Study On Selection Of Modifier And Rehydration Mechanism Of Freeze-Dried Dumplings

Dumplings are one of the most widely loved traditional foods in China.With the improvement of people's living standard and the acceleration of fast-paced life,the instant dumplings have attracted more attention from people.Hot air drying and other traditional methods usually decrease the quality of dumplings.Compared with the traditional drying methods,the freeze-drying products were able to ensure food protein,vitamins and other nutrients.Nevertheless,the rehydration effects are far from people's satisfaction.To solve this problem,aim at increasing the rehydration properties of freeze-dried dumplings,the freeze-dried process of the dumplings was optimized;the modifier was selected and the effects of hot air drying and freezed drying on the nutritional composition and microstructure of dumplings were also studied;the physical properties of modifier was determined;the rehydration model for freeze-dried dumplings was established by using the transfer mechanism in porous media,which can provide theoretical guidance for industrialized production of freezedried dumplings and other freeze-dried foods.The main research contents and conclusions were as follows:The freeze-dried process of dumplings was optimized.It was that: at the prefreezing stage,frozen 3 h at-30 ?;at the sublimation drying stage,drying 4 h at-8 ? then 0 ? for 13 h;at the desorption drying stage,drying 6 h at 40 ?.The modifier for improving rehydration properties of freeze-dried dumplings was studied.At the aim of rehydration ratio,based on the single factor experiments and orthogonal experiments,a suitable formulation containing B-sugar of 4%,sucrose of 6%,NaCl of 8% was obtained,the rehydration ratio of freeze-dried dumplings was 1.90;the modifier were able to ensure food protein,vitamins and other nutrients,and modifier could improve the microstructure of freeze-dried dumplings;By comparing the effects of hot air drying and freeze-dried on the nutritional composition and microstructure of dumplings,it was proved that the freeze-dried way was better than hot air drying.The physical properties of modifier were measured,such as solubility,density,viscosity and conductivity.The measurement of solubility showed that: the solubility of B-sugar increased with the increase of temperature in 6% sucrose solution,8% NaCl solution and the mixed solution between 303.15 K~353.15 K.The experimental data were correlated with the modified Apelblat equation.The average relative deviation of each system was less than 7.5%.The solubilities calculated by the model showed good agreement with the experimental data.The dissolution enthalpy ?H and dissolution entropy ?S had been calculated from the experimental data.The dissolution enthalpies ?H and dissolution entropies ?S in the sucrose solution were positive,which indicated the dissolving process was entropy-driven.The measurement of density showed that: the density of 4% B-sugar solution,6% sucrose solution,8% NaCl solution and the mixed solution decreased with the increase of temperature between 323.15 K~353.15 K.The relationship between density and temperature were correlated and the parameters of the equation were calculated.The average relative deviation of each system was less than 0.063%.The measurement of viscosity showed that: the viscosity of 4% B-sugar solution,6% sucrose solution,8% NaCl solution and the mixed solution decreased with the increase of temperature between 323.15 K~353.15 K.The relationship between viscosity and temperature were correlated and the parameters of the equation were calculated.The average relative deviation was less than 0.749%.The measurement of conductivity showed that: the conductivity of 4% B-sugar solution,6% sucrose solution,8% NaCl solution and the mixed solution increased with the increase of temperature between 323.15 K~353.15 K.The corresponding molar conductivity was calculated.The relationship between molar conductivity and temperature was correlated with the Arrhenius equation and the parameters of the equation were calculateded.The average relative deviation of each system was less than 2.55%.The rehydration mechanism of freeze-dried dumplings was studied based on capillary flow of water within the dumplings in porous media,the mathematical model was found to suitably describe the rehydration behavior and the model could be used satisfactorily to predict the rehydration of dumplings,which would provide the technical support for the freeze-dried industry.