JP7778302B2 - Method for inhibiting oxidation of fats and oils - Google Patents

Description

The present invention relates to a method for inhibiting oxidation of fats and oils.

It is known that fats and oils oxidize when they come into contact with oxygen, causing their quality to deteriorate. In particular, fats and oils heated to high temperatures, such as cooking oils used for deep-frying, undergo oxidation and polymerization due to temperature changes, causing significant deterioration. In the food industry and restaurants, where large amounts of deep-fried food are cooked over long periods of time, fats and oils deteriorate quickly. Therefore, technology to inhibit the oxidation of fats and oils is important not only from the perspective of maintaining food quality but also from an economic perspective.

Various methods have been proposed for inhibiting the oxidation of fats and oils. Patent Document 1 describes a method in which alkaline ionized water with a pH of 10 or higher is sprayed onto the surface of frying oil. Another method involves adding antioxidants to the fat and oil. These antioxidants include natural tocopherol, as described in Patent Document 2, and synthetic compounds such as butylhydroxytoluene (BHT), butylhydroxyanisole (BHA), and isopropyl citrate, which are approved as food additives under the Food Sanitation Act. Patent Document 3 also describes a method in which an inert gas is converted into fine bubbles and dispersed in the oil to promote deoxygenation of the fat and oil, thereby preventing its oxidation.

JP 2010-193737 A Japanese Patent Application Publication No. 4-39397 Japanese Patent Application Laid-Open No. 2001-200288

However, the method described in Patent Document 1 uses strongly alkaline ionized alkaline water, which requires careful handling, and spraying a large amount onto the oil surface can cause dangerous oil splashes, making it difficult to say that it is versatile. Furthermore, the antioxidant effects of the tocopherol and synthetic compounds described in Patent Document 2 do not last long.

The method described in Patent Document 3 aims to deoxygenate oils and fats by mixing and dispersing finely bubbled inert gas into the oil during the process of using the oils and fats for cooking. This method is characterized by the fact that the oils and fats are heated to 60 to 240°C during this process.

However, recent research has shown that when room temperature oil is heated, the dissolved oxygen concentration in the oil drops sharply when the oil temperature reaches around 120°C, dropping to almost zero at around 180°C, and then rising sharply when heating is stopped and the oil temperature drops to around 60°C. The dissolved oxygen concentration then continues to rise until the oil temperature returns to room temperature, at which point it remains at a high level. It has also been shown that the same behavior occurs again when the oil is reheated.

Oxidation of fats and oils, which is caused by dissolved oxygen in the oil, progresses rapidly as the oil temperature drops when the oil is left at room temperature after heating. Once the oil temperature drops to around 60°C, a large amount of oxygen begins to dissolve rapidly in the oil, accelerating the oxidation of the oil.

The method described in Patent Document 3 not only injects the inert gas at a high temperature that actually contains almost no oxygen to be expelled, but also requires the oil or fat to be reheated for the injection process, resulting in unnecessary operating costs, waste, and inefficiency. Furthermore, because the injection process is performed while heating, if the injection process is performed after the day's cooking has finished in a factory or restaurant, the oil will remain at a high temperature, posing safety issues.

The present inventors have intensively studied these problems and have attempted to solve them. The problem that the present invention aims to solve is to provide an efficient method for inhibiting the oxidation of fats and oils, which can effectively inhibit the deterioration of fats and oils due to oxidation.

In order to solve the above problems, a method for inhibiting oxidation of fats and oils is provided, which comprises, after completion of heating of heated fats and oils, a step of lowering the temperature of the fats and oils to a temperature range lower than 60°C, while cooling the fat and oil, feeding ultrafine bubbles of an inert gas into the fat and oil during the cooling process, and continuing to feed the ultrafine bubbles of inert gas into the fat and oil during the cooling process even after the fat and oil have been cooled to the temperature range by cooling, thereby preventing an increase in the dissolved oxygen concentration in the fat and oil due to the decrease in temperature.

It is also preferable to start feeding ultra-fine bubbles of an inert gas before the temperature of the oil or fat drops from 60° C. It is also preferable that the cooling is forced cooling by a cooling means.

The heated oil and fat is high-temperature oil and fat that has been recovered after cooking and transferred to an oil tank for storage, and the method for inhibiting oxidation of oil and fat uses an ultra-fine bubble generator connected to the oil tank as a means for injecting ultra-fine bubbles of an inert gas into the oil and fat during the cooling process.

