Study On The Heat-pump And Hot Air Combined Drying And Conservation Of Squid

Low energy consumption, high-quality and long shelf-life of drying products are important for all the manufacturers. Heat-pump drying can effectively reduce power consumption and obtain better quality, but the problem of low drying efficiency existent in latter process . In this paper, heat pump - hot-air combined drying was used to dry squid and reduce the total energy consumption, meanwhile better quality can be yielded. During storage of dried squid, glass transition principle was used to determine the preservation conditions. A 2-factor theory based on water activity and glass transition temperature was applied to prolong the shelf life of dried squid.According to the results of heat pump drying of squid, a drying way of heat pump drying prior to hot air drying (HPD+AD) was used. Heat pump drying temperature, moisture content conversion point and hot air drying temperature were used as experiment factors, and SMER and T-VBN(Total Volatile Base-Nitrogen) values were used as indices of the experiment, then a response surface optimization analysis was done. Finally, the optimum parameters were: heat pump drying temperature(Xl) 54.3℃, moisture content conversion point (X2) 32.3% and hot air drying temperature(X3) 43.5℃. Under the optimal condition, comparisons of product quality and energy consumption between HPD, HPD+AD, AD were carried out. The squid quality dried by HPD+AD was better than that by hot air drying, and energy consumption also was reduced by 38.67%.2-factor theory based on water activity and glass transition temperature is a new method to extend food's shelf-life. Adsorption isotherms of dried squids were fitted to three models at four temperatures. The GAB model can best fit the sorption characteristics. The results of non-linear regression showed the Gordon-Taylor equation could predict the moisture plasticization effect well.GAB and Gordon-Taylor equations were used to determine the critical moisture content and water activity at 4 different preservation temperatures. The changes of dried product quality also were detected during 6 months at the 4 different storage temperatures. The kinetics models of acid value, peroxide value and total bacterial counts of dried squid versus storage time and temperature were established, so as to predicate and control the quality of dried squids during storage. The shelf life of the products at different temperature can be predicted precisely according to the experiment results. Finally, the longest safe storage time of dried squid can be prolonged to 18 months.