Research On Thermodynamic Property And State Diagram Of Penaeus Vanmamei Meat

On the basis of water activity and glass transition theory,the storage stability of Penaeus vanmamei meat was carried out by analying the moisture adsorption isotherm and state diagram in order to provide theoretical and technical reference during its processing and storage.The main research contents and conclusions are as follows:1.Moisture adsorption isotherms of freeze-dried P.vannamei meat containing 5%maltodextrin(PV-MD)and maltodextrin free samples(PV)were determined at temperatures of 5,15,25,35 and 45? with water activity(aw)ranging from 0.112 to 0.931.The adsorption behaviors and thermodynamic properties of P.vannamei meat with and without maltodextrin addition were also compared.The adsorption behaviors of both PV and PV-MD followed J type isotherms.The equilibrium moisture content of PV and PV-MD decreased with increasing temperature and increased with increasing aw.The monolayer content increased with addition of maltodextrin and the range for PV and PV-MD were observed to be 0.0611-0.0824 g water/g dry solids and 0.0734-0.1034 g water/g dry solids,respectively.Eight models were employed to fit experimental data and the GAB model achieved the best fit.For both PV and PV-MD,the differential enthalpy and entropy,and integral enthalpy decreased with increasing moisture content.The integral entropy was negative in value and increased with increasing moisture content.The spreading pressure increased with increasing aw and decreased with increasing temperature.A plot of differential enthalpy versus entropy satisfied the enthalpy-entropy compensation theory and the adsorption behavior of P.vannamei meat was enthalpy-driven and spontaneous.Addition of maltodextrin increased the differential enthalpy and entropy,integral enthalpy,and spreading pressure,and decreased the integral entropy of P.vannamei meat.2.Effects of scanning numbers,heating rate,annealing temperature,annealing time and moisture content of P.vanmamei meat on the results of differential scanning calorimetry(DSC)scanning have been investigated to optimize the DSC scanning procedure of P.vanmamei meat.Experimental results showed that for the sample containing unfreezable water,single scan program was approprited for DSC scanning.For samples containing freezable water,annealing at-35 ? for 30 min gave a minimum ?H value of 171.7±1.73 J/g in the annealing temperature range of-25 to-50 ?.The glass transition temperature(Tg)of P.vanmamei meat decreased with the decrease of the annealing temperature.With the increase of annealing time,Tg values decreased.And the optimum annealing time was found to be 30 minute or higher after statistical analysis.Tg value was found to be lower alone with the decreased heating rate and tended to be contant value at the rate of 5 ?/min or below.Because of the the plasticizing effect of water,the descending of Tg was quick when the moisture content was below 11.43%(w.b).In the range of 11.43-25.88%(w.b),the decline of Tg was slowed and when the moisture content was higher than 25.88%(w.b),Tg reduced very slowly and tended to be stable.3.DSC was used to determine the Tg and freezing point(TF)of PV-MD and PV.The data of Tg and TF was fitted by Gordon-Taylor and Clausius-Clapeyron equation in order to acquire the state diagram of P.vanmamei meat.The results showed that Tg decreased with increasing moisture content.Tg decreased from 30.73 to-71.03? as the moisture content of PV increased from 1.91%to 38.26%(w.b).Tg decreased from 37.55 to-66.67? as the moisture content of PV-MD increased from 2.15%to 40.87%(w.b).TF decreased with the increase of the solid content.According to the state diagram,the maximal freeze concentration glass transition temperature T'g of PV and PV-MD were-74.92 and-67.69?,respectively.The corresponding maximally freeze concentrated solutes concentration were 70.57%and 65.69%,with the content of unfreezable water were 29.43%and 34.31%,respectively.The T'm of PV and PV-MD were-32.25? and-26.01?,respectively.The addition of maltodextrin significantly increased the the maximal freeze concentration glass transition temperature T'g and unfreezable water,and therefore inproved the storage stability and quality of freezed P.vanmamei meat.At the room temperature of 25?,the critical water activity(CWA)and critical water content(CWC)of PV and PV-MD were 0.1512,0.0381g/g and 0.2582,0.0829g/g,respectively.Therefore,the addition of 5%maltodextrin can significantly improve the storage stability of freeze-dried P.vanmamei meat.