不同冻结温度下牛肉水分的状态变化

The Transformation of Water States during Beef Freezing

研究3个冻结温度（-8、-23、-38℃）条件下牛肉冻结过程中的水分状态的变化。借助低场核磁共振波谱（low field nuclear magnetic resonance,LF-NMR）与核磁成像（magnetic resonance imaging,MRI）技术,分析牛肉在冻结过程中内部水分状态、弛豫时间T_2、水分信号幅度及~1H密度的变化。结果表明：样品中心温度降至-38、-23、-18℃分别耗时176、350、315 min,说明-38℃处理能够显著提高牛肉冻结速率;3个冻结温度LF-NMR分析表明,随着冻结时间的延长,自由水和不易流动水的峰面积、弛豫时间T_2及信号幅度均逐渐降低。3个冻结温度均能使样品中的自由水全部冻结,而结合水均不被冻结;-38℃能使不易流动水完全冻结,-18、-23℃分别使73.04%、99.60%的不易流动水冻结。~1H MRI成像技术也进一步证实了LF-NMR分析结果。

This paper studies the transformation of water states during beef freezing at 3 different temperatures（-18,-23and-38 ℃）.Internal water state,T_2 relaxation time,the change of signal amplitude and H proton density of frozen beef were analyzed by low field nuclear magnetic resonance（LF-NMR） and magnetic resonance imaging（MRI）.The results showed that the times elapsing until the internal temperature of the sample dropped to-38,-23 and-18 ℃ were 176,350 and315 min,respectively,suggesting the freezing of beef can be considerably sped up at-38℃.The LF-NMR data indicated that the peak areas of free water and immobile water,T_2 relaxation time and signal amplitude decreased gradually with the extension of freezing time at each temperature.The free water in beef was completely frozen at all three temperatures,whereas no bound water was frozen.At-38,-18 and-23℃,100%,73.04%and 99.60%of the immobile water was frozen,respectively.The LF-NMR analysis was confirmed by the results from ~1H MRI.