Effects of Different Drying Methods on the Rehydration and Quality Characteristic of Low-salt Pickled Abalone

To investigate the effects of different drying methods on the rehydration and quality characteristic of low salt pickled abalone, this study used vacuum freeze drying, cold air drying and hot air drying to dry them. The mass volume and rehydration rate of the rehydration process were studied. Low field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) were used to study the water distribution during the rehydration process and investigated the changes in the samples of color, texture, tissue morphology and free amino acids after rehydration. The results showed that the rehydration rate of vacuum freeze-dried abalone was 278.73% at 72 hours, which was significantly higher than that of cold-air dried abalone and hot-air dried abalone (P<0.05). According to the analysis of LF-NMR and MRI results, the immobilized water and free water content are the key drivers for the increase in moisture content of the three dried abalones. Vacuum freeze-dried abalone, cold-air dried abalone and hot-air dried abalone were rehydrated at 72 hours, 48 hours and 24 hours, respectively. Different drying methods affect the texture of rehydrated abalone samples. The results showed that there were significant differences in hardness and chewability among the three drying methods (P<0.05). The hardness and chewiness of vacuum freeze-dried abalone were the lowest after rehydration, which were 954.01 and 708.59 g, respectively. The hardness and chewiness of hot-air dried abalone were the highest after rehydration, which were 1230.14 and 920.02 g, respectively. The results of histological staining and scanning electron microscopy showed that the muscle tissue of vacuum freeze-dried abalone had a relatively loose porous structure. The tissues of cold-air dried abalone and hot-air dried abalone were relatively slender and dense. In summary, vacuum freeze-dried abalone has the highest rehydration rate, the lowest hardness and chewiness, and the best mouth feel. However, the taste may not be as excellent as that of hot-air dried abalone. The results of this study can provide a theoretical reference for understanding how different drying methods impact the quality of low-salt salty abalone products.