Studies On The Changes Of Flavored Nucleotides And Development Of A Reference Materials For Inosine Acid In Pork

With the improvement of living standards,people’s demand for meat products has changed from quantity to flavor and quality.Inosine acid is the main free flavor nucleotide,which has a high content in pork and has an important contribution to the flavor of pork.Inosinic acid is easy to degrade in pork,and it is easy to be affected by varieties,post-mortem treatment,storage methods and other factors.In this study,the content of inosinic acid and its degradation products,inosine and hypoxanthine were determined by.HPLC to explore the differenceof inosinic acid,inosine and hypoxanthine,and the changes of inosinic acid and its degradant under different storage methods and the influence of different thawing methods and times of freezing-thawing on the content of inosinic acid and its degradant were investigated,and the certified reference material of inosinic acid in pork freezing-dried powder was developed to provide an effective basis for the evaluation of pork freshness.The main contents and results of this paper are as follows:.(1)The establishment of HPLC for simultaneous determination of inosine and hypoxanthine in pork.In this part,6% perchloric acid was used extraction of inosinic acid and its metabolites from pork,which was separated by ZORBAX SB-C18 column(250 mm×4.6 mm,5 m).1% triethylamine(pH adjusted to 3 by phosphoric acid)and methanol were used as mobile phase for the gradient separation at98:2 and the determination was carried out under the uv wavelength of 250 nm.The results showed that the recoveries were 85% ~ 110% and the RSD was less than 5% in the add concentration(inosine acid:20,50,100 mg / L,inosine: 10,20,50 mg / L,hypoxanthine: 2,5,10 mg/L).The method is sensitive,rapid(25 min),accurate and reproducible.It is suitable for the determination of inosine and its metabolites in pork.(2)Comparative study on inosinic acid and its metabolites of different pork breeds and parts.In this part,the contents of inosinic acid and its metabolites in the raw meat of five breeds of Northeastern pig,Beijing black pig,Wuzhishan pig,Berkshire and Northeastern pig and Duroc,Landrace and Yorkshire crossbred pig(DLY),three carcass part of Longissimus dorsi and streaky and hind leg were compared and analyzed.It was found that,among the three carcass part,the content of inosinic acid was the highest,the content of inosine and hypoxanthine was the lowest on Longissimus dorsi,and the umami was the best,while the content of inosinic acid was low,the content of inosine and hypoxanthine was high in hind leg.Among the five breeds,the content of inosine acid in the longissimus dorsi of Northeastern pig was the highest,,and that in the hind leg of Wuzhishan pig is the highest,while there is no significant difference in the content of inosinic acid in the streaky among Northeastern pig,Wuzhishan pig and DLY.The results showed that the umami of Longissimus dorsi in Northeastern pig was better than other breeds and parts.(3)Study on the effects of different storage methods and repeated freezing and thawing on the content of inosinic acid and its metabolites in pork.In this part,the effects of different thawing methods and freeze-thaw cycles on the contents of inosinic acid and its metabolites were investigated,and thefresh bitter ratio was calculated to evaluate the change trend of pork flavor.The results showed that thawing mode had no significant effect on the content of inosinic acid,but had a very significant effect on the content of hypoxanthine,and the effect on the content of inosinine was related to the freeze-thaw cycles.The content of inosinine and the content of hypoxanthine in pork was lower under microwave thawing and 70℃ water bath thawing conditions.When thawing by the four methods,the content of inosine acid in pork decreased with the increase of freezing-thawing times,and the content of inosine and hypoxanthine increased significantly with different freezing-thawing times,compared with that of fresh meat.However,there was no linear relationship between the content of inosine and the increase of freezing-thawing times.It was found that the fresh-bitter ratio of pork was mainly affected by the freezing-thawing times and decreased with the increase of freezing-thawing times in different thawing ways.(4)The concentration of inosine acid was determined by HPLC and nine international laboratories were selected for the joint evaluation.Cochran statistical analysis yielded the values reported here.The concentration of inosine acid CRM was assigned to be 5.70 mg/ g(dry weight)with an expanded uncertainty of is 0.79mg/ g(k=2).In the development of inosinic acid CRM,the sample preparation,constant value analysis,homogeneity testing,stability monitoring and uncertainty evaluation were studied systematically and comprehensively.The results indicate that the CRM is homogenous and stable at-20℃ for at least 12 months.The new CRM can be applicable to analytical method validation.