pinene, are particularly prone to oxidation. The air provides oxygen, and oxidation is the chemical reaction in which oxygen adds onto another substance, to form a new compound. Small amounts of essential oil should not be kept in large bottles with a large amount of air above the oil. As the oil is used up, its level goes down and the amount of air above it increases. If an oil is stored in a large bottle, the number of times it is opened will also probably be more than for a smaller one, and this also exposes it to the air each time. 

It may seem strange to classify a type of bond as a functional group, but you will see later that C=C double bonds impart reactivity to an organic molecule just as functional groups consisting of, say, oxygen or nitrogen atoms do. Some of the compounds produced by plants and used by perfumers are alkenes (see Chapter 1). For example, pinene has a smell evocative of pine forests, while limonene smells of citrus fruits. 

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