JP4762928B2 - Heat treatment method for liquid egg - Google Patents

Description

  The present invention relates to a heat treatment technique for a liquid egg in which the liquid egg is heat sterilized by energization heating using Joule heat.

  Liquid eggs used as food for cooking include liquid egg yolk only of egg yolk, liquid egg white only of egg white, and liquid whole egg in which egg white and egg yolk are mixed, and each is heat-sterilized and commercialized. Liquid whole eggs are produced by heat treatment at 60 ° C. for 3.5 minutes or more, and liquid egg white is produced by heat treatment at 55.5 ° C. for 3.5 minutes or more. The liquid egg yolk is commercialized by heat treatment at 61 ° C. for 3.5 minutes or more. Such sterilization conditions are determined by the standard of food and additives based on the Food Sanitation Law.

  Conventionally, a plate-type heat exchanger is used to heat and sterilize the liquid egg, and hot water is supplied by supplying the liquid egg contained in the container to the heat exchanger with a liquid feed pump. The liquid egg is heated by a heat exchanger as a heating medium. However, if the liquid egg is heat sterilized using a heat exchanger, the deposits due to thermal denaturation of the liquid egg adhere to the heat transfer surface of the plate as a scale, so that heat sterilization can be performed continuously. Is limited to about 4 hours, and after performing a predetermined continuous operation, a great amount of time is required for the cleaning process for cleaning the heat exchanger. The reason why the scale adheres to the heat transfer surface when the liquid egg is heated by the heat exchanger in this way is to supply the heat to the heat exchanger in order to heat the liquid egg by heat transfer from the heating medium through the plate. This is because the temperature of the medium needs to be set higher than the heat sterilization temperature of the liquid egg, so that the liquid egg in contact with the heat transfer surface is heated to a temperature causing thermal denaturation.

Patent Documents 1 and 2 describe a heat sterilization apparatus that heats and sterilizes a liquid egg by energizing the liquid egg. By supplying food and drink having fluidity such as juice and soup to the Joule heat. Patent Document 3 describes a technique for heating.
JP-A-6-319499 JP 2004-337020 A JP 2006-320402 A

  The heat sterilization apparatus described in Patent Documents 1 and 2 stirs the liquid egg with an electrode for energizing the liquid egg in a state where the liquid egg is contained in the container, or the electrode and the liquid egg. The heat treatment is a batch type. Patent Document 3 discloses a heating device that continuously heats food and drink, which is an object to be heated. If a liquid egg can be heated by such a continuous Joule heating device, it is efficient. It becomes possible to heat sterilize the liquid egg.

  In order to efficiently heat sterilize liquid eggs, the inventor tried to heat sterilize continuously with a heating device while flowing the liquid eggs in the flow path of the tube in the same manner as juice and soup. As in the case of using, the precipitates resulting from the thermal denaturation of the liquid eggs adhered to the inner surface of the tube provided with the electrodes as scales, and the inner surface of the tube had to be washed frequently. When a fluid object to be heated such as a liquid egg flows in the flow path and energized to heat the object to be heated by Joule heat, the heating status includes the power density, the viscosity of the object to be heated, and the flow. It will vary greatly depending on multiple factors such as the flow velocity in the road.

  Therefore, various experiments were conducted to continuously heat sterilize the liquid egg while changing these multiple factors, and the relationship between the Reynolds number of the liquid egg flowing in the flow path and the power density was constant. It has been found that when the liquid egg is heated to a range, the liquid egg can be heated to a desired sterilization temperature without any scale adhering to the inner surface of the tube.

  An object of the present invention is to enable heating to a desired sterilization temperature by Joule heat while flowing a liquid egg in a flow path.

  An object of the present invention is to allow a liquid egg to be heated continuously over a long period of time without a scale adhering to the inner surface of a tube forming a flow path through which the liquid egg flows.

The liquid egg heat treatment method of the present invention is a liquid egg heat treatment method in which the liquid egg is sterilized and heated by Joule heat while continuously transporting the liquid egg into the flow path as an object to be heated. The heating unit having a tubular member formed with the above-mentioned flow path and having a pair of electrodes provided to the heating unit has a power density P in the flow path according to the Reynolds number Re of the liquid egg flowing in the flow path. (KW / m ³ ) is set to a value of P ≦ 9.4Re−352.4 and the liquid egg is heated to the sterilization heating temperature, and the liquid egg heated to the sterilization temperature by the heating unit is the liquid egg holding unit. And a cooling step of cooling the liquid egg conveyed from the liquid egg holding unit by a cooling unit. The heat treatment method for stationery according to the present invention includes a preheating step of heating the liquid egg to a preheating temperature lower than the sterilization temperature before flowing into the heating unit. The liquid egg heat treatment method of the present invention is characterized in that the liquid egg is a liquid whole egg, a liquid egg white, or a liquid egg yolk.

