Protein deterioration and α-dicarbonyls in precooked fish during storage and reheating affected by the severity of precooking treatments

This research was to investigate the protein deterioration (oxidation, glycation, hydrolytic cleavage, the Maillard reaction) of precooked fish during storage (0 ℃, 1 – 7 d) and reheating (75 ℃, 10 min) as affected by precooking treatments (90 °C, 8 – 25 min) similar to home cooking and commercial pasteurization. The amounts of trichloroacetic acid (TCA)-soluble peptides (3.68 ± 0.39 – 5.10 ± 0.87 μmol try/g) and fluorescence advanced glycation end-products (AGEs) (718.3 ± 56.3 – 870.1 ± 90.6 AU) in precooked fish continuously increased during storage while the corresponding tryptophan fluorescence (699.0 ± 41.8 – 882.4 ± 82.8 AU) decreased, implying the concurrence of hydrolytic cleavage, glycation and oxidation of proteins. More severe precooking treatments generally resulted in higher levels of TCA-soluble peptides and fluorescence AGEs, although the mild reheating applied had no significant effect on the amount of fluorescence AGEs. The levels of 3-deoxyglucosone, glyoxal, methylglyoxal, 2,3-pentanedione, and 2,3-butanedione in precooked or reheated fish had no obvious relationship ( r  = 0.046 – 0.598) with each other, but their cluster analysis result was in agreement with their chemical natures and formation pathways. While 3-deoxyglucosone was the dominant α-dicarbonyl, accounting for an average of 69.8% of the sum of five α-dicarbonyls in precooked fish with or without being reheated, the mean level of 2,3-pentanedione was 3.3 times more than 2,3-butanedione, implying that this α-diketone should not be overlooked.