Amino Acid Transformation and Decomposition in Saturated Subcritical Water Conditions

The reactions of amino acids under subcritical water conditions in the temperature range 503−563 K using a pressure value corresponding to the saturated vapor pressure of water at the employed reaction temperature (hereafter called saturated subcritical water) were investigated. As reactants, solutions containing a single amino acid or a mixture of 17 different amino acids were used, and the obtained results in both cases were compared. Glysine, alanine, valine, and proline were produced as intermediate products during the thermal transformation of other amino acids. Generally, the results showed that the existence of amino acids together in a mixture decreased the overall stability since the activation energy values of decomposition of individual amino acids reduced significantly due to their presence in a mixture of amino acids. Most of the amino acids were found to be labile at acidic and near-natural pH values and more stable at a highly basic pH value.