Metabolite release and protein hydrolysis during the in vitro digestion of cooked sea bass fillets. A study by 1H NMR

Proton Nuclear Magnetic Resonance (1H NMR) was used to study micro-wave cooked European sea bass (Dicentrarchus labrax) fillets, along five different points of their in vitro digestion: after oral digestion, after gastric digestion and subsequent increasing of the pH to 5.0, and after 90 and 180 min of duodenal digestion. During the gastric phase, the appearance of broad signals in different spectral regions, typical of amino acid protons, provided evidence for the expected release of unstructured fragments of denatured proteins, whilst smaller peptides, with sharper signals in the same spectral regions, were becoming visible only after duodenal digestion. Prior digestion, the spectral features of trichloroacetic acid extracts, from raw and cooked fish fillets, have been analysed to assess whether a significant protein hydrolysis or metabolite release (e.g., amino acids, organic acids, saccharides, and nucleotide derivatives) already occurred during cooking, by comparing the spectral profiles of these extracts. No significant differences among the molecular profile of both extracts were found. The present study demonstrates the suitability of NMR spectroscopy to follow the kinetics of fish fillets digestion under in vitro conditions simulating human digestion.