LF-NMR Dynamic Analysis of Rehydration Characteristics on Dried Squid by Four Drying Methods

Squid was dried by sunshine drying,heat air drying,heat pump drying and vacuum freeze drying,respectively. Combined with the microstructure and the rehydration rate,the moisture migration and distribution of the dried squid were analyzed by low field nuclear magnetic resonance(LF-NMR)during dry rehydration,and the effects of drying methods on rehydration of dried squid were discussed. The results showed that,among the dried squid treated with four drying methods,the dried squid by vacuum freeze drying had the lowest moisture content and the lowest oxidation degree(1.5~6.7 times lower than those other three treatments). Its scanning electron micrograph showed lots of porous honeycomb structure. Moreover,it owned the fastest rehydration rate. In the process of rehydration,part of the bound water migrated to the immobilized water. The immobilized water increased significantly,accounting for more than 90%,and the content of free water also increased. LF-NMR analysis also showed that dried squid treated with vacuum freeze drying had the best rehydration effect,as well as more free water intercepted. The rehydration effect of the dried squid treated by heat pump drying was close to that of sunshine drying,while that of heat air drying was the worst. There was significant effect on the rehydration of dried products with different drying methods. Vacuum freeze drying technology and heat pump drying technology were conducive to the drying of aquatic products.