JPH0528096B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a low temperature sterilization method for grain flours such as wheat flour. [Prior Art] Since grain flours such as wheat flour have traditionally been manufactured in a dry state, sterilization is usually not possible. However, various attempts have been made to reduce the number of bacteria in response to consumer requests, but flour, which is a natural agricultural product, has a variety of bacteria called soil bacteria attached to it. This was an extremely difficult task. The heat sterilization method is the most common sterilization technique, and is performed by directly spraying heated air or high-temperature steam onto flour in a fluidized bed or air stream. However, the heating temperature, heating time, and moisture content of flour, which are the main factors that form the heat sterilization effect, are also factors that denature proteins and deteriorate the product. Therefore, it has been desired to develop a sterilization method that prevents deterioration of this product and at the same time has a high sterilization effect. In other words, in the dry heat sterilization method, there was little deterioration in the quality of flour, but the sterilization effect was low, while in the moist heat sterilization method, the sterilization effect was high, but there was a significant deterioration in quality. . On the other hand, JP-A-51-15648 discloses a method for improving this problem by adjusting the moisture content before and after the treatment in the flash drying method and/or fluidized bed drying method. There is. However, this method required an extremely high cost in terms of equipment, and there was also the problem of "burning" due to some of the flour remaining. Further, conventionally, wheat flour is continuously heated in a conveyor chamber. Heating methods include indirect heating in which a heating medium is passed through the jacket and stirring blades of the conveyor outer cylinder, and direct heating in which steam is passed directly into the conveyor chamber. Direct heating has the disadvantage of causing some of the powder to clump and overheating, while indirect heating tends to cause powder adhering to a part of the stirring blade to remain, making the processing time inconsistent.
This has the disadvantage of deteriorating the efficiency of heat transfer from the stirring blade. Uneven quenched flour mixed with wheat flour that has been partially overheated by conveyor heating causes the disadvantages of "sticky" and "sticky" texture in secondary processed products. The mechanism of improving the secondary processability of wheat flour is not yet clear, but it has been thought for a long time.
In recent years, extremely weak changes in starch have been emphasized as a cause other than protein denaturation. For example, chlorination has a selective effect on starch over protein denaturation;
The prevailing theory is that it improves dispersibility, and the improvement in float can be understood as a manifestation of this effect. In order to suppress protein denaturation and cause weak changes in starch during heat treatment, it is desirable to uniformly expose starch granules to heat under conditions that do not cause gluten aggregation, that is, without lumps. It turns out. However,
The thermal conductivity of wheat flour is extremely poor, and in addition, the starch grains in flour are lens-shaped, consisting mainly of oval particles with a major axis of 35 to 40 μm and circular particles with a diameter of 10 to 15 μm. Therefore, in order to uniformly heat these materials, it is considered important to efficiently bring them into contact with the heat transfer surface. In the conveyor heating method, there is a limit to the number of times starch granules can come into contact with the heat transfer surface, and if the stirring blades are devised and the stirring is strengthened, a superheated product with an extremely long residence time will be created. The method of heating wheat flour with an extruder is an extremely effective method because the processing conditions, ie, temperature, moisture, time, etc., can be precisely controlled. [Object of the Invention] Therefore, the object of the present invention is to sterilize flour by heating at low temperature, low moisture, and for a short time while maintaining the quality of the flour, and to reduce the general viable bacterial count to an almost sterile state.
The object of the present invention is to provide a method for low-temperature sterilization of flour, which makes it possible to obtain flour with a bacterial count of 300 or less. [Structure of the Invention] As a result of intensive research into the processing of flour using an extruder, the present invention has been developed to provide a method for keeping the powder in a fluidized state and passing it through the extruder.
The inventors have discovered that the above object can be achieved by adding ethyl alcohol and carrying out heating extrusion treatment such that the outlet temperature is 55° C. or less, and have completed the present invention. That is, the present invention provides low-temperature processing of flour, which is characterized in that flour is maintained in a fluid state using an extruder, ethyl alcohol is added, and heated and extruded so that the exit product temperature is 55°C or less. It is a sterilization method. Further, the present invention will be described in detail. The present invention is characterized by keeping the heating quality as low as possible in order to maintain the quality of flour, and making the sterilization effect effective. For this purpose, we utilize the complementary sterilization effect of ethyl alcohol and use an extruder to maintain the flour in a fluid state and heat extrude it under low moisture conditions and in a short period of time so that the exit quality is below 55℃. do. Ethyl alcohol is preferably added in an amount of 0.5 to 5% by weight, more preferably 1 to 2% by weight, based on the total amount of flour to be treated. If the alcohol content is 5% or more, an alcohol odor remains, which is not preferable. In addition, in order to heat the flour, in the present invention, the extruder barrel is electrically heated from the outside.
