Monoterpenes characteristics

The first observation is the similarity between the chemical compositions of both the Boswellia carteri and Boswellia sacra. For these three olibanum samples, a-pinene (2), (3-myrcene (8) and limonene (14) are the predominant monoterpenes. p-Caryophyllene (73) is the major sesquiterpene besides a-copaene (65), a-humulene (also called a-caryophyllene) (78) and caryophyllene oxide (95). The characteristic olibanum compounds isoincensole and isoincensole acetate (128) together with cembrene A (120) are the main diterpenes. 

B. frereana and B. papyrifera olibanum have very different terpenic composition from the others. B. frereana olibanum contains the same monoterpenes as olibanum from B. carteri, B. sacra or B. serrata, but is very poor in sesquiterpenes and contains none of the diterpenic biomarkers cited before. Two unidentified compounds (55 and 56) seem to be specific and the main diterpenes, present in high level, are four dimers of a-phellandrene. Dimer 3 (113) is the major component. On account of its absence in the other olibanum samples, it can be considered as characteristic of B. frereana olibanum. 

Catalytic conversions in the monoterpene field have been reviewed recently [13-15]. There is an ongoing transition from conventional homogeneous catalysts (mineral acids, zinc halides) to solid Bronsted and Lewis acid catalysts. Thus, limonene can be alkoxylated with lower alcohols using zeolite H-Beta as the catalyst [16] at room temperature already, with high selectivity and conversion (Scheme 5.3). The alkoxy compounds are applied as fragrances with, dependent on the length of R, characteristic odors. 

Another large volume monoterpene is (—)-menthol, a compound that belongs to a family of eight stereoisomers. Only (—)-menthol (1 R,2S,3R-configuration) possesses the characteristic peppermint odor and exerts the unique cooling sensation on the skin. Most (—)-menthol is obtained by freezing peppermint or cornmint oil, followed by recrystallization. Besides this natural menthol some 20% or 3000 t a-1 is made by (semi)-synthesis. 

In addition to 75% monoterpene hydrocarbons (Oa-pinene 5-21% /7-pinene 40-70% 3-carene 2-16%) and ca. 10% sesquiterpene hydrocarbons, galbanum oil contains a fairly large number of terpene and sesquiterpene alcohols and their acetates. Minor components, with entirely different structures and low odor threshold values, contribute strongly to the characteristic odor [284a, 515-519]. Examples are as follows ... 

Important aroma compounds of black currant berries have been identified mainly by GC-O techniques by Latrasse et al. [119], Mikkelsen and Poll [115] and Varming et al. [7] and those of black currant nectar and juice by Iversen et al. [113]. The most important volatile compounds for black currant berry and juice aroma include esters such as 2-methylbutyl acetate, methyl butanoate, ethyl butanoate and ethyl hexanoate with fruity and sweet notes, nonanal, /I-damascenone and several monoterpenes (a-pinene, 1,8-cineole, linalool, ter-pinen-4-ol and a-terpineol) as well as aliphatic ketones (e.g. l-octen-3-one) and sulfur compounds such as 4-methoxy-2-methyl-butanethiol (Table 7.3, Figs. 7.3, 7.4, 7.6). 4-Methoxy-2-methylbutanethiol has a characteristic catty note and is very important to blackcurrant flavour [119]. 

The root of carrot Daucus carota) is eaten raw or cooked. The characteristic aroma and flavour of carrots are mainly due to volatile compounds, although non-volatile polyacetylenes and isocoumarins contribute significantly to the bitterness of carrots [1,2]. More than 90 volatile compounds have been identified from carrots (Table 7.9) [207-215]. The carrot volatiles consist mainly of terpenoids in terms of numbers and amounts and include monoterpenes, sesquiterpenes and irregular terpenes. Monoterpenes and sesquiterpenes account... 

Parsley (Petroselinum crispum) is a member of the Apiaceae family. The fresh leaves of parsley and the dried herb are widely used as flavouring. More than 80 compounds have been identified in the volatile fraction, and the aromatic volatiles of parsley are mainly monoterpenes and the aromatics myristicin and api-ole. It is suggested that the characteristic odour of parsley is due to the presence ofp-mentha-l,3,8-triene, myrcene, 3-sec-butyl-2-methoxypyrazine, myristicin, linalool, (Z)-6-decenal and (Z)-3-hexenal [227, 228]. Furthermore, /3-phellan-drene, 4-isopropenyl-l-methylbenzene and terpinolene contribute significantly... 

