Effects Of Muscle Protein Changes On Textural Quality Of Eriocheir Sinensis

Eriocheir sinensis is one of the important freshwater aquaculture species in China,with a large market demand.Texture is one of the important factors affecting consumers'satisfaction with crab meat quality.The outstanding texture quality of aquatic products is tender and juicy,but many factors will affect the tender and juicy of crab.In this study,the crab meat of fresh Chinese mitten crab was studied.From the perspective of food raw materials,the myofibrillar protein was the main line,and the texture quality?tenderness and water holding capacity?was systematically studied around the protein properties.Firstly,while understanding the raw material properties of the crab muscle,an instrumental measurement method was established for effectively evaluating muscle tenderness.The correlation analysis between the histochemical index and the textural index of different muscle tissues was carried out,and the key component affecting the quality of the texture was preliminarily determined.Then,the differences in proteomics and water distribution between the crab meats of different growing rate groups were compared,and the structural proteins that can indicate the muscle texture were speculated.Finally,the secondary structure,water distribution and texture quality changes of crab meat from different locations,genders and batches of crab meat are dynamically correlated.The main findings are as follows:An instrumental measurement method was established for effectively evaluating muscle tenderness.By correlation analysis on the histochemical characteristics and texture quality of different muscle parts,the key components affecting the textural quality of were determined.?1?The muscle tissue of Eriocheir sinensis accounted for the largest proportion of total edible parts?male:70.58%,female:57.02%?.The protein was the main component of the three muscle tissues,and the content of the abdomen meat was the highest?90.03%,dry basis??P<0.05?,and the fat content was very low.It can be seen that the macromolecular substance that determines the texture of crab meat is water and protein.?2?The nitrogen distribution and protein pattern of the muscle tissues of Eriocheir sinensis showed that the myofibrillar protein fraction?11.13-13.99g/100 g wet basis,about 70 g/100 g protein?was the highest in the three muscle tissues?P<0.05?.The SDS-PAGE protein patterns of the myofibrillar protein components of the three muscle tissues are similar,and the myosin heavy chain and actin are the main protein components.The insoluble component?0.16-0.22 g/100 g wet basis?is mainly matrix protein,and its content is very low,resulting in a loose texture of crab meat.?3?In order to better understand the contribution of muscle fibers and connective tissue to texture.The meat was observed under an optical microscope,and the distribution of connective tissue was lower than that of the muscle fibers.The ultrastructure of the muscle was further observed under a transmission electron microscope.The average diameter of the meat of the abdomen,claw,and leg muscle was 23±3,21±2,19±2 nm?P<0.05?.?4?Under the same homogenization rate?uniform shear force?,the breaking rate of three edible muscle tissues of Eriocheir sinensis was higher than that of other species.The correlation between instrumental tenderness and sensory tenderness?R²=0.910?was very significant?P<0.01?,so the breaking rate after entropy analysis can quantitatively reflect the tenderness of different muscle tissues.Compared with the shear force method,this microscopic method is very suitable for meat with low fat,low connective tissue,and loose.?5?Myofibrillar protein,water distribution and textural quality have a strong correlation,the moisture content before steaming is positively correlated with water loss,and negatively correlated with tenderness.That is,the higher the water content before steaming,the weaker the water holding capacity after steaming,and the lower the tenderness of the meat sample.High levels of myofibrillar protein and myowater are associated with a higher tenderness.There is a significant positive correlation between the diameter of the thick filaments and immobilized water?r=0.809?.Based on the ultrastructure,we speculate that the irregular arrangement of the thick filaments may be closely related to the higher tenderness of the crab meat.The differences in proteomics and water distribution between the crab meats of different growing rate groups were compared,and the structural proteins indicating muscle texture were determined.?1?The chemical composition of different grade of Eriocheir sinensis was changed before and after steaming.The protein content of G 3?18.5±0.6%?and G 4?19.3±0.4%?was significantly higher than that of the other two grades.Compared with content changes before and after steaming,before steaming:G 2?81.6±0.2%?has the highest content,G 4?77.0±0.1%?has the lowest?P<0.05?;after steaming:G 1,G 2 and G 3 significantly