The Optimization On Combined Drying Technology And Prediction On Shelf Life Of Pseudosciaena Polyactis From East China Sea

Pseudosciaena polyactis is very popular because of its tender meat and rich nutrition.Currently, apart from fresh P. polyactis, there are a lot of dried P. polyactis products ofbeing produced. Drying is one of the important processes of producing dried products. Butthe existing drying methods have many problems. In order to improve the quality of driedP. polyactis products and reduce the energy consumption in drying process, the dryingprocesses of P. polyactis was studied, using heat pump and hot air combined dryingmethod to make full use of the advantages of both and avoid their disadvantages.In this research, the P. polyactis was dried with heat pump drying（HPD）, hot airdrying（AD）and combined drying of both（HPD+AD） until the moisture drop to25%.Then, rehydration ratio, chromatic aberration, T-VBN （Total Volatile Base-Nitrogen）value, total bacterial count, SMER （Specific Moisture Extraction Rate） and otherevaluation indexes were detected. The results showed that the HPD+AD technology issuperior to conventional AD technology and HPD technology. Further studies on singlefactor（the amount of material, wind velocity, temperature and relative humidity）affectingdrying rate and quality were carried out.Based on the preliminary experiments, HPD temperature, moisture conversion point,late AD temperature were used as independent variables in this optimization study. Amathematical regression model for predicting composite indicator Y of SMER and T-VBNvalue was established by fitting Box-Benhnken central composite design experimentalresults, the interactive effects of the independent variables on composite indicator Y ofdrying were investigated by response surface methodology. The optimal protocol for heatpump and hot air combined drying of P. polyactis was based on HPD temperature（A=50℃）, moisture changing point（B=32.62%）and hot air drying temperature（C=44.01℃）. Under optimal conditions, comparison of sample quality and energyconsumption was carried out between HPD, HPD+AD and AD. The quality of P. polyactisdried by HPD+AD was better than by AD, and the optimum energy consumption reduced34.8%. Kinetic models were developed to predict the shelf life of dried P. polyactis. Totalcolony count, acid value and peroxide value at different storage temperatures（30,35and40℃）were accessed to research the relation between the shelf life and temperature. Thekinetic models of total colony count, acid value and peroxide value with respect topreservation time and temperature were established based on Arrhenius equation. The highregression coefficients（R2>0.9）indicated the acceptability of the first order reaction andArrhenius model for predicting the changes of total colony count, acid value and peroxidevalue of dried P. polyactis. Activation energies（Ea）and rate constants（k0）of total colonycount, acid value and peroxide value were obtained. They were29.26kJ/mol,4.46×102,47.05kJ/mol,4.1×105,49.76kJ/mol,1.53×106, respectively. Compared with observedshelf life of P. polyactis stored at37and42℃, relative error between predicted andobserved shelf life were-4.68%and-6.25%, respectively. Shelf life of dried P. polyactiswas500days at20℃and352days at25℃through extrapolation of Arrhenius equation.