Aroma grapefruit juice

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

Analysis of grapefruit juice [71] gave high OAV for 4-mercapto-4-methylpentan-2-one (MMP), ethyl (S)-2-methylbutanoate, (Z)-3-hexenal, ethyl butanoate, decanal, ethyl methylpropanoate and l-p-menthen-8-thiol (MTO, probably the R-enantiomer). The aroma of a solution containing 19 odorants in the levels found in grapefmits was very similar to the natural aroma of this fmit [71 ]. 

Buettner, A., Schieberle, P. (2001) Evaluation of key aroma compounds in hand-squeezed grapefruit juice (citrus paradisi Macfayden) by quantitation and flavour reconstitution experiments. J. Agric. Food Chem. 42, 1358-1363... 

The most obvious property of a low-molecular-weight thiol is its foul odor. Ethanethiol is added to natural gas so that leaks can be detected without special equipment—your nose is so sensitive that it can detect less than one part of ethanethiol in 10,000,000,000 parts of air The odor of thiols weakens with the number of carbons, because both the volatility and the sulfur content decrease. 1-Dodecanethiol, for example, has only a faint odor. On the positive side, of the hundreds of substances that contribute to the aroma of freshly brewed coffee, the one most responsible for its characteristic odor is the thiol 2-(mercaptomethyl)furan. Likewise, the contribution of p-l-menthene-S-thiol to the taste and odor of freshly squeezed grapefruit juice far exceeds that of most of the more than 260 other volatile components so far identified. 

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]. 

Fatty acids and amino acids are precursors of a great number of volatile aldehydes, while carbohydrate degradation is the source of ethanal only. Due to its aroma activity at higher concentrations ethanal is of great importance for the fresh note, e. g., in orange and grapefruit juice. 

Two character impact compounds have been proposed for grapefruit flavor, the first being nootkatone, a sesquiterpene. The fresh juicy note of grapefruit juice is attributable to l-p-menthene-8-thiol. This compound has a detection threshold of 10 ppt, among the lowest values reported for aroma chemicals (28). The (+)-R-isomer was found to have a lower aroma threshold in water than the racemic mixture, and it imparts a pleasant, fresh grapefruit juice character, as opposed to the extremely obnoxious sulfur note contributed by the (-)-S-epimer. 

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

The concentrations of the two sulphur compounds, MMP and MTO, in grapefmit juices were 0.8 and 0.01 pg/kg, respectively [71 ]. Omission experiments indicate that the grapefruit-like odour was lacking when MMP was absent. MTO, which occurs in even lower concentration in oranges, contributes to the aroma but its impact is not so typical when compared to that of MMP. 

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