Mango is one of the most popular and best known tropical fruits [44] and possesses a very attractive and characteristic flavour. Some authors reported great differences in flavour compounds (including esters, lactones, monoterpenes, and sesquiterpenes) [14]. 

The different terpenoid content of plants has served as a finger printing method helpful in botanical identification, especially in cases where differentiation by morphological characteristics has failed The striking difference in the chemotaxonomy of Jeffery and ponderosa pines serves as an example. The turpentine from the former species consists almost entirely of the paraffinic hydrocarbon ji-lieplaiie. Turpentine from ponderosa pine consists largely of the monoterpenes, 6-pinene and A3-carene. 

Gas-phase ozonolyses of ethene, cis- and trans-but-2-ene, isoprene, as well as several monoterpenes such as o-pinene, /3-pinene, 3-carene, limonene, and /3-myrcene have been performed by trapping the reaction products in C>2-doped argon matrices and recording the IR spectra <2000SAA2605>. Bands characteristic for the secondary ozonides were identified after bleaching by broad-band UV-Vis photolysis. In the case of isoprene 34, a secondary ozonide appears to be formed more likely at the more substituted double bond however, the two possible carbonyl compounds 35 and 36 could not be put into evidence by infrared (IR) in the reaction condensate as these reacted further with O3 (Scheme 6). 

Ginger owes its characteristic organoleptic properties to two classes of constituents the odour and the flavour of ginger are determined by the constituents of its steam-volatile oil, while the pungency is determined by non-steam-volatile components, known as the gingerols. The steam-volatile oil comprises mainly of sesquiterpene hydrocarbons, monoterpene... 

The odour of pepper oil is described as fresh, dry-woody, warm-spicy and similar to that of the black peppercorn (Purseglove et al., 1981). The flavour is rather dry-wood and lacks the pungency of the spice since the alkaloids are not extracted by steam distillation. Very few studies are reported in the literature on correlation of oil composition to odour characteristics. Hasselstrom et al. (1957) attribute the characteristic odour of pepper oil to the small amounts of oxygenated constituents present. Lewis etal. (1969) consider that a number of monoterpenes present in the oil are necessary for strong... 

The essential oil content of cumin seed ranges from 2.3 to 5.0%. Cumin fruits have a distinctive bitter flavour and a strong, warm aroma due to their abundant essential oil content. Of this, 40-65% is cuminaldehyde (4-isopropylbenzaldehyde), the major constituent and important aroma compound, and also the bitterness compound reported in cumin (Hirasa and Takemasa, 1998). The odour is best described as penetrating, irritating, fatty, overpowering, curry-like, heavy, spicy, warm and persistent, even after drying out (Farrell, 1985.) The characteristic flavour of cumin is probably due to dihydrocuminaldehyde and monoterpenes (Weiss, 2002). 

For this sample the results show identification of 13 major components out of 289, making up 81.25% of the total components. The volatile monoterpene -pinene (peak 1) is the first off the column. The alcohols citronellol (10) and geraniol (11) are responsible for the odour characteristics of geranium, which is lifted and activated by the two rose oxides (2 and 3). The 6,9-guaiadiene (7) is a non-terpene hydrocarbon that acts as a back note but it is not a powerful odour. Component 12 is geranyl butyrate component 13 is epi—eudesmol. Chromatograms and data supplied by Jenny Warden of Traceability. 

Figure 5.4 Mass spectra. The monoterpenes -pinene (A) and limonene (B) both have the molecular formula C10H16 and their mass spectra are similar however, the obvious differences at m/z 68 and m/z 93, coupled with accurate and reproducible retention times from GC, enable an identification for each compound. (C) The oxide eucalyptol (1,8-cineole), with molecular formula C H, produces this characteristic pattern when analyzed by mass spectrometry. MS data supplied by Bill Morden of Analytical Intelligence Ltd.

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