Thiamin degradation product formation

Figure 2 Formation of selected thiamine degradation products identified in YE aroma (27, 29-33)...

Physical Chemical Characterization. Thiamine, its derivatives, and its degradation products have been fully characterized by spectroscopic methods (9,10). The ultraviolet spectmm of thiamine shows pH-dependent maxima (11). H, and nuclear magnetic resonance spectra show protonation occurs at the 1-nitrogen, and not the 4-amino position (12—14). The H spectmm in D2O shows no resonance for the thiazole 2-hydrogen, as this is acidic and readily exchanged via formation of the thiazole yUd (13) an important intermediate in the biochemical functions of thiamine. Recent work has revised the piC values for the two ionization reactions to 4.8 and 18 respectively (9,10,15). The mass spectmm of thiamine hydrochloride shows no molecular ion under standard electron impact ionization conditions, but fast atom bombardment and chemical ionization allow observation of both an intense peak for the patent cation and its major fragmentation ion, the pyrimidinylmethyl cation (16). 

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. 

The economical value and high popularity of meat lead to the production of meat-like flavors through process chemistry. Several heat-induced reactions lead to the formation of meat flavors. These reactions are the pyrolysis of peptides and amino acids, the degradation of sugars, the oxidation, dehydration, and decarboxylation of lipids, the degradation of thiamin and ribonucleotides, and interactions involving sugars, amino acids, fats, H2S, and NH3 [110],... 

In some instances, the reactive forms or the intermediates themselves, show polarographic waves which are separated from those of reactants and products. The formation of the thiol form of thiamine, < ) the bicyclic form of protopine< > and the enediol forms of some sugars< > and pyridoine< ) are examples of the formation and detection of reactive forms. A few examples of the detection of intermediates, are the diketone and enediol produced during the alkaline degradation of phenylglyoxal< > and of a, -unsaturated ketone as an intermediate in the cleavage< ) of... 

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