Effects Of Kiwifruit Polyphenols On Mutton Quality During Refrigeration And Freeze-thaw And Proteomic Analysis

In the storage process,mutton faces quality deterioration and freeze-thaw problems,which would reduce meat quality and limit the rapid development of the mutton industry.Thinned kiwifruit is a huge amount of wasted berry resources,and there are a large number of phenolic substances in it.Thinned kiwifruit polyphenol was used as a natural antioxidant in the research of improving meat quality,which has important economic and environmental significance.This study takes Shaanxi specialty muttonHengshan mutton as research object,and the muscles（longissimus thoracis）were selected.The kiwifruit polyphenols was used to soak and spray mutton to explore the effect of polyphenols on mutton quality during cold storage and freeze-thaw process,and further explore the meat thawing effects of different thawing methods.Then,the proteins in the meat samples were analyzed by relative and absolute quantification（iTRAQ）labeling techniques,and the differential proteins were studied by liquid chromatography-tandem mass spectrometry（LC-MS/MS）.The identified differential proteins were subjected to GO（Gene Ontology）annotation and KEGG（Kyoto Encyclopedia of Genes and Genomes）pathway analysis.This study aims to facilitate our understanding of proteome changes and mechanisms behind the decline in the mutton quality during freeze-thaw processing,which provides a certain theoretical basis for the mutton quality control during transportation and storage.The specific research results are as follows:（1）Study on the effect of kiwifruit polyphenols on the mutton quality during cold storage and freeze-thaw process.Analyzing the changes of mutton quality during cold storage after thinned kiwifruit polyphenol treatment,we found that the kiwifruit polyphenol treatment on mutton was beneficial to maintain the integrity of its muscle fiber structure.The hardness and springing of mutton showed a decreasing trend during cold storage.The hardness of mutton in the thinned kiwifruit polyphenol group was significantly the lowest（P<0.05）,and the springing of the thinned kiwifruit polyphenol group in the first 3 days was also lower than that of the other three groups（P<0.05）.The thiobarbituric acid reactive substances（TBARS）value of mutton first decreased and then increased with time.After 3 days of cold storage,the TBARS value was ranked as the thinned kiwifruit polyphenol group0.05）.The mutton TBARS values of the UT320 and UT180 groups were lower than those of the control group at 7 times of freeze-thaw,and the PUFA content of the UT320 and UT180 groups during freeze-thaw was higher than that of the LT control group（P<0.05）.The principal component analysis of the mutton physicochemical properties showed that the main components of the UT320 group with the same number of freeze-thaw cycles were distributed at the top,while the LT group was distributed at the bottom.Microstructural analysis showed that UT320 ultrasound treatment was conducive to maintaining the integrity of the mutton fiber structure compared with the control group.The amino acid contents of mutton samples were analyzed by clustering.The initial sample and the 3 times freeze-thaw ultrasound-assisted thawing treatment group were classified as the first category,with the highest amino acid nutritional quality,and the initial sample was closer to the UT320 group.Compared to the mutton freeze-thaw 3 times,the composition and ratio of essential amino acids in the mutton of the UT320 and UT180 groups were kept stable in the freeze-thaw cycle 7 times.Therefore,compared to refrigerated thawing and hydrostation thawing,the 320W ultrasonic-assisted thawing treatment on mutton had excellent quality retention ability,and could maintain mutton amino acid quality by reduce protein loss.（3）Based on iTRAQ technology,we performed LC-MS/MS identification and quantitative analysis on the differential proteins of frozen-thawed mutton.The total number of identified proteins was 951,and the number of proteins that could be quantified was 835.In total,further analysis identified 29（upregulated:25,downregulated:4）,127（upregulated:106,downregulated:21）and 133（upregulated:112,downregulated:21）proteins as differentially expressed proteins（DEPs,FC≥1.5 or≤2/3 and P value<0.05）in FT1-vs-CON,FT2-vs-FT1,and FT2-vs-CON,respectively.More specifically,4 DEPs showed consistent abundance changes during the freeze-thaw process,in which 3 upregulated DEPs were the elongation factor 1-gamma（EF-1γ）,cAMP-dependent protein kinase catalytic subunit alpha（PKA C-alpha）and 40S ribosomal protein S12（RPS12）,and the downregulated DEPs were collagen alpha-2（IV）chains（COL4A2）.In addition,GO enrichment analysis showed that the cellular components were concentrated in vesicles and golgi among the three comparative groups,which were involved in the synthesis and secretion of proteins.The molecular functional analysis indicated that hydrolase,ammonia ligase activities and binding functions were predominant in the three comparative groups,suggesting that they play important roles in the quality differences of meat during freeze-thaw processing.Moreover,this study focused on the comparison of differential proteins after freeze-thaw treatment and the associated mechanism of continuous freeze-thaw cycles.The DEPs of the FT1-vs-CON comparison were mainly enriched in the Ras signaling pathway,protein digestion and absorption,PI3K-Akt signaling pathway,AMPK signaling pathway,ECM-receptor interaction,and regulation of lipolysis in adipocytes of KEGG pathways.The DEPs of the FT2-vs-FT1 comparison were mainly enriched in protein processing in the endoplasmic reticulum,ubiquitin-mediated proteolysis,proteasome,regulation of lipolysis in adipocytes,and Rap1 signaling pathway of KEGG pathways.Therefore,it was confirmed that the treatment of repeated freeze-thaw could affect protein digestion and fat decomposition in mutton.