JPH0520060B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention comprises a wall portion that is easily permanently deformed during heat sterilization treatment and is filled and sealed with a liquid food such as curry, leaving a head space. The present invention also relates to a method of sterilizing a sealed container having self-shape retaining properties in a rotary pressure heating sterilization cauldron.

(Prior Art) Pressure and heat sterilization treatment of foods packed in relatively large sealed containers, so-called retort sterilization treatment, takes a relatively long time and is therefore likely to cause quality deterioration of the food contents. Therefore, conventionally, for the sterilization of relatively large cans (for example, No. 1 cans) filled with liquid foods, a rotary pressurized heat sterilization pot, which requires a relatively short heat sterilization time, has been preferably used. was.

However, for sealed containers that are self-retaining and have relatively low rigidity walls that are prone to permanent deformation during heat sterilization, and are filled with liquid food with a head space left, rotary processing is not recommended. A pressure-heating sterilization kettle has not been used in the past.

The reason may be as follows. When heat sterilization is performed in a pressurized heat sterilization pot, if there is a difference between the internal pressure of the container and the pressure inside the sterilization pot, permanent deformation occurs in a convex or concave shape on the wall, which has relatively low rigidity, and the product value is lost. Particularly when this pressure difference is large, problems such as the heat-sealed portion peeling off and loss of sealing performance, or in extreme cases, the wall portion rupturing, are likely to occur.

To prevent such troubles, the pressure difference between the internal pressure of the sealed container and the internal pressure of the sterilization pot must be reduced to virtually no, or normally this pressure difference must be reduced to approximately 0.3 kg/cm ^2.
It is necessary to heat sterilize while keeping the temperature within the range.

However, in the case of a rotary pressurized heat sterilization kettle, since the sealed container revolves around the axis of the kettle, it is practically difficult to control the pressure as described above. For example, a viewing window may be installed in the sterilization pot, and workers can observe slight deformations such as dents and bulges in the wall through the viewing window, and make sure that these deformations are corrected and the wall returns to its normal shape. To,
One possible method is to control the pressure in the sterilization pot. However, since the container is rotating, it is difficult to visually detect slight deformation of the wall, and even if it is possible, the operator will be extremely fatigued, making it difficult to use in actual work.

(Problems to be Solved by the Invention) The present invention provides a self-shape-retaining seal that is filled with a liquid food leaving a head space, has a wall portion that is susceptible to permanent deformation during pressure and heat sterilization treatment, and has a self-shape retention property. The pressure difference between the container internal pressure and the sterilization pot internal pressure,
The purpose of the present invention is to provide a heating sterilization method for sealed containers that can be sterilized in a rotary pressurized heating sterilization pot under automatic control to the extent that permanent deformation or rupture of the wall does not occur. .

(Means for Solving the Problems) The present invention provides a self-shape-retaining hermetic seal that is filled with a liquid food leaving a head space, has a wall portion that is susceptible to permanent deformation during pressurized heat sterilization treatment, and has a self-shape retaining property. A method of sterilizing a container in a rotary pressure heating sterilization pot, in which a sample container similar to the sealed container except that water is filled instead of the liquid food is placed in the sterilization pot together with the sealed container. During the period when the medium temperature Tr in the sterilization pot is equal to or higher than the temperature Tw of the water in the sample container, the pressure in the sterilization pot is kept at the temperature Tw of the water in the sample container. so that the pressure is substantially equal to the sum of the air partial pressure Pa in the headspace and the saturated vapor pressure Pw of water.
and the medium temperature Tr is the temperature of the water in the sample container.
During the period lower than Tw, the air partial pressure Pa in the head space and the saturated vapor pressure of water at the medium temperature Tr are
The present invention provides a method for heat sterilizing a sealed container, which is characterized by controlling the pressure to be substantially equal to the sum of Pw.

