Study On The Changes Of Amino Acid Contents And The Preparation Of Amino Acid Matrix Standard Material In Pork

Amino acid is not only a key nutritional content in meat but also an important flavor compound.However,Amino acids are water-soluble compounds whose contents is easily affected by many factors,for example animal species,post-slaughter treatment and storage conditions.In addition,the problem of selling low-priced hybrid pigs as high-priced local pigs appears in the market at present.However,China currently lacks effective,reliable and traceable matrix reference material for the determination of amino acids,which makes the data obtained by market supervision incomparable,and ultimately leads to the problem of fraud that cannot be solved well.Therefore,the amino acid analyzer method in the national standard "GB 5009.124-2016 National Food Safety Standard for Amino Acids in Food" was used to determine the content of 16 amino acids in pork in this study,investigated the differences of amino acid contents in different breeds of pork(including local pigs and crossbred pigs)and identified the key factors influencing the identification of individual local pigs and exotic pigs by multivariate statistical analysis;the change of amino acid contents in pork with storage time under different storage conditions(greenhouse and 0-4℃);the effect of thawing method and freeze-thaw times on amino acid contents in pork.We prepared pork lyophilized powder and investigated of the homogeneity and stability of the lyophilized powder,laying the experimental foundation for the next development of amino acid matrix reference material in pork.The conclusion of this study are as follows:1.Comparison of the differences in the contents of 16 amino acids in seven breeds of pork.In this study,four local pigs(Wuzhishan pigs,Northeastern folk pigs,Laiwu pigs and Shenxian pigs)and three crossbred pigs(Beijing black pigs,Luchuan crossbred pigs and outer ternary pigs)were selected for the comprehensive comparison of amino acid content differences among different pork breeds.In our research,the contents of threonine or methionine in the three crossbred pigs were higher than that of the four local pigs;the content of valine in the three crossbred pigs was significantly higher than that in the Wuzhishan or Laiwu pigs,but not significantly different from that in the Northeastern People’s Pig and Shenxian Pig;the pattern of lysine content was similar to that of valine.But the content of glutamic acid and aspartic acid in the three cross-bred pigs has no significant difference,but both are higher than those in the four native pigs.In addition,the multivariate statistical analysis model was used to identify individual local pigs and exotic pigs,and the projection of importance of variables(VIP)in the model was used to identify three important substances,including aspartic acid,glutamic acid and arginine,and it was hypothesized that these three amino acids might be the key influencing factors to identify individual local pigs and exotic pigs.2.Changes of amino acid content in pork by storage method,thawing method and number of freeze-thaws.In this experiment,the effects of two storage methods,four thawing methods and three freeze-thaws cycle on the content of 16 amino acids in pork were investigated.In our study,most of the amino acid contents in pork increased and then decreased with storage time when stored at room temperature or 0-4℃,and the amino acid contents started to decrease after 12 h at room temperature and 24 h or 48 h at 0-4℃;most of the amino acid contents were significantly lower in high temperature thawing(microwave or 50℃ water bath thawing)than in low temperature thawing(0-4℃ thawing)at the first or second thawing.The content of most amino acids in high temperature thawing(microwave or 50℃ water bath thawing)was significantly lower than that in low temperature thawing(room temperature or 0-4℃ thawing)under the first or second thawing,while there was no significant difference between them under the third thawing.3.Preparation of pork lyophilized powder and examination of its homogeneity and stability.In this study,pork freeze-dried powder was prepared by grating,freeze-drying,grinding,sieving,mixing and dispensing,and then study its homogeneity and stability.In our study,the homogeneity of 15 amino acids was good and remained stable at-20℃;except for serine,glutamic acid,glycine,valine,lysine and proline,which were unstable within 14 days at 60℃ transportation condition,the contents of the other amino acids remained stable within 14 days at 0-4℃,20℃ and 40℃ transportation condition,respectively.