Hydrocarbon, aroma substance

Fruits and vegetables (e. g., pineapple, apple, pear, peach, passion fruit, kiwi, celery, parsley) contain unsaturated Cn hydrocarbons which play a role as aroma substances. Of special interest are (E,Z)-l,3,5-undecatriene and (E,Z,Z)-1,3,5,8-undecatetraene, which with very low threshold concentrations have a balsamic, spicy, pinelike odor. It is assumed that the hydrocarbons are formed from unsaturated fatty acids by P-oxidation, lipoxygenase catalysis, oxidation of the radical to the carbonium ion and decarboxylation. The hypothetical reaction pathway from linoleic acid to (E,Z)-l,3,5-undecatrieneis shown in Formula 5.25. 

The fresh ginger root has a citrus and camphorlike, flowery, musty, fatty and green odor. In a column chromatographic preliminary separation of an extract, the characteristic aroma substances appeared in the fraction of the oxidized hydrocarbons. The highest FD factors in dilution analyses were obtained for geraniol, linalool, geranial, cit-ronellyl acetate, bomeol, 1,8-cineol and neral. 

Mixtures of gaseous or liquid hydrocarbons which can be vaporized represent the raw materials preferable for the industrial production of carbon black. Since aliphatic hydrocarbons give lower yields than aromatic hydrocarbons, the latter are primarily used. The best yields are given by unsubstituted polynuclear compounds with 3-4 rings. Certain fractions of coal tar oils and petrochemical oils from petroleum refinement or the production of ethylene from naphtha (aromatic concentrates and pyrolysis oils) are materials rich in these compounds. These aromatic oils, which are mixtures of a variety of substances, are the most important feedstocks today. Oil on a petrochemical basis is predominant. A typical petrochemical oil consists of 10-15% monocyclic, 50-60% bicyclic, 25-35% tricyclic, and 5-10% tetracyclic aroma tes. 

From our aroma research on boiled small shrimps, almost one hundred volatile components were identified. Among them, more than forty components were determined as sulfur- and/or nitrogen-containing heterocyclic substances, together with various kinds of volatiles that are well known to be thermally generated such as hydrocarbons, carbonyl compounds, alcohols and phenols. The shrimp... 

Some measured values, D and K, (Koszinowski 1986, and Koszinowski and Pirin-ger, 1990) are contained in Table 9-7. These data deal mainly with the partition coefficients of hydrocarbons, alcohols, phenols and a series of aromas between polyolefins and a liquid phase (ethanol, methanol) as well as diffusion coefficients of these substances in the polymer. 

This same hydrocarbon, first isolated from compressed illuminating gas by Michael Faraday in 1825, is now called benzene. It is the parent hydrocarbon of a class of substances that we now call aromatic compounds, not because of their aroma, but because of their special chemical properties, in particular, their stability. Why is benzene unusually stable, and what chemical reactions will benzene and related aromatic compounds undergo These are the subjects of this chapter. 

An important hydrocarbon is benzene, which has the formula CgHg. It is a volatile liquid (m.p. 5.5°C, b.p. 80.rC, density 0.88 g cm ). Benzene and other hydrocarbons similar to it in structure are called the aromatic hydrocarbons Their derivatives are called aromatic substances —many of them have a characteristic aroma (agreeable odor). Benzene itself was discovered in 1825 by Faraday, who found it in the illuminating gas made by heating oils and fats. 

The aroma of apricots (Armeniaca vulgaris, syn. Prunus armeniaca, Rosaceae) is composed of a large number of different substances. Important components are monoterpenic hydrocarbons, alcohols and aldehydes (myrcene, hmonene, p-cymene, terpinolene, a-terpineol, geranial, geraniol and hnalool in particular) and aldehydes with green flavour, such as (Z)-hex-3-enal and acetaldehyde. Other volatile components include products of oxidation of fatty acids, such as (2 ,6Z)-nona-2,6-dienal, (Z)-octa-l,5-dien-3-one, lactones (y-hexalactone, y-octalactone, y-decalactone, y-dodecalactone, 8-decalactone and 8-dodecalactone), carboxylic acids (especially, 2-methylbutanoic and acetic acids) and degradation products of carotenoids, such as P-ionone. 

