JPH11142354A - Method for evaluating interior quality of fruit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable nondestructive and speedy evaluation of a sugar concentration, etc., of fruit, by measuring longitudinal relaxation time and traverse relaxation time of a nucleus of an atom present in a certain region of fruit by a nuclear magnetic resonance method, and evaluating the interior quality of the fruit on the basis of each relaxation time and a ratio between both relaxation time. SOLUTION: A watermelon 15 is placed at an approximate center of a bore of a main coil 1, and a longitudinal relaxation time T1 and a traverse relaxation time T2 of an atomic nucleus of hydrogen contained in a water molecule at the center region of the watermelon 15 are measured through the user of an MRI device. At this time, a stimulated echo method is used for the measurement to obtain an NMR signal while changing echo time and repetition time. Then through the use of the longitudinal relaxation time T1, the transverse relaxation time T2, and a ratio between both relaxation time T1/T2, sugar concentration is predicted by an equation for predicting sugar concentration; sugar concentration =-10.35×T1-5.3×T2-8.5×T1/T2+20.5. By this, it is possible to evaluate sugar concentration nondestructively without being affected by temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for non-destructively and quickly evaluating the internal quality of fruits, such as watermelon and melon, whose internal quality such as sugar content and ripening degree cannot be discriminated from the outside. In particular, the method of the present invention is applied to a shipping line of a fruit producer or a stock inspection line of a fruit and vegetable distributor, and is useful in optimizing the shipping timing of a product by classifying fruits and judging maturity. Internal quality assessment method.

[0002]

2. Description of the Related Art For fruits such as watermelons and melons whose internal qualities, such as sugar content and ripening, cannot be discerned from the outside, the timing of shipping is conventionally determined based on human experience and intuition. That is common. For example,
In watermelons, a method is employed in which the sound is determined by tapping the outer skin of the watermelon, or the softness of the chin is used. However, these judgment methods depend on personal ability, and a plurality of people work on the stocking line handling a large amount of fruit.
Variations in the determination of the product occur due to the individual differences, and dissatisfaction from the consumer side often occurs.

[0003] In particular, for relatively expensive fruits such as watermelons and melons, consumers often buy a single product, and the image of the product tends to be determined by the product purchased. In the case of relatively expensive fruits as described above, consumers must naturally demand a price commensurate with the price, but if the consumer purchases unsavory fruits, it will be extremely low in probability. Even if it is a product, the image of the whole product will be deteriorated, and not only will the trust in the producer be lost, but also the sales competitiveness will be lost. Further, in a situation where it is preferable that producers attach their own brands and add value to commodities as in recent years, deterioration of the image of commodities may have a decisive impact on producers. For these reasons, recently, various evaluation methods for fruits using various measurement techniques have been studied.

[0004]

Among the methods for evaluating the internal quality of fruits that have been studied so far, methods using the optical principle occupy the mainstream.
A method has been proposed in which an apple is irradiated with near-infrared light and the sugar content and the sourness of the apple are determined from its reflection spectrum. However, in this method, a good judgment result can be obtained for a fruit whose outer skin is relatively thin such as an apple and near-infrared light reaches the pulp, but the outer skin is relatively thick such as a watermelon and a melon. It has the disadvantage that it cannot be applied to fruits. In addition, this method has the disadvantage that only the quality near the outer skin can be measured, and the internal quality important for judging the degree of ripening of the fruit cannot be evaluated.

As another method utilizing the optical principle, there has been proposed a method in which fruit is destroyed to extract pulp, and the refractive index of juice squeezed from the pulp is optically measured. This method utilizes the fact that as the amount of solute dissolved in water increases, the dielectric constant of the entire solution increases, thereby increasing the refractive index of light. This method is called a refraction type sugar content measurement method, and is generally adopted as a method that can relatively easily measure the sugar content of fruits.
As a device for performing this method, a refraction type refractometer (see Examples described later) is commercially available, and the refraction measured by this device is expressed in units of Brix%.

[0006] However, this method has problems that it takes a long time to cut the fruit, it is difficult to apply the method online, and it is necessary to destroy the fruit to be evaluated. In particular, destruction of fruit is the most hated point of expensive fruit and cannot be applied to 100% inspection.

