| The purpose of this research was to investigate the biochemical and physicochemical properties of normal and pale, soft and exudative (PSE) muscle and extracted natural actomyosin (NAM) during refrigerated storage, frozen storage and thermally-induced gelation. For each set of experiments, the loin muscle from 8-15 animals was classified as either PSE or normal pork and samples of the longissimus dorsi retained for further investigation.; The surface hydrophobicity (S0-ANS) of NAM from PSE pork was significantly higher (p < 0.05) than that from normal pork when meat was stored at -20°C for up to 6 months and further increased with duration of frozen storage, indicating that NAM from PSE pork was more susceptible to denaturation. The S0-ANS of NAM was negatively correlated with the water-binding capacity of meat. The conformational changes of NAM may be subtle since sulfhydryl groups and apparent viscosity of NAM did not change with storage and alpha-helical content only showed limited change. Measuring S0-ANS may be valuable in the classification of meat quality. Electrophoresis and Western blotting analysis showed that proteins from PSE pork are more susceptible to degradation in fresh meat and during frozen storage. The addition of sodium nitrite reduced the alpha-helical contents of NAM, possibly due to disruption of hydrogen bonds.; The meat gels prepared from PSE pork had lower shear stress and shear strain at failure and hardness as measured by torsional gelometry and texture profile analysis, respectively. The water holding capacity of the meat gels prepared from PSE pork was also lower than that from normal meat as shown by higher cooking loss, expressible moisture and purge. Differential scanning calorimetry analysis suggested that the inferior quality of meat gels from PSE meat may have resulted from their lower protein thermal stability. A five-step gelation mechanism, which included energy absorption, protein denaturation, unfolding, aggregation and network formation is proposed. NAM from normal pork underwent aggregation with a higher amount of hydrophobic interactions and disulfide bonds, and higher temperatures at maximum velocity of S 0-ANS, unfolding and turbidity increase than that from PSE meat. As a consequence, NAM from normal pork had superior rheological properties than that from PSE meat. |