In this specification, liquid food refers to food that is liquid at room temperature or heat sterilization temperature and easily flows in the container as the container rotates (revolutions) in the sterilization pot, and refers to cooked food consisting only of liquid or It is a cooked food that is a solid-liquid mixture (the solid is usually in the form of pieces, small particles, dice, etc.) and contains water. Examples of liquid foods include soup, jelly, stew, white sauce, curry, and sweet corn (whole kernel or cream style).

In addition to the body wall, the wall includes a lid, a bottom wall, and the like. A self-shape-retaining sealed container with a wall that is susceptible to permanent deformation during heat sterilization may be a cup made of a relatively thin plastic sheet or a laminate of plastic film and metal foil. A molded container in which a lid made of plastic film or a flexible laminate containing plastic film and metal foil is heat-sealed to the flange of the container body, or a plastic container having a body wall with relatively low rigidity. Examples include bottles, drawn and ironed cans, and the like. Although a relatively large sealed container is preferably applied to the present invention, a relatively small sealed container may also be used.

(Function) In the rotary pressure heating sterilization, liquid food 12
The sealed container 10 containing the shaft 9a (see Fig. 2)
Rotation (revolution) around the axis of as shown in Figure 1 a
As a result, the food 12 is fluidized and agitated, and the main wall portions in contact with the head space 10c change continuously to include a lid portion 10b, a body portion 10d, a bottom portion 10e, and a body portion 10d. A thin layer 12a of the liquid food 12 is formed inside the wall portion in contact with the head space 10c.

Heating period of liquid food 12, i.e. TrT _F
(T _W ) (see Figure 4, period up to time t ₂ )
The temperature of this thin layer 12a is higher than that of the center of the liquid food 12 where the temperature sensor 31 is inserted (in this specification, the position corresponding to the center of the erect state is referred to as the center). Therefore, the internal pressure in the head space 10c is equal to the saturated vapor pressure P _W of water in the thin layer 12a and the partial pressure of air in the head space 10c.
It is considered to be approximately equal to the sum P ₁ (see Figure 3) of P _a .

As shown in FIG. 1b, the sample container 14 also rotates in the same manner as the sealed container 10, and the lid part 14b,
Head space 14 including trunk 14d, bottom 14e, etc.
A thin layer 13a of water 13 is placed inside the wall portion in contact with c.
is formed. In this case as well, the thin layer 13a is heated faster than the center of the water, but since the water 13 has low viscosity and is constantly being fluidized and stirred (the water in the thin layer 13a moves to the main body of water, Water is a thin layer 1
(repeat the process of moving into layer 3a), thin layer 1
It is considered that the temperature of 3 a is substantially equal to the temperature of water 13 , that is, the temperature of temperature sensor 16 .

However, the temperature of the water in the thin layer 12a of the liquid food product 12 is considered to be substantially equal to the temperature of the thin layer 13a of water in the sample container 14, and thus the temperature of the water 13. Also, the head space 10 of the sealed container 10
It is considered that the average temperature within c can be approximately approximated to the temperature of the thin layer 12a and therefore the temperature of the water 13 in the sample container 14. Therefore, the internal pressure of the sealed container 10 during this period is considered to be approximately equal to the sum P ₁ of the air partial pressure P _a in the head space and the saturated vapor pressure P _W of water at the temperature of the water 13 in the sample container 14 .

When the liquid food 12 enters the cooling period and T _r <T _W , the head space 10c of the sealed container 10
The temperature of the wall part in contact with is the medium (cooling water) temperature.
The temperature of the head space 10c approaches T _r and becomes lower than the temperature of the nearby head space.
The water vapor in the head space 10c condenses into a thin layer 12a, reducing the saturated water vapor pressure, and the saturated water vapor pressure in the head space 10c is dominated by the medium temperature T _r . Similarly, the air partial pressure in the head space 10c is approximated by the medium temperature T _r . Therefore, the internal pressure of the sealed container 10 during this period is equal to the medium (cooling water) temperature T _r
It is considered to be approximately equal to the sum P ₂ of the air partial pressure P _a in the headspace and the saturated vapor pressure P _W of water.

