Combined High Pressure And Thermal Treatment Effects On The Quality Of Post-Rigor Beef Muscle

High pressure processing is a kind of new technology and gets a rapid development in the last ten years, because of tenderizing meat and extending shelf life without destroying meat nutrition and flavor. High pressure treatment can tenderize meat when applied pre-rigor, but it does not have a good effect for post-rigor meat at room temperature. However, it is difficult for pre-rigor meat to be treated by high pressure in meat industry. Spore is stable to high pressure at lower temperature, and it could be inactivated when high pressure combined with moderate temperature. Therefore, high pressure technology tend to be applied with heat treatment combination. In this thesis, the effects of high pressure (to 800 MPa) applied at different temperatures (20 to 70C) for 20 minutes on beef post-rigor longissimus dorsi texture, ultrastructue, proteolytic activities, lipid oxidation and color were studied.1. The effects of high pressure (to 800 MPa) applied at different temperatures (20 to 70 C) for 20 minutes on beef post-rigor longissimus dorsi texture were studied. Texture profile analysis showed that when heated at ambient pressure there was the expected increase in hardness with increasing temperature and when pressure was applied at room temperature there was again the expected increase in hardness with increasing pressure. Similar results to those found at ambient temperature were found when pressure was applied at 40 C. However, at higher temperatures, 60 C and 70 C it was found that pressures of 200 MPa caused large and significant decreases in hardness. The results found for hardness were mirrored by those for gumminess and chewiness.To further understand the changes in texture observed, intact beef l. dorsi samples and extracted myofibrilar proteins were both subjected to differential scanning calorimetry after being subjected to the same pressure/temperature regimes. As expected collagen was reasonably inert to pressure and only at temperatures of 60 to 70 C was it denatured/unfolded. However, myosin was relatively easily unfolded by both pressure and temperature and when pressure denatured a new and modified structure was formed of low thermal stability. Although this new structure had low thermal stability at ambient pressureit still formed in both the meat and myofibrilar protein fractions when pressure was applied at 60 C.It seems unlikely that structurally induced changes can be a major cause of the significant loss of hardness observed when beef is treated at high temperature (60 to 70 C) and 200 MPa and it is suggested that accelerated proteolysis under these conditions is the major cause.2. The effects of high pressureand temperatures on beef post-rigor longissimus dorsi ultrastructue, isolated myofibril solubility and its electrophoresis were studied. Transmission electron micrographs showed that 200MPa pressure treatment at room temperature induced the absence of M-lines in the central region of A-bands, but the integrity of myofibril were still retained. On 400MPa, a loss of I-band, widen of H region, increased space between fibers, shorten sarcomeres, thicken Z-disc and disorganized thick and thin fibers were observed. When pressure increased above 400MPa at room, disruption of myofibril ultrastructrue was intensified. No significant changes were found when muscle heated at 40and 60 C, but part breaks of myofibril at Z-lines were seen. 200MPa pressure treatment at 40 C and higher temperature induced M-line loss, Z-lines thickening and bending, which maybe caused by part of proteins denatured and aggregation. These modifications were extended with the increasing temperature. When pressure up to 600MPa, the significant change was Z-disc disappeared, thick and thin filaments coagulated and myofibril structure disrupted.Protein solubilizaton increased with increasing temperature, especially from 40 C to 60 C. A regular trend of protein solubilization were found when isolated myofibril subjected to high pressure at different temperature, an increase was observed with the increasing pressure a...