  According to the present invention, the scale is formed on the inner surface of the tube forming the flow path by setting the power density P in the flow path within a specific range according to the Reynolds number Re of the liquid egg flowing in the flow path of the heating unit. The liquid egg can be continuously heated for a long time without adhering, and the liquid egg can be sterilized continuously while flowing the liquid egg into the flow path. Since sterilization heating can be performed continuously by heat sterilization, not by batch processing, by joule heating of liquid eggs, liquid eggs can be processed efficiently.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view showing a liquid egg heat treatment apparatus according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing the heating unit shown in FIG.

  The liquid egg to be sterilized by heating is accommodated in the container 10, and the liquid egg accommodated in the container 10 is supplied to the heat exchanger 12 by the liquid feed pump 11. The heat exchanger 12 includes a preheating unit 12a, a cooling unit 12b, and a saving unit 12c disposed therebetween, and these units are combined to form the heat exchanger 12. The liquid egg discharged from the liquid feed pump 11 is supplied to the preheating unit 12a through the communication pipe 13 via the saving unit 12c. The preheating unit 12a includes a liquid egg flow path and a hot water supply unit through which the liquid egg flows. 14 through which the preheating medium flows. These flow paths are partitioned by plates, and the liquid egg is preheated by the preheating medium circulating in the medium flow path.

  The liquid egg heated to the preheating temperature by the preheating unit 12a is supplied to the heating unit 16 through the supply pipe 15, and the heat treatment apparatus shown in FIG. 1 includes five heating units 16 connected in series. Have.

  FIG. 2 is an enlarged cross-sectional view showing the heating unit 16, and the heating unit 16 has a heating pipe having a circular cross section, that is, a tubular member 22, in which a flow path 21 for guiding the liquid egg is formed. The tubular member 22 is composed of seven ring-shaped electrodes 23 and six cylindrical bodies 24 disposed therebetween. As described above, the heating unit 16 includes the tubular member 22 including the plurality of electrodes 23 and the plurality of cylindrical bodies 24, and the adjacent electrodes 23 are provided in pairs on the tubular member 22. Each electrode 23 is formed of a conductor such as titanium, and each cylindrical body 24 is formed of an insulator such as resin. At both ends of the tubular member 22, inflow and outflow side joint portions 25 and 26 made of an insulator are attached. A power supply unit 27 is connected to each electrode 23 via a cable, and a high frequency current is supplied from the power supply unit 27 so that the pair of electrodes 23 adjacent to each other in the flowing direction of the liquid egg have opposite polarities. Is done. In addition, the number of the electrodes 23 provided in the heating unit 16 is arbitrarily set according to the heating temperature or the like.

  As shown in FIG. 1, the liquid egg that has passed through all the heating units 16 and has been heated to a predetermined sterilization temperature is supplied to the liquid egg holding unit 31 through the communication pipe 17. The liquid egg holding unit 31 is formed by a pipe covered with a heat insulating material, and is long enough to hold the liquid egg heated to the sterilization temperature at the sterilization temperature for a predetermined time, for example, 3.5 minutes or more. Have The liquid egg that has passed through the liquid egg holding unit 31 is supplied to the saving unit 12 c through the communication pipe 18.

  The saving unit 12c has a liquid egg flow path through which the liquid egg before heating supplied by the communication pipe 13 flows, and a liquid egg flow path through which the heated liquid egg that has passed through the liquid egg holding unit 31 by the communication pipe 18 flows. These flow paths are partitioned by plates, and the unheated liquid eggs supplied from the saving unit 12 c to the preheating unit 12 a are heated by the heated liquid eggs that have passed through the liquid egg holding unit 31. Thereby, the thermal energy of the liquid egg after heating is transmitted to the liquid egg before heating, so that the thermal energy is saved.

  The cooling unit 12b has a liquid egg flow path through which the liquid egg that has passed through the saving unit 12c flows and a cooling medium flow path through which the cooling liquid supplied from the cooling water supply unit 32 flows. These flow paths are partitioned by a plate. The liquid egg is cooled to a temperature of 10 ° C. or lower by the cooling liquid circulating in the cooling medium flow path. The liquid egg that has passed through the cooling unit 12 b is discharged into the collection container 20 through the discharge pipe 19.

