Application of Mass Spectrometry and Isotope Labelling Technique to Study the Role of Various Derivatives of [alpha]-dicarbonyl Moiety in the Generation of Strecker and Maillard Reaction Products PDF Download

Author: Paula Vanessa Guerra Quiroz
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Languages : en
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Book Description
"The interaction of carbonyl moieties with free amino groups initiates one of the most important chemical transformations in food, the Maillard reaction. Numerous studies have shown the interaction of a single amino acid with one of the most reactive structures produced in the Maillard reaction, 1,2-dicarbonyl moieties. However, no systematic studies have been reported on the ability of these [alpha]-dicarbonyls to undergo multiple addition reactions with amino acids. Since 1,2-dicarbonyl moiety can be found as part of other chemical structures such as cyclic lactones, [alpha]-keto acids and o-quinones, a comprehensive understanding of the potential of these moieties to participate in Maillard and Strecker-type reactions was assessed. For this purpose, appropriate model systems were evaluated using isotope labelling technique with various precursors in conjunction with pyrolysis gas chromatography mass spectrometry or high resolution liquid chromatography mass spectrometry of thermally reacted model systems. Initially, a model system composed of glycine and 2,3-butanedione was evaluated under dry pyrolytic conditions at 250 °C. These studies indicated the unexpected formation of 2,3-dimethylpyrazine and 2,3,5-trimethylpyrazine in addition to the expected tetramethylpyrazine. Based on isotope labelling studies using labelled glycine, the formation of 2,3-dimethylpyrazine was rationalized through the double addition of glycine to 2,3-butanedione, or by a sequential Schiff base formation. The development of the previously reported 4,5-dimethyl-1,2-benzoquinone from the 2,3-butanedione/glycine model system was also examined, as well as its involvement as a precursors of 2,3,6,7-tetramethylquinoxaline through Strecker-type transformations. Based on those observations and given that ring-B of catechins is susceptible to oxidation and formation of such o-benzoquinone moieties, the potential of ring-B of catechins to undergo similar interactions to form adducts with amino acids was evaluated. For this purpose high resolution ESI-TOF mass spectrometry and MS/MS analysis were used to assess the reactivity of glycine with (+)-catechin heated at 120 °C for 70 min. Isotope labelling incorporation pattern of individually labelled glycine indicated that (+)-catechin formed various adducts with glycine through formation of Schiff bases. Further evaluation of the double addition and double Schiff base formation principle was carried out through the reaction of glucose and two amino acids with different side chains, glycine and cysteine. Both its volatile and non-volatile products were studied. The formation of a non-volatile adduct demonstrated the occurrence of this principle for the first time through sequential Amadori rearrangements. The reactive dicarbonyl moiety present in [alpha]-keto acid structures was also investigated as precursors of Strecker or Maillard reaction products. A model system consisting of glyoxylic acid and glycine was reacted under pyrolytic conditions at 200 °C. The isotope labelling analysis with individually labelled glycine confirmed the hypothesized pathways through the formation of dihydropyrazine moieties, similar to those of the dimerization product of the [alpha]-amino carbonyl compounds generated through the Strecker reaction. Finally, when studying the role of [alpha]-keto acids, 3-amino-4,5-dimethyl-2(5H)-furanone, a known precursor of sotolone, was observed for the first time under thermal conditions from two model systems, from pyruvic acid and glycine and from glyoxylic acid and alanine model systems. Isotope labelling studies have indicated the formation of 3-amino-4,5-dimethyl-2(5H)-furanone from 4,5-dimethylfuran-2,3-dione after its reaction with an amino acid through a variant of the Strecker reaction. These results suggests that the use of model systems with 1,2-dicarbonyl type precursors serves as an effective approach for unraveling new pathways of formation of aroma related products." --