Abstract: In order to improve the drying rate and rehydration of tilapia meat, the freeze-drying characteristics and quality changes of blanched or steamed fish meat were analyzed. The effect of heat pretreatment on the quality of freeze-dried fish meat was elucidated by considering the denaturation degree of myofibrillar protein, water distribution and microstructural changes in fish meat during the drying process. The results showed that heat pretreatment could effectively improve the drying rate of tilapia meat, shortening the drying time by nine hours compared with the control group; blanching was more effective than steaming. The rehydration temperature range for tilapia meat was expanded by heat pretreatment, and good rehydration was observed at 50–80 ℃. The rehydration temperature for the control samples was 80 ℃, and the rehydration rate of the 10 min heat treatment group was more than 60%, indicating that the dried product can be rapidly rehydrated. The hardness of the rehydrated fish meat was similar to that of cooked fresh fish meat, and it had good mouthfeel. Heat pretreatment caused significant denaturation of myofibrillar protein and consequently changes in water distribution and a conspicuous increase in the peak area of transverse relaxation time T23, indicating that the increase in free water content after heat treatment is an important reason for the increase in freeze-drying rate. The experimental results can provide technical support for the development of ready-to-eat dried fish products that are suitable for rehydration.

Key words: tilapia; freeze drying; heat treatment; drying rate; rehydration