Therefore, the period of time T _r T _W for the pressure inside the sterilization pot 1 is substantially equal to the sum P ₁ of the air partial pressure P _a in the head space and the saturated vapor pressure P _W of water at the temperature of the water 13 in the sample container 14. and during the period T _r <T _W , the pressure P ₂ is substantially equal to the sum of the air partial pressure P _a in the headspace and the saturated vapor pressure P _W of water at the medium temperature T _r . By controlling the pressure so as to achieve so-called equal pressure control, it is possible to prevent troubles such as permanent deformation and rupture of the wall of the sealed container 10 from occurring.

(Example) In Fig. 2, 1 is a hot water type rotary pressure heating sterilization pot (so-called rotary retort), in which hot water 3 sent from a hot water tank 2 is stored leaving a space 4. has been done. 5 is a pressurized air pipe for raising the air pressure in the space 4 to a predetermined pressure; 6 is a steam pipe for raising the temperature of the hot water 3 during the heating period and maintaining a predetermined sterilization temperature; 7 is a steam pipe for raising the temperature of the hot water 3 during the heating period; hot water 3
This is a cooling water pipe for lowering the temperature during the cooling period. Further, 8 is an exhaust pipe for reducing the pressure in the space 4. The hot water 3 is circulated during operation through a circulation system (not shown) so that the temperature distribution in the sterilization pot 1 is uniform.

Reference numeral 9 denotes a rotating drum for storing baskets 11, each of which includes sealed containers 10 (not shown, but in large numbers) filled with liquid food 12;
and one sample container 1 filled with water 13
4 are stored. The rotating drum 9 is rotated in a fixed direction or alternately left and right (usually 1 to 30 rpm) by a gear 9b and a shaft 9a that mesh with a gear 9c provided in a drive mechanism (not shown).
Thus, the sealed container 10 and the sample container 14 are configured to rotate (revolution) around the axis of the shaft 9a.

15 is a temperature sensor for measuring the temperature (i.e., medium temperature) of the hot water 3 and cooling water 30 (described later), and 16 is attached to the sample container 14 so as to be able to measure the temperature of the center of the water 13 in an upright state. temperature sensor. The output of the temperature sensor 15 (usually on the order of mv) is input to the amplifier 17a, and the output of the temperature sensor 16 is passed through the shaft 9a.
The signal is inputted to the amplifier 17b via the slip ring mechanism 19. Note that 19a is a slip ring, 19b
is a fixed ring. Amplifiers 17a and 17b
The output is input to the programmable arithmetic unit 20.

The computing unit 20 compares the medium temperature (T _r ) with the center temperature (T _W ) of the water 13 in the sample container 14 and calculates that when T _r T _W , that is, the output of the sensor 15 is higher than the output of the sensor 16. In this case, output the sum P ₁ (voltage conversion value) of the saturated vapor pressure of water P _W and the headspace air partial pressure P _a at T _W from Fig. 3 (this figure will be explained later), and find that T _r < When T _W , that is, when the output of the temperature sensor 15 is smaller than the output of the temperature sensor ₁₆ , from _{FIG .}
A program that instructs to output P ₂ (voltage conversion value) is input from the programmer 21.

The output from the calculator 20 is input to the current-air pressure converter 22 via a signal converter (not shown) and is converted into an air signal. The output of the converter 22 is input to the pressure controller 23, and the pressure controller 23 opens and closes the control valve 25 provided in the pressurized air piping 5, so that the pressure inside the sterilization pot 1 is adjusted to the above P ₁
It is also controlled to be equal to P ₂ .

Figure 3 shows the temperature T _r or T _W , the headspace air partial pressure (P _a curve), and the saturated vapor pressure of water (P _W curve) when the sample container 14 is filled with water 13 at 20°C and sealed. ). The P _a curve was created by calculation based on the Boyle-Schard law, assuming that the influence of thermal expansion of water can be ignored.

