Effects of the hydration process on water-soluble proteins of preserved cod products

Electrophoresis and chromatography were used to analyse the water-soluble proteins of fresh, salted and dried cod (Gadus morhua L.) and of re-hydrated products. Sodium dodecyl sulphate pore gradient gel electrophoresis showed that there was a great loss of water-soluble proteins during stockfish re-hydration. Furthermore, comparison of the electrophoresis patterns of cod products, under reducing and non-reducing conditions, showed the presence of cross-linked protein aggregates, related to the oxidation of SH groups and oxidative stress. Similar results were obtained by high performance liquid chromatography, which confirmed a great loss of water-soluble proteins and a higher level of SH oxidation in hydrated stockfish samples. Finally, capillary electrophoresis allowed definition of the unfolded state of denatured proteins in salted cod. This technique also proved a fast and useful way to differentiate the two products by analysis of water-soluble proteins.