Racemization of amino acids during classical and microwave oven hydrolysis- application to aspartame and a Maillard reaction system

The conventional acid hydrolysis routinely used in protein analysis induces partial racemization of the amino acids. An alternative method, using micr owave heating, was evaluated with the aim of assessing its efficiency in pr eserving the amino acids in their original configuration. The method was em ployed on the dipeptide aspartame. The results showed that some advantages, implying less racemization, could be gained by using the microwave techniq ue, but the method was applicable only at temperatures under 150 degreesC. Mild, conventional hot oven-hydrolysis, involving a shorter hydrolysis time , could have the same mild effect. The different techniques were applied to aspartame treated at different pH, a soft drink and a Maillard reaction mo del system. The results showed that aspartame was insusceptible to racemiza tion in acid and neutral environments, and not until very high pH did racem ization start. The soft drink contained a small amount Of D-amino acids, 0. 27 Mg D-asp and 0.14 Mg D-phe/100 ml. The model system exhibited no racemiz ation. (C) 2001 Elsevier Science Ltd. All rights reserved.