higher than the G 4?P<0.05?.In terms of cooking loss,the cooking loss of G 2 was significantly higher than other grades?P<0.05?,and the water holding capacity of G 2 was the worst,indicating that the high moisture content before steaming is more likely to cause greater cooking loss.?2?The main form of water in all samples before and after steaming is immobilised water.However,before steaming,the T₂₁ of different grades crab meat are different,The G 4crab meat has the closest combination of water and protein,and the combination of water and protein in the G 2 crab meat is the weakest.During the steaming process,the immobilised water is partially converted into free water.After steaming,there is no significant difference in the relaxation time T₂₁ corresponding to the immobilised water of crab meat of different grades,but compared with T₂₁ before steaming,T₂₁ is significantly smaller after steaming,indicating that heating causes denaturation of muscle protein.In turn,the combination of protein and the immobilised water is tighter.?3?From the comparison of the two tenderness evaluations,the tenderness of the G 2meat is significantly higher than other grades.Compared with the sensory tenderness,the instrument has a greater discrimination to the tenderness of different grades of crab meat.?4?The diameter and density of the thick filaments can explain the tenderness and water holding capacity of the steamed crab meat to a certain extent.The diameter of thick filaments of the G 2 crab meat are obviously more sparse,larger,and consistent with the high protein content;the corresponding myofibrils protein have larger internal space and more moisture content.Its T₂₁ is larger,the water-to-protein binding ability is less,and the water holding capacity is lower,but there is still a higher moisture content and tenderness.?5?We compared the G 1,G 3,and G 4 crab meats with the G 2,and analyzed the mass spectrometric identification of the differentially expressed proteins in the different control groups.The common differential proteins in the three control groups were myosin regulatory light chain 2,ancient ubiquitous protein 1,tubulin alpha-2 chain.Combining the difference multiples,the G 1,G 3,and G 4 have higher abundance of myosin light chain 2 and ancient ubiquitous protein 1,and the tubulin alpha-2 chain abundance is lower.The most likely protein for indicating muscle tenderness and water holding capacity is myosin light chain 2 and ancient ubiquitous protein 1,and the tubulin alpha-2 chain,followed by troponin I,fibrillin-2-like,leupaxin isoform X 2 and actin 2.The protein secondary structure,water distribution and textural quality of different locations,genders and batches of crab meat were dynamically correlated.?1?The tenderness was related to the moisture and T₂₁ before steaming,the water,T₂₁ and free water after steaming with a positively correlation,especially the moisture content after steaming.The tenderness was positively correlated with the?-turn content before steaming and?-sheet content after steaming,and negatively correlated with?-helix content after steaming.Water holding capacity was related to the bound water,protein and?-sheet before steaming,and?-sheet,moisture,T₂₁ and free water after steaming are positively correlated,especially with moisture content after steaming.Water holding capacity was negatively correlated with moisture,T₂₁,immobilised water and random coil before steaming,and random coil after steaming.?2?As the batch?growth phase?is delayed,the total moisture and bound water content increase,the content of the immobilised water decreases,and the relaxation time T₂₁ increases.In general,the absorption of water by the space inside the myofibril increases,and the high content of intra-myofibrillar water and the low content of extra-myofibrillar water are related to the high tenderness and water holding capacity.In the T 1 and T 2 batches,the immobilised water is transferred to the bound water and free water during the steaming process,and the corresponding meat quality is poor in water holding capacity.In the latter two batches,the bound water will transfer to the immobilised water,and the corresponding water holding capacity is guaranteed.The high water content may be due to the decrease in the bound water content in the muscles of the crabs as the batch is delayed.The less bound water after steaming,the more immobilised water and free water are not easy to flow,the greater the T₂₁,and the higher the tenderness of the corresponding meat,the better the water holding capacity.?3?The four coastal regions?CD,FD,GM and HB?showed strong regularity.Before steaming,the water and?-sheet content of the meat sample is high,the T₂₁ value is large,the moisture content after steaming,free water,high content of?-helix and?-turn,and the T₂₁ value is large,and the corresponding meat tenderness is high and the water holding capacity is strong.This is likely to be related to the high salinity of the water environment of different rigions.