Tomato odorant

F. Quantification of Fresh Tomato Odorants by Gas Chromatography Mass Spectrometry... 

Quantification of fresh tomato odorants was performed as previously described [6] using the same analytical instruments, internal standards mass spectrometry (MS) fragment ions, and recovery values. One additional compound, 2-isobutylthiazole, was included in the quantitative analysis. The ion used for quantification was m/z 99, and the recovery value determined for the solvent assisted flavor evaporation (SAFE) sample preparation method was 78%. 

Table 4 Odor Thresholds of Important Fresh Tomato Odorants in Water...

Table 5 Comparison of Odor Units of Potent Fresh Tomato Odorants in Four Cultivars... 

To confirm the identification of all important fresh tomato odorants—that the concentrations of the flavor compounds were determined correctly and that the differences between the cultivars were caused by concentration differences we prepared aroma model solutions of all cultivars (by mixing together the odorants in the concentrations determined) and compared each aroma model to its corresponding real tomato. The aroma models were prepared in citrate buffer at pH 4.3. The odorant composition of an aroma model of one of the more preferred tomatoes compared to that of a previously published aroma model is given in Table 6 [15]. When it is compared to the earlier model, there are many more compounds in the... 

Celery Seed. Celery spice is the dried ripe fmit of y piumgraveolens L. (UmbeUiferae) a biennial, sometimes aimual, herb native to southern Europe and grown extensively in India, China, Mexico, and the United States. The seed is 0.42 cm long and brown. The odor of the seed is characteristic and warm and the taste somewhat bitter. It is used in tomato ketchup, sauces, soups, pickles, pastries, salads, and certain cheeses. 

The flavor of the tomato pulls together odor and taste... 

Model experiments have been performed to show the yields of the odorants in the isolation procedure [21-23]. As an example, the values found for odorants from tomatoes by distillation with the SAFE method [23] are listed in Table 16.2. In agreement with other experiments, the result demonstrates that the losses of most of the odorants are high in the isolation procedure. In case of... 

Table 16.2 Yields of odorants from tomatoes obtained by distillation (solvent-assisted flavour evaporation) ...

Conclusive held evidence has been obtained with the manipulation of odor emissions of free-standing plants. Thaler (1999), for example, observed an increase in parasitism of S. exigua larvae on tomato after the plants had been treated with JA. This treatment induces the octadecanoid pathway, which results in the production of various defense compounds, including volatiles. In an earlier study in a tobacco held, De Moraes et al. (1998) had already found that the specialist parasitoid... 

In studies on the flavors of fresh and processed tomatoes, Buttery and coworkers [76, 77] also found that the number of odorants needed to simulate either the fresh tomato flavor or the flavor of a tomato paste was much lower than the number of aroma compounds detected by the OAV concept [4],... 

Sulfur Heterocyclics. Sulfur containing compounds (thiols, thiophenes, thiazoles,. .. etc.) play a major role in the flavor of raw and processed foods. These compounds have characteristic flavor notes and the flavor thresholds are mostly low. Several reviews (ill, 112, 113) demonstrate the important role of sulfur compounds in food flavors. Organoleptic properties of these compounds may be pleasant, strong nut-like odor of U-methyl-5-vinylthiazole which is present in cocoa (llU) objectionable pyridine-like odor of thiazole (115) quinoline-like odor of benzothia-zole (ll6) strong tomato leaf-like odor of isobutylthiazole (117) and bread crust flavor of acetyl-2-thiazoline (ll8). A mixture of oxazoles, thiazoles, thiazolines, imidazoles, trithiolanes and... 

Aroma properties of some alkylthlazoles have been reviewed (30). The most typical alkylthiazole is probably 2-isobutylthlazole. This compound was Isolated from tomato flavor and was described as having a strong green odor resembling that of tomato leaf (31). When added to canned tomato puree or paste at levels of 20 to 50 ppb, 2-lso-butylthlazole develops an intense fresh tomato-like flavor. Most of the alkylthlazoles are described as green, nutty and vegetable-like (32, 33). 

Analysis of the vacuum volatile constituents of fresh tomatoes was carried out using capillary GLC-MS and packed column GLC separation with Infrared, NMR and CI-MS analysis. Evidence was obtained for the presence of the unusual components 3-damascenone, 1-nltro-2--phenylethane, 1-nltro-3-methylbutane, 3-cyclocltral and epoxy-3-1onone. A method for the quantitative analysis of the volatile aroma components In fresh tomato has been Improved and applied to fresh tomato samples. The quantitative data obtained have been combined with odor threshold data to calculate odor unit values (ratio of concentration / threshold) for 30 major tomato components. These calculations Indicate that the major contributors to fresh tomato aroma Include (Z)-3-hexenal, 3-lonone, hexanal, 3-damascenone, 1-penten-3-one, 3-methylbutanal, (E)-2-hexenal, 2-lso-butylthlazole, 1-nltrophenylethane and (E)-2-heptenal. 

