| Aquatic products are seasonal and easy to corruption, which should take effective preservation and treatment immediately after fishing. Drying is one of these common processing methods. Hot-air drying is often used in modern industry, but its high temperature would easily cause the loss of thermal sensitive composition in aquatic products. The deterioration of food caused by microorganisms, enzymes and non-enzymatic can be delayed and reduced in the low temperature and low humidity (LTLH) environment, meanwhile the quality of product could be maintained effectively. However, low temperature drying takes longer time. As a high efficient heat source, infrared radiation drying can greatly reduce the drying time. Choose Pike eel as the research object to investigate aquatic products drying in LTLH environment and combined infrared radiation, which could provide theory and technical support. The main contents of this paper are listed as follows:1. Based on the two-stage heat pump dehumidification drying system, test equipment required was designed and manufactured. The equipment applied a closed cycle drying system to provide stable temperature and humidity environment. It could also make air velocity adjustable in the same time. Selected the SiC plate as radiation element in the infrared drying system, and monitored surface temperature of the material in real time by infrared thermometer.2. Studied Pike eel diying kinetic characteristics in cold air drying at temperature of10"C～30"C. The results showed Pike eel directly entered the falling rate period without constant rate period in the very beginning time. The lower temperature used the longer drying time took, but the material surface hardening shrinkage was less and the apparent quality was better. Compared different model regressions obtained that Page model fitting the drying curves better.2.6197X10-10～4.0224X10-10m2/s and15.23kJ/mol respectively for effective moisture diffusivity and activation energy were calculated from Fick's second law and Arrhenius relationship.3. The influence of different power on Pike eel's, surface temperature was discussed under infrared radiation combined diying. It was found that the greater the power, the greater the material surface temperature changed. The material was relatively safe when the radiation power was under600W. When the power increased to750W, the surface temperature was too high in a short time to be suitable for this experiment.4. Influence of drying temperature, relative humidity, air velocity and radiation power on TBA of Pike eel was studied, results indicated that TBA reduced respectively with the decreasing of drying temperature, relative humidity and radiation power, and also decreased with the raising of air velocity. Using response surface methodology to obtain a regression model about TBA, and the optimum combined drying conditions were:17.93℃drying temperature,42.43%relative humidity,2.49m/s air velocity and304.99W radiation power.5. Comparing cold-air drying, hot-air drying and infrared combined drying showed that the infrared combined drying had advantages both in drying rate and product quality. Drying time of300W infrared combined drying was three times shorter than cold-air drying. Late during drying, infrated radiation still provided the material strong energy, so it could maintain a high drying rate. |
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