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 microwave heating, was evaluated with the aim of assessing its efficiency in preserving the amino acids in their original configuration. The method was employed on the dipeptide aspartame. The results showed that some advantages, implying less racemization, could be gained by using the microwave technique, but the method was applicable only at temperatures under 150°C. 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 model system. The results showed that aspartame was insusceptible to racemization in acid and neutral environments, and not until very high pH did racemization 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 racemization.