Thiamine thermal decomposition

The major precursors in meat flavors are die water-soluble components such as carbohydrates, nucleotides, thiamine, peptides, amino acids, and the lipids, and Maillard reaction and lipid oxidation are the main reactions that convert these precursors in aroma volatiles. The thermal decomposition of amino acids and peptides, and the caramelization of sugars normally require temperatures over 150C for aroma generation. Such temperatures are higher than those normally encountered in meat cooking. During cooking of meat, thermal oxidation of lipids results in the formation of many volatile compounds. The oxidative breakdown of acyl lipids involve a free radical mechanism and the formation of... 

For example, thiamine hydrochloride in aqueous solution has E = 92.18 kJ/mol and A = 9.58x10 ° 1/min. Processing such solution at 90°C for 10 min would result in c/cq = 0.949 (i.e., about 5% loss). One has to remember that thermal decomposition is usually influenced by water content of the processed material. 

G.J. Hartmann et al. (1 4 ) and G.A. Reineccius and R. Liardon (J 5J have recently studied the volatile products from thermally degraded thiamin. A number of different decomposition components were identified including... 

Among the volatile compounds listed in Table II, only thiazole compounds are derived from the thermal degradation of thiamin. 5-(2-hydroxyethyl)-4-methylthiazole and 4-methyl-5-vinylthiazoIe are well-known thermal degradation products of thiamin. 5-(2-Chloro-ethyl)-4-methylthiazole may form through the interaction of 5-(2-hydroxyethyl)-4-methylthiazole with hydrogen chloride. However, the most abundant product, 4-methylthiazole, has never been identified as a decomposition product of thiamin. The mechanism for its formation is not clear. 

Thiamine stability in aqueous solution is relatively low. It is influenced by pH (Fig. 6.2), temperature (Table 6.8), ionic strength and metal ions. The enzyme-bound form is less stable than free thiamine (Fig. 6.2). Strong nucleophilic reagents, such as HS03 or OH , cause rapid decomposition by forming 5-(2-hydroxyethyl)-4-methylthiazole and 2-methyl-4-amino-5(methyl-sulfonic acid)-pyrimidine, or 2-methyl-4-amino-5-hydroxymethylpyrimidine (see Reactions 6.7). Thermal degradation of thiamine, which also initially yields the thiazole and pyrimidine... 

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