Impact of the frying temperature on protein structures and physico-chemical characteristics of fried surimi

In this work, protein structures and properties and physico-chemical characteristics of surimi fried at different temperatures were studied. The effect of frying on surimi protein structure was characterised by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), intrinsic fluorescence, surface hydrophobicity, intermolecular interaction and Fourier transform infrared spectroscopy (FT-IR). SDS-PAGE analysis observed the appearance of new peptide bands and the weakening of myosin heavy-chain and actin bands after frying. In addition, frying damaged the hydrogen bond and ionic bond but promoted formation of the disulphide bond. Moreover, beta-sheet and random coil were increased after frying, while alpha-helix and beta-turn were decreased. After frying, the surface hydrophobicity of fried surimi decreased and the fluorescence maximum emission wavelength showed a red shift. The above changes indicated occurrence of protein denaturation and degradation, which were dependent on the frying temperature. Moreover, the effect of the frying temperature on physicochemical properties of fried surimi was characterised by measuring the hardness, oil absorption, porosity and water absorption capacity of fried surimi. The moisture loss, oil uptake, porosity and water absorption capacity of the fried surimi increased gradually with the frying temperature. However, the hardness of fried surimi was not positively correlated with the frying temperature but strongly dependent on the porous structure. These results showed that the physico-chemical properties of the fried surimi were dependent on not only degree of protein denaturation but also the porous structure.