| Esox lucius in Xinjiang, one of the main economic cold water fish with rich nutrition,delicious and unique flavor characteristics, is paid more attention by consumers. Recent years,with the gradually expansion of the farming scale, it is particularly important for maintaining better quality to select appropriate storage conditions. Therefore, the economy of Xinjiang native fish industry wants to be larger and stronger, the changing regularity of meat quality must be clarified. And these results will provide a theoretical basis for the production of a high-quality products. While the existence of the antifreeze protein(AFP) in Esox lucius, lowering freezing point of solution, inhibiting ice crystal growth, has been researched and developed as a new food antifreeze additive. And it could effectively reduce growth of ice crystal and recrystallization,enhance the quality of cold chain food. Consequently, analysis the functional properties of antifreeze proteins could lay a basic foundation for its application and enhance the quality of products during the cold storage process to.The main purpose of this study was based on fresh Esox lucius. And then the experiment discussed the changes of physical-chemical properties and texture properties during the different storage time at the different storage temperature, finally revealing the rules of its meat quality change and determining the optimum cold storage conditions. At the same time, two AFP sequences were obtained from its muscle and skin tissue, named AFP-Elm(from muscle tissue)and AFP-Els(from skin tissue), respectively. Additionally, bioinformatics technology and modern network services has been applied to clearly analysis the protein composition, molecular weight,isoelectric point and physical-chemical properties. The main results were as follow:1. Changes of physical-chemical properties of Esox lucius during cold storageThe results revealed that the physical and chemical properties were, to a large extent, changed varyingly degree with the increasing of temperature and prolonging of storage time under the condition of different storage temperature of-4℃, 0℃, 4℃. The value of TVB-N was increased from the initial of 8.97±0.015 mg N/100 g to 27.54±0.82, 34.78±1.88 and 40.67±1.57 mg N/100 g,respectively; and the weight loss rate was increased from 0% to 2.5%, 5% and 10%, respectively;and the color value △E was increased from 0 to 3.456±0.069, 7.645±0.189 and 9.877±0.056;the p H value was increased from 6.78 to 7.0±0.028, 7.13±0.013 and 7.21±0.019.In particularly, the initial value of(0.21 + 0.01) mg MDA/Kg was up to the value(0.49 + 0.01)of TBARS at the end of storage by 133.33%. Besides, at the temperature of 4 ℃, TVB-N was up to(40.67±1.57)mg N/100 g, over the edible standard limit(30 mg N/100g).2. Changes of muscle texture characteristics of Esox lucius during the cold storageThe muscle hardness of Esox lucius was diversely decreased at different cold temperatures with the prolonging of storage time. According to the experimental data, we can clearly find the hardness declined from the initial value of 847.5 to 656.5 in 10 days, reduced by 26.90%.Similarly, under the same conditions, the chewing decreased from 319.7 to 266.9, reduced by47.08%. In addition, the muscle elasticity, aggregation ability and recovery ability decreased by57.63%, 34.06% and 73.97% in the last stage of storage, respectively.3. bioinformatics analysis of antifreeze proteins from Esox luciusResults showed the amino acid residues of AFP-Elm was 58, the molecular weight was about6174.5 Da, and the theoretical isoelectric point was 6.14. And the data revealed that AFP-Elm has strongly hydrophobicity, no signal peptide. And second structure of AFP-Elm was predicted, theoutcome indicated that a proportion of α-helix was 20.69%, β-sheet was 12.07%, random coil was62.06%, respectively. The accuracy of prediction model was 66.62%. In addition, the3D(three-dimensional) structure of AFP-Elm was predicted and found a homologous protein,4ur6.1.A. Taking the protein as a model template, the 3D model of the target sequence was constructed. The results showed that the QMEANscore4 of AFP-Elm 3D model was 0.68. Which showed that the model was well matched, and the reliability was better high.The data revealed the amino acid residues of AFP-Els was 56, the molecular weight was about 6000.3 Da, and the theoretical isoelectric point was 7.98. Besides, the results indicated that AFP-Els has strongly hydrophobicity and signal peptide. And the splice site of the signal peptide is located between the 16 th and 17 th amino acids. Additionally, AFP-Els may contain a transmembrane helical regions and locate between the 1st and 18 th amino acids. It had a strong preference for the transmembrane helical region in the direction from inside to outside membrane.The sequence was as following:Met-Met-Val-Phe-Val-Leu-Leu-Cys-Thr-Glu-Leu-Ile-Pro-Ile-Asn-Thr-Ala-Leu.More over, second structure of AFP-Els was predicted, the proportion of α-helix, β-sheetwas and random coil was 15.68%, 36.04%, 48.28%, respectively. The prediction model accuracy was66.62%. The 3D structure of AFP-Els was predicted and found a homologous protein, 1ops.1.A.Taking the protein as a model template, the 3D model of the target sequence was constructed. The results showed that the QMEANscore4 of the model was 0.68. Which showed that the model was well matched, and the reliability was better high. |
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