Effect And Mechanish Of Freezing At Different Time Postmortem On Pork Quality

Frozen meat is the main raw material of manufacturing meat products, which plays an importantrole in morden meat processing. The quality of raw meat directly affects the final quality of meat products.The thesis regards the porcine skeletal muscle as objects and takes western ham as the carrier to investigatethe effect of postmortem chilling time and following freezing on pork tenderness and processing properties.Proteomic analysis was performed to explore the variation regularity and changing mechanism of porktenderness as postmortem time prolonged. The results can provide a theoretical basis and technique for thefrozen storage and processing of pork. The contents and results are as follows.1. Uniform design was applied to examine the effects of postmortem chilling time and followingfreezing on the eating quality of pork meat. The pH value, color, cooking loss, shear force and myofibrillarfragmentation index (MFI) of pork were measured. The results showed that the postmortem chilling timeand following freezing both had significant influence on pH value, color, cooking loss, shear force and MFIand the effect existed obvious interaction (p<0.05). As postmortem chilling time prolonged, pH, cookingloss, shear force decreased. The MFI, a*value firstly increased then decreased, whereas the b*valuechanged in reverse. The L*value of the frozen samples falled down as the postmortem time increasedwhile that of the unfrozen samples ascended firstly then declined.2. Uniform experimental design was adopted to investigate the effect of homogenizing orfreezing at different time postmortem on quality of western ham. The yield, thiobarbituric acid reactivesubstances (TBARS), color, textural properties and sensory evaluation were measured. The results showedthat there existed significant effects of the two factors considered on yield, L*value, a*value, b*value,hardness, springiness, adhesiveness and chewiness and the effects of the two factors on them were nonlinear, there were interactions between the two factors considered. But they had no significant effectson sensory evaluation. The TBARS value, cohesiveness, resilience had a non-linear relationship with thetime postmortem, but had nothing to do with freezing or not. If only taking yield into consideration, weshould choose fresh meat as raw meat for selection of processing materials. The results showed that betterquality of western-style ham can come from fresh pork materials and earlier processing.3. Uniform design was adopted, and two factors, i.e., frozen at different time postmortem witheight levels, thawing at different thawing rate with four levels, were considered. The yield, TBARS, color,textural properties and sensory evaluation were measured. The results showed all the two factorsconsidered had significant effects on yield, TBARS, L*value, b*value, springiness, adhesiveness,chewiness, cohesiveness, resilience and the effects of the two factors on them were nonlinear, there wereinteractions between the two factors considered. But they had no significant effects on sensory evaluationand a*value. The hardness had a non-linear relationship with the frozen time postmortem, but had nothingto do with thawing rate.4. A comparative proteomic analysis in Sus domesticus after partial hepatectomy was firstlyperformed using iTRAQ (Isobaric tags for relative and absolute quantitation) technology．Differentiallyexpressed proteins in the postmortem time (45min,4h,8h,12h,24h,48h,72h,96h) were profiled.There were1583proteins were identified. Most proteins participated in basic biological process such ascellular process (13.01%) and metabolic process (10.94%). Most of proteins were categorized into cell andcell part of celluar component. Binding (47.70%) and catalytic activity (29.54%) contained the mostproteins in molecular function. COG annotation results indicate the largest cluster of proteins identified wasin general prediction function (240proteins). Pathway analysis revealed that there are1388proteinsassociated with232pathways, and the most were annotated to metabolic pathway. Taking the45min postmortem samples as control,862differential proteins were identified at all other time points．Nineproteins were screened, which had similar change trend with pH as the postmortem time prolonged. Theseproteins were down-regulated with significance at12h postmortem. Other nine proteins were filtered out,which had similar variation trend with shear force as the postmortem time increased. These proteins wereup-regulated with significance at12h postmortem. Meanwhile, nine proteins were screened, with thesemblable change trend with MFI as the postmortem time prolonged. These proteins were down-regulatedwith significance at8h postmortem. The results suggested8h and12h postmortem may be the key timepoints affecting the tenderness of pork meat.