| Meat quality is determined by many factors including the palatability, nutritional valueand safety. Among these characteristics, meat tenderness is deemed to the most importantattribute of beef palatability, which determines the commercial value of meat products.Postmortem temperature affects the rate and extent of sarcomere shortening and activityand content of induced endogenous proteinases, which determines the variation in tenderness.Fast chilling occurring early postmortem can generate severe a significant cold shorteningwhile slow chilling rate can induce heat shortening and risk of microbial contamination. Inaddition, very fast chilling has challenged the traditional concept of cold shortening. Thesebased on the confounding contributions of calcium ions released by lower pre-rigor chillingconditions to the extent of cold shortening (generally increasing toughness) and stimulation ofproteolysis (decreasing toughness). Therefore, the research evaluated the meat quality afterchilling of pre-rigor muscles at14,7,0, or-21°C and related meat tenderness variation withultra-structural changes during ageing, in order to provide reference for the optimaltemperature condition for improving beef quality.In this study, the main results are as follows:The rate of pH decline decreased with lower temperature. Muscles chilled at0and7°Chad shorter sarcomere length, higher initial Warner Bratzler shear force value (WBSF), lowermyofibril fragmentation index (MFI) and color stability, and more purge loss compared tomuscles chilled at14°C. However, muscles under0°C and7°C treatments have greaterabsolute amount of tenderization (WSBF) than thoses of other treatments. Very fast chillingresulted in the lowest sarcomere length and higher purge loss. It improved MFI, and had nosignificant negative effect on toughness. The amount of tenderization was the lowest,sarcomere length excessively shortening and ageing rate (%change in WBSF) were slower. Itshould be prudent in some applications to apply very fast chilling (-21°C) to excised muscles.Ageing counteracted the toughening effect of lower temperature on beef tenderness. Extendedageing could improve the vacuum packaged meat tender regardless of cold tougheninghappens induced by lower temperature.14°C treatment could ensure meat tenderness anddecrease purge loss.By analysis of ultra-structural variation, both0°C and7°C chilled samples exhibitedvariable sarcomere shortening. The cold-induced toughening muscles chilled at0°C had extremely shortened sarcomeres with intact Z-lines, but, I bands and H zone had completelydisappeared. In the images of7°C chilling treatment, the disappearance of I band wasobserved frequently and Z lines turned thick. Very fast chilling (-21°C) of muscles created thesuper-contraction, ruptured Z-lines and myofibril cleavage, resulting in lower WBSFcompared to samples chilled at0°C. Ageing of muscles improved tenderness by degradationof Z-lines and apparently lengthening of the sarcomere. The ultra-structure of14°C chilledsamples had intact myofibrils with wide I-binds, which showed that14°C degraded Z lines,with decreased the ageing time to get optimal tenderness.In the present study, significant correlation coefficients were found among sarcomerelength and WBSF, MFI, and purge loss of all treatments during ageing. Because shortsarcomere length stands for high shear stress values and increased drip loss, we need strictlyregulate the sacrcomere length during rigor to improve meat quality. |
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