Tomato 2-isobutylthiazole

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... 

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. 

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)...

Thiazoles occur in nature as substances with an aromatic odour, for instance 4-methyl-5-vinylthiazole in the aroma of cocoa beans and passion fruit, 2-isobutylthiazole in tomatoes and 2-acetylthiazole in the aroma of roasted meat. 

Potatoes 2-Isopropyl-3-methoxypyrazine together with 2,5-dimethylpyrazine (see pyrazines) dominate in raw potatoes. Key compounds in boiled potatoes are meAional and 2-ethyl-3,6-dimethylpyrazine. Tomatoes The highest flavor values in fresh tomatoes are exhibited by (Z)-3- and ( )-2-hexenals (see alkenals), j3- ionone, hexanal (see alkanals), 8-damascenone, I-penten-3-one (CsHgO, Mr 84.12, CAS [1629-58-9], 3-methylbutanal (see alkanals), and 2-isobutylthiazole. The most important flavor components in tomato pulp are dimethyl sulfide, )8-damascenone, )5-ionone, 3-methylbutanal, I-nitro-2-phenylethane (CgH,N02, Mr 151.16, CAS [24330-46-91), eugenol, methional, and 3-methylbutanoic acid. ... 

Studies on banana tissue slices have shown that valine and leucine concentrations increase about threefold following the climacteric rise in respiration [10]. Radioactive labeling studies have shown that valine and leucine are transformed into branched chain flavor compounds that are essential to banana flavor (2-methyl propyl esters and 3-methyl butyl esters, respectively). As can be seen in Figure 4.6, the initial step is deamination of the amino acid followed by decarboxylation. Various reductions and esterifications then lead to a number of volatiles that are significant to fruit flavor (acids, alcohols, and esters). Recent work has shown that amino acids play a role in apple flavor as well. For example, isoleucine is the precursor of 2-methyl butyl and 2-methyl butenyl esters in apples [24,25]. An unusual flavor compound, 2-isobutylthiazole, has been found to be important to the flavor of tomato. It is hypothesized that this compound is formed from the reaction of 3-methyl-l-butanal (from leucine) with cysteamine. 

It is most common that varietal differences in flavor are due to quantitative differences in flavor composition rather than qualitative differences. For example, studies have shown that tomatoes may differ in 2-isobutylthiazole content by a factor of two- to threefold. 

Isobutylthiazole (compound V, Table 5.22) contributes to tomato aroma (cf. 17.1.2.6.13). It is probably obtained as a product of the secondary metabolism of leucine and cysteine (cf. postulated Reaction 5.30). 

The aroma of tomatoes Solarium lycopersicum, syn. Lycopersicum esculentum, Solanaceae) represents about 400 different compounds. Important components of the aroma of fresh ripe tomatoes are 2-isobutylthiazole, which is also the bearer of the typical aroma of the whole plant. The precursors of 2-isobutylthiazole are 3-methylbutanal, which arise by deamination and decarboxylation of leucine, and cysteamine (2-mercaptoethylamine) are formed by... 

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%. 

In summary, we may conclude that the basic fresh tomato aroma is composed of the same compounds in all four cultivars, especially (Z)-3-hexenal and tra 5-4,5-epoxy-( )-2-decenal, and that the aroma differences between the cultivars that are responsible for differences in preference are caused by concentration differences of odorants with less impact, i.e., lower odor units. The more preferred tomatoes contained more l-penten-3-one, (E,E)- and (ii,Z)-2,4-decadienal, and 4-hydroxy-2,5-dimethyl-3(2F/)-fura-none (Furaneol). High concentrations of phenylacetaldehyde and 2-phenylethanol (as in the R 144 cultivar) or 3-methylbutanal and 2-isobutylthiazole (as in the R 175 tomato) had a negative influence on preference. 

All three sample preparation techniques were suitable for characterizing the two cultivars. With all three methods, the relative peak areas of the aroma volatiles hexanal and 2-isobutylthiazole differed significantly for the two cultivars studied. Krumbein and Ulrich concluded that SPME is a suitable screening method for tomato fiavor. 

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