Grapefruit oil

Grapefruit oil is obtained by cold pressing of the outer peels of the fruits of Citrus paradisi Macfad. (Rutaceae). It is a greenish-yellow liquid, with an odor resembling that of sweet orange oil, but more herbaceous and bitter. 

Grapefruit oil is produced mainly in the United States and its composition varies with the species. White grapefruit oil obtained from the varieties Marsh seedless and Duncan that are grown in Florida, contains more than 90% terpene hydrocarbons ((+)-limonene, 93.5-95%), 0.5% alcohols (mainly linalool), 1% aldehydes (mainly octanal and decanal), 0.05-0.8% nootkatone [371]. Worldwide production is ca. 200 t/yr. 

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

QUANTIFICATION OF TOTAL ALDEHYDES IN ORANGE AND GRAPEFRUIT OIL USING A-HYDROXYBENZENESULFONAMIDE... 

Grapefruit, typically, has harsher flavor notes. Similar to other citrus oils, grapefruit oil is predominately composed of terpenes. There have been 206 volatile compounds identified in grapefruit juice. However, the flavor impact compounds are more dominant. Nootkatone and l-p-methene-8-thiol are the major compo-... 

Table Gl.5.9 is a summary of the total available oil for various citrus cultivars. Table G1.5.10 is the aldehyde composition for orange and grapefruit oils.

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... 

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

Although nootkatone is a flavor impact compound in grapefruit, it does not by itself provide the full-bodied flavor provided by good quality cold-pressed grapefruit oil. The proper blend of nootkatone, aldehydes, other as yet unidentified components, and perhaps esters is necessary for full-bodied grapefruit flavor. 

Moshonas, M. G. Analysis of carbonyl flavor constituents from grapefruit oil. J. Agric. Food Chem., 1971, 1 , 769-770. 

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