Methods such as heating the flour indirectly with high-temperature steam or the like, or directly heating the flour by blowing heated air through a vent provided in the extruder barrel are used. Ethyl alcohol can be added through the inlet along with the flour, or through a vent provided in the barrel. The extruder used in the present invention may be a single-shaft type or a two-shaft type, and an orifice die is not particularly required. It is necessary to make the ratio of the opening area of the orifice to 30% or more, preferably 50% or more. If the open area ratio is less than 30%, the desired fluidized state of the flour cannot be achieved. The two-shaft fully interlocking directional rotating extruder, which has recently been developed in the field of plastics industry, is characterized by an extremely weak calendering effect (shearing force) and self-cleaning effect, and also has a good mixing effect, making it the most suitable for use in the present invention. It is a device that has In order to keep the flour in a fluidized state, it is necessary to increase the number of revolutions of the screw. When using a twin-screw extruder, this fluidized flour slows down inside the extruder due to the contact resistance of the barrel surface, and the screw flights that face each other move in a constant reversing motion while drawing a circular trajectory. It is divided into two parts and sent to the tip of the screw. If the number of flights is 24 with a standard twin-screw extruder (double thread L/D = 13), then 2 ²⁴ divisions =
It will be divided into 16777216. It is thought that if this and the movement equivalent to rotational movement are added, each grain of flour almost certainly comes into contact with the heated barrel and is heated evenly. Although heating by the extruder of the present invention is a short-time process, it is characterized by the fact that there are many opportunities for contact with the outer peripheral barrel due to the mixing effect. The rotation speed should be 60 to 350 rpm, preferably to fluidize the powder.
150rpm or more is appropriate. Increasing the rotational speed will shorten the residence time. In this case, it is desirable to use a screw with a short flight pitch or a screw with a long L/D. The intensity of heat treatment is indicated by the treatment temperature and average residence time, but when L/D is short, the degree of heat treatment can be determined by the exit temperature of the product. If L/D is long, the outlet temperature will be almost the same as the barrel set temperature. If the throughput is increased, fluidity will be lost and the amount of heating energy from the barrel will be insufficient, so 60% of the theoretical transfer amount calculated by the screw and barrel space.
It is desirable to do the following. When processing a large amount, it is desirable to set the temperature higher than the desired quality. [Effect of the invention] Generally, secondary processed products such as noodles produced using grain flour such as wheat flour that has been heat-treated at high temperature and high moisture have drawbacks such as "stickiness" and "stickiness" in texture. However, according to the low temperature sterilization method of the present invention,
It is possible to obtain a sterilization method in which the number of viable bacteria is generally 300 or less, which is considered to be almost sterile, without causing any deterioration in the quality of the flour. In addition, sterilization of flour under sufficiently fluidized conditions is
Compared to other methods, such as paddle conveyor heat sterilization, the heating time is extremely shortened to reach a predetermined temperature, and the sterilization effect is also extremely significant. The powder is transported almost uniformly, and the residence time distribution is narrow. There are no lumps in the product, and there is very little deterioration in quality, which is undetectable even in secondary processed products. [Example] Comparative example Biaxial extruder (manufactured by Toshiba Machine; TEM
-50, 6 barrels, L/D=20), the flour was sterilized at various temperatures. For comparison, sterilization was performed using a paddle conveyor.
The treated powder was used to measure the number of general viable bacteria and the number of heat-resistant bacteria using a planar culture method. It was possible to obtain sterile powder with a general bacteria count of 300 or less using an extruder, which had an outlet temperature of 73.
This was only the case when the temperature was above ℃. With a paddle conveyor, even when the outlet temperature is 93°C, the general number of viable bacteria is 300.
(See Table 1)

[Table] Example 1 Sterilization was performed in the same manner as in the comparative example, and ethyl alcohol was blown into the flour together with the flour. As a result, it was possible to obtain a sterile powder with a general viable cell count of 300 or less even at an outlet quality of 38°C (see Table 2).

[Table] Example 2 Various flours were sterilized using an extruder in the same manner as in Example 1. Sterilization treatment is for each flour, no treatment, exit temperature.
Add ethyl alcohol at 75℃ and outlet temperature 50℃.
We compared the types (see Table 3). After sterilization, a noodle-making test was conducted using wheat flour as it was and other ingredients mixed at 50% with wheat flour. The results of the sensory test showed that the product treated at an outlet temperature of 75°C had a slight stickiness.

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【table】

Claims (1)

[Claims] 1. A low-temperature sterilization method for flour, which is characterized by maintaining flour in a fluidized state using an extruder, adding ethyl alcohol, and performing heating extrusion treatment so that the outlet temperature is 55°C or less.