Aroma compounds monoterpenes

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]. 

Terpenoids are synthesised by the condensation of a series of isoprene (2-meth-ylbuta-1,3-diene) units, followed by enzymatic cyclisation by a terpene cyclase, and subsequent modification such as hydroxylation, and are grouped on the basis of their carbon chain length. Monoterpenes and sesquiterpenes consisting of ten and 15 carbon atoms, respectively, are ranked among the most important aroma compounds. Despite their diversity, all terpenoids are synthesised... 

The volatile oil of nutmeg constitutes the compounds monoterpene hydrocarbons, 61-88% oxygenated monoterpenes, i.e. monoterpene alcohols, monoterpene esters aromatic ethers sesquiterpenes, aromatic monoterpenes, alkenes, organic acids and miscellaneous compounds. Depending on the type, its flavour can vary from a sweetly spicy to a heavier taste. The oil has a clovelike, spicy, sweet, bitter taste with a terpeny, camphor-like aroma. 

As for coriander, in the unripe fruits and the vegetative parts of the plant, aliphatic aldehydes predominate in the steam-volatile oil and are responsible for the peculiar aroma. On ripening, the fruits acquire a more pleasant and sweet odour and the major constituent of the volatile oil is the monoterpene alcohol, linalool. Sotolon (also known as sotolone, caramel furanone, sugar lactone and fenugreek lactone) is a lactone and an extremely powerful aroma compound and is the major aroma and flavour component of fenugreek seeds (Mazza et al., 2002). 

The major monoterpene hydrocarbons present in pepper oil are a- and (3-pinenes, sabinene and limonene. Chemical structures of major aroma compounds are illustrated in Fig. 2.1. 

It contains the same aroma compounds as nutmeg but in smaller amounts, mainly monoterpenes (87.5%), monoterpene alcohols (5.5%) and other aromatics (7%). Like nutmeg essential oil, the main constituents of mace essential oil are sabinene, a-pinene, (3-pinene, myrcene, limonene, 1,8-cineole, terpinen-4-ol, myristicin, y-terpinene and safrole. Mace oil is more expensive than nutmeg oil. 

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). 

The release of glycosidically-bound aroma compounds, such as monoterpenes, C13 norisoprenoids, and aliphatic alcohols, can be achieved by the action of glycosi-dase enzymes. 3-Glycosidase activity has not been much studied in wine LAB. McMahon et al. (1999) detected a low p-glycosidase activity in O. oeni OSU and a... 

Monoterpenes, norisoprenoids - some C13 megastigmane compounds -some benzenoid compounds called shikimates because of their origin from shikimic acid, and some polyfunctional sulphured compounds, are the most important grape-derived aroma compounds. In the winemaking process, these molecules are transferred to the wine both as free and bound forms. 

Essential oils contain a variety of compounds divided into two main groups hydrocarbons and oxygenated compounds. For garden mint, the essential oil is mainly carvone (oxygenated monoterpene) and limonene (monoterpene hydrocarbon). How does the microwave energy effect differ for these two different aroma compounds It would be reasonable to believe that the more polar the compound the more readily the microwave irradiation is absorbed, because of the better interaction between the electromagnetic wave and compound, so the oil obtained contains more of the more polar aromatic components. This would seem to correspond well to the observed behavior of carvone (polar compound) and limonene (non polar compound) (Table 22.5). 

The volatile fractions of many plants are isolated by steam distillation, distillation, or by solvent extraction (Banthorpe, 1991). The resulting volatile compounds that make up the essence or aroma of plants are called essential oils. Altiiough essential oils are comprised of many types of compounds, monoterpenes are major among them. These oils may also contain metabolically modified fatty acids, aldehydes, hydrocarbons, esters, phenylpropanoid compounds, acetylenic compounds, volatile alcohols, volatile alkaloids, phenylpro-panoids, and other shikimic acid derivatives. 

Hydroformylation, which yields aldehydes, seems to be of particular value for the production of aroma compounds [1]. One important reason is associated with the chemical structure of starting compounds and products. Thus, in several cases pleasantly smelling olefins, mainly terpenes, are found in nature. Such terpenes (preferentially monoterpenes and some sesquiterpenes) with their sometimes multiple C=C-double bonds constitute one of the most important feedstock in flavor and fragrance industry. 

The two ethyl-homologous carbonyl compounds (286) and (289) have so far only been found in tea oil (49J). The possibility that 5-ethyl-6-methylheptan-2-one (286) originates from the metabolism of a monocyclic monoterpene cannot be excluded (49J), although this ketone seems more likely to be formed by oxidative biodegradation of the sitosterol side chain. Thus, for instance, all the aroma compounds (282) to (291) listed here except (286) and (289) were detected in tobacco oil (777, J42, 306, 463, 590). 

Citrus oils contain up to 95% monoterpene hydrocarbons (usually limonene, but others as well, e.g., lemon oil also contains a-terpinene and /3-pinene). The important aroma-determining components of citrus oils are functionalized terpenes and aliphatic compounds (predominantly carbonyl compounds and esters), present only in relatively low concentrations [358]. Thus, several methods are employed to concentrate citrus oils on an industrial scale. The monoterpene hydrocarbon... 

The aroma of intact black currant fruit is mostly produced by anabolic pathways of the plant, and production of fruit volatiles occurs mainly during a short ripening period [112]. The aroma profile of black currant shares similarities with that of other berry fruits, although terpenes are more abundantly present in black currant [107]. Black currant is mainly used for the production of juice. Over 150 volatile compounds have been reported from either black currant berries and/or juice, of which the major groups are monoterpenes, sesquiterpenes, esters and alcohols [107]. Processing of berries to juice has been shown to lead to major changes in the aroma composition [113-118]. 

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... 

A wide range of volatile compounds from Indian mango were identified by pioneer group research [20,21]. Esters, lactones, monoterpenes, sesquiterpenes, and furanones were among the volatiles. It has been suggested that the ratio of palmitic to palmitoleic acids determines the flavour quality of the ripe fruit, a ratio of less than 1 resulting in strong aroma and flavour [44]. 

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