Norisoprenoid derivatives precursors

Knapp, H., Straubinger, M., Stingl, C., and Winterhalter, P. (2002). Analysis of norisoprenoid aroma precursors. In Carotenoid-derived aroma compounds, ACS Symp. Series 802, Am. Chem. Soc., Washington DC. 

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. 

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. 

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). 

In an acid medium, several not very odoriferous oxygenated Ci3-norisoprenoids undergo chemical modifications that may result in the formation of odoriferous /i-damascenone (Skouroumounis et al., 1992 Winterhalter, 1993) (Figure 7.5). Certain non-megastigmane Ci3-norisoprenoids, in particular TDN, are also derived from megastigmanes by chemical modifications in an acid medium (Winterhalter, 1993). However, Ci3-norisoprenoids are mainly present in grapes in the form of non-volatile precursors (carotenoids and gluco-sides). 

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