Citrus essential oil

In the case of citrus essential oils, LC pre-fractionation can be used to obtain more homogeneous chemical classes of compounds for analysis by GC without any problems of overlapping peaks. 

Mondello et al. (54) have developed some applications of on-line HPLC-HRGC and HPLC-HRGC/MS in the analysis of citrus essential oils. In particular, they used LC-GC to determine the enantiomeric ratios of monoterpene alcohols in lemon, mandarin, bitter orange and sweet orange oils. LC-GC/MS was used to study the composition of the most common citrus peel, citrus leaf (petitgrain) and flower (neroli) oils. The oils were separated into two fractions, i.e. mono- and sesquiterpene... 

Mondello, L., Casilli, A., Tranchida, P.Q., Dugo, R, Dugo, G. (2005) Comprehensive two-dimensional GC for the analysis of citrus essential oils. Flavour Fragrance J. 20 136-140. 

This process is also used to obtain very highly concentrated, high-quality isolates from plant juices [23] and the recovery of volatiles from waste streams, notably apple or berry pumice, citrus and onion waste [22]. For example, the see is claimed to efficiently recover more than 90% of the citrus essential oils traditionally lost with the centrifuge waste [22]. 

Shaw, P.E. 1979. Review of quantitative analyses of citrus essential oils. J. Agric. Food Chem. 27 246-257. 

Shaw, P. E. Citrus essential oils. Perfurn. Flav., 1979, 3, 35-39. 

Introduction. Citrus essential oil is one of the most important constituents that contribute to the flavor of juice. 

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). 

Figure 10.11 Comparison of the mass spectra of a neroli oil peak (camphene) obtained by HPLC-HRGC-MS (a) and GC-MS (b) with a library spectrum of the same compound (c). Reprinted from Perfumer and Flavorist, 21, L. Mondello et al., On-line HPLC-HRGC in the analytical chemistry of citrus essential oils , pp. 25-49, 1996, with permission from Allured Publishing Corp.

L. Mondello, G. Dugo, P. Dugo and K. Bartle, On-line HPLC-HRGC in the analytical chemistry of citrus essential oils , Perfumer Flavorist 21 25 -49 (1996). 

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,... 

Mondello, L., Stagno D Alcontres, I., Del Duce, R., and Crispo, F. (1993). On the genuineness of citrus essential oils. Part XL. The composition of the coumarins and psoralens of calabrian bergamot essential oil [Citrus bergamia Risso). Flavour Fragr. J. 8, 17—24. 

The essential oil is a pale yellow with a light, bitter-sweet floral odour. The absolute is darker and more viscous with an odour closer to the original flower. The main chemical components of the essential oil are the alcohol lin-alool (30-37%), the ester linalyl acetate (6-17%) and monoterpenes limonene (12-18%) and [3-pinene (12-15%). Also present geraniol (2-3%), nerol (1-3%), nerolidol (3-6%), citral and jasmone. Both the plant and the essential oil have many established uses. The essential oil is considered to be one of the most effective as a sedative, carmative and antidepressant and often used to treat insomnia. It is also claimed to be relaxant for smooth muscle (internal, involuntary muscles) especially those of the gut. Suitable for all skin types, both the essential oil and hydrolat are versatile materials for the aromatherapist. Considered safe as it is nonirritant and non-sensitizing and an example of a non-phototoxic citrus essential oil. 

Citrus essential oils and many herbal essential oils that are rich in highly volatile, low boiling point monoterpenes will deteriorate very quickly if not kept cool. Ideally they should be used within six months of purchase, but if they are stored and handled carefully this can be extended for up to a year. Most other essential oils should be used within a year of purchase or first opening, but this may be extended to two years if they are handled carefully and stored in a refrigerator. These effects can be explained by the fact that the rate of deterioration doubles for every 10°C rise in temperature. 

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. 

Flavones in citrus essential oils Antraquionones in rhubarb Antraquionones in rhubarb Triglycerides of vegetable and fish oil Fatty acids of vegetable and fish oil Unsaturated fatty acids methyl esters Glycosphingolipids Cannabinnoids... 

Oils and juices are obtained from plant sources by expression. Citrus essential oils are almost exclusively obtained by this method. Thoroughly washed unripe citrus fruits are cold pressed manually, or mechanically, to rupture oil cells in the rind. The oil is collected by draining and centrifuging. Manual operation is labor intensive and has been replaced by machines. 

Braddock, R.J., Temmelli, F., and Cadwallader, K.R. 1986. Citrus essential oils—a dossier for material safety data sheets. Food Technol. 40(11) 114—116. 

Slater C.A, and Watkins W.T. (1964) Citrus essential oils. IV. Chemical transformations of lime oil. J. Sci. Food Agric. 15, 657-64,... 

Isotope Ratio Analysis by HRGC-MS of Monoterpene Hydrocarbons from Citrus Essential Oils... 

In principle, it is possible to obtain the isotope ratio from MS data. The authors have previously shown, in fact, a practical use for the isotope ratio from mass spectrometry. (10) However, more detailed analytical conditions need to be found to achieve more precise measurement. The intensity of each molecular ion peak is not very strong. In addition, the isotope peak is approximately 10% of that of the molecular ion peak in the case of monoterpene hydrocarbons in citrus essential oils. 

The modified Ir data for monoterpene hydrocarbons from the three species of citrus oils were subjected to a multivariate analysis. According to principal component (PC) analysis, the citrus essential oils examined were clearly discriminated, with 93.3% of the accumulation contribution ratio of both PCI and PC2 (Fig. 4A). As shown in Fig. 4B, p-pinene (PCI, 0.530 PC2, -0.80), a-terpinene (0.685 0.062) and P-phellandrene (0.324 0.810) were large for the absolute value of the eigenvector of monoterpene system hydrocarbons, followed by terpinolene (0.367 -0.010). These compounds greatly contributed to the modified Ir discrimination of the citrus essential oils. 

These results suggest that, in addition to an enantiomeric analysis, (16,17) this analytical method can be applied to evaluate the genuineness of essential oils. Furthermore, it is expected that this technique of isotope ratio analysis will be applicable to evaluate the origin of citrus essential oils and their products, and also to specify organic compounds from natural resources. 

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