Effect Of Repeated Freeze-thaw On The Collagen Properties And Quality Of Bovine Rumen Smooth Muscle

The bovine stomach is one of the main bovine by-products.The rumen is the stomach with the largest volume in the bovine stomach,accounting for about 80% of the bivine stomach.Its smooth muscle collagen content is 10% higher than that of skeletal muscle.After the bovine are slaughtered,the rumen needs to be thoroughly cleaned,frozen and stored before being transported and sold for consumption.During this process,the repeated freeze-thaw phenomenon caused by the unsound cold chain technology and the denaturation of muscle protein under the action of reactive oxygen species and various enzymes lead to the destruction of protein structure,which in turn affects its functional characteristics and muscle quality characteristics.At present,protein denaturation and the changes in functional properties and structural properties during rumen freeze-thaw and the change mechanism are still unclear.Therefore,in this study,the rumen of bovine was taken as the research object,and the changes of smooth muscle tenderness,water holding capacity and other quality characteristics,collagen functional,structural characteristics,degradation,cross-linking stability and aggregation characteristics under multiple freeze-thaw cycles were analyzed.The aim is to explore the changes in the stability of bovine smooth muscle quality during repeated freeze-thaw and the mechanism of change,and to reveal the influence mechanism of the number of times of freeze-thaw on the quality of bovine smooth muscle,in order to provide a theoretical basis and data reference for the development,utilization and quality control of smooth muscle.The specific research results are as follows:1.Repeated freeze-thaw reduced the original functional properties of Bovine smooth muscle collagen.The content of collagen decreased and the solubility increased significantly(P <0.05)with the increase of freeze-thaw cycles,the emulsifying property,emulsifying stability,foaming ability,foam stability and oil absorption of collagen decreased significantly(P < 0.05),the decrease was 54.46%,36.45%,27.19%,44.45% and 19.08% respectively,and the surface hydrophobicity increased significantly(P < 0.05),the increased was 80.02%.2.Repeated freeze-thaw destroys the collagen structure and reduces its thermal stability.Under different freeze-thaw times,the UV absorption peak of collagen extracted from rumen smooth muscle of bovine appeared near 230 nm,and the characteristic absorption peak was not obvious at 280 nm.With the increase of freeze-thaw times,the content of ?-helix of collagen decreased significantly(P < 0.05),the content of ?-fold increased significantly(P <0.05),but the content of ?-turn and irregular coil did not change significantly(P > 0.05).The thermal enthalpy and denaturation temperature of collagen decreased with the increase of freeze-thaw times.3.Bovine smooth muscle collagen is significantly degraded with the increase of freezethaw times,so that smooth muscle tenderness is improved.The activity of ?-galactosidase(?-gal)increased first and then decreased(P < 0.05),and the activity of ?-glucuronidase(?-GD)increased significantly(P < 0.05).SDS-PAGE results showed that the molecular weight of bovine smooth muscle collagen mainly ranged from 100 KDa to 245 KDa,and the bands of high-molecular-weight collagen weakened,but there were no small-molecule protein bands with the increase of freeze-thaw times.4.Repeated freeze-thaw treatment accelerated cross-linking of collagen.With the increase of freeze-thaw cycles,the activity of lysine oxidase(LOX),the content of dihydroxylysine leucine(DHLNL),the content of hydroxylysine pyridinoline(HP)and lysine pyridine(LP)increased significantly(P < 0.05).5.Repeated freeze-thaw cycles increased the aggregation degree of bovine smooth muscle collagen,resulting in protein aggregation denaturation.The turbidity and viscosity of bovine smooth muscle collagen solution increased significantly with the increase of freeze-thaw cycles(P < 0.05),and the increase of turbidity was 82.35%.6.The tenderness of bovine smooth muscle was improved and water holding capacity decreased during repeated freeze-thaw.With the increase of freeze-thaw times,the cutting force,connective tissue mechanical strength,hardness and p H increased first and then decreased.Elasticity,cohesion and chewiness decreased significantly(P <0.05),thawing loss,pressuring loss and cooking loss increased significantly(P <0.05).The muscle tissue structure was destroyed by the formation of ice crystals during freeze-thaw,resulting in the decrease of shear force and mechanical strength of connective tissue.In summary,this paper studied the changes of collagen function,structure,degradation,cross-linking,and aggregation characteristics and their correlation with the quality of Bovine smooth muscle during repeated freeze-thaw.The results showed that the function of collagen extracted from smooth muscle was decreased,the structure was destroyed,the degree of the degradation,cross-linking and aggregation of collagen were increased,so that the tenderness of collagen was improved and the water holding capacity was decreased.Correlation analysis shows that the main reason for the improvement of smooth muscle tenderness is the degradation of collagen and the destruction of ice crystals.The decrease in water retention is mainly due to the cross-linking and increased aggregation of collagen and the destruction of muscle microstructure by ice crystals.The thawing loss rate increases faster,and the shear force decreases slower after three times of freeze-thaw.Considering the food quality and commercial value,the freeze-thaw times of rumen should be controlled within 3 times in the process of transportation,storage and marketing,which can provide theoretical basis and data reference for the further study of smooth muscle.