The sealed container 10 has a cup-shaped container body 10a.
It has a lid part 10b heat-sealed to its flange part 10a ₁ (see Figure 1), and has a head space 10c inside (approximately 10
~40% by volume), the liquid food product 12 is filled and sealed at 20° C. in this example.

The container main body 10a has a self-shape retaining property at room temperature, but is composed of a wall portion that is susceptible to permanent deformation due to external pressure or internal pressure during heat sterilization treatment. i.e. relatively thin, e.g. about 0.4 to 1.0 thick
mm, polypropylene sheet, or a plastic laminate sheet such as a 5-layer laminate of polypropylene-carboxylic acid-modified polypropylene-ethylene/hynyl alcohol copolymer-carboxylic acid-modified polypropylene-polypropylene, or polyolefin (e.g. polypropylene)-adhesive It is formed by vacuum forming, press forming, etc., a laminate consisting of an agent layer (eg, polyurethane-based) and metal foil (eg, aluminum foil), or a blank consisting of a single metal foil.
The lid portion 10b is also made of the above-mentioned material.

In the case of this embodiment, one of the sealed containers 10 is equipped with a temperature sensor 3 capable of measuring the temperature at the center of the liquid food 12.
1 is inserted, and its output is recorded via a slip ring mechanism 19 on a temperature recorder (not shown) for setting sterilization conditions. In the case of actual work, since the sterilization conditions have already been set, it is not necessarily necessary to insert the temperature sensor 31.

The container body 14a and the lid part 14b (see FIG. 1b) of the sample container 14 are respectively connected to the sealed container 1.
It is formed from the same material as the container body 10a and lid portion 10b of No. 0. The volume of the head space 14c (FIG. 1b) of the sample container 14 is also equal to that of the head space 10c of the sealed container 10.

Using the above-described apparatus, heat sterilization of the liquid food 12 in the sealed container 10 is carried out as follows.

The basket 11 containing one sample container 14 and a large number of sealed containers 10 is loaded into the rotating drum 9 of the rotary pressure heating sterilization pot 1, and the temperature sensor 1
6 and 31 are connected to the slip ring 19a.

Next, the hot water supply valve 33 is opened, hot water 3 is supplied from the hot water tank 2 to the sterilizing pot 1 to a predetermined level, and the rotary drum 9 is rotated at a predetermined number of rotations. Thereafter, the on-off valve 28 of the steam pipe 6 is opened, and steam is sent to sterilize the hot water 3 at a temperature T _rn (maximum temperature of T _r ;
(see figure). When the hot water temperature reaches _Trn , the on-off valve 27 is opened and closed to control the temperature. After the hot water is delivered, a circulation pump (not shown) is operated to circulate the hot water 3 through the sterilization pot 1 through a circulation system (not shown). During this time, the level of the hot water 3 is maintained at a predetermined level above the basket 11.

As shown in FIG. 1, the sealed container 10 revolves around the axis of the shaft 9a as the rotating drum 9 rotates, and the liquid food 12 therein is heated while being fluidized and stirred. The temperature at the center of the liquid food 12 (the temperature measured by the temperature sensor 31) rises, and the predetermined sterilization value F ₀
When the time t ₂ (see Fig. 4; the time t ₂ when the temperature sensor 31 is not inserted into one of the sealed containers is determined in advance by experiment) is reached, the on-off valve 2 is closed.
8, open the on-off valve 26 of the cooling water pipe 7 to feed the cooling water 30, and mix it with the hot water 3 (while returning the hot water 3 to the hot water tank 2).
Cooling.

An example of the heating/cooling cycle during this period is shown in FIG. The temperature T _F of the liquid food 12 in the sealed container 10 is based on the temperature sensor 31;
The reason why T _F rises slower than temperature T _W is because the liquid food 12 has a higher viscosity than water 13, so the heat transfer from the container wall to the inside of the food due to rotational stirring is smaller than in the case of water. This is thought to be due to this. Also, the reason why the temperature T _F rise curve is wavy is probably because the temperature of the contents is not uniform, so that high and low temperature areas hit the sensor due to rotation.