It is preferable that the ultra-fine bubble generator is equipped with a pump for mixing gas and liquid and a static mixer.

It is preferable that the ultra-fine bubble generator be equipped with a cooling mechanism that cools the oil or fat to an appropriate temperature.

It is preferable to supply an inert gas to the space within the oil tank where the recovered oil and fat is stored.

It is preferable to feed ultra-fine bubbles of inert gas into the oil while adjusting the temperature of the oil to above its melting point.

It is preferable to further inject ultra-fine bubbles of inert gas into the oil or fat during or after heating using a throw-in type ultra-fine bubble generator.

The present invention makes it possible to provide an efficient method for inhibiting oxidation of fats and oils, which can effectively inhibit deterioration of fats and oils due to oxidation.

FIG. 1 is a diagram showing steps of an embodiment of the present invention and the temperature of fats and oils in each step. 1 is a schematic diagram of an oil and fat oxidation suppression device used in a first embodiment of the present invention. FIG. FIG. 4 is a schematic diagram of an apparatus for inhibiting oxidation of fats and oils used in a second embodiment of the present invention. FIG. 1 is a graph showing changes in the amount of dissolved oxygen in fats and oils with changes in the temperature of the fats and oils. FIG. 1 is a graph showing the transition of the amount of dissolved oxygen in fats and oils during temperature reduction in Examples and Comparative Examples.

The following describes an embodiment of the invention. As shown in Figure 1, in an embodiment of the present invention, in a deep-frying process using edible oils and fats, oxidation of the oils and fats is suppressed by injecting ultrafine bubbles of inert gas into the oils and fats during the cooling process after heating. The oil and fat used in this embodiment is palm oil, but the type of oil and fat is not limited to this. In addition, various types of ingredients can be used for deep-frying.

(About ultra-fine bubbles)
Here, we will explain ultrafine bubbles. According to the definition of the International Organization for Standardization, bubbles with a diameter of less than 100 μm are called fine bubbles. Furthermore, among fine bubbles, bubbles with a diameter of 1 μm or more but less than 100 μm are called microbubbles, and bubbles with a diameter of less than 1 μm are called ultrafine bubbles.

A static mixer (e.g., JP 2020-163241 A) can be used to generate ultrafine bubbles, but any other method, such as a micro-hole type, swirling liquid flow type, Venturi type, static mixer type, pressurized dissolution type, or ultrasonic type, can also be used.

(Ultra-fine inert gas bubbles)
By converting an inert gas into ultrafine bubbles, a large amount of the inert gas can be contained in the oil, which is the dispersion medium. The ultrafine bubbles of the inert gas have a very large contact area with the oil due to their small particle size, so they can quickly absorb and remove oxygen dissolved in the oil, resulting in a low-oxygen oil. The amount of dissolved oxygen in the oil or fat containing the ultrafine inert gas bubbles of the present invention is preferably 2 mg/L or less.

Another characteristic of ultrafine bubbles is their long-term stability, which allows them to remain in the dispersion medium for long periods of time. This long-term stability is unique to ultrafine bubbles; because they are subjected to little buoyancy, they do not rise to the surface, but move by Brownian motion and can remain in the dispersion medium for long periods of time, measured in months. Furthermore, the surfaces of ultrafine bubbles are negatively charged, causing them to repel each other, so they do not aggregate and their number concentration is unlikely to decrease. Therefore, ultrafine bubbles of inert gas not only reduce the amount of dissolved oxygen, but also suppress the re-rise of dissolved oxygen, allowing an anoxic state to be maintained for a long period of time.

In the present invention, nitrogen is preferably used as the inert gas used to create ultrafine bubbles. Nitrogen is a food additive used in gas-filled packaging to prevent food oxidation. In embodiments of the present invention, nitrogen is used as the inert gas. In addition to nitrogen, argon or a mixture of nitrogen and argon may also be used. Like nitrogen, argon is an effective substance for preventing food deterioration due to oxidation. It is approved for use in fruit and vegetable juices and wine in the United States, and is generally approved for use in all foods in the European Union. It was also approved as a food additive in Japan in 2019. Experiments conducted by the inventors suggest that using argon is more effective than nitrogen in suppressing the re-elevation of dissolved oxygen in oil. However, there is a price difference between the two, so the choice of which to use can be made based on factors such as cost.

