Compounds essential oils

Prerequisites for the use of GC, such as volatility and thermal stability of the analytes, restrict exclusive application of this technique. Thus, this very power-fill technique for enantioselective analysis of many natural compounds (essential oils, terpenoids, food components, etc.) may fail for most pharmaceutical and biomedical applications, where the samples are polar and nonvolatile or too thermolabUe. 

Occurrence In small amounts in many flavor compounds, essential oils, and flower aromas. The main ingredient of bitter almond oil B. is formed by hydrolysis of the glycoside amygdalin. For analytical distinction from synthetic B., see Lit.. ... 

Essential oils (Section 26 7) Pleasant smelling oils of plants consisting of mixtures of terpenes esters alcohols and other volatile organic substances Ester (Sections 4 1 and 20 1) Compound of the type... 

The flavor chemist is responsible for the basic knowledge of sensory and appHcation properties of each of this large number of raw materials the large number of possible combinations of these items to produce specifically flavored finished compounds is readily apparent. It is not uncommon to develop a flavor that combines essential oils, plant extractive, fmit juices, and synthetics. The choice of materials depends on type of product, conditions of manufacture, labeling, and intended use. 

Applications. The most ubiquitous use of infrared spectrometry is chemical identification. It has long been an important tool for studying newly synthesi2ed compounds in the research lab, but industrial identification uses cover an even wider range. In many industries ir spectrometry is used to assay feedstocks (qv). In the flavors (see Flavors and spices), fragrances (see Perfumes), and cosmetics (qv) industries, it can be used not only for gross identification of feedstocks, but for determining specific sources. The spectra of essential oils (see Oils, essential), essences, and other natural products vary with the season and source. Adulteration and dilution can also be identified. 

Other commonly occurring chemical groups ia essential oils iaclude aromatics such as P-phenethyl alcohol, eugenol, vanillin, ben2aldehyde, cinnamaldehyde, etc heterocycHcs such as iadole (qv), pyra2iaes, thia2oles, etc hydrocarbons (Liaear, branched, saturated, or unsaturated) oxygenated compounds such as alcohols, acids, aldehydes, ketones, ethers and macrocyclic compounds such as the macrocyclic musks, which can be both saturated and unsaturated. 

Volatiles or Aroma. The essential oil, or aroma, of tea provides much of the pleasing flavor and scent of green and black tea beverages. Despite this, volatile components comprise only - 1% of the total mass of the tea leaves and tea infusions. Black tea aroma contains over 300 characterizing compounds, the most important of which are terpenes, terpene alcohols, lactones, ketones, esters, and spiro compounds (30). The mechanisms for the formation of these important tea compounds are not fully understood. The respective chemistries of the aroma constituents of tea have been reviewed... 

Essential Oils. Volatile oils from plants are referred to as essential oils. The oils can be obtained through steam distillation, solvent extraction, or separation of the oils from pressed fmit. They consist of oxygenated compounds, terpenes, and sesquiterpenes. The primary flavor components of essential oils are oxygenated compounds. Terpenes contain some flavors but are often removed from the essential oil because they are easily oxidized (causiag off-flavors or odors) and are iasoluble. Essential oils are prepared from fmits, herbs, roots, and spices. 

Perfumes, Flavors, Cosmetics, and Soap. Many naturally occurring esters in essential oils and some synthetic esters are important fragrance and flavor compounds (61,62). They are used in perfumes, flavors, cosmetics, soaps, detergents, and air fresheners. Benzyl, butyl, ethyl, methyl, and phenyl esters of benzoic acid are used as flavors, perfumes, and food preservatives. Glyceryl 4-aminobenzoate [136-44-7] and 2-ethyUiexyl 4-dimethylaminobenzoate [21245-02-3] are used in cosmetic sunscreen preparations. Alkyl esters of 4-hydroxybenzoic acid, called parabens, have been used under various names for fungus infections of the skin, and as preservatives in lotions and creams (101). Soap and cosmetic fragrances use large amounts of amyl and benzyl saHcylate. Benzyl saHcylate [118-58-1] is also used in deodorant sprays. 2-Ethylhexyl saHcylate [118-60-5] and 2-ethylhexyl 4-methoxycinnamate [5466-77-3] are used in sunscreen formulations (102). 