In this way, the temperature T _F rises more slowly than the temperature T _W , so at the time t ₁ when the temperature T _W reaches the heat sterilization temperature T _rn , the temperature T _F has not yet reached T _rn . Time t ₂
Until then, T _r T _W , but after time t ₂ , the decrease in temperature T _W lags behind that of temperature T _r and becomes T _r < T _W.
The drop in temperature T _F is even later than that in temperature T _W
T _W < T _F.

In order to prevent permanent deformation of the container wall due to the pressure difference between the inside and outside of the sealed container 10 during this heating and cooling period, during this period, using the programmable calculator 20 and the pressure controller 23, according to the method described above,
The pressure inside the sterilization pot 1 is adjusted by adjusting the amount of air fed into the sterilization pot 1 and the amount of exhaust air sent out from the sterilization pot 1. After the liquid food 12 in the sealed container 10 has been cooled to a predetermined temperature, the sterilization pot 1 is opened and the sealed container 10 and sample container 14 are taken out.

The present invention is not limited to the above examples; for example, the filling and sealing of the liquid food 12 and water 13 may be performed at a temperature other than 20°C, for example 50°C. However, in this case, the temperature of the head space is
If it can be considered as 50℃, then the sum P ₁ of saturated vapor pressure P _W and air partial pressure P _a at 50℃ is 1 atm.
It is necessary to shift the position of the air partial pressure straight line P _a in FIG. 3 to the P _a ' line.

The sealed container may also be a relatively thin-walled plastic bottle sealed. Furthermore, a steam-air type pressurized heat sterilization kettle may be used.

Furthermore, the temperature sensor 16 inside the sample container 14 is
It may be located at an appropriate position within the water 13. This is because there is almost no difference in the temperature of the water 13 depending on the location due to the rotation.

A specific example will be explained below.

Internal volume from 1.0mm thick polypropylene sheet
A cup-shaped container body 10a of 200 c.c. is formed, and 20
After filling the curry 12 with a head space 10c of 50 cc at a temperature of 10.degree. C., the lid 10b was heat-sealed to the flange _10a1 to produce a sealed container 10. Note that the inner layer of the lid portion 10b has a thickness of
70μm polypropylene film, middle layer thickness
It was formed from a laminate consisting of a 9 μm aluminum foil and an outer layer of a 12 μm thick polyester film. In this case, the lid portion 10b is more easily deformed than the container body 10a.

A sample container 14 was prepared in the same manner as described above except that water 13 was filled.

Temperature sensors 16 and 31 each consisting of a thermocouple are installed in the center of the water 13 and curry 12 for each of the sample container 14 and the sealed container 10.
was attached, and the space between the temperature sensors 16, 31 and the container wall was sealed with an attachment.

After placing 800 of the above sample containers 14 and sealed containers 10 with temperature sensors, as well as ordinary similar sealed containers 10 to which no temperature sensor can be attached, in the basket 11, hot water pressure heating of the type shown in FIG. 2 is carried out. It was placed in a sterilized pot, and the sensors 16 and 31 were connected to the slip ring 19a.

Next, after feeding the hot water 3 from the hot water tank 2 to the sterilizing pot 1, while rotating the rotary drum 9 at a speed of 10 times per minute, the valve 28 of the steam pipe 6 is opened to send steam and heat the water. Water 3 was heated to 120°C.

After the water temperature in the sample container 14 and the curry temperature in the sealed container 10 reach 120°C and the curry sterilization value F ₀ is satisfied, the valve 28 is closed and the valve 26 is opened to supply cooling water, and until then, was replaced with hot water. The heating and cooling cycle at this time is shown in FIG. During this time, the pressure inside the sterilization pot was controlled to be equal to the pressure as shown in the example.

