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Tomato powder drying method
Jul 19, 2018

(1) Freeze drying method

In this method, the tomato concentrate is frozen at a low temperature, and then the water is sublimated under high vacuum to be dried. The resulting tomatoes still retain them

The original structure without damaging its original shape and size. Therefore, the freeze-dried particles have a porous structure, retaining the space originally occupied by moisture without collapse, thereby facilitating rapid rehydration of the product. However, this method consumes a lot of energy, and the freeze-drying equipment is very expensive, resulting in high product cost.

(2) Puffing and drying method

The puffing drying method uses a puffing drying apparatus to dry the tomato concentrate. The absolute pressure of 2.6 mm Hg is usually required for dehydration, and the temperature of the tomato concentrate material is usually 60 to 70 °C. In order to achieve a moisture content of 3% in the final product, the drying time is usually from 90 minutes to 5 hours. Before the vacuum is removed, the product should be cooled down to avoid collapse of the bulky structure of the product, because the obtained tomato powder is thermoplastic; the tomato powder prepared by the method is relatively rigid in structure and volume is similar to the volume of the concentrate, and the product is complex. Poor water performance. In addition, the expansion must be carried out under vacuum conditions, and the cost is relatively high, resulting in a relatively expensive product.

(3) Spray drying method

The 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 (double-layered tower wall, which can be cooled by air to dry the inner wall) is used for drying; if the heating medium is pre-dehumidified dry air, Then, the inlet air temperature during drying is generally about 150 to 160 ° C, the outlet temperature is 77 to 85 ° C, and the feed concentration is generally 20% to 30%.

There are already some modified spray drying equipment on the market that can be used to process fruit and vegetable flour. Some use air as a drying gas, drying at a medium inlet air temperature of 75 to 95 ° C, which can increase the production speed; others are dehydrated air as a drying gas at a lower inlet air temperature (25-50). °C) Drying. However, all of these spray drying equipment used to dry tomatoes are very tall, which increases the cost of establishing a factory.

(4) Foam layer drying method

The key to this drying process is primarily the formation of stable foams in tomato concentrates by the addition of foaming materials such as soy protein, globulin, fatty acid fats, glycolipids and glyceryl monostearate. The gas temperature in the dryer is about 93 ° C and the speed is about 100-130 m / s, which is added in a countercurrent manner. The drying time depends on the characteristics of the product and the drying conditions used. The drying time is generally 15 to 18 minutes.

(5) Roller drying method

The rotation speed of the drum is generally 3.5 rpm, the vapor pressure is 3.5 kg/cm 2 , and the spacing between the rolls is 0.2 mm. In order to enable the water vapor generated during drying to be quickly taken away, air is required to pass through, and the flow of the person passing through is opposite to the direction of rotation of the drum, that is, reverse flow; and the humidity of the air 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. Since the obtained product has a moisture content of at least 7%, it is necessary to continue to dry with a gas stream at 20 ° C for more than 24 hours. Otherwise, the color, flavor and nutritional value of products with a moisture content of 7% or more will be seriously reduced during storage.