Research On Drying Kinetics And Quality Properties Of Penaeus Vanmamei Dried By Ultrasound-assisted Meat Pump Dehumidifier

Heat pump drying is widely used in aquatic dehydration.However,the drawback of this method is lower drying rate and high energy consumption in the later period of drying.The drying kinetics and quality properties of penaeus vanmemai dried by ultrasound-assisted heat pump dehumidifier were therefore investigated in this paper.The optimum technique parameters of ultrasound-assisted heat pump drying were obtained.The moisture adsorption isotherms and thermodynamic properties of penaeus vanmemais were analyzed.The effects of ultrasound pretreatment on moisture adsorption isotherms and thermodynamic properties of penaeus vanmemai were also discussed.The glass transition temperature of penaeus vanmemai was measured and the state diagrams were plotted.The effect of ultrasound pretreatment on storage stability of penaeus vanmemai with heat pump dried was disussed.The main study contents and results are as follows:1.The effects of ultrasonic power,ultrasonic frequency,ultrasonic pretreatment time,temperatures and air velocity on penaeus vanmemai drying kinetics and qualities properties(hardness,toughness,colour,shrinkage,rehydration and astaxanthin content)dried by heat pump dehumidifier were studied.The results showed that under certain temperature and air velocity,drying rate increased with decreasing of ultrasound power and frequency,and with increasing of the ultrasound pretreatment time.The ultrasound has little influence on the quality of penaeus vanmemai(p>0.05).Overall consideration,the optimum technique parameters of ultrasound-assisted heat pump drying penaeus vanmemai were 35kHz of the ultrasonic frequency,90W of the ultrasonic power and 30min of the ultrasonic pretreatment time.The temperature and air velocity of heat pump drying have a significant impact on penaeus vanmemai drying kinetics and qualities properties.The drying rate increased with the increasing heat pump drying temperature and air velocity.Under certain air volecity,the hardness and toughness of penaeus vanmemai increased with the increasing drying temperature.The color change is the smallest at 35℃.The shrinkage and rehydration have less difference dried by different air volecity.The astaxanthin content is the highest at 35℃.Under certain drying temperature,the hardness,toughness and color change first increased then decreased with the increasing of air volecity;the shrinkage and rehydration have little difference dried by different air volecity.The astaxanthin content increased with the increasing of air volecity.Overall consideration,the optimum parameters of heat pump drying temperature and air volecity were:temperature at 35℃ and air velocity at 1.5m/s.Eight mathematical models were applied to fit the experienmental data.The Two Term model was used as the best fitting model.Under certain temperature(35℃)and air velocity(1.5m/s),the effective moisture diffusivity coefficients(Deff)of penaeus vanmemai with ultrasound-assisted heat pump drying ranged from 3.19 to 5.56x 10-10 m/s.Under certain ultrasound pretreatment,the Deff of penaeus vanmemai with ultrasound-assisted heat pump drying ranged from 2.782 x 10-10 to 7.774×10-10 m2/s.The Deff of penaeus vanmemai without ultrasound pretreatment ranged from 2.489 x 10-10 to 6.110×10-10 m2/s.The activation energy of penaeus vanmemai with ultrasound pretreatment was found to be 23.01 KJ/mol and without ultrasound pretreatment was found to be 29.16 KJ/mol.Therefore the ultrasound pretreatment increased the effective diffusitivity coefficients and decreased the activation energy of penaeus vanmemai during heat pump drying and then increased the drying rate.2.The effect ultrasound pretreatment on moisture adsorption isotherms and thermodynamic properties of penaeus vanmemai were studied and estimated the applying of entropy enthalpy complementary theory in adsorption.Then the best fitting model of moisture adsorption isotherm was determined.The results showed that in the course of adsorption,equilibrium moisture content increased with the increasing of water activity(aw).Temperature of 25 to 45℃ and aw of 0.11 to 0.90,GAB model is regardaged as the best model to describe moisture adsorption propertries of penaeus vanmemai.The net isosteric heat of adsorption,differential entropy of penaeus vanmemai decreased with the increasing of aw and spreading pressure of penaeus vanmemai decreased with the increasing of temperature but increased with the increasing of aw.Ultrasound pretreatment decreased the net isosteric heat,differential entropy and spread pressure.The moisture adsorption process of penaeus vanmemai can be seen as entropy driven.3.Differential scanning calorimetry(DSC)was used to deterrmined the glass transition temperature(Tg)and freezing point temperature(TF)of penaeus vanmemai.Fitting the equation with the experienmental data could obtain the state diagram of penaeus vanmemai.As can be seen from the state diagram of penaeus vanmemai,the maximally-freeze-concentrated solutes with ultrasound pretreatment at 0.776g/g with the characteristics temperature of end point of freezing(Tm’)being-32.6℃ and the maximally-freeze-concentrated solutes of glass trsnsiton temperature(Tg’)being-54.66℃.The maximally-freeze-concentrated solutes without ultrasound pretreatment at 0.795g/g with the characteristics temperature of end point of freezing(Tm’)being-31.7℃ and the maximally-freeze-concentrated solutes of glass trsnsiton temperature(Tg’)being-53.52 ℃.Glass transition theory and aw preservation thoery can predict the storage stability of penaeus vanmemai.