Aroma grapefruit

Some reported odor threshold values for nootkatone were considerably lower than the taste threshold values. Odor thresholds of 0.8 ppm in water and 30 ppm in air were reported for (+)-nootkatone, the enantiomer of this sesquiterpene ketone present in grapefruit (35). An odor threshold of 0.15 ppm in water was reported for crystalline nootkatone isolated from grapefruit oil (36). In that study, mother liquor from crystallization of nootkatone was 30 times more potent (odor threshold of mother liquor 5 ppb) than nootkatone alone and the panel felt that the aroma of the mother liquor more closely resembled grapefruit aroma... 

The most important (and also the most expensive) grapefruit aroma compound is the bicyclic terpene nootkatone. It is manufactured by oxidation of valencene, which is extracted from Valencia oranges. Figure 1.23 shows two routes for this oxidation, a stoichiometric reaction using chromium trioxide, and a catalytic alternative using sodium hypochlorite (bleach) in the presence of 1 mol% osmium tetraoxide catalyst. 

Furusawa, M., T, Hashimoto, Y. Noma, and Y. Asakawa 2005b. Highly ef cient production of nootkatone, the grapefruit aroma from valencene, by biotransformation. 53 1513-1514. 

The grapefruit aroma, (-H)-nootkatone (2) was administered into rabbits to give 11,12-diol (6,7). The same metabolism has been found in that of biotransformation of nootkatone by miCTOorganisms as mentioned in the previous paragraph. Compounds (6, 7) were isolated from the urine of hypertensive subjects and named urodiolenone. The endogenous production of 6, 7 seem to occur inter-dentally from the administrative manner of nootkatone or grapefruit. Synthetic racemic nootkatone epoxide (14) was incubated with rabbit-liver microsomes to give 11,12-diol (6, 7) (Ishida, 2005). Thus, the role of the epoxide was clearly confirmed as an intermediate of nootkatone (2). 

The aromatic properties of essential oils are perhaps the most conspicuous and account for a wide range of traditional applications. Many terpenoids have characteristic odors, some of them are presented in Tables 96.3 and 96.4 [55-57]. The odor thresholds however may vary greatly and depend on the matrix. (—)-Limonene with citrus-like aroma is a key odorant of orange juice and neral/ geranial the key odorants of lemons. l-p-Menthene-8-thiol present in grapefruit juice and responsible for the grapefruit aroma has with 0.02 ng/L one of the lowest odor threshold values [42]. 

The characteristic grapefruit aroma and flavor of grapefruit oil is reported to be due primarily to nootkatone and other carbonyls... 

Fumsawa M, Hashimoto T, Noma Y, Asakawa Y. Highly efficient production of nootkatone, the grapefruit aroma, from valencene hy hiotransformation. Chem. Pharm. Bull 2005 53 1513-1514. 

Buettner, A. and Schieberle, P. Evaluation of key aroma compounds in hand-squeezed grapefruit juice (Citrus paradisi... 

The sesquiterpene ketone nootkatone is primarily responsible for the characteristic aroma of grapefruit oil [370a], [370d], [372-379a]. 

Table VIII. Effect of nootkatone content on aroma and taste of grapefruit oil and juice.

SulfanyUiexan-l-ol (3SH) is always present in Sauvignon blanc, at concentrations of several hundred ng/L, ranging up to a few pg/L in some wines. As a result, this compound, which smells of grapefruit and has a perception threshold of 60 ng/L, also has considerable olfactory impact. Wines containing the most 3SH also have the highest concentrations of its acetate. The citrus zest aroma of... 

Typical Scheurebe wines are characterized by a jfruity aroma, which is described as redcurrant-like, often with a grapefruit note. In 1995 Darriet et al. identified 4-mercapto-4-methylpentan-2-one (MMP), responsible for the distinctive odor of box tree and cat urine (7). The perception threshold of this compound in wine has been reported to be very low (3 ng/1). Recent studies by Guth and coworkers (2) showed that MMP also significaiitly influences the aroma of Scheurebe wines. 

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