The Effect Of Different Oxygen Concentrations In Modified Atmosphere Packaging On Water Holding Capacity Of Chilled Meat

In this paper,the mechanism of different oxygen content in modified atmosphere packaging on the meat quality and water holding capacity was investigated,to provide theoretical basis for storage quality and control the purge loss of pork in modified atmosphere packaging.Firstly,the pork meat was cut into suitable size for packaging,and four oxygen concentrations（0%,20%,50%,and 80%）were set.All packages were balanced with N₂ and contained 20%CO₂ to inhibit the microbial growth.Pork steaks overwrapped with airpermeable polyvinylchloride film was used as control.After packaging,the samples were stored at 4°C for 7 days.After storage,the quality indicators of meat samples from different packaging treatments were determined.Subsequently,the water-holding capacity and oxidation indexes of meat samples were measured.Finally,the purge loss of meat samples from different oxygen concentrations were collected to conduct proteomic experiments.The protein in the purge loss were identified by mass spectrometry.At the same time,the differential abundance proteins between different packaging treatments were analyzed and performed bioinformatics analysis.The specific results were as follows:Compared with air-packaging,MAP can effectively delay the spoilage and extend the shelf life of pork meat.The highest a*and b*value of meat samples was occurred in samples after storage in 80%oxygen,which indicating that high oxygen packaging has a positive effect on the color of meat.However,other quality parameters（such as elasticity,chewiness,cohesiveness,WBSF,hardness,TVB-N and TVC）of meat samples from 80%oxygen packaging were worse than those of other groups.The water holding capacity of meat samples decreased with increasing oxygen concentrations.The purge loss and cooking loss increased（P<0.05）with increasing oxygen contents.The results of LF-NMR and MRI of pork muscle were consistent with these results,substantiating that the higher oxygen content resulted in lower water retention properties in meat steaks.Meat packaged in MAP generally showed increasing carbonyl mean values,protein surface hydrophobicity,and TBARS values,which indicated that the degree of lipid oxidation and protein oxidation become larger.It can be seen that the purge loss was highly correlated（P<0.01 or P<0.05）with protein surface hydrophobicity（r=0.61,P<0.05）,TBARS value（r=0.82,P<0.01）,carbonyl content（r=0.68,P<0.05）and free thiol content（r=-0.61,P<0.05）.We also found that cooking loss was highly correlated（P<0.01 or P<0.05）with protein and lipid oxidation parameters when the heating temperature was 50°C.However,the degree of correlation between cooking loss and oxidation parameters became lower with the heating temperature increased.The results of microstructure and ultrastructure of meat samples from different packaging treatments showed that the most destructive changes of suructure in meat myofibrils occurred in 50%and80%oxygen.It showed a higher degree of disintegration.All these physiological changes were closely associated with the changes of the water holding capacity of pork muscles.By using the proteomics method,the differential abundance proteins between different packaging systems were found.The multiple reaction monitoring（MRM）test was performed to verify the reliability of the iTRAQ results.The GO analysis of proteins extracted from purge loss showed that it mainly distribute in cell component biosynthesis,cell component size,and muscle structure composition.Following statistical analysis,a total of 40 differential abundance proteins were identified in this study.Among them,18 differential abundance proteins existed in the 20%O₂ treatment group,11 proteins existed in the 50%O₂ treatment group,and 20 proteins were present in the 80%O₂ treatment group,and three proteins occurred in all groups（including two proteins that were not identified by mass spectrometry）.Therefore,Keratin 75 can be used as a potential biomarker to predict the WHC of pork meat.The differentially expressed proteins between 20%O₂ and 0%O₂ were classified into three functional categories:metabolic enzymes,stress response proteins,and structural proteins.GO annotations of these proteins indicated that ion transport,enzyme activity regulation,cytoskeleton and organelles were predominant.According to KEGG analysis,the differentially abundance proteins between 20%O₂ and 0%O₂ are mainly enriched in glycolysis/gluconeogenesis,metabolic pathways,and carbon metabolism.The differentially expressed proteins between 50%O₂ and 0%O₂ were classified into2 functional categories:metabolic enzymes and structural proteins.GO annotations of these proteins indicated that transmembrane transport of regulatory ions,the cytoskeletal portion,and the organelle were predominant.KEGG analysis of these proteins are mainly enriched in metabolic pathways.Differentially expressed proteins between 80%O₂ and 0%O₂ were classified into 3 functional categories:metabolic enzymes,stress response proteins and structural proteins.GO annotations of these proteins indicated that response of the cell to external stimuli,skeletal muscle contraction,molecular function,cytoskeletal parts,organelles,cytoplasmic parts were predominant.KEGG analysis of these proteins are mainly enriched in metabolic pathways,glycolysis/gluconeogenesis.In summary,the metabolism level of muscle cell and integrity of cytoskeletal structure may affect the water holding capacity of muscle through affecting proteins involved in these biological processes.