Aroma Properties of Some Alkylthiazoles

Thiazoles are a class of compounds possessing a five-membered ring with sulfur and nitrogen in the 1 and 3 positions (figure 1). Although thiazole and its derivatives have been known to organic chemists for a century, their sensory properties were not appreciated until relatively recently. The potential of thiazole derivatives as flavorants became evident through the work of Stoll et al. who found that the strong nut-like odor of a basic fraction obtained from a cocoa extract was due to a trace amount of 4-methyl-5-vinylthiazole. Since then, numerous thiazoles were identified in food flavors.

The occurrence of thiazoles in food flavor has been reviewed. More recently, thiazoles have been identified in baked potato, roasted peanuts, roasted beef, cocoa butter, fried bacon and fried chicken. Thiazoles have also been reported in various model system reactions involving either degradation of glucose in the presence of hydrogen sulfide and ammonia, or more frequently, fragmentation of cysteine or cystine, or reaction of these with xylose, ribose, pyruvaldehyde, furaneol or glucose.

Aroma properties for some alkylthiazoles have been reviewed. The most typical alkylthiazole is probabIy 2-isobutylthiazole. This compound was isolated from tomato flavor and was described as having a strong green odor resembling that of tomato leaf. When added to canned tomato puree or paste at levels of 20 to 50 ppb, 2-isobutylthiazole develops an intense fresh tomato-like flavor. Some 4,5-dialkylthiazoles were synthesized and reported to have potent bell pepper-Iike aroma. The flavor threshold value for 4-butyl-5-propylthiazole was judged to be 0.003 ppb in water. Most of the alkylthiazoles were described as green, nutty and vegetable-like.

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