Factors That Affect Change Of ATP Related Compounds’ Decomposition For Stored Fish Muscle And Quality Evaluation

Freshness is an important index to evaluate the quality of aquatic product. Degradation of ATP reflected the biochemical changes after the death of fish. And K value based on degradation of ATP is an important index to assess freshness of fish; Besides, IMP is the main flavor of umami in fish and its decomposition is the rate-limiting step of the whole process. In a word, degradation of ATP reflects the change of both quality and flavor in fish. However, there is little research related with this part in our country as so far. Therefore, research on the factors affecting degradation of ATP related compounds is of great important. We re-examined ATP-related compounds and K-value change in flounder muscle when stored at low temperatures focusing on the IMP decomposition by HPLC, and further studied on factors that affect these changes. At last, we give a comprehensive assessment to the quality of flounder combined with traditional index, aiming at providing scientific guidance for preservation and freshness evaluation of fish. The main result and conclusion of this research is as follows:(1) We examined contents of ATP-related compounds in flounder muscle when stored at different temperatures by HPLC,and also studied about the effect from species, shape of meat and exogenous nucleotides on degradation of ATP. The result showed that, the metabolic pathway of ATP is as follow: ATP�'ADP�'AMP�'IMP�'Hx R�'Hx. Decomposition of IMP is the rate-limiting step and its IMP content decreased slowly in an early phase, while it dropped rapidly at the final stage of the storage showing biphasic change; Low temperature significantly slowed down the degradation of ATP related compounds; The tendency of ATP related compounds’ changing and K value differed from species of fish; Flounder and atka mackerel belong to the Hx generating type, gold-eye and rockfish pacific cod belong to the Hx R generating type; The shape of stored fish affected ATP degradation but hardly had any effect on IMP decomposition. AMP deaminase and Hydrolytic enzyme is active. However, The activity of IMP decomposing enzyme is limited and the exogenous nucleotides didn’t have any effect on the enzyme.(2)Adding chloramphenicol to prevent the growing of bacteria and examined contents of ATP-related compounds in flounder muscle when stored at different temperatures by HPLC; Adding chloramphenicol to crude enzyme of flounder to exclude the effect on IMP decomposing enzyme from chloramphenicol. The results showed that chloramphenicol can prevent the growing of bacteria significantly and it was obviously that IMP content decreased much slowly in the presence of the antibiotics,showing linear change. IMP decomposition in the latter phase included the reaction by the enzyme coming from microorganism. K value is not only depended on the biochemistry reaction in fish itself, but also affected by microorganism. As the result, the existence of microorganism in latter stored phase is the main factor that affects change of IMP decomposition. So it should be noted that well control of bacteria is the key point in the process of preservation of fish.(3) Adding Tritonx-100 to dissolve the membrane structure and break the stabilization inside the cell and examined contents of ATP-related compounds in flounder muscle when stored at different temperatures by HPLC; Extract the crude enzyme from fish meat with Tritonx-100 of different concentrations to discuss the effectfrom surface active agent on IMP decomposition. The results showed that IMPdecomposition in the presence of the Triton X-100 was quicker than that without it.Triton X-100 of higher concentration could extract higher concentration of crude IMPdecomposing enzyme, which indicating that modifying character of cell membrane bydetergent also had effect on IMP decomposition. Therefore, in order to prolonged shelflife of fish products, ensuring the stabilization of enzyme system and intracellularenvironment is the key point to prevent excessive degradation of IMP which leading tothe loss of freshness and flavor.(4)Freshness evaluation of flounder: we give a comprehensive assessment to thefreshness and sensory of flounder stored at 5 、0、5℃combined with traditionalindex(sensory evaluation, TBC,TVB-N, K value and p H). The result showed that:whenflounder meat stored at-5℃, TVB-N<20mg/100 g,K value<15%,TVC<6Log CUF/gat 20 d,fish is still edible; Fish began to corrupt from 10 d when stored at 0℃, K value>40%,TVC>6Log CUF/g after 10d; K value>60%,TVC>6Log CUF/g after 6dwhen stored at 5℃ and fish began to corrupt from 6d. As the result, the shelf life offlounder stored at 5、0、5℃ are 20 d,10d and 6d respectively. Low temperature caneffectively extend the shelf life of fish. Microorganism interacted with K value andTVB-N and K value is better than TVB-N to show the change of freshness in earlystored phase.