JPH09318616A - Evaluating method of rice freshness - Google Patents

Abstract

PROBLEM TO BE SOLVED: To evaluate freshness of rice with simplicity and certainty by extracting an oily component from rice dipped in an alcoholic solution by means of supercritical liquid extraction and measuring degree of oxidation with use of iodimetry. SOLUTION: An apparatus of supercritical liquid extraction comprises: a pressure raise section including a route from a cylinder 1 to a stop valve V2; a water thermostatic oven 13 disposed in a downstream position of the pressure raise section; and an extraction section in the water thermostatic oven 13. Rice, which is already subjected to a pretreatment using the alcoholic solution, is charged in an extraction cell 10 and the cell 10 is placed in a predetermined position in the water thermostatic oven 13. Carbon dioxide is supplied to the pressure raise section from the cylinder 1 in a condition of the valve 2 being closed and the supply is controlled by a pressure control valve V1, while a water temperature of the water thermostatic oven 13 is controlled. Carbon dioxide is supplied to the extraction section in conditions that stop valves V3, V4 and a flow rate control valve V5 are closed and the valve V2 is opened. Then the valve V3 is opened, the valve V4 is closed and in the conditions, the oily component of the rice charged in the cell is extracted. A degree of oxidation of the oily component in the rice is measured by iodimetry.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating freshness of rice. More specifically, the oil content in rice is extracted by supercritical fluid extraction, and the degree of oxidation of the oil is measured to obtain rice. Relates to a method of evaluating freshness of.

[0002]

2. Description of the Related Art In recent years, with the opening of the rice market, domestically produced rice and foreign rice have come into circulation. Along with this, consumers are expected to post an indicator of freshness so that they can buy rice with peace of mind.

Conventionally, it has been known that components such as fats, carbohydrates and proteins contained in rice are oxidized and decomposed with time to produce fatty acids and other organic acids. The degree of oxidation of fatty acids obtained by extracting the fatty acids in the product with a fatty solvent or water and neutralizing with an alkaline normal solution, or the degree of oxidation of water-soluble substances is an indicator of the freshness of grains and their products. It has been used as "Theory and Practice of New Edition Agricultural Product Inspection and Quality Control" edited by Food Inspection Agency.

[0004]

However, in the measurement of the degree of oxidation by this method, the degree of oxidation is greatly influenced by the grain size of the rice and the method of rice polishing, and the higher the degree of oxidation of rice, the higher the degree of oxidation. However, when comparing the numerical values of the test data, it was necessary to carefully check the measuring method and the rice polishing method, which was a troublesome confirmation work. In addition, since alkali acts in addition to acid, if the leachate contains contaminants, accurate evaluation may not be possible.

[0005]

Therefore, the purpose of the present invention is to make the oxidation degree of rice more objectively and accurately, and to extract the oil content in the rice using a supercritical fluid, and then to determine the oxidation degree of the oil content by iodine. An object of the present invention is to provide a method for determining the freshness of rice by using the oxidative titration method.

[0006]

The present invention has been proposed to achieve the above object, and is characterized by having the following constitution. That is, the present invention provides a method for evaluating freshness of rice, which comprises extracting oil from rice by supercritical fluid extraction and measuring the degree of oxidation of the oil by iodine oxidation titration.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION A supercritical fluid is a constant pressure (critical pressure) and a constant temperature (critical temperature: a value peculiar to nuclear matter, above which temperature the gas can be liquefied at any pressure. It is a high-density gas that exists in a region above the range of 0.3 to 1.0.
Density of about 0.001g / c that ordinary gas shows under atmospheric pressure at g / cm ^3.
It can be seen that it is significantly larger than m ³ . The most widely used carbon dioxide as a supercritical fluid has a critical pressure of 7
The atmospheric pressure is 2.9 atm and the critical temperature is 31.1 ° C.

Generally, a gas becomes a liquid when the pressure is increased under a constant temperature condition below its critical temperature, but at a temperature above the critical temperature it does not become a liquid even if the pressure is increased, but becomes a supercritical fluid.

Further, the gas density near the critical point is close to the liquid density, but the viscosity is about several times that of a normal gas. On the other hand, the diffusion coefficient is about 100 times larger than that of liquid. Furthermore, a big feature is that the density changes abruptly with a slight pressure change. In the solubility of the component of interest in the supercritical gas slightly above the critical temperature, the density of the gas phase rapidly increases with an increase in the pressure, so that the solubility of the solute significantly increases in the region above the critical pressure. On the contrary, this means that the solubility can be drastically lowered by reducing the pressure, which means that the solute and the extraction medium (supercritical gas) can be separated only by the depressurization operation. A method of extracting and separating a specific substance from a mixture using such a principle is called supercritical fluid extraction.

