JPS62205759A - Low-temperature sterilization of grain flour - Google Patents

Abstract

PURPOSE:To obtain a sterilized grain flour at a low temperature in a shot time without deteriorating the quality, by feeding a grain flour to an extruder, keeping the grain flour in a fluidized state, adding ethyl alcohol at the same time, adjusting the material temperature at the outlet and extruding the resultant material while heating. CONSTITUTION:A grain flour, e.g. wheat flour, buckwheat flour, rice flour, corn flour, etc., is fed to a single screw or twin-screw type extruder having, e.g. >=30% opening ratio, and, as necessary, a barrel is heated from the outside by electric heat, high-temperature steam, etc., to rotate the screw at 60-350r.p.m. and keep the flour in a fluidized state. 0.5-5wt% ethyl alcohol is simultaneously added to extrude the resultant material under low moisture condition in a short time while heating to give <=55 deg.C material temperature at the outlet. Sterilization is carried out to afford the aimed low-temperature sterilized grain flour having <=300 general viable cell number.

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.

[Conventional technology]

Traditionally, grain flours such as wheat flour have been commercialized in a dry smoked state, so it is usually impossible to sterilize them. However, various attempts have been made to reduce the number of bacteria in response to consumer requests;
Grain flour, which is a natural agricultural product, is resistant to various types of bacteria called soil bacteria, and it has been extremely difficult to sterilize the product without deteriorating its quality.

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 is little deterioration in the quality of flour, but the sterilization effect is low;
On the other hand, thermal sterilization has a high sterilization effect, but has problems such as significant deterioration of quality.

On the other hand, JP-A-51-15648 discloses a method for improving this problem by adjusting the moisture content before and after treatment in flash drying and/or fluidized bed drying. There is. However, this method requires an extremely high cost in terms of equipment, and due to the retention of some of the flour,
There was also the problem of "burning."

Further, conventionally, wheat flour is continuously heated in a conveyor chamber. The heating method is indirect heating by passing a heat medium through the jacket of the conveyor outer cylinder and stirring blades,
There is a direct heating method in which steam is passed directly into the conveyor chamber. Direct heating has the drawback of causing some lumps and overheating, while indirect heating tends to cause powder adhering to a part of the stirring blade to remain, making the processing time inconsistent and causing the powder to clump from the stirring blade. It has the disadvantage of deteriorating the heat transfer efficiency.

Uneven quenched flour mixed with wheat flour that has been partially overheated by conveyor heating causes the disadvantage of a "sticky" or pasty texture in secondary processed products.

Although the mechanism of improving the secondary processability of wheat flour is not yet clear, in recent years extremely weak changes in starch have been considered important as a factor other than protein denaturation, which has long been considered. For example, there is a theory that cumulative salt treatment has a selective effect on starch over protein denaturation and 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, and mainly consist of oval particles with a major axis of 35 to 40 μm and circular particles with a diameter of 10 to 15 μm. In order to uniformly heat these components, 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.

[Purpose of the invention]

Therefore, the purpose of the present invention is to sterilize starch by heating at low temperature, low moisture, and for a short time while maintaining the quality of flour, and to produce flour with a general viable bacterial count of 300 or less, which is considered to be sterile. The object of the present invention is to provide a method for low-temperature sterilization of flours, which makes it possible to obtain flours of various types.

[Structure of the invention]

As a result of intensive research into the processing of flour using an extruder, the inventor of the present invention found that when the powder is kept in a fluidized state and passed through the extruder, ethyl alcohol is added to the product so that the outlet temperature is 55°C or less. The present inventors have discovered that the above object can be achieved by carrying out a heating extrusion treatment to achieve this, and have completed the present invention.

That is, the present invention provides a flour that is characterized in that the flour is maintained in a fluidized state using extrusion, ethyl alcohol is added, and the flour is heated and extruded so that the outlet temperature is 55°C or less. It is a low temperature sterilization method.

Further, the present invention will be described in detail. The present invention is characterized by keeping the temperature of the heated product as low as possible in order to maintain the quality of the flour and making the sterilization effect effective.

For this reason, we utilize the complementary sterilizing effect of ethyl alcohol,
In addition, by using an extruder, the flour is kept in a fluidized state, and the outlet temperature can be raised to 55°C in a short time under low moisture conditions.
Heat and extrude as follows. 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 heated from the outside with electric heat, high-temperature steam, etc., and the flour is indirectly heated, or the extruder barrel is heated through a vent provided in the extruder barrel. blow heated air,
Methods such as directly heating flour 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 -shaft type or a twin-shaft type, and an orifice die is not particularly required. It is necessary that the ratio of the opening area of the orifice to the area be 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 biaxial 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 suitable for use in the present invention. This is the most suitable device.

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 with a constantly reversing movement, the entire flour is divided into two parts by opposing screw flights while following a gourd trajectory. While being fucked, he is sent to the screenie tip.

Standard twin-screw extruder (double screw L/D=
13) and the number of flights is 24, then 224 divisions = 167
It will be divided into 77216 parts. It is thought that if this and the movement equivalent to rotational movement are added, each shell powder grain almost certainly comes into contact with the heated barrel and is heated uniformly.

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 is 60 to fluidize the powder.
~350 rpm, preferably 150 rpm or more is suitable. Increasing the rotational speed will shorten the residence time. In this case, use a screw with a short flight pitch, or
It is preferable to use a long one.

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, the fluidity will be lost and the heating energy agitation from the barrel will be insufficient, so it is desirable that the amount be 60% or less of the theoretical transfer amount calculated between the screw and barrel space. When processing a large amount, it is desirable to set the temperature higher than the target product temperature.

〔Effect of the invention〕

In general, secondary processed products such as noodles made from grain flour such as wheat flour that has been heat-treated at high temperature and high moisture have a "
However, according to the low-temperature sterilization method of the present invention, the quality of the flour does not deteriorate and the number of viable bacteria is reduced to 3, which is considered to be in a sterile state.
Sterilized powder below 00 can be fG.

Furthermore, when flour is sterilized under sufficiently fluidized conditions, 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 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 twin-screw extruder (manufactured by Toshiba Machine, TEM-50,
Wheat flour was sterilized at various temperatures using a 6 barrel, L/D = 20). For the first school, sterilization was carried out 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 a sterilized powder with a general viable cell count of 300 or less only when an extruder was used and the outlet product temperature was 73°C or higher. In the paddle conveyor, the outlet product temperature is 93
Even at ℃, the number of viable bacteria did not fall below 300 (see Table 1).

Rotation speed 15 orpm, feed ff 145 kg/) (
Example 1 Sterilization was carried out in the same manner as in the comparative example, during which ethyl alcohol was blown in together with the flour.

As a result, we were able to obtain a sterile powder with a general viable cell count of 300 or less even at an outlet temperature of 38°C (see Table 2).

Table 2 Example 2 Various flours were sterilized using an extruder in the same manner as in Example 1. Sterilization treatment for each flour was: no treatment, outlet temperature 75℃, outlet temperature 50℃.
A comparison was made between three types of ethyl alcohol addition at °C (see Table 3).

After sterilization, a noodle making test was conducted using the wheat flour as it was and by mixing the other ingredients with the wheat flour at 50%. The results of the sensory test showed that the product treated at an outlet temperature of 75°C felt slightly sticky.

Table 3

Claims (1)

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