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Effects Of Various Low-temperature Storage On The Quality Changes Of Black Carp Fillet

Posted on:2017-01-22Degree:MasterType:Thesis
Country:ChinaCandidate:H X YangFull Text:PDF
GTID:2271330488982534Subject:Food Science and Engineering
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With the fast development of aquaculture and the great improvement of living standards, the demands for high quality aquatic products in market are also increasing. Temperature is one of the key factors affecting the quality of aquatic products during storage. The objective of this study was to make a comprehensive comparison of the effect of storage temperatures(4oC,-0.5oC,-3oC and-20oC) above and below freezing point(-0.8oC) on the quality of black carp, one of the “four major cultured fish species” in China. The changes in basic physicochemical properties, water status, protein structure and tissue structure were measured.The basic physicochemical property indexes included total volatile basic nitrogen compounds(TVB-N), p H value, whiteness, drip loss and shear force. For fish fillets stored at 4oC and-0.5oC, the TVB-N values increased rapidly, especially at 4oC reached about 32 mg/100 g on the 12 th day; while the TVB-N values of fish fillets stored at-3oC and-21oC were under 20 mg/100 g during the whole storage period. The pH values of fish fillets stored at the four degrees decreased at the beginning and then increased during the following storage period, with the changes being more significant at 4oC and-0.5oC. The whiteness of fish fillets increased with both storage time and temperature. For fish fillets stored at 4oC and-0.5oC, The drip loss increased gradually with storage time at the four degrees, with the finial results showing-20oC>-3oC>4oC>-0.5oC. Shear forces decreased gradually with storage time at the four degrees, with the finial results showing-20oC>-3oC>-0.5oC>4oC.The transverse relaxation time(T2) and T2 weighted image showed that water mobility increased slowly for fish fillets stored at 4oC and-0.5oC; while for fish fillets stored at-3 oC and-20oC, water mobility increased sharply with storage time.Light microscopy(LM) and transmission electron microscopy(TEM) observations showed that the myofibers and myofibrils gradually detached from the membrane structure and the sarcolemma respectively for fish fillets stored at 4oC and-0.5oC, with the changes being more significant at 4oC. Besides, the TEM observations also showed the gradual disappearance of intermediate filaments and the breakdown of myofibrils and sarcolemma at 4oC. These changes might lead to the decrease of the shear force of fish fillets stored at 4oC and-0.5oC. The severe breakdown of myocommata and myofiber caused by ice crystals, which might lead to the increase of drip loss, was observed for fish fillets stored at-3oC and-20oC.The changes in advanced and primary structures of proteins were measured using differential scanning calorimetry(DSC), sodium dodecyl sulphate-polyacrylamide gel electrophoresis(SDS-PAGE), matrix-assisted laser desorption/ionization-time of flight-mass spectrometry(MALDI-TOF/TOF) and free hydroxyproline content determination. The results showed that fish proteins, including myofibrillar proteins(myosin, titin, α-actinin, myomesin, etc.), collagen and some proteases degraded significantly at 4oC and-0.5oC. These changes might lead to the tissue destruction for fish fillets stored at 4oC and-0.5oC. While no significant protein degradations were observed for fish fillets stored at-3oC and-20oC. The ice crystals might be the primary cause of the tissue destruction for fish fillets stored at-3oC and-20oC, which was together with the change of myosin advanced structure accelerating the drip loss.In conclusion, the storage temperature above the freezing point is not good for maintaining the texture of fish fillets, while the temperature below the freezing point is not good for maintaining the water holding capacity of fish fillets.-0.5oC is good for maintaining quality of fish in short period(1 week) storage;-3oC is good for maintaining quality of fish in relatively longer period(2~3 weeks) storage.
Keywords/Search Tags:drip loss, shear force, water status, tissue structure, protein structure
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