JPH0258907B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a method for producing dried okara. In the past, okara was mainly used as feed, but from the perspective of effective resource utilization, various uses as food ingredients have been developed, and it has also been developed for its health value, such as its low calorie content and ``intestinal cleansing effect.'' Demand for food applications is also increasing due to the importance placed on them. This trend demands that the standards for okara products be more strictly defined and controlled than ever before. However, it is difficult to dehydrate the residue (wet okara) obtained by water extraction of soybeans or defatted soybeans to less than 80% by simple squeezing or centrifugation, and bacteria cannot grow. It has a tendency to easily occur. In recent years, several okara drying devices have been developed, and the shelf life of dried okara itself has improved, but the drying process itself has little bactericidal effect, and the use of bactericidal agents also reduces the residual atmosphere in the product. Although no analytical technology has been established to confirm this, there is a strong desire to supply dried okara that has been sterilized without the use of sterilizers. On the other hand, one of the important functional properties of okara that is expected to be used in food is its strong water absorption.
This property is thought to be due to the porous structure containing water-insoluble polysaccharides. However, proteins usually remain in okara, and intense treatments for sterilization and drying tend to impair water absorption, perhaps because they denature the proteins and seal the porous structure. The problem is that residual oligosaccharides are also involved, causing browning and reducing product value. Furthermore, as mentioned above, wet okara has about 80% water content even after dehydration, and even though it is wet, it is difficult to handle it as a low-viscosity liquid raw material. The present inventors have developed a method and apparatus for efficiently producing dried okara with a reduced number of bacteria while overcoming these difficulties of wet okara. This invention is a method for producing dried okara, which consists of passing wet okara through a pressure-sealed heating zone and then drying it. This can be carried out using a bean curd processing device connected to a back pressure generator. In this invention, the wet okara is usually obtained by dehydrating or not dehydrating the water-extracted residue of soybeans or defatted soybeans obtained by a conventional method. The moisture content when passing through the pressure-sealed heating zone is preferably 70 to 90%. If the amount of water passing through the heating zone is too small, the sterilizing effect will be low, and even if forced passage is attempted, clogging will likely occur. If there is too much moisture, the efficiency in the next drying process will be poor, and if dehydration is attempted after passing through the heating zone and before drying, it will be susceptible to bacterial contamination. The heating zone through which the wet okara passes must be pressure-sealed; a non-pressure-sealed heating zone, i.e., a heating zone under normal pressure, will have a sterilizing effect and produce dried okara with good functional and color quality. It is difficult to satisfy both. By passing through the heating zone, the temperature of the wet okara reaches 90 to 120°C, and the length or passing speed of the heating zone is set so that the temperature of the wet okara reaches 90 to 120°C, and the length of the heating zone or the passing speed is set so that 5 to 25 minutes pass in the temperature range in the zone. It is better. In the temperature range, the higher the temperature is adjusted, the shorter the heating time is, and the lower the temperature is adjusted, the longer the heating time is. Even at temperatures below 90°C, for example 80°C, a certain sterilization effect can be achieved by heating for a longer period of time, but in that case, the functional and color quality of the resulting dried okara is impaired, and on the other hand, 120°C
Even at temperatures exceeding ℃, the functional quality of dried okara is impaired, and the quality and sterilization effect of dried okara are affected.
It is suitable to process the product at a temperature of 90 to 120°C. A certain force is required for the wet okara in the moisture region to pass through the heating zone, and by passing the okara through the heating zone with this force, continuous heating treatment of okara becomes possible, and dry okara can be efficiently processed. can be produced. Because the heating zone is pressure-sealed and the wet okara is not very fluid, this forcing requires a pressure of at least 1 Kg/cm ² and usually 1.5 Kg/cm ² or more. is necessary. Heat exchangers such as votators, crush heaters, and thermo-breakers can be used in the pressure-sealed heating zone, but heating conditions suitable for okara can be easily designed and the equipment is simple. Therefore, a processing device that is connected to a piston pump, a heating tube, and a back pressure generator is optimal. The heating tube may be of a type in which steam is blown into the tube, or a double-wall type in which steam is indirectly contacted with the heating medium, but preferably a stirrer is provided in the middle of the heating tube, and the stirrer is a state-type one. A mixer is preferred because it has excellent stirring efficiency and does not require power. As the back pressure generating device, a damper, a rotary pump, etc. can be used, and it is sufficient if the back pressure there is about 1 kg/cm ² G. The wet okara passed through the heating zone is then dried, preferably using heating drying,
It is preferable to dry the wet okara immediately after it comes out of the heating zone without lowering the temperature below 80° C., in terms of maintaining the sterilizing effect and energy costs. Drum dryers, flash drying, etc. are suitable as heat drying methods. In particular, a combination method in which the moisture content is reduced to at least 50% or less using a drum dryer and then flash drying is applied, reduces the equipment scale and reduces the need for drum dryers. This is a preferred embodiment because waste heat can also be used and energy costs are low. However, even in the drying process, maintaining the product temperature below 120℃ is essential.
The preferred quality of dried okara is the same as in the case of heating zone passage. Examples and comparative examples of the present invention will be given below. Example Add 10 times the amount of water to low denatured defatted soybeans, adjust the pH to 7.5 with sodium hydroxide, extract the protein while stirring at room temperature for 30 minutes, and add 5 times the amount of water to the resulting residue. Similarly, adjust the pH to 7.5 and re-extract.
After centrifugation, wet okara with a water content of 84% was obtained. This wet okara is equipped with a screw hopper (1 in the attached drawing) and a rotary piston pump (2 in the attached drawing).
A pushing pressure of 15% is applied to the heating tube (4) by a high pressure piston pump (3)
Kg, supplied at an inlet temperature of 45°C. A static mixer (5) is installed in the middle of the heating tube, and 140
It is surrounded by a jacket (No. 6) through which steam at ℃ is passed, and the outlet is pressure-sealed by a rotary piston pump (No. 7), and the pipe length is approximately 15 m. The temperature of the wet okara that came out from the outlet was 110°C, and the time it took to pass through the tube was 20 minutes. This wet okara was immediately dried to a moisture content of 30% using a drum dryer (No. 8) (maximum product temperature 90°C), and then further sent to a flash dryer (No. 9) to dry to approximately 6% moisture, resulting in a product. .

