Fruits and vegetables are indispensable foods in people's daily life. They are rich in nutrients and can maintain the normal physiological functions of the human body and maintain human health. However, the fresh-keeping time of fruits and vegetables is very short, and they are easy to deteriorate and destroy nutrition. It is inconvenient to eat and store, especially Seasonal vegetables, local dishes, special dishes, etc. are difficult to be eaten and sold throughout the year and nationwide. Although the fresh-keeping vegetables and quick-frozen vegetables processed by the existing technology can appropriately prolong the fresh-keeping time of vegetables and fruits, they are subject to storage conditions. Restrictions, can not be eaten anytime, anywhere, so freeze-dried fruits and vegetables appeared.
With the rapid development of life rhythm and healthy diet, freeze-dried fruit and vegetable products have become a new healthy diet craze. Freeze-dried fruit and vegetable products can meet the requirements of quick access to nutrition and long-term preservation of fresh fruit and vegetable products. Freeze-dried fruit and vegetable products can be industrialized or home-produced.
The mini freeze-drying machine adopts vacuum freeze-drying technology, which pre-freezes the water-containing materials, and then sublimates the water in a vacuum state, so that the items can be dried. The original biological and chemical properties of freeze-dried articles are basically unchanged, but after adding water, they can be restored to the state before freeze-drying, and their original biochemical properties can be maintained, so it is easy to store for a long time. It is suitable for freeze-drying vegetables, fruits, meat and other items at home.
Mini Freeze Dryer at Home Freeze-dried Fruit and Vegetable Production Process:
Raw material selection → finishing → pre-freezing → sublimation drying → post-processing → packaging and storage.
Raw material selection and finishing
Pretreatment Generally, pretreatment refers to all treatments before sublimation drying, so freezing before drying also belongs to pretreatment.
The pretreatment of raw materials is the same as that of conventional fruit and vegetable drying and fruit and vegetable quick-frozen products, such as selection, cleaning, peeling, cutting, blanching, cooling, etc. When freeze-drying fruit or vegetable juices, it is pre-concentrated using less expensive processing methods, and the product is then granulated during pre-freezing.
Pre-freeze
Pre-freezing is to freeze the pre-treated raw materials, which is an important process of freeze-drying. Since a series of complex biochemical and physicochemical changes will occur in the freezing process of fruits and vegetables, the quality of pre-freezing will directly affect the quality of freeze-dried fruits and vegetables. The key consideration in the freezing process is the effect of the freezing rate of the frozen material on its quality and drying time. The difference between quick freezing and slow freezing is as follows: the ice crystals produced by quick freezing are smaller, and those produced by slow freezing are larger; large ice crystals are conducive to sublimation, and small ice crystals are not conducive to sublimation; small ice crystals have less impact on cells, and the smaller the ice crystals , the more it can reflect the original organizational structure and performance of the product after drying. However, the freezing rate is high and the energy consumption required is also high. Comprehensive consideration should be given to select an appropriate freezing rate to ensure the quality of freeze-dried food while keeping the required freezing energy consumption low.
Sublimation Drying
Sublimation drying is the core process in the production of freeze-dried food.
The quality of the food to be dried on the drying plate per unit area of the mini freeze dryer is an important factor in determining the drying time. The thickness of the food being dried is also a factor that affects drying time.
During freeze-drying, the drying of the material is pushed from the outer layer to the inner layer. Therefore, when the material to be dried is thicker, a longer drying time is required. During actual drying, the dried material is cut into a uniform thickness of 15-30mm. The amount of material that should be loaded on the drying plate per unit area should be determined according to the heating method and the type of dry food.
In order to shorten the drying time, the heat required for ice crystal sublimation must be effectively supplied when using a mini freeze dryer for freeze drying, so various practical heating methods have been designed. The drying temperature must be controlled within the range that does not cause ice crystals in the dried material to melt and the dried part will not cause thermal denaturation due to overheating. Therefore, in a single heating method, the temperature of the drying plate should be controlled at 70-80°C in the early drying stage when sublimation is vigorous, 60°C in the middle drying stage, and 40-50°C in the later drying stage.
Post-processing
Post-processing includes unloading, sorting of semi-finished products, packaging and other processes.
After freeze-drying using a small freeze-drying machine, it is necessary to inject nitrogen or dry air into the drying chamber to break the vacuum, and then immediately remove the material in a closed environment with a relative humidity below 50%, a temperature of 22-25 °C, and a small amount of dust. And in the same environment for the selection and packaging of semi-finished products. Because the freeze-dried material has a huge surface area and is very hygroscopic, it is necessary to complete these operations in a relatively dry environment.
