Norisoprenoid derivatives

Table 7.2. Example of the distribution of free and bonded forms of the main monoterpenols and several Ci3-norisoprenoid derivatives in ripe grapes...

The oxidative degradation of carotenoids (Figure 7.3), terpenes with 40 carbon atoms (tetrater-penes), produces derivatives with 9, 10, 11 or 13 carbon atoms (Enzel, 1985). Among these compounds, norisoprenoid derivatives with 13 carbon atoms (Ci3-norisoprenoids) have interesting odoriferous properties. These compounds are common in tobacco, where they were initially smdied (Demole et al., 1970 Demole and Berthet, 1972), but they have also been studied in grapes (Schreier et al., 1976 Simpson et al., 1977 Simpson, 1978 Sefton et al., 1989 Winterhalter, 1993). 

From a chemical point of view these norisoprenoid derivatives are divided into two main forms megastigmane and non-megastigmane. Each of these includes a large number of volatile compounds (Figure 7.4). The megastigmane skeleton is characterized by a benzene cycle substituted on carbons 1, 5 and 6, and an unsaturated aliphatic chain with four carbon atoms attached to Ce. 

In the natural world, carotenoid oxidation products are important mediators presenting different properties. Volatile carotenoid-derived compounds such as noriso-prenoids are well known for their aroma properties. Examples include the cyclic norisoprenoid P-ionone and the non-cyclic pseudoionone or Neral. Carotenoid oxidation products are also important bioactive mediators for plant development, the best-known example being abscisic acid. Apo-carotenoids act as visual and volatile signals to attract pollination and seed dispersal agents in the same way as carotenoids do, but they are also plant defense factors and signaling molecules for the regulation of plant architecture. 

The aglycon part of glycoside is often represented by monoterpenes, C13-norisoprenoids, benzene derivatives, and long-chain aliphatic alcohols (Fig. 18) [74, 75]. 

Several volatile C.- norisoprenoids have previously been identified in steam-distilled quince fruit oil, in which they are regarded to contribute to the overall flavor impression. These include isomeric theaspiranes, various bicydononane derivatives, 3,4-didehydro- 3-ionol, and isomeric megastigmatrienones and theaspirones (4,5). This report concerns the identification of additional norisoprenoids and their natural precursors in quince fruit. 

Winterhalter, R, Sefton, M.A., Williams, P.J.. (1990). Two-dimensional GC-DCCC analysis of the glycoconjugates of monoterpenes, norisoprenoids, and shikimate-derived metabolites form Riesling wine. 7. Agric. Food Chem., 38, 1041-1048. 

Monoterpenes, Norisoprenoids, Aliphatics, Benzene-derivatives Long-chain polyfunctional thiols Transformation products... 

It is well known that the secondary metabolites of grapes provide the basis of varietal character in wine. The important secondary metabolites are represented by several groups of compounds that contribute to the distinctive aroma profile of wines made from particular varieties of Vitis vinifera. They include terpenes, Ci3-norisoprenoids, aliphatics, benzene-derivatives, volatile phenols and long-chain polyfuntional thiols. While constituent aroma compounds within these groups occur in most grape varieties, it is only when one or more of these compounds occur at concentrations well above their odour threshold that a distinctive varietal aroma emerges. 

Numerous volatiles are released upon hydrolysis of glycoside isolates (1, 13), many of which are presumed to be acting as flavor compounds. Different grape varieties apparently produce glycosides which, when hydrolyzed, release differing proportions of monoterpenes, Cn norisoprenoids and benzene derivatives, as well as other volatiles. However, there is little reliable aroma threshold information regarding many of these compounds, and there has been no systematic attempt to relate the volatile composition of the hydrolysates to their sensory properties. 

An examination of hydrolysates produced by glycosidase enzyme or pH 3.2 acid treatment of reversed-phase isolates frcm juices of "non-floral " itis vinifera vars. Chardonnay, Sauvignon Blanc and Semilion demonstrated that these grapes contain conjugated forms of monoterpenes, C, norisoprenoids, and shikimic acid-derived metabolites. The volatile conpounds obtained hydrolytically from the conjugates were produced in sufficient concentration to permit ready analysis by GC/MS. The products of pH 3.2 hydrolysis have sensory significance when assessed in a neutral wine. The study further develops the precursor analysis approach as a technique to facilitate research into varietally specific constituents of grapes. 

Conversely, many of the major norisoprenoid aglycons recorded in Table I do not appear to contribute significantly to the products given by acid hydrolysis. The hydrolytic chemistry of vomifoliol 28 and 3-oxo-u-ionol 24 has been studied (25) only trace amounts of 3-oxo-a-ionone 25 and an isomer of 3,4-dihydro-3-oxoactinidol 19, which are derivable from the former aglycon 28, were observed, and none of the products reported ( ) from 3-oxo-a-ionol 24 were found. 

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. 

Finally, we would like to emphasize the HS-SPME technique as a very useful tool for evaluating non-polar compounds in traces as shown in Figure 5.2, such as esters like ethyl 9-decenoate or monoterpenes, as well as some norisoprenoids and monoterpenols derivatives such as the ethoxyethers (Carlin, 1998 Versini et al., 1999). HS-SPME efficiency in the higher alcohols quantification was verified by evaluating results with those obtained by direct injection of the wine distillate. 

Gunata, Z., Wirth, J.L., Guo, W. and Baumes, R.L. (2002) C13-norisoprenoid aglycon composition of leaves and grape berries from Muscat of Alexandria and Shiraz culti-vars, In Carotenoid-derived aroma compounds, ACS Symp. Series 802, Am. Chem. Soc., Washington DC. 

The subsequent recognition of glycosides of C13 norisoprenoid compounds and of shikimic acid-derived metabolites as precursors of non-floral grape flavor, was a later development (6). Further aspects of the involvement of glycosides in the flavor of grapes and wines have been recently discussed (7-9). 

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