Effects Of Different Freezing And Thawing Methods On Pork Quality

China is the world biggest pork consumption country.Frozen meat is the main raw material of all kinds of meat products in the production of pork.The freezing and thawing process will have a certain impact on meat quality.This mainly effects of freezing and thawing are ice crystals,the destruction of pork tissue structure,water holding,texture,and taste changes,fat oxidation,protein degradation.In this study,pork was used as the material,the common family refrigerator freezing temperature at-18?,-27 ?,and ultra-low temperature refrigerator of-70? and three kinds of common thawing methods(at 4? low temperature,25 ? with water,25 ? in air)were used.The aims of this study were to find out the specific effects of freezing and thawing on pork,and to find out the main influencing factors in this process.The main results of this study are as follows:1.The freezing characteristics and physical properties of pork were measured after different freezing temperatures.The freezing curve,conductivity,texture and ice crystal morphology of pork at-18?,-27? and-70? were measured.The texture changes(cohesion,elasticity,chewiness)of pork which freezing in-70?are more closer to the fresh meat.elasticity chewiness and hardness of the pork which frozen in different temperature were significantly decreased with the decrease of the freezing temperature compared with the fresh meat,From the ice crystal cross-section observation,pork tissue were damaged after frozen,and with the freezing temperature increasing,the area of ice crystals increased,the diameter of ice crystals increased,and the roundness decreased.From the longitudinal observation of muscle fibers,it can be seen that the frozen pork muscle fibers were broken,and the fracture was more serious as the freezing temperature increases.2.The changes of pork quality at different frozen temperature with different thawing methods were studied.Through the multivariate analysis of variance,the freezing and thawing processes had different effects on pork quality in different aspects.The results showed that the thawing loss rate and protein solubility of pork were significantly affected by the freezing and thawing methods.The effect of freezing method on the TBARS value of pork was not significant,which was probably due to the low temperature inhibit the fat oxidation.Thawing temperature and thawing time lead to different degrees of oxidation.Thawing in low temperature can inhibit fat oxidation,and thawing in 25?air have the maximum TBARS value.Tastes changes of pork are influenced by the freezing,thawing methods and thawing methods which the most significant impact on the taste.3.The effects of different freezing and thawing on the microstructure and protein of pork were studied.The results showed that the structures of pork after freezing with different temperature were damaged,and the higher freezing temperature,the more serious destruction of pork tissue.SDS-PAGE gel electrophoresis can be seen that the protein is denatured and decomposed after freezing and thawing.The Total sulfhydryl content and Ca2+-ATPase activity decreased after the thawing and the lower the freezing temperature,the lower the rate of descending.From the thawing methods mentioned above,thawing in 25 ? water cause more serious destruction of pork protein compared with thawing in 4?and 25 ? air.Thawing in 4? can maintain quality of pork protein.From the DSC results,the temperature of the denatured protein degradation was changed;the thermal stability of the protein was lower after the different thawing methods.