(First embodiment)
A first embodiment of the present invention will be described with reference to a schematic diagram of an oxidation suppression device used in the present invention. As shown in FIG. 2, in the first embodiment, oil placed in an oil tank 1 is heated by an optional heating means and, once heated to an appropriate temperature, is used for deep-frying. The appropriate cooking temperature varies depending on the food material, but is generally about 180°C. Heating is stopped once a predetermined amount of cooking has been completed. After heating is stopped, the oil is promptly filtered through a filter 2 to remove fried debris and the like. Note that filtering of the oil may be performed in parallel with deep-frying, for example, by providing a filter within the oil tank 1.

The oil filtered by the filter 2 is sent to the storage tank 3 for storing the oil at a high temperature of approximately 100°C or less. One of the reasons why the oil is not left in the oil tank 1 after cooking but is instead collected and stored in the storage tank 3 is to reduce the area where the oil comes into contact with air and prevent oxidation of the oil.

In the first embodiment, ultrafine bubbles of inert gas are pumped into the oil recovered and sent to the storage tank 3 after heating is complete, suppressing an increase in the dissolved oxygen concentration in the oil. As mentioned above, as the temperature of the recovered oil decreases after heating is stopped, the dissolved oxygen concentration in the oil rises sharply once it reaches around 50-60°C, as shown in Figure 4. Therefore, in the present invention, the pumping of ultrafine nitrogen bubbles into the oil begins before the temperature of the oil falls below 60°C.

The method for injecting ultra-fine nitrogen bubbles in the first embodiment will be described. In the first embodiment, an ultra-fine bubble generator is used, which includes an oil supply line 41 connected to the storage tank 3, a nitrogen supply line 46 connected to the oil supply line 41, a pump 48 for gas-liquid mixing, and a static mixer 49.

Oils and fats sent from the storage tank 3 through the oil and fat supply line 41 are mixed with nitrogen through the nitrogen supply line 46, pressurized by the gas-liquid mixing pump 48, and sent to the static mixer 49. The static mixer 49 is a device that houses a laminated structure made up of multiple perforated flat plates inside a casing, and micronizes the air bubbles contained in the liquid as the liquid supplied from one side passes through the laminated structure in a zigzag pattern. As the liquid passes through the static mixer 49, the nitrogen bubbles in the oil and fat are micronized to form ultrafine bubbles, and the oil and fat containing the nitrogen ultrafine bubbles is returned to the storage tank 3. The bubble diameter can be further reduced by circulating the oil and fat and passing it through the ultrafine bubble generator multiple times.

The ultra-fine bubble generator used in the present invention is not limited to the circulation type described above. It can also be a one-pass type in which the oil or fat that has been infused with nitrogen ultra-fine bubbles is not returned to the storage tank 3 but is instead discharged to a location of your choice.

When nitrogen ultrafine bubbles are injected into the oil or fat during the cooling process, the oil or fat may be cooled naturally, but it is more preferable to use forced cooling using a cooling means 42 installed in the ultrafine bubble generator, as shown in Figure 2. The forced cooling means can be a water-cooled heat exchanger equipped with a cooling water supply line 43, as shown in Figure 2, but any other means, such as air cooling using a fan, can also be used. Forced cooling of the oil or fat allows it to pass as quickly as possible through the temperature range of 60°C to room temperature, where oxygen is easily absorbed into the oil, and further suppresses the increase in dissolved oxygen concentration and the progression of oxidation. The cooling means 42 may also be installed between the oil tank 1 and the storage tank 3.

In the first embodiment, the oil temperature when incorporating ultrafine nitrogen bubbles into fats and oils is approximately 100 to 180°C at the highest. At this temperature range, the viscosity of the fats and oils is lower than at room temperature, making it easier to incorporate ultrafine nitrogen bubbles. Therefore, according to the present invention, even fats and oils that solidify at room temperature, such as palm oil and coconut oil, can be sufficiently filled with ultrafine nitrogen bubbles.

Even if the oil temperature drops to a low temperature of 100°C or below and the viscosity increases, the ultra-fine bubble generator of this embodiment is designed so that the oil is pressurized by the gas-liquid mixing pump 48 and sent to the static mixer 49, allowing nitrogen ultra-fine bubbles to be sent efficiently and the amount of dissolved oxygen in the oil to be reduced.

Furthermore, when using oils and fats that solidify at room temperature, such as palm oil or coconut oil, it is preferable to install a temperature control device that maintains the temperature above the melting point to prevent the oil and fat from solidifying. The melting point varies depending on the type of oil and fat, but for example, palm oil solidifies at around 37°C, so the oil temperature is controlled so that it does not fall below approximately 40°C. Maintaining a temperature above the melting point and keeping the oil and fat in a liquid state prevents the oil and fat from clogging, and allows nitrogen ultrafine bubbles to be continuously pumped in even after some time has passed since heating ended.

