Formation of advanced glycation end-products in fish muscle during heating: Relationship with fish freshness

The purpose of this study was to investigate the formation of advanced glycation end-products in raw and heat treated fish muscle as affected by fish freshness. The amounts of free and protein-bound N-epsilon-carboxymethyllysine (CML) and NN epsilon-carboxyethyllysine (CEL) in raw and heat-treated (100 degrees C, 5, 30 min) white muscle from cultivated grass carp (Ctenophatyngodon idellus) (n = 12) and catfish (Clarias leather) (n = 24) steaks previously stored at 0 C-degrees for 0-21 days were quantified with an HPLC-MS/MS method. The levels of free and protein-bound CML and CEL in raw fish muscle did not change significantly during 21 days of ice storage. However, the longer the fish muscle was stored at 0 degrees C, the more protein-bound CML and CEL were formed upon heating. The heat-induced formation of protein-bound CML in catfish muscle previously stored at 0 degrees C for 21 days increased by 107% (5 min heating) or 172% (30 min heating), and CEL increased by 448% (5 min heating) or 191% (30 min heating), as compared with that in heat-treated freshly killed catfish muscle. In grass carp muscle, the increases were from 144% (5 min) to 131% (30 min) for protein-bound CML, and 135% (5 min) to 95% (30 min) for protein-bound CEL.