| Nuodeng ham is one of the typical dry-cured hams,that is deeply loved by people.However,the high salt content in ham will have an impact on human health,which is also an important factor limiting the development of the Nuodeng ham industry.Developing a new compound curing agent to reduce the salt content of products has become a hot research topic at present.Protein is an important component of meat products,but there is no report about the effect of low sodium compound salts on protein characteristics in Nuodeng ham.Based on this,18 hind legs of Nuodeng black pig were randomly divided into two groups,9 in each group,and Nuodeng ham was processed with 100% Na Cl(group C)and compound curing agent(group T)respectively.After fermentation,Fourier transform infrared spectroscopy(FTIR),sodium dodecyl sulfate polyacrylamide gel electrophoresis(SDS-PAGE),TMT-labeled total quantitative proteomics and UHPLC-QE-MS were used to analyze the protein structure changes and the differences of degradation products of Nuodeng ham to clarify the effects of compound curing agents on the protein characteristics of Nuodeng ham,and to provide a scientific theoretical basis for developing the salt-reducing processing technology of Nuodeng ham.The main results are as follows:1.Compound curing agent is an important factor affecting the stability of the protein in ham.The composition and proportion of protein chemical interaction in Nuodeng ham in Group T and Group C were similar(P>0.05),and hydrophobic interaction and disulfide bond were the main interaction forces to maintain the stability of the protein(P<0.05).It was found by NMR that the water in the ham was mainly bound water.Compared with group C ham,the contents of bound water,bound water and free water in group T ham were higher,which indicated that the composite curing agent has weak damage to the muscle fiber structure.2.Compound curing agents have an important influence on the degradation and oxidation of proteins.Compared with group C ham,the solubility and sulfhydryl content of myofibrillar protein in group T ham increased significantly(P<0.05),while the carbonyl content,disulfide bond content and binding amount of bromophenol blue(BPB)decreased significantly(P<0.05),while the solubility and sulfhydryl content of sarcoplasmic protein were slightly higher(P>0.05),and the carbonyl content decreased significantly(P<0.05).The protein turbidity of both groups of ham increased with the increase in temperature.At lower a temperature(30-40℃),the turbidity of myofibrillar protein in group T was significantly lower than that in group C(P<0.05).The results of SDS-PAGE showed that the degradation degree of myofibrillar protein in group T was lower than that in group C,and the content of sarcoplasmic protein was less than that in group C.The results showed that the compound curing agent could inhibit the oxidation of proteins to a certain extent.3.The protein structure changes of proteins in ham were detected by FTIR.It was found that both groups of ham had strong absorption peaks in amide Ⅰ,and the β-corner structure was the secondary structure with the highest proportion of myofibrillar protein and sarcoplasmic protein(P<0.05).Compared with group C ham,the proportion of myogenic fibrous protein and β-sheet in group T ham increased slightly(P>0.05).Intrinsic fluorescence spectrum showed that the fluorescence intensity of myofibrillar protein and sarcoplasmic protein in group T was higher than that in group C,and the phenomenon of blue shift occurred,which indicated that the secondary and tertiary structures of Nuodeng ham were damaged slightly by the compound curing agent.4.By TMT-labeled full-quantitative analysis,a total of 1424 proteins were identified in Nuodeng ham protein proteomics,and 22 differentially expressed proteins were screened under the conditions of FC>1.5 and P<0.05,among which 9differentially expressed proteins were highly expressed in T-group ham,mainly including actin-related proteins T2(F1RJB0),actin-1(Q4PS85),actin-3(A0A5G2QM25)and superoxide dismutase [Cu/Zn](A0A2C9F3F0).Through GO functional annotation analysis,it was found that the number of differentially expressed proteins with high abundance in molecular function,cellular components,and biological processes was divided into 11,15 and 2.5.By UPLC-QE-MS technology,270 kinds and 261 of small molecular compounds were detected from Nuodeng ham in positive ion mode and negative ion mode,which were mainly divided into amino acids and their derivatives,organic acids and their derivatives,alkaloids,ketones,alcohols,indoles and their derivatives,glycerophosphates,pyrimidines and their derivatives,nucleosides and their derivatives,etc.Among them,48 kinds of differential metabolites(VIP≥1.3,P<0.05)were the important components that affected the flavor difference of ham between the two experimental groups.Metabolic pathway analysis found 20 metabolic pathways,of which 8 were identified as key metabolic pathways(Impact>0.01,P<0.05).Through metabolic pathway analysis,20 metabolic pathways were found,of which 8 were identified as key metabolic pathways(Impact>0.01,P<0.05).Through the mapping of KEGG,Pub Chem and other metabolite databases,14 key metabolites were accurately matched,including 20-HETE,4-acetylaminobutyric acid,L-aspartic acid,13(S)-HpOTrE,9-oxononanoic acid and jasmonic acid. |
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