The aroma of carrots root Daucus carota, Apiaceae) is very complex. It consists of various aldehydes, ketones, mono- and sesquiterpenic hydrocarbons and other compounds. The important hydrocarbons are myrcene, sabinene, terpinolene, P-caryophyUene, y-bisabolene and a-pinene, which are present in the largest quantities. The significant carbonyl compounds are acetaldehyde and (2 ,6Z)-nona-2,6-dienal. One of the typical aromatic substances determining the basic odour of carrots is 2-sec-butyl-3-methoxypyrazine. During the cooking of carrots, the contents of methanal, ethanal, propanal, octanal, (Z)-dec-2-enal and some sulfur compounds, such as dimethylsulfide and ethanethiol, increase. At the same time, the contents of monoterpenes and P-caryophyUene decrease. 

The primary aromatic substances in beer are derived from raw materials (barley or hops) that confer the beer s typical odour and taste. Bitter acids of hops have a bitter taste (see Section 8.3.5.1.3), but hop cones also contain 0.3-1% m/m of terpenoids (60-80% of hop essential oil), which have a considerable influence on the smell of beer. The main components of aromatic hop oils are sesquiterpenic hydrocarbons in which a-humulene, P-caryophyllene and famesene dominate. The major monoter-penic hydrocarbon is myrcene. For example, the essential oil content of fine aromatic varieties, such as Saaz, is 0.8% m/m, of which 23% is myrcene, 20.5% a-humulene, 14% famesene 6% and P-caryophyUene. Significant components of the hop aroma in beer are mainly isomeric terpenoid monoepoxides resulting from autoxidation and diepoxides of a-humulene and fS-caryophyUene, but also other terpenoids. Important components of hops odour are also various alcohols (such as geraniol and hnalool), esters (ethyl 2-methylpropanoate, methyl 2-methylbutanoate, propyl 2-methylbutanoate and esters of terpenic alcohols, such as geranyl isobutanoate), hydrocarbons, aldehydes and ketones formed by oxidation of fatty acids, such as (3E,5Z)-undeca-l,3,5-triene, (Z)-hex-3-enal, nonanal, (Z)-octa-l,5-dien-3-one, their epoxides, such as ( )-4,5-epoxydec-2-enal and sulfur compounds. Other important components of hops are so-called polyphenols (condensed tannins) that influence the beer s taste and have antioxidant effects. Less important compounds are waxes and other hpids. Hop products, such as powder, pellets and extracts (by extraction with carbon... 

Volatile components constitute about 0.1% of roasted coffee by weight Cojfea species, Rubiaceae), and more than 200 substances have been shown in green coffee. More than 800 compounds are known to make up the aroma of roasted coffee. Of these, only about 60 compounds have a significant role in the coffee aroma. Especially typical are a large number of heterocyclic compounds, mainly furans, pyrroles, indoles, pyridines, quinolines, pyrazines, quinoxalines, thiophenes, thiazoles and oxazoles, which arise in caramehsation and the MaiUard reaction during coffee roasting. In addition to heterocyclic products, other important volatiles are also some aliphatic compounds (hydrocarbons, alcohols, carbonyl compounds, carboxylic acids, esters, aliphatic sulfur and nitrogen compounds), alicyclic compounds (especially ketones) and aromatic compounds (hydrocarbons, alcohols, phenols, carbonyl compounds and esters). 

Most essential oils contain a significant proportion of terpenes (monoterpenic and sesquiterpenic hydrocarbons). For example, their level in some citrus essential oils is 95% or more. These substances are not usually essential to the smell and aroma character of essential oils, as the most important odoriferous compounds are alcohols, aldehydes, ketones, esters and other compounds. Furthermore, terpenic hydrocarbons are a reason for the limited solubility of essential oils in diluted ethanol and are often the cause of deterioration of essential oils that easily oxidise or polymerise. By removing hydrocarbons from essential oils, concentrates are obtained. Monoterpene-free or sesquiterpene-free essential... 

The aroma compounds of dry cured Parma ham have been analyzed by thermal desorption GC-MS after extraction by means of the DHS technique [7], Using GC MS, 122 substances, including hydrocarbons, aldehydes, alcohols and esters, were identified in the volatile fraction. The same research group used DHS and SDE techniques to isolate aroma components from Parmesan cheese [8], By means of GC MS, more than 100 substances were characterized in the extracts. This application is discussed later in this chapter in section 3. 

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