基于核磁共振及成像技术研究速冻汤圆在冻融过程中的水分迁移变化

Water migration of fast-frozen glutinous rice dumplings during freeze-thaw process based on nuclear magnetic resonance and imaging techniques

中文关键词:  速冻汤圆  低场核磁共振  冻融  水分迁移

英文关键词:fast-frozen glutinous rice dumplings  low-field nuclear magnetic resonance  imaging techniques  freezing and thawing  water migration

中文摘要:

      目的 研究冻融过程对速冻汤圆水分分布及迁移的影响。方法 采用低场核磁共振(low-field nuclear magnetic resonance, LF-NMR)及成像技术研究速冻汤圆在冻结和融化过程、反复冻融过程及储藏期间的水分分布变化。结果 在冻结状态下, 速冻汤圆中强结合水含量高达95.85%, 随着温度的升高, 强结合水向弱结合水转化, 当温度高于0℃时, 体系中的水分以不易流动水为主, T22发生右移, 水分自由度增加; 另外, 反复冻融造成汤圆水分的迁移损耗, 核磁共振成像(magnetic resonance imaging, MRI)图进一步证实冻融循环导致汤圆体系中的结合水向不易流动水和自由水转化; 随着储藏时间的延长, T21由0.62 ms增加为1.97 ms, 说明样品体系中结合水与基质结合的紧密度减低, 但储藏期间结合水、不易流动水等含量变化并未呈现出规律变化。结论 冻融循环增加了体系水分的自由度; 但在冻藏的过程中, 保持储藏温度的稳定性有利于提高速冻汤圆体系中水分的稳定性。LF-NMR分析可以快速反映温度波动、反复冻融等对速冻汤圆水分分布造成的影响, 进而评估速冻汤圆的品质变化。

英文摘要:

      Objective To study the effect of freeze-thaw process on the water distribution and migration of fast-frozen glutinous rice dumplings. Methods Low-field nuclear magnetic resonance (LF-NMR) and imaging techniques were used to study the changes of water distribution during repeated freeze-thaw process and storage. Results The strongly bound water content in the fast-frozen glutinous rice dumplings was as high as 95.85%. However, the strongly bound water was transformed into weakly bound water as the temperature rising. When the temperature was higher than 0℃, immovable water was the major state of water in samples, T22 shifted to the right, and the freedom of water increased. Furthermore, freezing-thawing cycles caused the migration loss of water in glutinous rice dumplings. Magnetic resonance imaging (MRI) further confirmed that the freezing-thawing cycles caused the conversion of bound water to immobile water and free water. With the prolonging of storage time, T21 increased from 0.62 ms to 1.97 ms, indicating that the tightness of binding water and dumplings matrix was decreased, but the content of binding water and immovable water did not display regular variations during storage. Conclusion Freeze-thaw cycle increases the degree of freedom of water in the system. But in the process of freezing storage, keeping the stability of storage temperature is conducive to improving the stability of water in the fast-frozen glutinous rice dumplings system. Therefore, LF-NMR analysis can quickly reflect the influence of temperature fluctuation, freezing-thawing cycles on the water distribution of fast-frozen glutinous rice dumplings, further evaluating the quality change of fast-frozen glutinous rice dumplings.