STUDY OF FREEZE-THAWING ON THE PROCESS OF TILAPIA FILLETS HEAT PUMP DRYING

In order to investigate the effects of freeze-thaw pretreatment on drying time of tilapia fillets by heat pump drying. The effects of freezing temperature (-10, -20, -30, -40 and -50 degrees C), freezing time (0.5, 1, 1.5, 2 and 2.5 h), thawing temperature ( 5, 10, 15, 20 and 25 degrees C) and melting time (1, 1.5, 2, 2.5 and 3h) on heat pump drying time of tilapia fillets and the drying speed of dried tilapia fillets were investigated in this paper. Furthermore, the heat pump drying speed curve of tilapia fillets had been gained under different freeze-thaw conditions, and results indicated that: drying time and drying speed were improved under moderate freeze-thaw condition. Along with the increase of freezing temperature, freezing time, melting temperature and melting time, drying time decreased firstly and then increased with a nadir. So, while under the same conditions, if the frozen temperature was between -20 degrees C and -30 degrees C, the melting temperature was 20 degrees C and the freezing time was restricted by an hour, then the drying time was shortened and the drying speed was accelerated. Moderate freeze-thaw condition can reduce the drying time of tilapia fillets and accelerate the drying speed by heat pump drying and a reference for the low temperature heat pump drying pretreatment technology to update similar aquatic products.