  FIG. 3 is a block diagram showing a control unit of the liquid egg heat treatment apparatus shown in FIG. 1. The electric motor 33 that drives the liquid feed pump 11 and the power supply unit 27 of each heating unit 16 are controlled by the controller 34. A signal is sent, and a control signal is also sent to an electric motor (not shown) of a pump provided in the hot water supply unit 14 and the cooling water supply unit 32. An operation panel 35 is connected to the controller 34, and operating conditions such as the number of revolutions of the liquid feeding pump 11 can be input by operating keys on the operation panel 35. As shown in FIG. 1, the controller 34 detects the temperature of the liquid egg flowing into the liquid egg holding unit 31 and the temperature sensor S <b> 1 for detecting the temperature of the liquid egg entering the heating unit 16 on the most upstream side. Temperature sensor S2, temperature sensor S3 for detecting the temperature of the liquid egg flowing out from the liquid egg holding unit 31, temperature sensor S4 for detecting the temperature of the liquid egg that has passed through the cooling unit 12b, and liquid feeding Each detection signal of the flow sensor F for detecting the discharge flow rate of the liquid egg from the pump 11 is sent.

  In the heat treatment apparatus for liquid eggs of the present invention, the liquid eggs sent by the liquid feed pump 11 are heated to a temperature about 10 ° C. lower than the sterilization temperature by the saving unit 12c and the preheating unit 12a. For example, when liquid whole eggs are sterilized by heating, the whole liquid eggs are preheated to a temperature lower by about 10 ° C. than the sterilization temperature of 60 ° C., and when liquid egg whites are sterilized by heat, the liquid egg whites are sterilized at the sterilization temperature. Preheat to about 10 ° C lower than 55.5 ° C. Similarly, when liquid egg yolk is sterilized by heating, the liquid egg yolk is preheated to a temperature about 10 ° C. lower than its sterilization temperature 61 ° C.

  As shown in FIG. 1, in the heating apparatus having five heating units 16, each heating unit 16 raises the temperature by about 2 ° C., and when the liquid eggs pass through all the heating units 16, respectively. Joule heating is performed to achieve a predetermined sterilization temperature.

FIG. 4 shows the inner surface of the tubular member 22 when the whole egg as a liquid egg is Joule-heated by changing the Reynolds number Re and the power density P (KW / m ³ ) of the liquid egg flowing in the flow path 21. It is a graph which shows the experimental result of the adhesion state of a scale. In FIG. 4, a circle indicates a case where no scale is generated, and a cross indicates a case where a scale is generated. Here, Reynolds number Re is represented by Re = DU / ν, where D is the inner diameter of the tube member, U is the average flow velocity of the liquid egg, and ν is the kinematic viscosity coefficient of the liquid egg.

  FIG. 5 is a characteristic diagram showing a boundary between a range where the scale does not adhere to the inner surface of the tubular member 22 and a range where the scale adheres. As shown in FIG. 5, the boundary characteristic is P = 9.4Re−352.4, and when the liquid egg is sterilized and heated by supplying power to the electrode 23 such that the power density P is in the range of P ≦ 9.4Re−352.4. It was found that no scale adhered to the inner surface of the tubular member 22. As described above, when the power density P flowing through the liquid egg in the flow channel 21 is set to a specific range according to the Reynolds number Re of the liquid egg flowing through the flow channel 21 in the tubular member 22, the scale is formed on the inner surface of the tubular member 22. Does not adhere, the liquid egg can be continuously heated for a long time.

  FIG. 6 is a viscosity table showing the relationship between the viscosity (mPasec) of liquid whole egg and temperature (° C.). The viscosity of whole egg liquid changes with temperature, and the viscosity of liquid egg white and liquid egg yolk also changes with temperature. To do. Therefore, as shown in FIG. 1, in the heating apparatus having the five heating units 16, it is preferable that the energization conditions in the respective heating units are made different.