During operation, the nearest sealed container 1 is
Deformation of the lid portion 10b of 0A was observed using a special device, but almost no deformation was observed. After the temperature of the curry 12 reached approximately 30°C, the sterilization pot was opened and the sealed containers 10 were taken out, but no abnormality such as deformation was observed in all of them.

For comparison, heating and cooling were performed in the same manner as described above, except that the output of the temperature sensor 31 inside the sealed container 10 was input to the amplifier 17a (the output of the temperature sensor 16 was not input to the amplifier 17a). In this case, it is thought that the internal pressure of the container became much lower than the sterilization pot pressure during the heating period, and conversely increased during the cooling period, but for all the sealed containers 10,
Deformation of the wall (such as a bulge in the bottom or a dent in the body) occurred.

The circle dots in FIG. 5 indicate the container internal pressure calculated according to the method of the present invention described above for the heating/cooling cycle shown in FIG. On the other hand, the solid line curve indicates that when the lid part 10b is observed through the viewing window when the sealed container 10A is sterilized in the above cycle,
This figure shows the temporal fluctuation of the pressure in the sterilization pot when it is manually adjusted to prevent the deformation. It can be seen that the two are in good agreement.

(Effects of the Invention) The heat sterilization method for a sealed container of the present invention has a wall portion that is filled with a liquid food leaving a head space and is easily permanently deformed during pressurized heat sterilization treatment, and is self-shape-retaining. It is possible to sterilize a sealed container with a rotary pressurized heat sterilizer by automatically controlling the pressure difference between the internal pressure of the container and the internal pressure of the sterilizer to a small level that does not cause permanent deformation or rupture of the wall. This effect is achieved. Since rotary pressure heat sterilization can be performed in this manner, it has the advantage that sterilization time can be shortened and high quality so-called retort sterilized foods can be obtained.

[Brief explanation of drawings]

Figures 1a and b are explanatory longitudinal cross-sectional views showing the state in which a sealed container and a sample container are rotated in the method of the present invention, respectively, and Figure 2 is an explanatory drawing showing an example of an apparatus for carrying out the present invention. , Figure 3 is a diagram showing an example of the relationship between air partial pressure and saturated water vapor pressure in the head space of the container and temperature.
The figure is a diagram showing an example of the relationship between the medium temperature in the rotary pressurized heat sterilization pot, the water temperature in the sample container, and the temperature at the center of the liquid food in the sealed container. FIG. 3 is a diagram showing the relationship between the calculated internal pressure of the sealed container and the sterilization pot pressure at which no deformation occurs in the sealed container and time. 1... Rotary pressure heating sterilization pot, 3... Hot water (medium),
10... Sealed container, 10b... Lid part (wall part), 10c
...Head space, 10d...Body (wall), 10
e...bottom (wall), 12...liquid food, 13...water,
14...Sample container, 30...Cooling water (medium).

Claims (1)

[Claims] 1. A closed container that is filled with liquid food leaving a head space, has a wall that is susceptible to permanent deformation during pressure and heat sterilization treatment, and has self-shape properties, is placed in a rotary pressure and heat sterilization pot. In this sterilization method, a sample container similar to the sealed container except that water is filled instead of the liquid food is stored in the sterilization pot together with the sealed container, and the pressure inside the sterilization pot is reduced. , during the period when the medium temperature Tr in the sterilization pot is higher than the temperature Tw of the water in the sample container, the air partial pressure Pa in the head space and the saturated vapor of water at the temperature Tw of the water in the sample container so that the pressure is substantially equal to the sum of the pressures Pw, and the medium temperature
During the period when Tr is lower than the temperature Tw of the water in the sample container, the pressure is substantially equal to the sum of the air partial pressure Pa and the saturated vapor pressure Pw of water in the headspace at the medium temperature Tr. A method of heat sterilization of a sealed container characterized by controlling.