Rehydration characteristics of dried icefish (Salangidae) with different drying methods by low‐field nuclear magnetic resonance and magnetic resonance imaging

Abstract Icefish (Salangidae) is a valuable aquatic product that is often dried for preservation. The purpose of this study was to investigate the effect of different drying methods on the rehydration quality of icefish. Low‐field nuclear magnetic resonance (LF‐NMR) was used to compare the rehydration rate, moisture migration and distribution of icefish dried by cold air (8, 10, 12°C) and hot air (40, 50, 60°C) The muscle fibers structure of dried icefish and magnetic resonance imaging (MRI) of icefish after rehydration were examined. The results showed that cold air drying resulted in higher values of these parameters than hot air drying. MRI analysis revealed that cold air dried icefish retained more water after rehydration than hot air dried icefish. The T 2 transverse relaxation spectra of rehydrated icefish exhibited three peaks corresponding to bound water, immobilized water and free water. The proportion of immobilized water increased significantly and accounted for more than 92% after rehydration, while the proportion of free water was around 2%–3%. Cold air drying preserved the muscle fiber structure and protein network better than hot air drying, which improved the rehydration quality of icefish. The study provides theoretical and data support for using cold air drying technology in aquatic product processing. Practical applications The focus of this study is to compare the effect of different drying methods on the rehydration rate of icefish. The results indicate that part of the bound water migrated to the immobilized water during the initial stage of rehydration, which increased the content of immobilized water and reduced the binding force of some bound water. The T 2 value shifts to the right in all groups, indicating that the binding force between biological macromolecules (such as myofibrillar protein) and icefish water was weakened. Different drying methods have a significant impact on changes in the internal water status of rehydrated icefish samples. Our results suggest that cold air drying is a better method for drying icefish compared to hot air drying, as it improves its rehydration quality. The findings of this study can be useful for food industry personnel who are involved in fish processing, preservation, and nutrition.