On the other hand, as means for nondestructively examining the state of fruit juice, nuclear magnetic resonance spectroscopy (MRS), which has been conventionally applied in the field of chemical analysis, has been receiving attention. This method is described in, for example,
As shown in the figure, the nuclear magnetic resonance frequencies of hydrogen atoms in molecules such as glucose and fructose contained in fruit juice are all different depending on the type of molecule, and nuclear magnetic resonance signals proportional to the concentration of each molecule Is used to measure the type and ratio of sugar in the juice.

[0008] This method is used for a sample, such as squeezed juice, in which the molecules therein can move relatively freely.
Good results are obtained. However, when the molecule is confined in a small area such as a cell gap, such as a juice component dispersed in the pulp, the molecular motion is restricted and the half width of the nuclear magnetic resonance signal is expanded, so that each component is , It becomes difficult to separate the signals, and the fruit juice component ratio cannot be actually obtained.

The present inventors have long studied from various angles in order to solve the above problems.
First, for the hydrogen nuclei in the water molecules contained in the juice, the longitudinal relaxation time (T
It has been found that there is a correlation between 1) and the transverse relaxation time (T2) and the sugar content of the juice measured by an optical method (Japanese Patent Application Laid-Open No. 8-313461). This technique evaluates the sugar content of watermelon by calculating the longitudinal relaxation time (T1) and the lateral relaxation time (T2) of a specific region in a fruit and applying these to the following equation (1). Sugar content = A × longitudinal relaxation time (T1) + B × lateral relaxation time (T2) + C (where A, B, and C are constants)

However, the present inventor has applied the above technique and further studied the evaluation of the sugar content in the central part of the watermelon. As a result, it has been found that the sugar content cannot be evaluated with desired accuracy depending on the conditions. That is, it was found that the measurement accuracy fluctuated greatly depending on the difference in the temperature of the fruit. The reasons could be considered as follows.

In the above invention, the temperature fluctuation of the fruit was not considered at all, but for example, "Pulse and Fourier Transform NMR" (Farrer, Becker;
According to Yoshioka Shoten, 1976), the longitudinal relaxation time (T1)
And the transverse relaxation time (T2) have been shown to be closely related to molecular motion, whereas molecular motion is known to be sensitive to temperature, so that the temperature is reduced by the longitudinal relaxation time (T1). It is fully expected to affect the value of the lateral relaxation time (T2).

The present invention has been made under such circumstances, and its object is to non-destructively control the internal qualities such as sugar content, acidity and ripening of fruits without being affected by the temperature of the fruits. Another object of the present invention is to provide a useful method for quick evaluation.

[0013]

Means for Solving the Problems The present invention which has achieved the above object is to select a certain region in a fruit and to longitudinally relax a nucleus of a certain atom present in the region by a nuclear magnetic resonance method. Time (T1) and transverse relaxation time (T2) are measured, and the internal quality of the fruit has the point of non-destructively evaluating the internal quality of the fruit based on each of these relaxation times and the ratio of the two relaxation times. This is an evaluation method. The method of the present invention is particularly effective when the fruit is watermelon, and is most effective as a method for evaluating the sugar content as an internal quality.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors first studied the temperature dependence of the longitudinal relaxation time (T1) and the transverse relaxation time (T2) of water molecules contained in watermelon. As a result, it was found that each of the relaxation times (T1, T2) exhibited temperature dependence, and particularly, the longitudinal relaxation time (T1) exhibited strong temperature dependence. FIG. 1 is a graph showing the temperature dependence of each relaxation time (T1, T2). The following is clear from the results. That is, the constants A, B and C in the above equation (1)
Is actually expressed as a function of temperature. As can be easily understood from this, the above-described technique is strongly affected by temperature.

In such a situation, in a place where there is no temperature control equipment, such as a fruit sorting place provided near the production site, every day (in extreme cases, every hour), the above (1)
Since the constants A to C in the equations fluctuate, the above technique cannot be applied as it is. Of course, in principle, it would be possible to apply this technique if the temperature inside the fruit could be measured. That is, the relationship between the longitudinal relaxation time (T1) and the lateral relaxation time (T2) and the temperature is obtained in advance, and the values of the longitudinal relaxation time (T1) and the lateral relaxation time (T2) measured at various temperatures are calculated as follows: If the value is converted into a value at a certain reference temperature, the influence of the temperature is corrected, and the sugar content can be accurately obtained. However, as a practical problem, it is difficult to accurately measure the temperature inside the fruit, and there is a problem that equipment costs required for a radiation thermometer and the like used for measuring the temperature also increase.

