| This study takes tilapia as the research object,explores the influence of microwave vacuum drying process parameters on its quality indicators,combines the response surface method to screen the best process parameters of tilapia microwave vacuum drying,and establishes tilapia according to the change law of moisture content in the drying process Kinetic model of microwave vacuum drying of fish fillets.At the same time,the MRI instrument was used to detect the drying process of tilapia fillets,and the qualitative and quantitative determination of the three states of moisture migration of tilapia fillets with different microwave power conditions with the drying process was obtained.Based on the optimization of process parameters,the adsorption characteristics and thermodynamic properties of tilapia fillets prepared by microwave vacuum drying were discussed.With a view to providing a theoretical basis and new ideas for the development and storage of new technologies in the tilapia industry.The results and conclusions of the main research work include:?1?The optimal process parameters of microwave vacuum drying tilapia fillets were obtained.Choose 3.5%Na Cl as the penetration treatment agent,with the thickness of fish fillet?3,5,7,9 mm?,microwave power?132,198,264,330,396 w?and vacuum degree?0.03,0.04,0.05,0.06,0.07 Mpa?is the investigation factor,and the composite score of the six observation indexes is the response variable,to explore the microwave vacuum drying quality characteristics of tilapia fillets.Based on the single factor,the process conditions are optimized by response surface analysis.The results showed that the optimal technological parameters of vacuum microwave drying tilapia fillet were:thickness 7 mm,microwave power 330 w,vacuum degree 0.06 Mpa.?2?The kinetic model of microwave vacuum drying tilapia fillet drying process was established.The results show that:the drying time is very dependent on the drying conditions,and changes with the thickness of the fillet T,microwave power W and vacuum degree V;the Weibull model has a good fit;the calculation based on the Weibull function is effective The water diffusion coefficient Dcalincreases in the range of(1.187 7×10-6?2.052 1×10-6)m2·s-1with the increase of microwave power W and vacuum degree V;geometric parameters Rgand thickness T,microwave The power W and the vacuum degree V are negatively correlated;the drying activation energy is calculated to be 0.92 w·g-1according to the Arrhenius equation within the experimental range.?3?With the help of nuclear magnetic resonance technology,the laws of moisture migration and change in the drying process of tilapia fillets under different microwave vacuum drying conditions were obtained.The results show that there are mainly three states of water?free water,hard-to-flow water and combined water?in tilapia fillets.The change of hard-to-flow water determines the drying effect of the material;the relaxation time T2xunder different microwave environments during the drying process Migrating in the direction of poor fluidity;for the entire drying process,the change trend of peak area S2xand peak ratio A2xunder different microwave environment conditions are more consistent,the greater the power,the more obvious the curve change;There is a good linear relationship between the moisture content of tilapia fillets and the peak area;nuclear magnetic images show that the migration of tilapia fillets in microwave vacuum drying is a recursive process from outside to inside.?4?The hygroscopicity and thermodynamic properties of tilapia fillet samples in microwave vacuum drying were obtained.The results show that the adsorption isotherms of dried tilapia fillets belong to the typical type?isotherm curve;at a given temperature,the equilibrium moisture content increases with the increase of water activity;the GAB model describes dried tilapia fillets Optimal model of adsorption kinetics;according to the optimal model,the relative safe moisture content and absolute safe moisture content of dried tilapia fillet products at different temperature conditions are obtained;the thermodynamic characteristic parameters show that the net equivalent adsorption heat qst and differential entropy?S are both It decreases with the increase of the equilibrium water content;the expansion pressure?decreases with the increase of temperature and increases with the increase of water activity;the net integral enthalpy?Hindecreases with the increase of the equilibrium water content,and the net integral entropy?SinIt increases with the increase of water content;the entropy-enthalpy complementary theory shows that the adsorption process of dried tilapia fillets is non-spontaneous and enthalpy-driven. |
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