Preliminary Investigation On The Preservation Mechanism To Superchilling Tan Mutton By Composite Coating

Tan sheep is a special and advantaged livestock breed in Ningxia,China,and it is favored by people for its tender meat,low fat without odor,and uniform fat content distribution.However,fresh mutton is easily affected by factors such as autolytic enzymes,microorganisms,and oxidative reactions,leading to spoilage and deterioration,which greatly limits the development of the sheep meat industry.With the increasing concern of people on food safety and nutritional value,how to maintain the storage quality of fresh meat and extend its shelf life has gradually become a research focus.In this study,the longissimus dorsi(LD)muscle of Tan sheep was used as the research object to investigate the synergistic antibacterial effects and optimal combination ratio of ε-polylysine(ε-PL),sodium lactate(SL),and Lycium barbarum leaves extract(LBLE)in the preparation of composite preservation coatings.The composite coatings were applied to the surface of Tan mutton to investigate their effects on the quality,protein,and lipid oxidation during superchilled storage.Furthermore,proteomic technology was utilized to identify differentially expressed proteins and their metabolic pathways caused by composite coatings during storage.The results of this study will provide theoretical basis for delaying the deterioration of Tan mutton under composite preservation coatings.The main research conclusions are as follows:(1)The exploration of synergistic antibacterial effects of ε-polylysine,sodium lactate,and Lycium barbarum leaves extract.The total flavonoid content of the prepared Lycium barbarum leaves extract was found to be 260.50 mg/g,containing the flavonoids chlorogenic acid,quercetin,and caffeic acid,among which chlorogenic acid had the highest content(162.50±0.24 mg/g).The synergistic antibacterial effects of εpolylysine,sodium lactate,and Lycium barbarum leaves extract were tested,and the results showed that the minimum inhibitory concentration(MIC)of the three preservatives against Staphylococcus aureus were 25 μg/mL,10 mg/mL,and 25 mg/mL,respectively,while the MIC against Escherichia coli were 50 μg/mL,10 mg/mL,and 20 mg/mL,respectively.Moreover,ε-polylysine and sodium lactate,as well as sodium lactate and Lycium barbarum leaves extract,exhibited a synergistic inhibitory effect against both bacterial strains.(2)Exploration of the optimal composite ratio and preservation effect of preservation coating.The optimal concentrations of ε-polylysine,sodium lactate,and Lycium barbarum leaves extract were obtained through single-factor experiments,which were found to be 1.5%,3%,and 1.5%,respectively.Subsequently,response surface experiments were conducted to obtain the concentrations ofε-polylysine,sodium lactate,and Lycium barbarum leaves extract in the composite coating,which were 1.61%,3.11%,and 1.53%,respectively.At this concentration,the composite coating exhibited the best preservation effect on superchilled mutton,extending the shelf life by 12 days compared to the control group.(3)Exploration of the effect of composite preservation coating on oxidative properties of superchilled Tan mutton.By applying the composite preservation coating,the contents of carbonyls and total thiols in myoglobin and myofibrillar proteins of superchilled Tan mutton were measured.The results revealed that the composite coating can maintain higher levels of oxygenated myoglobin,keeping the mutton’s fresh red color.The coating can also maintain the α-helical and β-turn content within the myofibrillar protein secondary structure,effectively stabilizing the protein structure and inhibiting the increase of carbonyl content and decrease of total thiol content caused by oxidation.During the investigation of the effect of the composite preservation coating on lipid oxidation during the storage of superchilled Tan mutton,it was found that the peroxide value(POV)was 3.09 mg/kg lower,and the thiobarbituric acid reactive substances(TBARS)content was 0.081 mg/kg lower in the treated group than in the control group at the end of the storage period.Scanning electron microscopy observations revealed that the treated group exhibited a more intact myofibril structure and a tighter arrangement of the microscopic structural configuration than the control group,indicating that the composite preservation coating plays a role in reducing oxidation of superchilled mutton.(4)Proteomic analysis of superchilled Tan mutton.The results showed that after 16 days of storage,analysis of differentially expressed proteins was performed with the screening criteria of fold change(FC)greater than 1.5 or less than 0.67 and P<0.05.A total of 104 downregulated and 58 upregulated proteins were found in the treated group(B16)compared to the control group(A 16).Subcellular localization analysis revealed that the differentially expressed proteins were primarily located in the cytoplasm,nucleus,and mitochondria.Functional analysis using Gene Ontology(GO)showed that the composite coating mainly affected the activity of ammonium transmembrane transport proteins and glycerolipid metabolism related functions in lamb muscle cells.Through the KEGG pathway analysis,the differentially expressed proteins caused by the composite coating treatment were mainly involved in biological regulation,including metabolic pathways related to glycerolipid metabolism,butyric acid metabolism,and folate biosynthesis.