Effects Of Protein Oxidation On The Quality Characteristics Of Peeled Shrimp(solenocera Melantho)

Solenocera melantho,commonly known as red shrimp,is a subtropical and tropical warm water species.It is distributed in the East China Sea,the Southern Yellow Sea and the South China Sea,and is deeply loved by consumers.In the process of processing,circulation and storage,the shrimp is inevitably affected by temperature,light,radiation,oxygen,water and catalyst.It is prone to protein degradation and lipid oxidation,leading to spoilage and short shelf life.In this paper,the quality changes of the shrimp were studied systematically and comprehensively during oxidation.The effects of COS-GA treatment were evaluated on the quality of tubulips chinensis during frozen storage.The changes of proteins in the hydroxyl radical oxidation system were analyzed by using label free quantitative proteomics technology,and the indicator proteins related to the quality changes of the shrimp were screened.Finally,the lipid changes of the shrimp were analyzed by lipomics after oxidation.The details are as follows:1.The changes of quality characteristics(physicochemical indexes,protein properties,protein and lipid oxidation)of Solenocera melantho were studied in hydroxyl radical oxidation system(including Fe Cl3 concentration of 0.01 mmol/L,ascorbic acid concentration of 0.1 mmol/L,hydrogen peroxide concentration of 0.5,1.0,2.0,4.0mmol/L).The results showed that p H increased,water activity and water content first increased and then decreased,a* value,EAI,ESI,springness and chewiness decreased,L*value,thawing loss rate and TVB-N all showed an upward trend(p<0.05)with the increase of oxidation degree.The damage of tissue structure and muscle fiber is more and more serious.In addition,the activity of Ca2+-ATPase,total sulfhydryl group and active sulfhydryl group showed a downward trend,while the content of carbonyl group increased continuously in myofibrillar protein.The results of SDS-PAGE electrophoresis showed that the macromolecular proteins(180 KDa)were crosslinked and aggregated in varying degrees,while the small proteins(25-17 KDa)were degraded.In the aspect of lipid oxidation,the TBA content of shrimp continued to rise,and a large number of lipid droplets were produced in muscle.In conclusion,the higher the degree of hydroxyl radical oxidation,the worse the quality characteristics of shrimp.2.Objective to evaluate the control effect of chitooligosaccharide gallic acid complex on the quality change,protein denaturation and lipid oxidation of Solenocera melantho during-7°C frozen storage.The results showed that there were obvious changes in protein degradation,lipid oxidation and sensory quality of CK,COS,GA and COS-GA during frozen storage.However,compared with other groups,COS-GA could effectively control the increase of p H value,L* value,thawing loss rate and TVB-N value,as well as the decrease of water activity,water content,a* value,EAI,ESI,springness and chewiness(p<0.05),and reduce the degree of tissue structure and muscle fiber damage.In addition,COS-GA significantly inhibited the decrease of Ca2+-ATPase activity and sulfhydryl content,and the increase of carbonyl content of myofibrillar protein(p<0.05);SDS-PAGE results showed that COS-GA could effectively inhibit protein aggregation and degradation,and maintain clear protein bands.In terms of lipid oxidation,COS-GA inhibited the increase of TBA content and reduced the production of red lipid droplets.Therefore,compared with CK,COS and GA,COS-GA has better antioxidant effect on shrimp,especially on protein and fat quality.3.The changes of muscle proteins in the shrimp,Solenocera melantho,were studied by using Label-free quantitative proteomics under oxidative stress.The results showed that2422 peptides and 612 proteins were identified in chilled shrimp and oxidized shrimp(H2O2 concentration 4.0 mmol/L,oxidized for 7 h).Compared with the control,there were178 differential proteins,of which 116 were up-regulated and 62 down regulated.Gene Ontology(GO)analysis showed that these daps were mainly involved in binding,catalytic activity,cell,cell part,cell process and metabolic process.These processes are related to protein structure and function.In addition,the results of homologous eukaryotic clusters(KOG)confirmed that the oxidation system destroyed the natural conformation,structure and function of DAPs and accelerated the degradation of muscle protein.The four differential proteins may be related to the color(L*,a*)and texture characteristics(springness and chewiness)of shrimp.They are expected to be indicators of quality changes in the oxidation process of Solenocera melantho.Some DAPs have antioxidant function,and the specific mechanism needs to be further verified.4.The lipid changes of muscle of Solenocera melantho were studied by LC-MS/MS.The results showed that there were at least 27 classes and 835 species of lipids in the fresh shrimp and oxidized shrimp(4.0 mmol/L hydrogen peroxide oxidation for 7 h),and the main lipids were analyzed by Principal component analysis(PCA),partial least squares discriminant analysis(PLS-DA)and orthogonal partial least squares discriminant analysis(OPLS-DA).Through screening,15 classes and 120 species of different lipids were obtained.Compared with chilled shrimps,33 species of lipid were up-regulated and 87 species of lipid were down regulated in oxidized shrimps.ROC curve analysis showed that the diagnostic value of 57 different lipids in the oxidation process was excellent.This study provides more data for understanding the lipid oxidation changes in muscle of Solenocera melantho during storage.