The words lyophilization and freeze drying are synonymous. Freeze drying is a water removal process that is done to increase the life of moisture-sensitive materials or to move them more easily. Freeze drying is done by freezing the material and then reducing the pressure and increasing the temperature (in order to sublimate the solvent).
The main application of the freeze dryer
It is used to dry materials sensitive to heat, which cannot be dried with normal methods. This method is often used in various industries such as pharmaceutical, food, biotechnology, medicine, petrochemical, biochemistry, etc. In fact, in this method, the material is first It is frozen, then the water or solvent changes from a solid state to a gas state. With this drying method, the chemical and physical properties of the material will be preserved.
In medical engineering, this method is used to make cellular scaffolds. With this method, it is possible to create a porous material with interconnected pores so that the cell is a suitable substrate for cell growth.
All kinds of fruit and vegetable dryers
Dryers are technically and technologically divided into several categories, each of which has its own performance and characteristics and is suitable for a specific task.
Consider that the quality and quantity of the input and output product is another factor that is important in different fruit and vegetable dryers.
The main stage of freeze drying
The most important phase of this process is the freezing phase. Proper freezing can lead to a 30% reduction in drying time.
freezing phase
There are different ways to freeze matter. This process can be done with the help of a freezer or a cold bath, or on the shelves of a freeze dryer. Cooling the material below its triple point ensures that melting and vaporization will not occur in subsequent steps, instead of sublimation, and in fact, causes the material to retain its physical form.
Larger crystals freeze-dry faster. Note that slow freezing or annealing results in the production of larger crystals. In the case of biological materials, if the crystals are too large, they can lead to the breaking of the cell wall and create unfavorable results. To prevent this from happening, it may have been necessary to do the freezing quickly and prevent the formation of large crystals. For materials that have a strong tendency to precipitate, annealing can be used. In this way, he quickly froze the material and then slightly increased its temperature so that the crystals grow.
Primary drying
in the primary drying phase (sublimation), in order to sublimate the solvent; The pressure is reduced and heat is given to the substance. As the vacuum increases, the speed of sublimation increases. But note that increasing the vacuum too much can reduce the speed of sublimation. In this phase, the surface of the condenser is very cold, which causes the absorption of solvent vapor and its solidification. In general, 95% of the solvent is removed in this step. Primary drying is a slow and time-consuming process. Excessive temperature increase can change the structure of the material.
Secondary drying
In this phase, molecules of the solvent that have formed intermolecular bonds with the molecules of the main substance are removed. This process occurs through a further increase in temperature and the breaking of bonds. At the end of this phase, the structure of the final product will be very porous. At the end of the process, the vacuum can be broken with the help of a neutral gas and the pressure can be increased to atmospheric pressure.
Problems that should be avoided during freeze drying
- Increasing the temperature of the product too much can lead to melt-back or collapse.
- Condenser overload can occur due to high sublimation rate, high sublimation surface, small condenser surface or improper refrigerant.
- Choking of steam: steam is produced at a faster rate than the exit speed of the chamber, and as a result, the pressure of the chamber increases.
Important words in the freeze drying process
Eutectic temperature: It is the temperature at which the product is only in the solid phase and represents the lowest melting point.
Not all materials have a eutectic temperature; At the same time, some materials have several eutectic points.
Critical temperature: the highest possible temperature in freeze drying, without melt back or collapse.
Amorphous: There are multiple mixtures that do not crystallize and do not have a eutectic point. They turn into a glassy state due to cooling. Freeze drying of amorphous materials should be done below their glass transition temperature.
Collapse temperature: It is the temperature at which the material becomes soft and flows and will not be able to maintain its structure. This phenomenon can lead to the following problems:
- Loss of physical structure
- Incomplete drying
- Decreased solubility
Freeze-Drying or lyophilistation products
This method preserves the natural taste, aroma, and appearance of the product, and most importantly, all the nutritional value, vitamins, and vivid colors are similar to the fresh product. These products do not contain preservatives and the cell structure and preserved shape of the product make it quickly hydrated. These products are premium raw materials for bakery products, breakfast series, chocolate and fruit snacks. To meet the needs of baby food preparation, GreenField company created its vacuum steam sterilization department.
Freeze-dried fruits
- Freeze-dried Fruit: Apple, apricot, chokeberry, banana, black currant, red currant, blackberry, blueberry, bilberry, black olive, green olive, lingonberry, cherry, Cranberry, Elderberry, Gooseberry, Grape, Grapefruit, Peach, Kiwi, Mango, Melon, Orange (peeled and peeled), Elderberry (Sea Buckthorn), strawberry, wild strawberry, raspberry, papaya, pomegranate, pear, pineapple, lemon, lemon peel, orange peel, watermelon, etc.
- Freeze-dried vegetables: asparagus, barley sprouts, beets, broccoli, cauliflower, cabbage, wild mushrooms, celery, cooked sauerkraut, collard greens, corn, carrots, cucumbers, kale, White onion, red onion, horseradish, garlic, green beans, red pepper, green pepper, leek, parsley root, parsley leaf, wild carrot, potato, pumpkin, radish, red pepper, rhubarb, spinach, tomato, Zucchini, etc
- Freeze-dried wild mushrooms: (Latin names) Boletus, Shiitake, Chanterelle, Xerocomus and…
- Freeze-dried herbs: basil, dill, ginger, parsley, spring onion, marjoram, oregano, tarragon, thyme, etc.
- Freeze-dried meat and seafood: chicken, goose, turkey, beef, shrimp, crab.