Study On Changes In The Quality Of Grass Carp In The Process Of Postmortem

Taking grass carp as the research object,the characteristic volatile components present in different parts of grass carp were studied in this paper.The flavors in different parts of grass carp meat with different body weights were compared.Quality changes of grass carp in the process of postmortem stored at room temperature and 4? were also studied.Finally,the effects of different seasons on the quality of grass carp a in the process of postmortem were studied.The dorsal meat,belly meat,red meat,fish skin,fish intestines and fish gills of grass carp were used as experimental objects to determine the volatile compounds present in different parts using the monolithic material sorptive extraction gas chromatography–mass spectrometry and the electronic nose.The results showed that Although the electronic nose was able to distinguish the flavors of the red meat,skin,intestines and gills,the dorsal and belly meat could not be differentiated.For dorsal meat,belly meat,red meat,fish skin,fish intestines and fish gills,56,55,58,67,59,and 68 volatile compounds,respectively,were identified,the majority of which were aldehydes and alcohols.Relative odor activity value method identified that there were 9,7,9,12,7,and 9 predominant components were identified in dorsal meat,belly meat,red meat,fish skin,fish intestines,and fish gills.The fishy smell detected from strongest to weakest were: fish gills,fish intestines,fish skin,red meat,and dorsal meat/belly meat.In order to explore the effects of different parts of grass carp meat with different body weights on its water-soluble and volatile flavor components,taking dorsal meat,belly meat and red meat of three different sizes of grass carp as research objects,the water-soluble components and volatile components in different parts of three species of grass carp were determined by high performance liquid chromatography,amino acid automatic analyzer,electronic nose,solid phase microextraction-gas chromatography-mass spectrometry,and the pH value and the content of lactic acid were also measured.Results showed that for fresh sweet amino acids content: small grass carp > large grass carp > medium grass carp,the K value of each part of the small grass carp was the minimum and the freshness was good,K value of each part of medium grass carp is the largest.The freshness of the dorsal meat is better than the belly meat.The pH value of dorsal,belly and red meat of large grass carp and small grass carp was higher than that of medium grass carp,and the pH values of each part of big grass carp were the highest,the pH value of the dorsal meat is the largest,and the pH value of the red meat is the smallest.The change of pH value in different parts of grass carps was negatively correlated with the change of lactic acid content.The results of electronic nose showed that apart from the difference between the belly meat of large grass carp and the dorsal meat and belly meat of medium grass carp,it can better distinguish the belly meat and red meat of large grass carp,the red meat of medium grass carp,the dorsal meat,belly meat and red meat of small grass carp.Principal component analysis showed that there were the greatest differences in odor between the dorsal meat of large grass carp and other groups.37,42 and 45 volatile components were identified in the dorsal meat,belly meat and red meat of small grass carp,46,43 and 48 in the medium grass carp and 34,39 and 48 in the large grass carp,respectively.Carbonyl compounds and alcohols were the main volatile components.In summary,1.5 kg of grass carp should be selected during the processing.In order to study the quality changes of grass carp during postmortem at room temperature(25?),the changes in texture,pH,lactic acid,free amino acids,and ATP-related compounds,total volatile basic nitrogen(TVB-N)and volatile components in the dorsal meat of grass carp were measured.The results showed that hardness and chewiness of the grass carp reached its maximum at 23 h and then rapidly decreased,while springiness,cohesiveness,and resilience of grass carp decreased with the extension of storage time.pH showed a trend of decreasing first and then increasing,and it reached its maximum at 23 h.while the content of lactic acid was the opposite,which reached its minimum value at 23 h.The total amount of fresh sweet amino acids gradually decreased during the postmortem process,while bitter amino acids were just the opposite,which increased during the postmortem process.The K value and TVB-N increased during the postmortem process.The change in K value indicated that grass carp could maintain high freshness after storage for 10 h at room temperature,and it reached 68.99% at 27 h,which showed that the fish had spoiled at that time.The electronic nose analysis results showed that there was an overlap of odors between samples stored at 0 h and 5 h,23 h and 27 h after storage,and it showed that fresh fish(0 h)had the largest difference in odor between that stored for 30 h.45,43,48,46,56,46,47,43 volatile substances were detected at 0,5,10,15,19,23,27,and 30 h,mainly aldehydes and alcohols substance.We tracked changes in the pH,texture,lactic acid,ATP-related compounds,K value,thiobarbituric acid-reactive(TBA),lipase activity and free amino acids(FAA)contents in the dorsal meat of grass carp stored at 4°C for 192 hr.Sensory and electronic tongue assessment were also performed.The results showed a consistent trend in the hardness and chewiness,reaching the maximum at 24 h,while springiness,cohesiveness,and resilience of grass carp decreased with the extension of storage time.The pH value is closely related to lactic acid content and hardness.The pH showed a trend of decreasing first and then increasing,while the content of lactic acid increased initially and then decreased.The fresh sweet amino acids gradually decreased with time while the opposite occurred with the bitter amino acids.The content of IMP showed a trend of decreasing on the whole,while the content of Hx and HxR increased gradually.K value,TVB-N value and TBA value kept increasing during the whole storage process,the change in K value indicated that grass carp could maintain high freshness after storage for 48 h at 4°C.Lipase activity showed a trend of increased first and then decreased,lipase peaked on the first day of storage.The sensory score decreased gradually.The electronic tongue indicated that the differences were distributed in various areas between the first 2 days and the last 6 days.Overall,it was suggested that grass carp should be consumed within 6 days and the best edible time was 4 to 8 h when stored at 4°C.The quality changes of grass carp in different seasons during postmortem at 4°C were studied.We tracked changes in the pH,texture,lactic acid,ATP-related compounds,K value,total viable counts(TVC),fresh sweet amino acids and the bitter amino acids contents in the dorsal meat of grass carp stored at 4°C for 192 hr in spring,summer,autumn and winter.Sensory assessment was also performed.The experimental results showed that pH value showed a trend of decreased first and then increased in the four seasons,which was contrary to the trend of lactic acid change.The hardness reached its maximum at 24 h.During the whole storage period,the K value in spring and winter was always lower than that in summer and autumn.With the extension of storage time,the total viable counts and TVB-N of grass carp meat increased significantly in the four seasons.Sensory evaluation showed that the edible period of grass carp was 6 days.