Effects of cryogenic freezing by liquid nitrogen on the quality and microstructure of silver pomfret (pampus argenteus)

Effects of cryogenic freezing by liquid nitrogen on the quality and microstructure of silver pomfret (pampus argenteus)

Lu, J., Yu, H.-X., Yang, S.-B., Jiang, Q.-Q., Liu, W.-J., Dong, K.-C., Hu, Y.-Q.

      银鲳鱼经液氮喷淋方法(中心温度达-40 ℃,需20 min)冻结后于-18 ℃进行冻结贮藏试验。作为对照,对大小相近的同批原料进行平板冻结(中心温度达-20 ℃,需6 h)及冰柜冻结(中心温度达-18 ℃,需20 h)处理,冻藏条件与液氮速冻样品相同。结果表明,液氮速冻、平板速冻、冰柜冻结的样品的pH值在第105天降至最低(6.42、6.35、6.11),冻藏150天后盐溶蛋白质浓度分别为6.71、3.24、1.38 mg/g,Ca2+-ATPase活性分别为1.73×10-3、0.76×10-3、0.56×10-3 μmol/(min?mg)。冻结温度愈低,K值、TVBN值增加愈小。TPA图谱分析显示,硬度、弹性和回复性均随着冻藏时间的延长呈显著降低趋势(P<0.05);较低的冻结温度可使各指标数值变化趋缓。微观结构观察发现,贮藏150天的液氮组样品肌纤维间隙最小、细胞完整致密,与新鲜样品最为接近;液氮深冷速冻对银鲳冻藏品质维持效果最佳。
英文摘要: Abstract:
      Silver pomfret (Pampus argenteus) was pretreated with liquid nitrogen (LN2) by spray freezing (central point temperature of -40°C in 20 min), followed by freezing storage at -18°C. For the control, samples with similar sizes in the same batch were pretreated by plate freezing (central point temperature of -20°C in 6 h) or frozen directly using a freezer (central point temperature of -18°C in 20 h). Control samples were subsequently stored at -18°C, similar to LN2 samples. The results showed that the pH values of the LN2-frozen samples, plate-frozen samples, and freezer-frozen samples reached minima at 6.42, 6.35, and 6.11, respectively, on the 105th day; the salt-soluble protein contents were 6.71, 3.24, and 1.38 mg/g, respectively, and the Ca2+-ATPase activities were 1.73 × 10-3, 0.76 × 10-3, and 0.56 × 10-3 μmol/(min?mg), respectively. The increases in K values and total volatile base nitrogen were limited with lower prefreezing temperatures. Texture profile analysis (TPA) showed that the hardness, springiness, and resilience of frozen fish meat decreased significantly (P < 0.05) with prolonged storage time. In contrast, a low prefreezing temperature may result in slower changes in these indices. Microstructure observations showed that LN2-frozen samples appeared the most similar to the fresh material, with a narrow gap between the myofibrils and excellent cell integration after storage for 150 days. The results indicated that the LN2 spray method was the best of the three tested methods for maintenance of the quality of silver pomfret.

words: liquid nitrogen cryogenic freezing  silver pomfret (Pampus argenteus)  K value  total volatile base nitrogen value  Ca2+-ATPase activity  texture profile analysis  microstructure


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