Myowater Dynamics and Protein Secondary Structural Changes As Affected by Heating Rate in Three Pork Qualities:A Combined FT-IR Microspectroscopic and ~1H NMR Relaxometry Study

摘要

The objective of this study was to investigate the influence of heating rate on myowater dynamics and protein secondary structures in three pork qualities by proton NMR T_2 relaxation and Fourier transform infrared (FT-IR) microspectroscopy measurements. Two oven temperatures at 100 °C and 200 °C corresponding to slow and fast heating rates were applied on three pork qualities (DFD, PSE, and normal) to an internal center temperature of 65 °C. The fast heating induced a higher cooking loss, particularly for PSE meat. The water proton T_(21) distribution representing water entrapped within the myofibrillar network was influenced by heating rate and meat quality. Fast heating broadened the T_(21) distribution and decreased the relaxation times of the T_(21) peak position for three meat qualities. The changes in T_(21) relaxation times in meat can be interpreted in terms of chemical and diffusive exchange. FT-IR showed that fast heating caused a higher gain of random structures and aggregated beta-sheets at the expense of native alpha-helixes, and these changes dominate the fast-heating-induced broadening of T_(21) distribution and reduction in T_(21) times. Furthermore, of the three meat qualities, PSE meat had the broadest T_(21) distribution and the lowest T_(21) times for both heating rates, reflecting that the protein aggregation of PSE caused by heating is more extensive than those of DFD and normal, which is consistent with the IR data. The present study demonstrated that the changes in T_2 relaxation times of water protons affected by heating rate and raw meat quality are well related to the protein secondary structural changes as probed by FT-IR microspectroscopy.