南极磷虾肉冻融循环过程水分的迁移及微观结构变化

Moisture Migration and Microstructure Changes of Antarctic Krill Meat during Multiple Freeze-thaw Cycles

以冷冻南极磷虾肉为研究对象,基于低场核磁共振(LF-NMR)及磁共振成像(MRI)技术,结合解冻汁液损失率、离心损失率,分析南极磷虾肉在反复冷冻-解冻循环过程中水分的迁移规律。借助电子、光学显微成像和SDS-PAGE观察反复冻融后南极磷虾肉肌原纤维结构及蛋白质的变化,并通过硫代巴比妥酸值(TBA)判断其脂质氧化情况。结果表明:随着反复冻融次数的增加,南极磷虾肉的解冻汁液损失率和离心损失率均显著增加(P<0.05),同时MRI氢质子加权伪彩图亮度逐渐下降,表明南极磷虾肉内水分含量逐渐降低。LF-NMR结果显示:强结合水和结合水含量无显著性变化(P>0.05),不易流动水含量显著减少(P<0.05),自由水含量显著增加(P<0.05),表明冻融循环中南极磷虾肉的不易流动水向自由水迁移。由相关性分析结果可知,不易流动水和自由水的NMR参数与解冻汁液损失率极显著相关性(P<0.01)。反复冻融后冰晶生长使南极磷虾肉的肌原纤维排列由整齐紧密变为杂乱,甚至发生断裂,SDS-PAGE分析表明南极磷虾肉经反复冻融后其肌球蛋白重链完全降解,肌动蛋白、肌钙蛋白T和肌球蛋白轻链均有不同程度的降解,而TBA值无显著变化(P>0.05)。结论:反复冻融使南极磷虾肉水分迁移、蛋白降解,而对脂质氧化影响不显著。

Moisture migration of Antarctic krill meat during multiple freeze-thaw cycles was analyzed using low-field nuclear magnetic resonance(LF-NMR)and magnetic resonance imaging(MRI)techniques,combining with the results if the loss rate of thawed juice and centrifugal loss rate.The structure and protein changes of myofibrils after multiple freeze-thaw cycles were observed by electron microscopy,optical microscopy and SDS-PAGE,and the lipid oxidation was determined by thiobarbituric acid(TBA)value.The results showed that thawing loss rate and centrifugal loss rate of Antarctic krill meat significantly increased(P<0.05)and the brightness of the MRI hydrogen proton-weighted pesudo-color map gradually decreased with increase if freeze-thaw cycles times,indicating that the moisture content if Antarctic krill meat gradually deceased.As seen from LF-NMR results,there was no significant change in the content of strongly bound water and bound water(P>0.05),the content of immobile water significantly reduced(P<0.05),and the content of free water significantly increased(P<0.05),indicating the immobile water in Antarctic krill meat was easily converted to free water during freeze-thaw cycles.According to the correlation results,the NMR parameters of immobile water and free water had a very significant correlation with the thawing rate(P<0.01)after multiple freeze-thaw cycles.Due to the growth of ice crystals,the myofibril arrangement of Antarctic krill meat changed from neat and compact to disorder,and even broken.Further,SDS-PAGE results showed that the myosin heavy chain was completely degraded,and that the actin,troponin T and myosin light chain were degraded to varying degrees.Nevertheless,the TBA value did not change significantly(P>0.05).The above results showed that multiple freeze-thaw cycles could cause moisture migration and protein degradation of Antarctic krill meat,but the effect on lipid oxidation is not significant.