Study On Freeze-drying Technology And Rehydration Mechanism Of Freeze-dried Dumplings

Dumpling is a traditional Chinese food, which is delicious, nutritious, and suitable for both young and old. Yet, the process is much complicated. On the other hand, high moisture content in fresh dumplings brings more inconvenience to its storage, sales, and transportation, which doesn’t fit the fast-paced life style in modern society. Freeze-drying is an advanced drying method, therefore in this paper, freeze-drying technology, was adopted, effects of additives on freeze-dried dumplings and rehydration mechanism were studied and optimized, which can provide theoretical guidance for industrialized production of freeze-dried dumplings. The main research contents and conclusions are as follows:1. Rehydration ratio, sensory index and drying rate were as evaluation standards, freeze-drying process was studied, and the optimal freezing-drying conditions were obtained. Results show: prefreezing phase is-30 for 1.75 h and ℃-45 for 1.75 h℃; sublimation drying phase is-8 ℃ for 5 h then 0 for 15 h; desorption drying phase ℃is 40 for 6℃ h, moisture content of freeze-dried dumplings was below 5 %.2. The rehydration property of freeze-dried dumplings is not satisfactory. To improve rehydration properties of freeze-dried dumplings, sodium citrate, mannitol, guar gum, CMC-Na, Na Cl, Na2CO3, composite phosphate, lecithan and β-cyclodxtrin were chosen to study the effects on rehydration ratio, sensory index and drying rate of freeze-dried dumplings. Single factor experimental results show: nine food additives all can improve rehydration properties. Additionally, β-cyclodxtrin, CMC-Na, guar gum, composite phosphate have better and stronger effect on rehydration properties than other food additives. When food additive is added alone, sodium citrate being 0.30 %, mannitol being 0.30 %, guar gum being 0.35 %, CMC-Na being 0.10 %, Na Cl being 6 %, Na2CO3 being 6 %, composite phosphate being 0.10 %, lecithan being 0.60 % and β-cyclodxtrin being 4 %, rehydration ratio, sensory index and drying rate of freeze-dried dumplings can be improved to some extent. Based on single factor experiments, results of two-component experiments show: When two food additives are combined, rehydration ratio of freeze-dried dumplings is 2.05 with β-cyclodxtrin being 4 % and composite phosphate being 0.30 %. Rehydration ratio of freeze-dried dumplings is 1.84 with β-cyclodxtrin being 4 % and sodium citrate being 0.35 %. Rehydration ratio of freeze-dried dumplings is 2.06 with β-cyclodxtrin being 4 % and guar gum being 0.45 %. Based on two-component experiments, L9(33) orthogonal experiments show that three constitutes of β-cyclodxtrin, composite phosphate, sodium citrate can improve rehydration properties and rehydration ratio is 1.89 with β-cyclodxtrin, composite phosphate, sodium citrate being 3 %,0.1 %,0.35 %, respectively.3. Rehydration kinetics of freeze-dried dumplings was studied and the effect of rehydration temperature on rehydration rate was researched. Results show: Fick Diffusion Law, Peleg model, and Weibull model can be applied to model rehydration process and predicted equilibrium water content, yet Fick Diffusion Law shows worse fitting accuracy than Peleg model and Weibull model. Thermodynamic analysis of rehydration process is endothermal, and non-spontaneous.4. Rehydration mechanism is researched. Based on capillary theory, the mathematical model of one dimensional steady was established. The established model is verified, calculation values are in good agreement with experimental values, which means capillary theory can well explain rehydration mechanism of freeze-dried dumplings, and provide theoretical support for industrial production of freeze-dried food.