Metabolomic Analysis Of The Dorsal Longest Muscle Of Debao Black Pigs With Repeated Freeze-thaw Conditions

Debao black pig is one of the excellent local pig breeds in Guangxi.Because of the decline of the population,the breed is on the verge of extinction.Although the population has increased after breed protection in recent years,Debao black pig still has great potential for market promotion.Cold chain logistics is a common means of keeping fresh in raw meat transportation,but due to technical problems such as cold chain connection,repeated freezing and thawing will be caused by temperature fluctuations in the process of meat transportation.In order to further strengthen the market promotion of Debao black pigs and explain the effect of repeated freezing and thawing on the muscle quality of Debao black pigs,the dorsal longest muscle of Debao black pigs were frozen and thawed for 0,1 and 3 times(Set as F0,F1,F3,freezing and thawing conditions: the sample was frozen at-20℃ for24 hours,and thawed to 0-4℃ at room temperature.),respectively.The changes of physical and chemical indexes and metabolomics were detected.The main research contents and results are as follows:(1)The physical and chemical indexes and tissue structure of the dorsal longest muscle Debao black pigs with different freeze-thawing times were detected: With the increase of freezing and thawing times,the thawing loss and cooking loss of the dorsal longest muscle of Debao black pigs increased significantly(P<0.05),the shear force and p H value increased at first and then decreased,and the content of MDA increased significantly after three freezing and thawing times(P<0.05).With the increase of freezing and thawing times,the intercellular space of the dorsal longest muscle of Debao black pig gradually increased,and the cells were arranged from dense and orderly to loose and messy.(2)The metabolites and metabolic pathways of F1 and F0,F3 and F0,F3 and F1 were screened by liquid chromatography-mass spectrometry(LC-MS).Then the common differential metabolites of the three groups were used to screen the key metabolic pathways of the dorsal longest muscle of Debao black pigs under repeated freeze-thaw conditions: 105 significant differential metabolites were screened from F1F0,of which 74 were up-regulated and 31down-regulated;333 metabolites with significant differences were screened in F3F0,of which 209 were up-regulated and 124 were down-regulated;291 metabolites with significant differences were screened in F3F1,of which 183 were up-regulated and 108down-regulated.According to the classified statistics of the differential metabolites in the three comparison groups,it was found that the differential metabolites accounted for a relatively high proportion in lipids and lipid-like molecules,organic oxygen compounds and organic acids and their derivatives.A total of 27 common differential metabolites were screened,of which 25 differential metabolites,such as Stearidonic acid,Propionylcarnitine and DG(16:0/18:2(9Z,12Z)/0:0),were correlated with freeze-thawing times,which could be used as potential marker metabolites of freeze-thawed dorsal longest muscle in Debao black pigs.Choline metabolism in cancer and Retrograde endocannabinoid signaling were selected as key metabolic pathways.And there are four key metabolites in these two metabolic pathways:DG(16:0/18:2(9Z,12Z)/0:0),glycerophosphoric acid,choline and arachidonic acid,which are the key marker metabolites.In conclusion,repeated freezing and thawing will lead to the decrease of water holding capacity of the dorsal longest muscle of Debao black pig,the change of p H value and tenderness,the deepening of oxidation,and the change of metabolite and metabolic pathway.This study helps to clarify the mechanism of meat quality changes during freezing and thawing,and provides a new way to distinguish frozen-thawed meat from fresh meat.