[Table] The number of bacteria (cells/g) on okara in each process is as shown in the table, indicating that it has been well sterilized, and the water absorption of dried okara {10g of the product is mixed with 100g of hot water (initially about 100℃)
After 20 minutes, centrifuge at 1000G for 5 minutes in a centrifuge tube equipped with a step with water holes, and measure the separated water (A). (100-A) ÷ 10 } was 4.2 times higher, and the color tone was also good. Comparative example (1) So that the product temperature at the outlet of the heating zone is 125℃,
Dried okara was produced in the same manner as in the example except that the conditions for passing through the heating zone were set, but the water absorption of this product was 2.2 times worse, and the color tone was reddish.
It also had a slight burnt odor. (2) When the same wet okara raw material as in Example was immediately dried to about 6% moisture by air drying alone, the number of viable bacteria was 6 x 10 ⁵ /g. This is sterilized using superheated steam (2Kg/cm ² , 150℃, 5 seconds)
However, 8 x ¹⁰⁴ general viable bacteria/g remained, and there was almost no bactericidal effect. (3) The same wet okara raw material as in the example was heated in boiling water for 20 minutes, dehydrated to 80% moisture, and dried using a drum dryer and flash drying in the same manner as in the example. Although this product had no problem with the number of bacteria, its water absorption was 2.7 times lower.

[Brief explanation of drawings]

The drawings are explanatory diagrams of embodiments of the present invention.

Claims (1)

[Claims] 1. A method for producing dried okara, which comprises forcibly passing wet okara through a pressure-sealed heating zone and then drying it. 2. During passage through the heating zone and during drying, the temperature of the treated article is
The manufacturing method according to claim 1, wherein the temperature is maintained at 120°C or lower. 3 In the heating zone, set the temperature of wet okara to 5~5
The manufacturing method according to claim 2, wherein the temperature is 90°C or higher for 25 minutes.