Studies to develop and apply quantitative methods to the analysis of fresh tomato volatiles have been recently carried out by some of the authors (J.,2). Besides the known major compounds a number of compounds were detected In the gas liquid chromatography (GLC) analysis which had spectral data unlike that of any of the 400 compounds previously reported as tomato volatiles (cf. 3 ). As these compounds occurred In reasonable amounts In fresh tomato It seemed necessary to determine their Identities In order to give a satisfactory quantitative picture of fresh tomato volatiles. It also seemed desirable to determine the odor threshold of these compounds to have a better understanding of their probable contribution to tomato aroma. 

The identification of 1-nitro-3-methylbutane in tomato had been reported previously by Wobben et al. (5) although they had not published any GLC or mass spectral data. None of the other numerous studies of tomato volatiles (of. 3.) had reported finding this compound. It is a relatively prominent component of fresh tomato occurring at a concentration as much as 200 ppb in some varieties such as Ace and related varieties but in other varieties it occurs at lower levels (10-50 ppb). However, it does not seem to be important to fresh tomato aroma because it is a relatively weak odorant with an odor threshold of 150 ppb. 

Nitro-2-phenylethane bears a similar relationship to phenylalanine and phenylacetonitrile. The nitro compounds are possibly formed by oxidation of these amino acids. Stone et al., ( ) had previously presented evidence (using radioactive isotopes) that leucine was one of the precursors of 2-isobutylthiazole. 1-Nitro-2-phenylethane is a moderately potent odorant with an odor threshold of 2 ppb and as later discussed probably contributes to the tomato aroma. 

P-Cyclocitral had not been previously reported in tomatoes except by the authors (2). Structurally related to p-ionone it probably also results from oxidative degradation of P-oarotene. With an odor threshold of 5 ppb it is a moderately potent odorant. 

Epoxy-P-ionone had been reported previously by Viani et al.,(13), Schreler et al., (J 4) and V/obben et al., ( ). In the present study besides the mass spectrum an infrared absorption spectrum was also obtained and was found to be identical to that of an authentic sample. An odor threshold was determined in water solution to be 100 ppb. It is, therefore, a relatively weak odorant and as its concentration, in all fresh tomato samples examined, is well below this figure it seems unlikely that it can contribute to fresh tomato aroma. 

Odor descriptions of dilute water solutions of P-damascenone and 1-nitro-2-phenylethane were also obtained using a panel of 18-20 judges. p-Damascenone as a 10 ppb solution in water was described as having an odor most similar to (1) prunes (2) apple (3) sweet character and (4) tomato in that order (i.e. being most like prunes). The odor of 1 ppm solutions of 1-nitro-2-phenylethane were described as (1) green (2) geranium (3) tomato and (4) oily in that order. 

Concentrations of major volatile fresh tomato components using blending procedure, odor thresholds in water solution and Log Odor Units. Compounds listed in descending order of their Log odor units... 

S ome of the common characteristics of night ades ate alternating, simple leaves that are often hairy in texture and may have a strong odor. The size and ape of the leaves, however, vary greatly within the family. The flowers of these plants generally have a tubular shape, oflen with five petals attached, as in the petunia. The stamens of the flowers are connected at their base. When the ovary of the flower matures into a fruit, it is either flediy like a tomato, or a dry fruit called a capsule, as in the tobacco plant. 

However, not only the odour threshold is an important parameter to consider, but also the specific note that the odorant may impart. 2-Isobutylthiazole is a well-known example that is essential in tomato top notes, but has a relatively high threshold of 3 pg/L water. Another recent example is the identification of 2-heptanethiol (Fig. 5.55) in bell pepper extracts having a sulphury, onion-like and vegetable-like note, reminiscent of bell pepper at lower concentrations [31 ]. This odorant can impart the characteristic bell pepper note to complex top notes despite its moderate threshold value of 10 pg/L water. 

Fig. 5.55 Sulphur-containing impact odorants used in top notes to impart specific notes, e.g. bis-(2-methyl-3-furyl)disulphide (BMFD, meaty), 2-isobutylthiazole (IBT, cooked tomato), 2-heptanethiol (2-HT, bell pepper), 2,3,5-trithiahexane (TTH, cooked broccoli)...

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