Oils and fats that have had their dissolved oxygen concentration sufficiently reduced by the ultrafine nitrogen bubbles introduced and their temperature lowered to room temperature are then stored in storage tank 3 until the next cooking process. At this time, supplying an inert gas such as nitrogen into the space inside storage tank 3 to create an inert gas atmosphere inside storage tank 3 prevents the surface of the oil and fat from coming into contact with oxygen, further suppressing oxidation of the oil and fat.

It is preferable that the supply of inert gas into the storage tank 3 be carried out periodically and automatically using a timer. Alternatively, the dissolved oxygen concentration of the oils and fats in the storage tank 3 may be measured, and the supply of inert gas may be controlled based on this measurement.

The oil stored in storage tank 3 will be used in the next cooking process. Before the next cooking process begins, ultrafine nitrogen gas bubbles may be introduced into the oil again. By introducing ultrafine nitrogen bubbles again before the next heating process, it is possible to prevent the oil from coming into contact with air when being filled into oil tank 1, thereby preventing an increase in the dissolved oxygen concentration, which is preferable from the perspective of preventing oxidation of the oil.

Second Embodiment
A second embodiment will now be described. In the second embodiment, as a means for incorporating ultrafine nitrogen bubbles into fats and oils, a method is adopted in which ultrafine nitrogen bubbles are generated by installing an immersion-type micropore bubble generator 5 in a storage tank 3, as shown in Figure 3. Note that the process up to the step of filtering the fats and oils after heating and sending them to the storage tank 3 is the same as in the first embodiment.

The immersion-type micropore bubble generator 5 comprises a cylindrical porous ceramic tube 51 and a nitrogen supply line 52 that supplies nitrogen to the inner surface of the porous ceramic tube 51. The porous ceramic tube 51 has numerous micropores ranging in size from μm to nm, and nitrogen supplied to the inner surface of the tube passes through these pores and is released to the outer surface of the tube, converting it into microscopic bubbles and generating ultrafine bubbles. By using the micropore bubble generator 5 to add ultrafine nitrogen bubbles to the heated oil sent to the storage tank 3, the increase in dissolved oxygen concentration in the oil during the cooling process is suppressed, preventing the oil from oxidizing.

In the second embodiment, when ultrafine nitrogen bubbles are injected into the oil during the cooling process, the oil temperature can be lowered by natural cooling, but it is more preferable to use a water-cooled cooling means equipped with a cooling water supply line 43 as shown in Figure 3 to lower the temperature by forced cooling. However, other forced cooling methods may also be used. Furthermore, filling the space inside the storage tank 3 with an inert gas such as nitrogen prevents the surface of the oil from coming into contact with oxygen, further suppressing oxidation of the oil. Furthermore, ultrafine nitrogen gas bubbles may be injected into the oil again before the oil is used for the next cooking.

In the method for preventing oxidation of fats and oils of the present invention, ultrafine nitrogen bubbles are injected precisely at the time when the oil temperature is dropping, when the concentration of dissolved oxygen in the oil increases and oxidation progresses, thereby eliminating unnecessary operating costs and making it possible to efficiently suppress the oxidation of fats and oils.

The present invention has been described above using exemplary embodiments, but the present invention is not limited to the above embodiments and can be implemented in various forms. For example, in embodiments 1 and 2, ultra-fine bubbles of an inert gas may be further introduced into the oil or fat during or after heating using a throw-in type ultra-fine bubble generator. Simply placing the throw-in type ultra-fine bubble generator in the oil tank 1 or filter 2 requires no special construction work and further oxidation suppression can be easily achieved.

The present invention will be explained in detail below by showing examples of the present invention, but the present invention is not limited to these examples in any way.

Example 1
In Example 1, canola oil was heated, and the injection of ultrafine nitrogen bubbles into the oil was initiated when the oil temperature reached 50°C. Heating was continued for 30 minutes while maintaining the oil temperature at 50-60°C, and ultrafine nitrogen bubbles were also continuously injected. After heating was stopped, the oil was cooled until the temperature dropped to 40°C, with ultrafine nitrogen bubbles still being injected. A static mixing ultrafine bubble generator was used to inject the ultrafine nitrogen bubbles. The change in the amount of dissolved oxygen was measured as the oil temperature dropped from 60°C at the start of measurement to 40°C at the end of measurement, and the results are shown in Figure 5.