Martinek [182] has described the reverse procedure for relatively volatile substances (e.g. essential oil components), where the compound to be detected is "distilled onto the reagent plate and reacts with the reagent there. 

It is the determination of volatile organic compounds produced from natural products that requires separation techniques that allow isolation of stereoisomers. The most commonly determined groups are the terpene and sesquiterpene species present in essential oils, which are used as key indicators of biological factors such as the growth season, geographic location, climate, etc. These species are also released directly into the atmosphere by very many plants and trees, and make a substantial contribution to global biogeochemical cycles. 

A. Mosandl, K. Eischer, U. Hener, P. Kieis, K. Rettinger, V. Schubert and H.-G. SchmaiT, Stereoisomeiic flavor compounds. 48. Cliirospecific analysis of natural flavor s and essential oils using multidimensional gas cliromatography , ]. Agric. Food Chem. 39 1131-1134(1991). 

P Dugo, L. Mondello, E. Sebastian , R. Ottana, G. Eirante and G. Dugo, Identification of minor oxygen heterocyclic compounds of citi us essential oils by liquid chromatography-atmospheric pressure chemical ionisation mass specti ometiy , J. Liq. Chromatogr. 22 2991-3005 (1999). 

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. 

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 specti um of the same compound (c). Reprinted from Perfumer and Flavorist, 21, L. Mondello et al., On-line HPLC- HRGC in the analytical chemistiy of citms essential oils , pp. 25-49, 1996, with permission from Allured Publishing Coip.

Supercritical fluid extraction (SFE) has been extensively used for the extraction of volatile components such as essential oils, flavours and aromas from plant materials on an industrial as well as an analytical scale (61). The extract thus obtained is usually analysed by GC. Off-line SFE-GC is frequently employed, but on-line SEE-GC has also been used. The direct coupling of SEE with supercritical fluid chromatography (SEC) has also been successfully caried out. Coupling SEE with SEC provides several advantages for the separation and detection of organic substances low temperatures can be used for both SEE and SEC, so they are well suited for the analysis of natural materials that contain compounds which are temperature-sensitive, such as flavours and fragrances. 

Often, planar chromatography is used as a preparative step for the isolation of single components or classes of components for further chromatographic separation or spectroscopic elucidation. Many planar chromatographic methods have been developed for the analysis of food products, bioactive compounds from plant materials, and essential oils. 

P Kreis and A. Mosandl, Chfral compounds of essential oils. Part XIII. Simultaneous chirality evaluation of geranium oil constituents , Flav. Fragr. 7. 8 161 -168 (1992). 

D. Bartschat, D. Eehmann, A. Dietrich, A. Mosandl and R. Kaiser, Chfr al compounds of essential oils. XIX. 4-methyl-5 decanolide chfr ospeciflc analysis, str ucture and properties of the stereoisomers , Phytochem. Anal. 6 130-134 (1995). 

D. Jukelka, A. Steil, K. Witt and A. Mosandl, Chiral compounds of essential oils. XX. Cliirality evaluation and authenticity profiles of neroli and petitgrain oils , ]. Essential Oil Res. 8 487-497 (1996). 

Numerous methods for the determluation of " mustard oil," that is, of the thiocyanate compound, in the essential oil, or in preparations llioreol,... 

In the case of sweet basil, Ocimwn basilicum, Charabot and Hubert have examined the essential oils distilled from plants which had been cultivated in full light and from those kept shaded from the light. Jn the former case the oil contained 57 3 per cent, of estragol and 42 7 per cent, of terpene compounds, whilst in the case of the shaded plants the estragol had risen tO 74 2per cent, and the terpene compounds fell to 25 8 per cent. 

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