Semicarbazide: Natural occurrence and uncertain evidence of its formation from food processing

Abstract

The use of nitrofuran antibiotics in food-producing species has been banned within the European Union (EU) since 1993. Analysis of their residues in food has focused on using LC-MS/MS for the determination of their metabolites using stable isotopes as internal standards. Since AB SCIEX launched the first commercial LC-MS/MS instrument in 1989, most of these have used Selective Reaction Monitoring (SRM) technique. Triple quadrupole LC-MS/MS systems suffer from cross-talk, which can lead to incorrect identification and quantitation. Concern over residual nitrofuran has persisted for a long time, with most of the nitrofuran alerts originating from semicarbazide (SEM) in shrimp. The aim of this study is to review evidence from the literature and experimental studies concerning the formation of SEM from food processing and to discuss the natural occurrence of SEM in shrimp and aquatic organisms. Although SEM can form from azodicarbonamide, biurea, and homologous compounds, biurea readily reacts with 2-nitrobenzaldehyde (2-NB) to form a derivative that LC-MS/MS has incorrectly identified as SEM. Concerning the natural occurrence of SEM in crustaceans, cross-talk and misleading data have been frequently reported in the literature. Cross-talk symptoms should be carefully considered because they can affect the reliable detection and determination of SEM using a stable isotope as the internal standard. Twelve cases of non-compliance in shrimp from China and Korea were investigated: 7 cases of amino-2-oxazolidinone (AOZ) in the steamed meat of Pacific white shrimp, 1 case of AOZ in freshwater prawns, and 4 cases of SEM in freshwater prawns. The ease of purchasing medical-grade nitrofurans on the web and monitoring data suggest that the natural occurrence of SEM in prawns and shrimp is questionable, and that adulteration is a more likely scenario.