Example 2
In Example 2, the treatment of canola oil as in Example 1 was carried out using ultrafine argon bubbles instead of nitrogen. As in Example 1, the change in the amount of dissolved oxygen was measured while the oil temperature decreased from 60°C at the start of the measurement to 40°C at the end of the measurement, and the results are shown in Figure 5.

(Comparative Example)
In the comparative example, canola oil was heated for 30 minutes while maintaining the oil temperature at 50 to 60°C. After heating was stopped, the oil was cooled until the oil temperature reached 40°C. In the comparative example, no inert gas was introduced. The change in the amount of dissolved oxygen was measured while the oil temperature decreased from 60°C at the start of the measurement to 40°C at the end of the measurement, and the results are shown in Figure 5.

As shown in Figure 5, in the comparative example in which ultrafine nitrogen bubbles were not fed, the amount of dissolved oxygen rose sharply once the oil temperature dropped to around 55°C, reaching 2 mg/L at an oil temperature of 40°C, whereas in Examples 1 and 2, values of 0.4 mg/L or less were maintained. In particular, in Comparative Example 2, in which argon was used, the amount remained low at 0.03 mg/L even at an oil temperature of 40°C, demonstrating a very high effect in suppressing the increase in dissolved oxygen.

The above experimental results demonstrate that by injecting ultrafine bubbles of inert gas into fats and oils, it is possible to suppress an increase in the dissolved oxygen concentration in the oil. Furthermore, it was found that even when ultrafine bubbles of inert gas are injected at low temperatures of 60°C or less, the amount of dissolved oxygen is sufficiently reduced and the effect of suppressing a re-rise can be achieved. Therefore, it can be said that the oxidative deterioration of fats and oils can be efficiently and effectively suppressed by using the method of the present invention.

1 Oil tank 2 Filter 3 Storage tank 41 Oil supply line 42 Cooling means 43 Cooling water supply line 44 Suction pressure regulating valve 45 Pressure gauge 46 Nitrogen supply line 47 Air flow meter 48 Gas-liquid mixing pump 49 Static mixer 5 Micropore bubble generator 51 Porous ceramic tube 52 Nitrogen supply line

Claims (9)

After the heating of the heated fats and oils is completed, the temperature of the fats and oils is lowered to a temperature range lower than 60 ° C.
While cooling the oil or fat , ultrafine bubbles of an inert gas are sent into the oil or fat during the cooling process,
A method for inhibiting oxidation of fats and oils, comprising continuing to send ultrafine bubbles of the inert gas even after the temperature of the fats and oils has been lowered to the temperature range by cooling, thereby preventing an increase in the dissolved oxygen concentration in the fats and oils due to a decrease in temperature. 2. The method for inhibiting oxidation of fats and oils according to claim 1, wherein the supply of ultra-fine bubbles of inert gas is started before the temperature of the fats and oils drops from 60°C. The method for inhibiting oxidation of fats and oils according to claim 1 or 2, wherein the cooling is forced cooling by a cooling means. The method for inhibiting oxidation of fats and oils according to any one of claims 1 to 3, wherein the heated fat and oil is high-temperature fat and oil that has been recovered after cooking and transferred to an oil tank for storage, and an ultra-fine bubble generator connected to the oil tank is used as a means for injecting ultra-fine bubbles of an inert gas into the fat and oil in the cooling process. The method for inhibiting oxidation of fats and oils according to claim 4 , wherein the ultra-fine bubble generator is equipped with a gas-liquid mixing pump and a static mixer. The method for inhibiting oxidation of fats and oils according to claim 4 or 5 , wherein the ultra-fine bubble generator is provided with a cooling mechanism for cooling the fats and oils to an appropriate temperature. The method for inhibiting oxidation of fats and oils according to any one of claims 4 to 6 , further comprising supplying an inert gas to a space within the oil tank in which the recovered fats and oils are stored. The method for inhibiting oxidation of fats and oils according to any one of claims 1 to 7 , wherein ultra-fine bubbles of an inert gas are fed into the fats and oils while adjusting the temperature of the fats and oils to a temperature equal to or higher than the melting point. 9. The method for inhibiting oxidation of fats and oils according to claim 1, further comprising the step of supplying ultra-fine bubbles of an inert gas to the fat and oil during or after heating using a throw-in type ultra-fine bubble generator.