Potential Mechanisms To Investigate Effects Of High Oxygen And Carbon Monoxide Modified Atmosphere Packaging On Meat Color Stability Of Chilled Beef Steaks

Modified atmosphere packaging?MAP?has been wordwidely used to maintain meat safety and desired appearance duing the preservation and display of red meat,in a way of modified atmospheres.Commercially,high-oxygen modified atmosphere packaging?HiOx-MAP?,or carbon monoxide MAP?CO-MAP?are two most popular MAP methods due to their excellent color protection.Different mechanisms on the meat color protection of these two packaging methods cause beef steaks to have different meat color stability,which will determine the final color shelf-life of beef steaks.During the storage,changes in the physical and chemical properties of packaged beef steaks and the role of microorganisms are recognized as two critical factors affecting meat color stability.Therefore,we investigated the changes in meat color stability of beef steaks packaged in these two MAP methods during storage from the perspective of proteomics and microbial communities,and explored the underlying mechanism to explain the differences in meat color stability of both MAP beef steaks.Further understanding of the color protective mechanism of these two MAP methods was abtained in this study.This work was devided into two parts.In the first part,the beef steaks were packaged in HiOx-MAP?80%O₂/20%CO₂?,or CO-MAP?0.4%CO/30%CO₂/69.6%N₂?under aseptic conditions.All packaged beef steaks were held for either 5,10 or 15 days at 2°C in the dark,and conventional meat color traits,metmyoglobin reducing activity?MRA?,oxygen consumption rate?OCR?,pH values,lipid oxidation and headspace gases compositions were analyzed at initial day and each storage day.The subsequent proteome analysis and bioinformatics analysis were conducted to indentify and analyze the differentially expressed sarcoplasmic proteins.Correlation analysis and regression analysis were used to assess the relationship between protein biomarkers and meat color traits.In the second part,the beef steaks were packaged in the same HiOx-MAP,or CO-MAP methods under actural production conditions.All packaged beef steaks were held for either 5,10,15 or 20 days at 2°C in the dark,and conventional meat color traits,MRA,OCR,pH values,and headspace gases compositions were analyzed at initial day and each storage day.Microbial community dynamics analysis of these two MAP methods during storage was conducted by high-throughput sequencing and traditional microbial cultivation.Regression analysis was used to explore the microbial communities that are related to meat color stability.The main results and conclutions of this study are as follows:?1?The meat color stability of HiOx-MAP beef steaks was lower than that of CO-MAP beef steaks during storage.The OCR and MRA of HiOx-MAP beef steaks decreased significantly over time before 15 days and were significantly low than these of CO-MAP beef steaks from day 5.The low MRA and OCR levels reduced meat color stability of beef steaks.Afterwards,the OCR of Hi Ox-MAP beef steaks increased significantly from day 15,and thus the O₂ partial pressure around meat surface decreased drastically to the O₂ level range favoring the formation of metmyoglobin,which in turns promote the formation of metmyoglobin.Furthermore,the higher lipid oxidation in HiOx-MAP beef steaks than that in CO-MAP beef steaks also enhanced the development of metmyoglobin.?2?Proteomic results revealed that the differential expression of the sarcoplasmic proteome at different storage periods contributed to the variations in meat color stability between the two MAP methods.Compared with HiOx-MAP beef steaks,metabolic enzymes involved in the regeneration of NADH?alpha-enolase,pyruvate kinase,glycerol-3-phosphate dehydrogenase[NAD?+?],phosphoglucomutase-1,retinal dehydrogenase 1,lambda-crystallin homolog,malate dehydrogenase and 3-hydroxyisobutyrate dehydrogenasewere?were up-regulated in CO-MAP beef steaks.Moreover,haloacid dehalogenase-like hydrolase domain-containingprotein2,proteinDJ-1,peroxiredoxin-2,peroxiredoxin-6,thioredoxin-dependent peroxide reductase,lactoylglutathione lyase,and creatine kinase M-type,were also up-regulated in CO-MAP beef steaks compared to HiOx-MAP beef steaks.Compared with HiOx-MAP beef steaks,the over-expression of these aforementioned proteins may enhance the MRA and OCR levels in CO-MAP beef steaks,and then meat color stability were improved.?3?The proteins that were related with the change in meat color stability of Hi Ox-MAP beef steaks during storage mainly belong to some enzymes involved in glycolytic metabolism?pyruvate kinase,glyceraldehyde-3-phosphate dehydrogenase,fructose-bisphosphate aldolase and fructose-1,6-bisphosphatase isozyme 2?and energy metabolism?malate dehydrogenase and flavin reductase?.The down-regulated tendency of these metabolic enzymes reduced NADH and NADPH levels,which reduced meat color stability.The decrease in meat color stability also may be related to the down-regulation of myoglobin during storage.Peroxiredoxin-2 and protein DJ-1 were two differentially expressed proteins that were correlated with meat color traits,and they only existed in HiOx-MAP beef steaks compared with CO-MAP beef steaks throughout storage.?4?The metabolic enzymes,including glyceraldehyde-3-phosphate dehydrogenase,flavin reductase,and 14 kDa phosphohistidine phosphatase,were also differentially expressed proteins during the storage of CO-MAP beef steaks,however,glycerol-3-phosphate dehydrogenase[NAD?+?]and adenylate kinase isoenzyme 1 were proteins that only existed in CO-MAP beef steaks compared to HiOx-MAP beef steaks throughout storage.The expression of these proteins were down-regulated over time.During storage,the abundance of these three metabolic enzymes?glyceraldehyde-3-phosphate dehydrogenase,glycerol-3-phosphate dehydrogenase[NAD?+?]and flavin reductase?involved in the production of NADH and heat shock protein were all related to the meat color stability of CO-MAP beef steaks.?5?This study revealed that CO-MAP was superior to HiOx-MAP in delaying bacterial growth during storage,and could extend the shelf-life of beef steaks over 20 days.The microbial diversity of beef steaks in both MAP methods decreased with storage time.CO-MAP beef steaks had a more complex process of bacterial succession than HiOx-MAP beef steaks.B.thermosphacta and Pseudomonas spp.dominated in HiOx-MAP beef steaks,however,Pseudomonas spp.gradually replaced B.thermosphacta from day 10.Acinetobacter,Vagococcus,Leuconostoc,Lactobacillus,Lactococcus and Serratia dominated alternately in CO-MAP beef steaks over time,and Lactococcus were most prevalent at the end of storage.?6?Different microbial community compositions were another important reason for the differential meat color stability of two packaging methods.Among microbial communities,Pseudomonas spp.was the most important microorganism that causes the decoloration of HiOx-MAP beef steaks,and played an important role in microbial communities at late storage times.In HiOx-MAP,the influence of microorganisms on meat color depended primarily on the reduced oxygen partial pressure around meat surface through the respiratory of these aerobic microorganisms,and utilizing proteins and lipids as energetic substances and producing some metabolites that affect meat color.Lactic acid bacteria,especially Lactobacillus and Lactobacillus,were the predominant bacteria in CO-MAP beef steaks and played an important role in microbial communities during the late stage of storage.These bacteria could have a protective effect on meat color.