As described above, the supercritical carbon dioxide extraction using carbon dioxide, which is easy to separate from the solute and whose operating temperature is near room temperature (about 35 ° C. to 45 ° C.), as a supercritical fluid is a heat treatment of biological substances. There is little deterioration or alteration due to chemical substances, and its application as a method for separating and producing them is considered promising (4-144655). In particular, carbon dioxide used as a supercritical fluid is generally nontoxic and has a critical temperature of 304.2.
Since it is K, it can be operated at a low temperature of about 308.15 K, and it is inexpensive, so many studies using it have been made.

For example, as extraction from marine organisms,
There is a study (Japanese Patent Laid-Open No. 4-144655) that separates and produces highly unsaturated fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from fish oil by supercritical carbon dioxide extraction using a temperature gradient method. Has been done. Moreover, the extraction of limonoids from citrus seeds by supercritical carbon dioxide extraction (Nippon Shokuhin Kogyo Gakkaishi Vol.
9.No.8,684-689,1992), Extraction of picifueric acid or its analogs from cypress family plants such as Shinohiba and Sawara by supercritical carbon dioxide extraction (Japanese Patent Laid-Open No. 62-270547), supercritical fluid Leaves, stems of South American medicinal plants by extraction,
There is extraction of oil containing γ-linoleic acid in the presence of water and alcohol from the root (Japanese Patent Laid-Open No. 2-235996), but a certain component in the object is extracted using supercritical extraction,
There is not much research that evaluates freshness by analyzing its components.

Therefore, in the present invention, a method for evaluating the freshness of rice by extracting the oil content in rice using supercritical fluid extraction and measuring the oxidation degree of the oil content was examined.

Although the oil content can be extracted from the raw rice by supercritical fluid extraction as it is, it is preferable to perform it in a state where the rice is immersed in an alcohol solution. An ethanol solution is preferably used as the alcohol solution in the present invention, and carbon dioxide is suitable for the supercritical fluid as a solvent. Further, for the measurement of the degree of oxidation of the extracted oil, an iodine oxidation titration method in which iodine produced by the reaction of hydroperoxy groups and potassium iodide was titrated with sodium thiosulfate was used.

The technical feature of the present invention is that the rice is soaked in an alcohol solution as needed prior to the supercritical fluid extraction, and the freshness of the rice is determined from the oxidation degree of the extracted oil extracted with the supercritical fluid. This is because there is no damage or disintegration of rice grains caused by rapidly immersing wet ingredients,
By performing supercritical fluid extraction, the influence of contaminants on the analysis of the degree of oxidation can be reduced and the degree of oxidation of oil in rice can be detected efficiently. The alcohol solution has a strong affinity for the oil content in rice, and the inclusion of this increases the solubility of the oil content in the supercritical fluid,
Extraction becomes easy. Further, even when not immersed in an alcohol solution, the oil content in rice can be extracted by operating the temperature and pressure when performing supercritical fluid extraction.

In the present invention, the immersion time of rice in an alcohol solution is 1 hour to 24 hours, particularly 8 hours to
12 hours is preferable from the viewpoint that the supercritical fluid extraction can be performed efficiently. In the present invention, immersing rice includes not only immersing the rice for a predetermined time as pretreatment as described above, but also bringing the rice into contact with an alcohol solution and immediately performing supercritical fluid extraction.

In the present invention, the amount of the alcohol solution used is preferably 5 to 20 ml per 100 g of rice from the viewpoint of economic efficiency. Next, the normality of the sodium thiosulfate aqueous solution used for iodine oxidation titration is 0.0
It will be about 01N. In the present invention, the temperature for supercritical fluid extraction is 32 to 50 ° C, especially 35 to 40 ° C.
C is preferable in that the supercritical fluid extraction can be efficiently performed. The pressure for supercritical fluid extraction is 7.2
It is preferably from 30 to 30 MPa, particularly from 15 to 25 MPa, from the viewpoint of efficient supercritical fluid extraction.

The supercritical extraction apparatus used in the present invention will be described below in detail with reference to the drawings. As shown in FIG. 1, the supercritical extraction apparatus is provided with a pressure increasing section in which a path from the cylinder 1 to the stop valve V2 is formed, and an extracting section provided in the water thermostat 13 provided downstream thereof.

Booster Unit The booster unit has a cylinder 1 for supplying liquid carbon dioxide to a booster pump 4 described later. In the present embodiment, a siphon-type carbon dioxide cylinder is used as the cylinder 1.

