Quality Changes Of Pork Longissimus Dorsi With Different Frozen Storage Time

As a safe and efficient meat storage method,frozen storage is widely used in the processing,transportation and storage of pork process industry.However,with the extension of frozen storage time,the quality of meat will decline.This project mainly studied the quality changes of pork with 0 d and 1,3,6,9,12 and 15 months of frozen storage,including microstructure,physicochemical properties,protein changes,water migration and distribution,etc,and the correlation analysis was performed on all indicators.Conclusions are as follows:?1?Microstructure:In the meat sample frozen for 0 days,the muscle fiber cross section showed a close and orderly state.With the prolonged frozen storage time,the gap between muscle fibers gradually increased,bending and fracture occurred,the area of muscle fibers gradually decreased,and the volume of ice crystals increased.Physicochemical properties:The volatile nitrogen base?TVB-N?,thiobarbituric acid?TBARS?,thawing loss rate of pork longissimus dorsi muscle gradually increases with the prolonged storage time,and the rate of change increases.The protein solubility gradually decreased with the prolonged storage time.In the 15 months of the frozen storage inspection period,the most significant loss of amino acids was alanine,glutamic acid,threonine,lysine,and leucine.Serine.?2?With the prolonged storage time,the hydrophobic amino acid residues and sulfhydryl groups of myofibrillar protein are continuously exposed from the inside of the protein,which makes the surface hydrophobicity and thiol content of the protein increase.The degraded protein was mainly located near 67 kDa and 20 to 29 kDa range;within 15 months of frozen storage periods,the thermal stability of myosin and sarcoplasmic proteins is reduced,whereas actin is more resistant to degenerative changes.The analysis of protein in the thawing loss of meat sample during the frozen storage time indicated that there was no difference in the protein types in the thawing loss of meat with different frozen storage time.In general,protein solubility,structural changes,and thermal stability were maintained at a good level during the first 3 months of frozen storage.From the 6th month,the rate of change was accelerated,so that after 6 months of frozen storage Protein quality in the longissimus muscle began to decrease rapidly.?3?The low field nuclear magnetic resonance?LF-NMR?analysis showed that there are three components of water in the pork longissimus dorsi muscle:combined water(T₂₀),immobilized water(T₂₁)and free Water(T₂₂),relaxation time was T₂₀:0.1-10 ms,T₂₁:10-100ms,T₂₂:100-1000 ms,T₂₁ gradually decreased,and T₂₂ gradually increased.MRI showed that the distribution of water was more uniform in the early stage of frozen storage.The amount of signal at the edge of meat samples increased with 3 months of frozen storage,and the amount of signal in the middle was decreased.After 15 months of frozen storage,the water distribution was uniform.A one-dimensional frequency code scanning showed that the amount of moisture in meat gradually decreased with the extension of frozen storage period.The correlation analysis showed that T₂₁,T₂₂ showed a good correlation with the other quality indicators.At the same time,the frozen storage time had a significant correlation with TVB-N,TBARS,thawing loss,protein solubility,and T₂₂,it can be used to evaluate the quality of frozen pork.