Freeze-dried food has a porous sponge-like structure. Once the product is exposed to the air, it is easy to absorb moisture and oxidize and degrade. Therefore, freeze-dried food should be vacuum-packed, preferably nitrogen-filled. Secondly, freeze-dried food occupies a relatively large volume. It is not conducive to packaging, transportation and sales, so freeze-dried food is often compressed and packaged. In addition, the porous and loose structure makes the freeze-dried food extremely easy to break during transportation and sales. Therefore, for those freeze-dried food that is inconvenient to compress and pack, a certain protective packaging material or packaging form should be provided.
The commonly used packaging materials for freeze-dried food are PE bags and composite aluminum platinum bags. PE bags are often used for large packaging, and composite aluminum platinum bags are often used for small packaging. If necessary, when PE bags are used as inner packaging, in order to strengthen their function of isolating oxygen, water and steam, double layers are often used. If necessary, iron cans can also be used, but the price is high and the application is not very common. No matter what kind of packaging material is used, it is necessary to use vacuum and nitrogen, and add oxygen scavenger and desiccant.
Freeze-dried food should be stored in a cool and dry place. If possible, it is best to place it in a low temperature and low humidity environment. The shelf life is usually 1 to 2 years, and it can be appropriately extended when packaged in iron cans.
Fruit and Vegetable Freeze Dryer Processing Lemon Slices at Home
Lemon fruit juice is fleshy and crisp, with a strong aroma, rich in vitamins, citric acid, high potassium and low sodium, etc., which is very beneficial to the human body. Traditional consumption includes freshly squeezed juice, dried lemon slices, etc., which cannot meet modern consumption and nutritional preservation. Fruit and vegetable freeze dryer and become the most sought after freeze-dried food equipment.
The steps of processing lemon slices in a fruit and vegetable freeze dryer:
1. Selection of raw materials
Select C-grade lemon fruit with an inner cut surface diameter of 50-60mm;
2. Cleaning
Wash the selected lemons;
3. One-time freeze drying
The cleaned fruits were placed in the freezer under sealed conditions and freeze-dried at -15°C for 8 hours; then the frozen fruits were transferred from the freezer to the working chamber of Shanghai Tuofen vacuum freeze-drying machine, at a temperature of 1°C/min. The temperature was raised to 55°C and kept for 6 hours, and the vacuum degree was 5Pa;
4. Slicing
Cut the freeze-dried lemon into slices with a thickness of 5mm; the temperature when slicing is -5°C;
5. Soak
The sliced fruit pieces were placed in a chitosan-vitamin complex solution for 3 minutes at 5°C, and the chitosan-vitamin complex solution was composed of chitosan, vitamin C and ethanol in a weight ratio of 1. : a mixed solution of 6:93, the ethanol is an ethanol solution with a volume concentration of 95%,
6. Secondary freeze drying
Put the soaked lemon slices in the freezer and freeze-dry at -20°C for 5 hours under sealed conditions; then transfer the frozen lemon slices from the freezer to the working chamber of the vacuum freeze dryer at a speed of 3°C/min. After the temperature was raised to 45 °C, the temperature was kept for 8 hours, and the vacuum degree was 4Pa;
7. Packaging
Under aseptic conditions, the lemon freeze-dried tablets are packaged by nitrogen filling and food packaging film, wherein 2-3 freeze-dried tablets are packaged and sealed.
Features of ZZKD Mini Freeze Dryer:
1. Imported fully enclosed refrigeration unit is adopted, with low temperature and strong water capture capacity. Adopt air cooling method to dissipate heat without water cooling;
2. The vacuum connection adopts international standard parts, which is easy to disassemble and install, and has reliable sealing performance;
3. The temperature of the cold trap and the vacuum degree of the sample are displayed by LED digital, which is concise and clear;
4. The specially designed touch soft keys can quickly and accurately realize various function settings, and the operation is simple and convenient;
5. Transparent drying room, natural heating, safe and intuitive;
6. Specially designed stainless steel sample rack, the distance between ordinary sample trays can be adjusted, and the number of layers can be set freely;
7. Stainless steel cold trap and table, clean, hygienic, beautiful and corrosion-resistant.
Grouped equipment:
Rotary vane vacuum pump is an oil-sealed mechanical vacuum pump, which is one of the basic vacuum obtaining equipment in vacuum technology. Home benchtop freeze dryers need to be used with it.
The mini freeze dryers produced by ZZKD has stable performance and easy operation. In addition, we have spray dryers and other laboratory equipment. 13 years of production and export experience and a series of ISO9001 and CE certificates, with warehouses in the US, Spain, UK and Thailand.
If you want to know about our products, or want to buy our equipment, please feel free to contact us, ZZKD will provide you with the best prices for mini freeze dryers at home.
