Thiazoles aromas from

Some thiazoles arise from degradation of other sulfur-containing compounds. An example of these thiazoles is non-volatile 4-methyl-5-(2-hydroxyethyl)thiazole that is formed by degradation of thiamine either by the action of thiaminases or by non-enzymatic reactions. Its dehydration, however, yields 4-methyl-5-vinylthiazole, which is a constituent of cocoa aroma. 

A heterocyclic sulfur-containing compound, 2-methyl-thiophene, was identified in boiled crayfish tail meat and pasteurized crabmeat. Thiazole and 3-methylthiopropanal were identified in the crayfish hepatopancreas. Heterocyclic sulfur-containing compounds play important roles in generating meaty aromas in a variety of meat products and are considered important volatile aroma components of marine crustaceans (12— 14). The 2-methylthiophene could be an important flavor cemponent in boiled crayfish tail meat. Both thiazole find 3-methylthiopropanal were important contributors to the desirable meaty aroma associated with crayfish hepatopancreas. The 3-methyl-thiopropanal, identified in boiled crayfish hepatopancreas, is derived from Strecker degradation of methionine (15), and has been considered to be an important cemponent in basic meat flavor (16). Pyridine was detected in the headspace of the hepatopancreas from freshly boiled crayfish. Pyridine and 2-ethylpyridine have been previously reported as components in the atmospheric distillate from a sample of crayfish hepatopancreas frozen for three months (2). 

CIC (Z)-3-hexenal and 2-(2-methylpropyl)thiazole form the fresh, green, vegetable topnote and a trace of damascenone is responsible for the floral background. On cooking, the fresh note from (Z)-3-hexenal is covered by the sweet sulphurous note of dimethyl sulfide. In canned tomatoes, the sulphurous note is supported by the spicy, dove-like aroma of 4-vinyl guaiacol and eugenol. 

A remarkable study on nitrogen heterocycles in coffee aroma was realized by Vitzthum and Werkhoff (1974a,b) who identified 23 new thiazoles (Figure 5.13). These were isolated from the basic fraction of the extract obtained after adsorption of a steam distillate on Porapak Q, followed by an ether extraction. The identification was performed by using a combination of glass-capillary gas chromatography/mass spectrometry. The measured concentrations were of the order of 1-10 ppb and ca 0.1 ppb for thiazole itself. 

A review describes the pharmacological properties of l,2-benzisothiazoles. In connection with thiazoles, we find several reviews or papers thiazoles in food aromas patellamides, which are antineoplastic cyclic peptides, from the marine tunicate Lissoclinum patella, which contain an unusual fused oxazoline-thiazole unit and polythiazole-containing peptide antibiotics. An interesting total synthesis of the aglycon of bleomycin A2 should also be mentioned. ... 

Two excellent papers on YE aroma have arisen recently from Werkhoff s group at Haarmann and Reimer in Germany (13,14). Fifty sulfur compounds were reported in the first study (13) while 115 such components were described in the second paper (14). Aliphatic compounds, sulfur-substituted furans, thiophenes, thiazoles, 3-thiazolines, cyclic polysulfides, perhydro-l,3,5-dithiazines, a perhydro-1,3,5-oxathiazine, a perhydro-l,3,5-thiadiazine and aliphatic and heterocyclic dithiohemiacetals were all mentioned, and the structures of most of the newly identified compounds were confirmed by synthesis. These sulfur compounds elicit a wide variety of aromas but are often savory, e.g., meaty, vegetable-like, and YEs are a valuable source of potent components which provide meaty notes. 

Two hundred and sixty-eight compounds were identified in this study as components of YEs, and they are listed by class in Table II. Sixty-seven of the compounds identified contained sulfur (75) and are listed in Table III. The 34 compounds identified for the first time as components of YEs are denoted by ( ) in Table III. Twenty-eight of the newly identified components of YE were detected in Sample C while seven were identified in Sample B. None could be identified from Sample A. Eighteen of the newly-identified representatives listed are thiazoles. Some of the thiazoles reported in this study, i.e., thiazole, 4,5-dimethylthiazole and 2,4-dimethyl-5-ethylthiazole possess meaty qualities at certain dilutions (76). 2,4-Dimethyl-thiazole, which has not previously been reported as a component of YE aroma, possesses a "meaty, cocoa" or "slmnky-oily" odor (76). Other thiazoles listed in Table III may be expected to contribute green, nutty and vegetable-like notes (76). 

This characteristic feature appears to be required for a roasted odor. In fact, aU the pyrroUnes and pyridines listed in Table 5.23 as weU as 2-acetyl-thiazole, 2-acetylthiazoline (cf. Table 5.22) and acetylpyrazine (cf. Table 5.23) contain this structural element and have a roasted or cracker-hke odor. However, the thresholds of these compounds vary greatly. The lowest values were found for 2-acetyl-and 2-propionyl-l-pyrrohne. The length of the alkanoyl group also influences the aroma activity because in the transition from 2-propionyl- to 2-hutanoyl-l-pynoline, the roasted note suddenly disappears and the odor threshold increases hy several powers of ten. 2-Acetyl-l-pyrrohne (Apy) is responsible for the typical aroma of the cmst of white bread and it... 

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