A drying pipe 2 filled with a desiccant is provided between the cylinder 1 and the boosting pump 4, and the liquid carbon dioxide from the cylinder 1 is passed through the drying pipe 2 so that the liquid dioxide is discharged. Water in carbon is removed. As the drying tube 2, material SUS316, maximum working pressure 20MPa, inner diameter
It is 35.5mm long and 310mm long. As the desiccant, molecular sieve 5A (1/16 inch Pellet) manufactured by GL Science Co., Ltd. is used.

Further, the booster unit has a cooling unit 8. In this embodiment, BL-22 manufactured by Yamato Scientific is used as the cooling unit 8. The cooling unit 8 is filled with ethylene glycol, and this ethylene glycol is cooled to about -12 ° C. The liquid carbon dioxide from which water has been removed by the desiccant is cooled by this ethylene glycol and supplied to the pressurizing pump 4.

The booster pump 4 is a high-pressure single plunger pump AP manufactured by GL Science Co., Ltd.
S-5L (maximum pressure 58.8MPa, normal pressure 49.0MPa, flow rate 0.5
Or 5.2 ml / min) is being used. A cooler (not shown) is attached to the head portion of the booster pump 4 in order to prevent vaporization of liquid carbon dioxide. Further, a filter 3 is provided between the drying tube 2 and the boosting pump 4, and impurities such as dust are removed by the filter 3 to prevent impurities from being mixed into the boosting pump 4. To be done. In addition, in this embodiment, as the filter 3,
An average pore size of about 10 μm is used (GL Science FT4-10 type).

Further, a pressure adjusting valve V1 is provided in the pressure increasing portion, and the pressure in the system of the pressure increasing portion and the extracting portion is set to an arbitrary pressure by this pressure adjusting valve V1. . In this embodiment, the pressure control valve V1 is TE
I am using SCOM's 26-1721-24. This pressure control valve V1
The pressure inside the system can be controlled with a pressure of ± 0.1 MPa, and the maximum working pressure is 41.5 MPa.

Further, a pressure gauge 5A is provided in the booster section, and the pressure in the system is measured by the pressure gauge 5A. The pressure gauge 5A has an upper limit contact output terminal, and is installed so that the booster pump 4 of the pressure gauge 5A can be turned off at a specified pressure. As the pressure gauge 5A, a Bourdon type LCG-350 (maximum working pressure 34.3 MPa) manufactured by GL Science Co., Ltd. is used. The pressure gauge 5A is
The one that was calibrated by the economic pressure gauge PE-33-A (strain gauge type, accuracy ± 0.3%) manufactured by Jiken Co., Ltd. was used.

A stop valve V2 is arranged between the pressurizing unit and the extracting unit, and the pressure of the extracting unit can be controlled by the stop valve V2. In this embodiment, the stop valve V2 is a 2-way valve 02-0120 (maximum working pressure 98.0MP, manufactured by GL Science Co., Ltd.).
a) is used.

Further, a safety valve 6A is provided between the booster section and the extraction section of this embodiment to ensure safety. In this embodiment, as the safety valve 6A, a spring type valve manufactured by AKICO Co., Ltd. is used, and the pressure in the system is 34.3%.
Adjusted and calibrated to operate at MPa. In the pressure booster, except for the section from the cylinder 1 to the filter 3, the 1/16 inch stainless steel pipe (SUS316, outer diameter 1.
588mm, inner diameter 0.8mm), all other parts are 1 / 8inc
h stainless tube (SUS316, outer diameter 3.175mm, inner diameter 2.17m
m) is used.

Extraction Section The extraction section is installed in the water constant temperature bath 13 in which the height of the entire bath can be adjusted. A temperature controller DB1000 (not shown) made by Chinault is attached to the water constant temperature tank 13, whereby the water temperature in the water constant temperature tank 13 can be controlled at ± 0.1 ° C. In addition, the water thermostat 13 has a temperature measuring unit 12
As the temperature measuring unit 12, a platinum resistance temperature measuring device 1TPF483 manufactured by Chinault was used. As a result, the water bath 13
The water temperature inside is measured. The internal volume of the water constant temperature bath 13 is 80 dm ³ .

Further, a residual heat column 9 is provided in the extraction section, and liquid carbon dioxide is supplied from the pressurization section through the stop valve V2. Residual heat column 9
Is for preheating the solvent (carbon dioxide) to the equilibrium temperature to make it a supercritical fluid. A 1/8 inch stainless steel tube (SUS316, outer diameter 3.175 mm, inner diameter 2.17 mm, length about 4 m) is 55 mm in diameter, It is formed by transforming it into a spiral shape with a length of 140 mm.