  As shown in FIG. 1, the heat sterilization treatment of the liquid whole egg was performed using a heat treatment apparatus having five heating units 16. Each heating unit 16 has six current-carrying sections as shown in FIG. 2, and a tubular member 22 having an inner diameter D of 17.5 mm was used. The whole egg at 5 ° C. contained in the container 10 is supplied at a flow rate of 277 L / hr by the liquid feed pump 11, and from 5 ° C. to 54 ° C. by the saving unit 12 c and the preheating unit 12 a of the plate heat exchanger 12. Until preheated. The preheated liquid whole eggs were supplied to the five heating units 16, and Joule heating was performed by each heating unit 16 until the liquid whole eggs flowing out from the most downstream heating unit 16 reached 62.5 ° C. After heating to this sterilization temperature and holding the liquid whole egg in the liquid egg holding unit 31 for 5 minutes, the liquid whole egg was cooled to 5 ° C. by the cooling unit 12b.

The Reynolds number Re of the liquid whole egg flowing in each heating unit 16 is 580 from the inner diameter D, the flow velocity U and the kinematic viscosity coefficient ν of the tubular member 22, and the power density P in each heating unit 16 is 5050 KW / m ^3. Set to. After 5 hours of continuous operation under these heating conditions, water was rinsed and the heat exchanger 12 and the heating unit 16 were disassembled and inspected. No scale adhesion was observed. Moreover, when the heat-treated liquid whole egg thus prepared was stored at 5 ° C. for 72 hours and then visually confirmed, no precipitate due to heat denaturation of egg white was observed.
For example, when a liquid egg heated by a heat exchanger using a heating medium is put into hot water to cook egg soup, the liquid egg is hard to be solidified and the heated egg becomes cloudy Although the egg soup is in a state, when the liquid egg that has been heat-treated by the liquid egg processing technique of the present invention is put into hot water, the egg becomes hardened in the same manner as when an unsterilized egg is put into hot water. . Thereby, the liquid egg heat-processed by the processing technique of this invention can cook the egg dish which has the property similar to various foodstuffs, such as an omelet and oyakodon cooked using the unsterilized egg. .

  The present invention is not limited to the embodiments, and various modifications can be made without departing from the scope of the invention. For example, the plate heat exchanger 12 in which the preheating unit 12a, the cooling unit 12b, and the saving unit 12c are combined is used. However, the saving unit 12c may not be used, and the preheating unit 12a is replaced with the heating unit 16. It is good also as a Joule heating type similarly to. Further, as described in FIGS. 5 to 7 of Patent Document 3, the heating unit 16 is a heating unit in which plate-like electrodes are arranged opposite to each other inside a tubular member having a square cross section, and both ends of the tubular member. A heating unit in which plate-like electrodes are arranged opposite to each other, and a rod-like electrode is arranged in the center of the tubular member, and a cylindrical electrode is arranged on the inner surface of the tubular member A unit may be used.

It is the schematic which shows the heat processing apparatus of the liquid egg which is one embodiment of this invention. It is sectional drawing which shows the heating unit shown by FIG. It is a block diagram which shows the control part of the heat processing apparatus of the liquid egg shown in FIG. It is a graph which shows the experimental result of the adhesion state of the scale with respect to the flow-path inner surface of a heating unit at the time of changing Reynolds number and power density of a liquid egg. It is a characteristic diagram which shows the boundary of the range where a scale does not adhere to the flow path inner surface of a heating unit, and the range which adheres. It is a viscosity table | surface which shows the relationship between the viscosity (mPasec) of liquid whole egg, and temperature (degreeC).

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Liquid feed pump 12a Preheating unit 12b Cooling unit 16 Heating unit 21 Channel 22 Tubular member 23 Electrode 24 Cylindrical body 27 Power supply unit 31 Liquid egg holding unit 34 Controller (power control means)

Claims (3)

A liquid egg heat treatment method in which the liquid egg is sterilized and heated by Joule heat while continuously transporting the liquid egg into the flow path as a heated object,
A heating unit having a tubular member formed of an insulating material and having a pair of electrodes and electrodes is provided in the flow path according to the Reynolds number Re of the liquid egg flowing in the flow path. A heating step of setting the power density P (KW / m ³ ) to a value of P ≦ 9.4Re−352.4 and heating the liquid egg to the sterilization heating temperature;
A heat retention step of holding the liquid egg heated to the sterilization temperature by the heating unit by the liquid egg holding unit;
And a cooling step of cooling the liquid egg conveyed from the liquid egg holding unit by a cooling unit.   The liquid egg heat treatment method according to claim 1, further comprising a preheating step of heating the liquid egg to a preheating temperature lower than a sterilization temperature before flowing into the heating unit. 3. The liquid egg heat treatment method according to claim 1, wherein the liquid egg is a liquid whole egg, a liquid egg white, or a liquid egg yolk.

Images