基于低场核磁共振技术检测秋刀鱼腌干制过程水分状态变化

Changes in moisture status of Cololabis saira during salting and drying by low-field nuclear magnetic resonance

目的探讨腌干处理对秋刀鱼水分状态的影响,为秋刀鱼的高值化加工提供参考。方法秋刀鱼进行"三去"(去头、去尾、去内脏)处理,采用10%食盐溶液(料液比1:2)进行腌制,选取腌制2 h的样品进行40℃热风干燥,检测样品的水分含量、盐含量以及水分活度,利用低场核磁共振技术(low-field nuclear magnetic resonance,LF-NMR)测定腌干过程样品的水分存在状态。结果秋刀鱼样品腌干过程中均存在结合水、不易流动水和自由水3种状态水分。腌制10 h过程中样品的水分活度未低于0.90的细菌生长临界值。结合水比例呈现先增大后减小的变化趋势,自由水比例相对降低,不易流动水比例增大,表明腌制处理使得部分结合水与自由水转化为不易流动水。随干制时间的延长,样品的水分含量和水分活度均显著降低(P<0.05),结合水变化较小,不易流动水比例呈降低趋势,表明干制处理一方面使得秋刀鱼组织内不易流动水流失,另一方面使其部分转移成其他相态的水。同时,核磁共振成像灰度图和伪彩图深色区域面积逐渐增大,表明干制过程伴随油脂的溢出。结论腌制和干制处理降低了秋刀鱼鱼肉的水分活度,同时改变了水分存在状态。核磁共振成像灰度图和伪彩图表明干制处理改变了秋刀鱼样品的油水平衡。

Objective To analyze the effects of salting and drying treatment on the moisture distribution and status of Coloabis saira,and provide references for the high-value processing and utilization of Coloabis saira.Methods Gutted and eviscerated Coloabis saira with no head and tail was selected,10%NaCl solution （solid-liquid ratio was 1∶2） was used for salting,and 40 ℃ hot air was used for drying after salting for 2 h.Water activity （Aw）,moisture and salt content were determined.The distribution and migration of water during salting and drying process were detected by low-field nuclear magnetic resonance （LF-NMR）.Results There were three kinds of moisture status in Coloabis saira,which were bound water,free water and immobilized water.During salting process,the water activity of samples was less than the critical value of bacterial growth （0.90）,and the content of bound moisture increased in the early stage and then decreased.The ratio of free water decreased slightly,while the ratio of immobilized water increased.Salting treatment caused the partial transformation of hydration water or free water into immobilized water.The moisture content and water activity of the samples were significantly decreased （P〈0.05） during drying process,and the changes in bound water was slightly,while the proportion of immobilized water decreased obviously.Drying treatment caused the loss of immobilized water and the water phase change.Magnetic resonance imaging （MRI） results showed that the area of grayscale and pcolor increased,indicating the spill of lipid.Conclusion Salting and drying treatment reduce the water activity （Aw） and change the moisture status of Coloabis saira,and drying treatment destroy the oil/water balance of Coloabis saira.