Further, the extraction section is provided with a check valve 7 for preventing the backflow of the fluid, and carbon dioxide made into a supercritical fluid by the residual heat column 9 is checked by the check valve 7 (AKIC
O Co., Ltd. SS-53F4: The maximum operating pressure is 34.3MPa). Further, a stop valve V3 is provided in the extraction section, and by adjusting the stop valve V3, the supercritical fluid passing through the check valve 7 is introduced into the extraction cell 10 containing the extracted sample. It has become. Rice and alcohol solution are contained in the extraction cell 10. This extraction cell 10 is AKICO
This is a quick opening / closing type extraction cell manufactured by KK
Design pressure 39.2MPa (400kg / cm ^2), design temperature 423.15K
(150 ℃), inner diameter 55mm, height 220mm, and internal volume 500dm ³ are used.

The pressure in the extraction cell 10 is measured by the pressure gauge 5B. As this pressure gauge, Bourdon pressure gauge E930004 (maximum pressure 4
9.0MPa) is used. In addition, as this pressure gauge 5B, the one that was calibrated by the economic pressure gauge PE-33-A (strain gauge type, accuracy ± 0.3% FS, FS: kgf / cm ² ) manufactured by Jiken Co., Ltd. was used. There is.

Further, the extraction part is provided with a safety valve 6B, so that the explosion due to the pressure increase in the extraction cell 10 can be prevented. Safety valve 6B is AKICO
Use a spring type manufactured by Co., Ltd.
Adjusted and certified to operate at 34.3MPa.

Further, the present apparatus is provided with a flow rate control valve V5 so that the flow rate of the supercritical fluid can be controlled and the depressurization operation can be performed. Flow rate control valve V5
As for the high pressure flow control valve PF3 / 8-3- manufactured by AKICO Co., Ltd.
You are using 400K-NV. Further, a stop valve V4 is provided in the extraction unit, and the supercritical fluid (carbon dioxide) in which the sample is dissolved is discharged to the outside of the system through the stop valve V4 and the flow rate control valve V5. ing.

Further, a high-pressure filter 13 is provided on the upstream side of the flow rate control valve V5, so that the inside of the tube can be prevented from being blocked by the condensation of the sample. In this embodiment, NUPRO is used as the high pressure filter 13.
2TF-7 (average pore size of about 7 μm) manufactured by 2TF-7 is used. Further, a heating unit 14 is provided on the flow path from the outlet of the water constant temperature bath 12 to the trap 15 and outside the flow rate control valve V5.
The heating unit 14 is equipped with a ribbon heater and a casting heater for keeping the flow rate control valve warm, and can keep the temperature of the flow passage at about 120 ° C. at a voltage of about 30V. As a result, it is possible to prevent condensation of the sample due to depressurization and generation of dry ice due to the supercritical fluid (carbon dioxide). The heating unit
A temperature controller DB1000 made by Chino is used for the temperature control of 14, and the maximum operating temperature is 150 ° C.

Further, in this device, an ice bath 16 is provided, and a trap 15 is provided in the ice bath 16.
The sample was depressurized with the flow control valve V5, and the sample deposited by this was
It is designed to be collected in a trap 15 provided in the ice bath 16. In addition, this device is provided with a flow meter 18,
The flow rate of the supercritical fluid can be measured by the flow meter 18. In this embodiment, as the flowmeter 18, an integrating wet gas meter W-NK-0.5B (measurement accuracy of 0.
1dm ³ ) is used. Since the target gas is carbon dioxide, the water in the flow meter 18 is saturated with carbon dioxide before the measurement. Also, on the upstream side of the flow meter 18,
A saturation container 17 is provided so that the target gas (carbon dioxide) is saturated with water vapor.

The case where the oil content in rice is extracted by using the supercritical extraction apparatus configured as described above will be specifically described with reference to an example. The rice used as the material was Koshihikari produced in Chiba prefecture, which was produced in the 5th, 6th, and 7th fiscal years. Ethanol [special grade reagent (purity 99.7% or more) manufactured by Wako Pure Chemical Industries, Ltd.] was used for the alcohol solution as a co-solvent.
As the supercritical fluid, carbon dioxide (purity
99.5%) was used. The operation method is shown below. As a pretreatment, 200 g of rice was treated with 20% alcohol solution (ethanol).
ml was added and stirred, and the mixture was left for 12 hours.

First, 100 g of the above-prepared rice was charged into the extraction cell 10 and the extraction cell 10 was set at a predetermined position in the water thermostat 12. Next, with the valve V2 closed, carbon dioxide was supplied from the cylinder 1 to the pressurizing section, and the upper limit pressure of carbon dioxide was adjusted to 19.7 MPa with the pressure control valve V1. further,
The temperature of the water in the water bath 12 is controlled to 35 ± 0 by the temperature controller.
The temperature was controlled to 2 ° C.

