Pathways of Amino Acid Transformation and Decomposition in Saturated Subcritical Water Conditions

Abstract

The reactions of amino acids under subcritical water conditions were investigated. All reactions were carried out under a pressure value corresponds to the saturated vapor pressure of water at the employed reaction temperature (hereafter called the saturated subcritical water condition). The reaction temperatures were in the range of 503-563 K. As reactants, seventeen different amino acids were investigated including, glycine, alanine, valine, leucine, isoleucine, methionine, phenylalanine, tyrosine, serine, threonine, cysteine, proline, lysine, histidine, arginine, aspartic, and glutamic. The obtained data revealed that the major decomposition pathway were the deamination and decarboxylation. It was found that glycine, alanine, valine, and proline were synthesized as intermediate decomposition products of other amino acids. Glutamic acid is the only amino acid that decomposed through lactamization process to pyroglutamic acid. Based on the experimental data a general decomposition pathway of all tested amino acids was developed by considering that the decomposition reactions extended to produce final decomposition products, carbon monoxide, water, and ammonia.