Key Quality Variation Mechanism Of DFD Beef And Effects Of Modified Atmosphere On Quality Improvement Of DFD Beef

DFD beef is dark,firm and dry which is disliked by most of consumers.In order to reveal the mechanism of DFD beef development and to improve the quality,the meat color,water holding capability(WHC),shear force and other quality were measured;and differential proteomic was analyzed by iTRAQ and LC-MS/MS method;and the effects of different packages on DFD beef quality were also determined in order to find a suitable package method to improve the DFD meat quality.The results will be helpful in new control methods development to decrease the DFD beef incidence.Two experiments were conducted in this study.For the first one,in order to investigate the difference of DFD beef and normal beef in quality and anaerobic glycolysis,Luxi yellow cattle and crossing Luxi yellow were selected in this study.p H 24 h ? 6.10 was used to determine the DFD beef.The characters of pH,WHC,meat color,shear force,and NADH content were measured in both DFD beef and normal beef during aging period on 1,3,6 and 9 d.And the differential proteomic in samples of 24 h were also analyzed using iTRAQ technology.For the second experiment,the effects of vacuum package(VP),high oxygen modified atmospheres package(80% O2 + 20% CO2,80%O2-MAP)and CO modified atmospheres package(0.4% CO + 69.6 %N2 + 30% CO2,CO-MAP)on DFD beef quality were investigated by the analysis of pH,WHC,total viable count(TVC)and shear force.The main results were as follows.1 Quality changes in DFD beefBased on the results of the two breeds,the ultimate pH of DFD beef was significant higher than normal ones(P < 0.05).And the p H values of Luxi yellow cattle in DFD group or normal group was higher than those in Crossing Luxi cattle.The meat color stability had the same intendance with the meat color.The WHC in DFD beef was significant higher than normal ones with a lower drip loss and cooking loss(P < 0.05).The shear force of DFD group was also decreased(P < 0.05)compared to normal group.The order of the tenderness in different group was DFD beef of Yuxi yellow cattle > DFD beef of Crossing Yuxi yellow cattle > normal beef of Crossing Yuxi yellow cattle > normal beef of Yuxi yellow cattle.2 Differential proteomic analysis in DFD beefFor Yuxi yellow cattle,a total of 317 different proteins were detected,of which 168 different proteins were up expressed and 149 proteins were down expressed.Three pathways of glycolysis pathway,RNA degradation pathway and the pentose phosphate pathway were found related to DFD beef quality.In the glycolysis pathway,there were 23 enzymes were differently expressed.Most enzymes were up expressed except 6-fructose phosphate kinase,pyruvate dehydrogenase(Lipoamide)alpha 2 and Alpha-aminoadipic semialdehyde dehydrogenase.The down expression of phosphofructokinase could probably explain why the anaerobic glycolysis slowed and the ultimate pH higher in DFD beef.In the RNA degradation pathway,a total of 6 differential proteins were found.Of which,proteins of ENO2 protein,60 kDa heat shock protein,Beta-enolase and Alpha-enolase were all up expressed except stress-70 protein which was down expressed.In pentose phosphate pathway,9 differential proteins were detected with 8 proteins up expressed(Transaldolase,Uncharacterized protein,ATP-dependent 6-phosphofructokinase(muscle type),Fructose-bisphosphate aldolase,Fructose-1,6-bisphosphatase isozyme 2,Phosphoglucomutase-1,Fructose-bisphosphate aldolase)and one protein of ATP-dependent 6-phosphofructokinase down expressed.For crossed Yuxi yellow cattle,a total of 251 differential proteins were detected and there were 145 proteins were down expressed and 106 proteins were up expressed.And 7 pathways were found different significantly(P < 0.05).Those of Glutathione peroxidase 1,Isocitrate dehydrogenase and Microsomal glutathione S-transferase 3 were down expressed,while those of Glutathione S-transferase P,GSTM1 protein and Glutathione S-transferase Mu 1 were up expressed.Of which,glutathione metabolism pathway was closely related to DFD quality.3 Effects of different packages on DFD beef qualityCompared to VP and CO-MAP,80%O2-MAP had significantly decreased the TVC in DFD beef during storage(P < 0.05).With the storage time prolonged,the drip loss increased and then decreased again.The cooking loss and drip loss in 80%O2-MAP was higher than VP and CO-MAP(P < 0.05).Shear force was not affected by package methods(P > 0.05).Meat color of DFD beef was improved by 80%O2-MAP and CO-MAP.So,CO-MAP may be a good choice for DFD beef with improved color and low drip loss and cooking loss.