Next, the valve V2 was opened with all the valves in the extraction section, that is, the stop valves V3, V4, and the flow rate control valve V5 closed, and carbon dioxide gas was sent to the extraction section. Next, the valve V3 is opened, and the operating pressure in the extraction cell 10 is 1
It was left to stand until it reached 9.7 MPa.

Then, the stop valve V4 was opened, and the extraction of the oil component in the rice charged in the extraction cell 10 was started. At this time, the flow rate control valve V5 was used to reduce the measured flow rate of carbon dioxide to 0.07
Or adjusted to 4 dm ³ / min.

Further, the opening of the flow rate control valve V6 was increased, the pressure in the extraction cell was lowered, and in the trap 15, a sample (oil content, alcohol) precipitated from carbon dioxide having lost the dissolving power was recovered. In addition, rice could be recovered from the extraction cell 10. This rice was obtained by extracting oil without loss of starch.

By the above supercritical carbon dioxide extraction operation,
FIG. 2 shows the relationship between the integrated amount of recovered oil and the flow rate of carbon dioxide flowed. Further, even when no alcohol solution was added, supercritical carbon dioxide extraction was performed under the same conditions as above. This is also shown in FIG. From FIG. 2, it was shown that the oil was extracted from the rice using the supercritical carbon dioxide extraction method both in the case where the alcohol solution was added as a cosolvent and in the case where it was not added. In addition, after the supercritical extraction operation, the oil on the surface of the rice grain was extracted from the rice, and the surface had no gloss. When the alcohol solution was not added as a co-solvent, the oil in the rice could not be completely extracted, and some luster remained.

For the measurement of the degree of oxidation, acetic acid, carbon tetrachloride, potassium iodide, starch and sodium thiosulfate were used. As all reagents, special grade reagents (purity 99.7% or more) manufactured by Wako Pure Chemical Industries, Ltd. were used. By a supercritical carbon dioxide extraction operation, 0.2 to 0.6 g of the recovered oil was put into a 100 ml sample bottle and precisely weighed. To this, 3 ml of acetic acid, 2 ml of carbon tetrachloride and 200 μl of a saturated aqueous solution of potassium iodide were added.
The solution was gently shaken for 1 minute, and then left in the dark for 5 minutes. After 5 minutes, a few drops of a 1% starch aqueous solution and 10 ml of distilled water were added as an indicator, and the mixture was titrated with a 0.001N sodium thiosulfate aqueous solution. The point at which the color of the sample changed from brown to white was used as the end point of the titration, and the degree of oxidation of rice was determined by the following calculation formula. In addition, a blank test was conducted in parallel with the main measurement, in which no sample was put. Figure 3 shows the degree of oxidation of supercritical oil extracted from rice in each year. [Calculation] P: Milli-equivalent number (lipid oxidation degree) per 1 kg of sample [meq / k
g] V: Titration amount of sodium thiosulfate aqueous solution for this measurement [ml] V _B : Titration amount of blank test sodium thiosulfate aqueous solution [ml] N: Normality of sodium thiosulfate [N] F: For sodium thiosulfate Factor [-] W: Sample weight [g]

[0041]

According to the present invention, the oil content in rice can be efficiently extracted, and a method for easily and reliably evaluating the freshness of rice can be provided by simply determining the oxidation degree of the extracted oil by titration. .

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a supercritical extraction apparatus used in a rice oil extraction method according to the present invention.

FIG. 2 is a graph showing the relationship between the flow rate of carbon dioxide and the integrated amount of recovered oil in rice.

FIG. 3 is a graph showing the relationship between the age of rice and the degree of oxidation.

[Explanation of symbols] 1 cylinder 2 impression tube 3 filter 4 booster pump 5 pressure gauge 6 safety valve 7 check valve 8 cooler 9 residual heat column 10 extraction cell 11 stirrer 12 temperature measuring section 13 constant temperature bath 14 high pressure filter 15 filter 16 Trap 17 Ice bath 18 Saturator 19 Flowmeter V1 Back pressure valve V2-V4 Stop valve V5 Expansion valve

Claims (2)

[Claims] 1. A method for evaluating freshness of rice, which comprises extracting oil from rice by supercritical fluid extraction and measuring the degree of oxidation of the oil by iodine oxidation titration. 2. The method for evaluating freshness of rice according to claim 1, wherein the extraction is performed in a state where the raw rice is immersed in an alcohol solution.