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Beijing Songyuan Huaxing Technology Development Co., Ltd
The Effect of Annealing on Freeze Drying Efficiency of Fruits and Vegetables
Date: 2023-09-26Read: 6
Drying is an important processing method for extending the storage period of fruits and vegetables. The drying process is the process of heating and dehydrating materials, during which the physical and chemical properties of the material change, including microstructure, chemical properties, and sensory quality. Among all drying methods, vacuum freeze-drying is the most complete drying method that preserves the material's organizational structure, greatly preserving the nutrients and microstructure of the material, and endowing the product with low-density, porous, and crispy characteristics. However, the freeze-drying process requires a low-pressure and low-temperature drying environment, with a long production cycle and high energy consumption. Therefore, strengthening the heat and mass transfer in the freeze-drying process while ensuring good product quality has become an urgent problem to be solved.
Process improvement
Pre freezing is the first step in freeze-drying, and freezing conditions have a significant impact on the drying characteristics of materials and product quality. Studies have shown that compared to fast freezing (0.25 ℃/min) apple slices, slow freezing (0.05 ℃/min) and freeze-thaw treatment shorten the drying time of apple slices by 5% and 15%, respectively; The freeze-drying time is related to the ice crystal structure formed during the freezing process. When the ice crystal diameter of the material increases from 30 μ m to 60 μ m, the sublimation drying time of the material is shortened by about 32%. In the sublimation drying stage, due to the increase in the size of ice crystals inside the material, the mass transfer resistance decreases, while in the desorption drying stage, due to the decrease in the specific surface area of the material, the water splitting and absorption weaken.
The annealing procedure is the process of raising the temperature of a frozen sample to a certain level and then reducing the freezing. From a dynamic perspective, the annealing process follows the Gibbs Curie Ullop surface energy theory: the equilibrium shape of the crystal should be such that it has the minimum total surface area free energy per unit volume, which is simply the surface area; The volume ratio tends to minimize, that is, small volumes become large volumes, and flakes become spherical or cylindrical. From a thermodynamic perspective, there are two changes during the annealing process. The viscosity of amorphous materials decreases with increasing temperature above Tg ', leading to flow and polymerization; Crystalline substances, small ice crystal molecules will migrate towards larger ice crystals.
LG-03 Experimental Freeze Drying Machine (Desktop Freeze Drying Machine)
Based on the freezing characteristics and material composition of fruits and vegetables, a pectin sucrose solid simulation system was constructed. The influence of annealing temperature and annealing times on the ice crystal morphology, drying characteristics, texture, and microstructure of the vacuum freeze-drying solid simulation system was studied. Furthermore, the relationship between ice crystals, pore structure, and texture was analyzed to provide reference for analyzing the formation of texture quality of freeze-dried products. Annealing treatment increased the ice crystal diameter and irregularity of the pectin sucrose network. As the annealing temperature range increased, the ice crystal diameter increased and the fractal dimension decreased; As the number of annealing cycles increases, the diameter of ice crystals also increases. The simulated system annealed at 0 ℃ for 3 times has fewer ice crystals and a higher fractal dimension. Annealing treatment has a significant impact on the drying process of solid simulation systems. Increasing the annealing temperature and number of annealing cycles accelerates the drying rate and shortens the drying time of the simulation system. The drying time of the simulated system annealed at 0 ℃ for 3 times was reduced by 16% compared to the untreated group. Compared with the untreated group, annealing treatment reduced the hardness of the freeze-drying simulation system and increased the brittleness at the threshold of 0.098 N. Under the condition of annealing at 0 ℃ for 3 times, the hardness of the solid simulation system decreased by 1.44 N compared to the untreated group, and the brittleness at the threshold of 0.098 N increased by 0.078 compared to the untreated group. Overall, annealing treatment is an effective means of regulating solid food ice crystals. In practical production, increasing the number of annealing cycles and raising the annealing temperature can effectively shorten the drying time, reduce drying energy consumption, and improve product quality.
Technical points of supporting equipment
The Songyuan freeze-drying GZL series freeze dryer uses professional technology to make the partition, which is resistant to high pressure, has high flatness, and good temperature uniformity. Efficient mixed refrigerant medium with low freezing point and high boiling point, high heat transfer efficiency. The drying curve optimization control algorithm can control the heating rate and vacuum degree value of the product during the drying stage. The professionally designed LYO-CON control system can store multiple sets of process formulas and make real-time adjustments to the process during the drying process, improving the process optimization rate. In situ annealing and freeze-drying procedures, multi-stage pre freezing slope temperature control and other processes can be carried out.
Technical Support
Beijing Songyuan Huaxing combines more than 20 years of experience in freeze-drying equipment production to provide customers with a complete set of fruit and vegetable chip production lines: cleaning equipment, peeling equipment, de nucleating equipment, cutting equipment, vacuum freeze-drying equipment, and packaging equipment. Our business scope covers over 30 countries and regions around the world. Centered around customers, we provide a series of process development services from market research, feasibility studies, investment consulting, and other aspects. We have a professional pharmaceutical and food engineering design team, adhering to the design concept of green environmental protection, energy conservation and high efficiency. We provide a complete set of design drawings and digital 3D models for different products, from conceptual design to detailed design.
Songyuan Freeze Drying Daily Processing 1200Kg Food Freeze Drying Project
Beijing Songyuan Huaxing Technology Development Co., Ltd. was founded in 2000, focusing on the research and development, production, and sales of vacuum freeze-drying technology products. With "vacuum freeze-drying machine" as the core product, it has formed three series of products and targeted solutions for scientific research experiments, medical, and food industries, with different scales and applications. It is an influential supplier of vacuum freeze-drying equipment and targeted solutions in China.
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