Study of thermal degradation of aspartame and its products of conversion in sweetener using isothermal thermogravimetry and HPLC

Aspartame (APM) has been a center of discussion due to the toxicity of its metabolism products. This work studied the thermal degradation of aspartame and its products of conversion in a sweetener using isothermal thermogravimetry (TG), infrared (FTIR) and high-performance liquid chromatography (HPLC). The TG curves were performed using a Shimadzu Thermobalance, under air atmosphere, flow rate of 20 mL min−1 and heating rate of 10 °C min−1. The chromatograms were performed using a Shimadzu Chromatograph with diode-array detector at 210 nm, C18 column, water-acetonitrile (90:10) and 0.1% trifluoroacetic acid. The 5-benzyl-3,6-dioxo-2-piperazineacetic acid (5BZ) was identified as only one product of thermal conversion from aspartame (APM). The 5BZ and APM have been identified and quantified through the comparison of areas and retention time established with standards. The chromatograms had presented limits of quantification (LOQ) and detection (LOD) of 5; 2 μg mL−1 and 10; 5 μg mL−1 for 5BZ and APM, respectively. The samples have indicated recovery of 100.42 ± 1.34%. The content of APM in the sweetener was 19.08 mg ± 2.22%, this amount is within specifications (19 mg ± 10%). The standard APM was heated at 80-220 °C in TG-isothermal and chromatograms have indicated the total conversion of APM to 5BZ, which showed a maximum rate of conversion in a temperature range of 140-160 °C. In the sweetener the APM was converted to 5BZ in a temperature range of 120-140 °C. The TG-isothermal indicated a decrease in the temperature of conversion to 5BZ and its intensity, probably due to interaction with the lactose excipient contained in the sweetener.