Study On The Drying Characteristics And Quality Attributes Of Tilapia Fillets Processed By Osmotic Dehydration Combined With Microwave Drying

Tilapia is one of the most important species of freshwater aquaculture in China. It is popular with consumers all over the world for its tender meat and superior nutritional value. Due to the problems of low processing level and single products in tilapia processing industry, research and development of new processing technology is believed to be of great significance. Microwave drying has a series of impressive features, such as rapid heating rate and high thermal efficiency, while osmosis dehydration also obtains a lot of desired attributes, such as low energy consumption, less nutriment loss and well preservation of color, flavor and structure. Inheriting the merits of these two kinds of drying processes will get a new combined process (Osmotic dehydration combined with microwave drying (OD-MD)) with high drying speed, low energy consumption and high quality without large amount of economic input and will open up a new way for tilapia processing industry. The influence of osmosis conditions and microwave conditions on moisture indicators and quality characteristics of OD-MD tilapia fillets was investigated in this paper. Besides, a drying kinetic model was established according to the variation law of moisture. The aim is to provide the theoretical basis and scientific basis for the development of new tilapia processing technology. The specific works are as follow:1 Tilapia fillets were soaked in osmotic solution (using salt and sucrose as osmosis media respectively) with the solid/liquid ratio of 1:10～1:25, and the concentration of 10%～25% for 1～4 h at 10～30℃, respectively. And the moisture aspects were compared in terms of their moisture content and moisture activity. The results indicated that the dehydration effect of the saline solution was superior to the sucrose solution and the solid/liquid ratio had no obvious impact on the moisture indicators. Moreover, with the increase of osmotic concentration, the extension of osmosis time and the rise of osmosis temperature, the moisture content and moisture activity of dried tilapia fillets decreased within certain realms.2 Tilapia fillets were processed by different osmosis conditions as mentioned above. The quality aspects were compared in terms of their lightness index, shrinkage ratio, rehydration ratio and recovery ratio. The results indicated that the quality characteristics of the saline solution was better than the sucrose ones; and there was hardly any difference among the quality indexes that were obtained under different solid/liquid ratios. In addition, with the increase of osmotic concentration, osmosis time, and osmosis temperature, the rehydration ratio and recovery ratio of dried tilapia fillets decreased and the shrinkage ratio slightly increased within certain realms, while the lightness index did not change significantly. And the ideal combination for osmosis dehydration was that permeated the samples in 20% saline solution with the solid/liquid ratio 1:20 for 2 h at 30 ℃.3 The permeated tilapia fillets were dried in microwave oven with different microwave power (100-400 W), microwave time (1-5 min), and loadage (5-25 g) respectively. And the moisture aspects were compared in terms of their moisture content and moisture activity. The results indicated that with the increase of microwave power, the extension of microwave time and the decrease of loadage, the moisture indicators of dried tilapia fillets, namely of moisture content and moisture activity decreased significantly.4 The permeated tilapia fillets were processed by different microwave conditions as mentioned above. And the quality aspects were compared in terms of their lightness index, shrinkage ratio, rehydration ratio and recovery ratio. The results indicated that with the increase of microwave power, the extension of microwave time, and the decrease of loadage, the rehydration ratio increased and the recovery ratio decreased. The lightness index offered upgrade firstly than descending latter tendency along as the increasing of every factor. While the shrinkage ratio decreased firstly and slightly increased subsequently when microwave power increased and microwave time extended; However, it showed the opposite trend with the increase of loadage. The optimized microwave conditions were as follows:microwave power 400 W, microwave time 5 min, and loadage 10 g. Compared to hot air drying, OD-MD removed more moisture and kept better quality of tilapia fillets.5 The osmosis-microwave drying characteristics and drying kinetics of tilapia were investigated. The effect of osmosis dehydration, microwave power and loadage on microwave drying process of tilapia fillets were studied. The results indicated that, there were three stages during the microwave drying process:the accelerating drying period, the constant drying period and the falling-rate drying period respectively. And the trial group which processed by osmotic dehydration showed higher dehydrating rate. Besides, with the increase of microwave power and loadage, the dehydrating rate of tilapia fillets was increased. In addition, a drying kinetic model was established according to the moisture variation. The Midilli mode\(MR= ae-krv+bt) showed the best fit to the experimental drying data. The model equation was:It was proved that the predicted value was accordant to the experimental value, and this model could be used to describe the change in moisture of tilapia during the processes of osmosis-microwave drying.