Modern nutritional studies have found that tomatoes have extremely high nutritional value, low calories, anti-oxidation, and anti-cancer; they can remove freckles, beautify, prevent aging, and lose weight. Tomato powder is suitable for both internal and external use. It has the function of "beautiful". It is suitable for low-fat menu, weight loss and beauty. It is worth mentioning that tomatoes contain lycopene, which is a powerful antioxidant that helps delay aging and resist stress. And can balance moisture and oil secretion. Tomato powder is slightly changed to make different facial masks such as cleansing, repairing, spot removal and whitening.
So how did tomatoes go from powder to powder? Today, Xiaobian will lead you to explore the drying process of tomatoes.
There are many drying methods for tomatoes, mainly freeze drying, puff drying, drum drying, foam layer drying and spray drying.
(1) Freeze drying method
This method uses low temperature to freeze the tomato concentrate, and then sublimates the water in a high vacuum state for drying. The resulting tomatoes still retain their original structure without compromising its original shape and size. Thus, freeze-dried particles have a porous structure that retains the space originally occupied by moisture without collapsing, thereby facilitating rapid rehydration of the product. However, this method consumes a lot of energy, and the freeze-drying equipment is very expensive, so the cost of the obtained product is high.
(2) puffing drying method
The puff drying method utilizes puff drying equipment to dry the tomato concentrate. Usually an absolute pressure of 2.6 mm Hg is required for dehydration, and the temperature of the tomato concentrate material is usually 60-70 °C. In order to achieve a moisture content of 3% in the final product, drying times are typically 90 minutes to 5 hours. The product is cooled before the vacuum is removed to avoid collapse of the fluffy structure of the product, because the resulting tomato powder is thermoplastic; the tomato powder prepared by this method has a firmer structure and a volume similar to that of the concentrate, and the product is rehydrated poor performance. In addition, puffing must be carried out under vacuum conditions, and the cost is relatively high, resulting in relatively expensive products.
(3) Spray drying method
Tomato concentrate slurry should be homogenized prior to spray drying. The homogenization pressure is generally 150 to 200 kg/cm 2 . Generally, a centrifugal or two-fluid spray dryer with a cooling jacket on the tower wall (double-layer tower wall, the temperature of the inner wall of the drying chamber can be cooled by air) is used for drying; if the heating medium is pre-dehumidified dry air, Then the inlet air temperature during drying is generally about 150-160°C, the outlet air temperature is 77-85°C, and the feed concentration is generally 20%-30%.
There are already some modified spray drying equipment on the market that can be used to process fruit and vegetable powder. Some use air as drying gas, and use a medium inlet air temperature of 75-95 °C for drying, which can improve the production speed; others use dehydrated air as drying gas, and at a lower inlet air temperature (25-50 °C) °C) for drying. So this method is the best choice for drying tomatoes.
(4) Drying method of foam layer
The key to this drying method is the formation of a stable foam in the tomato concentrate by adding foaming substances such as soy protein, globulin, fatty acid lipids, glycolipids, and glycerol monostearate. The temperature of the gas passing through the dryer is about 93°C, the velocity is about 100-130 m/s, and it is added in a countercurrent manner. The drying time depends on the characteristics of the product and the drying conditions used. Generally, the drying time is 15 to 18 minutes.
(5) Drum drying method
The rotational speed of the drums is generally 3.5 rpm, the vapor pressure is 3.5 kg/cm 2 , and the spacing between the drums is 0.2 mm. In order to quickly take away the water vapor generated during drying, it is necessary to pass through the air. The air flow through the people is opposite to the rotation direction of the drum, that is, the countercurrent flows in; and the air humidity in the material collection area is controlled to be 15% to 20%. However, this drying method does not really achieve the purpose of drying tomato powder. Because the moisture content of the obtained product is at least 7%, it is necessary to continue drying with air flow for more than 24 hours at 20°C. Otherwise, the color, flavor and nutritional value of products with a moisture content of more than 7% will be severely reduced during storage.
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