Therefore, the present inventors have further studied a technique capable of accurately grasping the internal quality of a fruit without being affected by the internal temperature. As a result, two certain regions in the fruit are selected, and the longitudinal relaxation time (T1) of the nucleus of a certain atom present in the two regions is determined by the magnetic resonance method.
And measuring the lateral relaxation time (T2) and evaluating the internal quality of the fruit based on the ratio of the measured values of each relaxation time, it was found that the effect of the fruit temperature could be reduced, and its technical significance was recognized. Therefore, the application was filed earlier (Japanese Patent Application No. 8
No. 113679).

However, there is still room for improvement in the present invention. That is, in this method, the longitudinal relaxation time (T1) and the transverse relaxation time (T2) of the nucleus of a certain atom existing in two regions are measured for one sample. There was a problem that time was long.

Under these circumstances, the present inventors have conducted further intensive studies to solve the problems in the above method. As a result, a certain region in the fruit is selected, and the longitudinal relaxation time (T1) and the transverse relaxation time (T2) of the nucleus of a certain atom present in the region are measured by the nuclear magnetic resonance method. Non-destructive evaluation of the internal quality of the fruit based on the relaxation time and the ratio of the two relaxation times can shorten the measurement time and accurately measure the internal quality of the fruit without being affected by the internal temperature. The present inventors have found that the present invention can be grasped and completed the present invention.

In the present invention, the longitudinal relaxation time (T1)
And the target for measuring the value of the lateral relaxation time (T2),
The nucleus of a certain atom existing in a certain region in the fruit may be used, and is not particularly limited. Examples of the atom include carbon and hydrogen. However, from the viewpoint of shortening the measurement time, the measurement target is preferably a hydrogen nucleus. It is preferable that the same hydrogen nucleus belongs to a water molecule for the same reason as described above. That is, water has the largest ratio among the juice components, and the nuclear magnetic resonance signal obtained therefrom is greater than that from any other part, and the measurement time can be reduced. Further, if the measurement target is a hydrogen nucleus of a water molecule, there is an advantage that signals from other sugar components and the like can be relatively neglected, and the measurement system can be simplified.

According to the present invention, since the location where the longitudinal relaxation time (T1) and the lateral relaxation time (T2) are measured may be in one area, the measurement time can be greatly reduced, and practical application online. Will be able to respond sufficiently.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples are not intended to limit the present invention, and any design change in the spirit of the foregoing or the following is not limited to the present invention. It is included in the technical scope.

[0022]

FIG. 2 is a block diagram of an example of an MRI apparatus configured to carry out the method of the present invention, and FIG. 3 is a timing chart when the apparatus is applied. Here, the center axis of the bore will be referred to as the z-axis, the vertically upward direction orthogonal to this straight line will be referred to as the y-axis, and the horizontal direction will be referred to as the x-axis.

In FIG. 2, reference numeral 1 denotes a main coil formed of a superconducting magnet to form a static magnetic field, and 2 denotes three gradients for forming a magnetic field gradient in each of a z-axis direction, a y-axis direction, and an x-axis direction. Magnetic field coils 3 and probe coils 3 respectively transmit a 90-degree pulse and detect an NMR signal.
In connection with the probe coil 3, a matching network 4 for efficiently transmitting and receiving signals, a preamplifier 5 for amplifying a small NMR signal, and a duplexer 6 for preventing a 90-degree pulse with a large amplitude from entering. Are provided respectively.

The receiver 7 further amplifies the signal from the preamplifier 5 to perform phase detection, and sends the signal to the control signal processing computer 8. The three gradient magnetic field coils 2
Is controlled by the control signal processing computer 8 via three gradient amplifiers 9 and generates a predetermined magnetic field gradient according to the timing chart shown in FIG. The transmitting amplifier 10, the synthesizer 11, the modulator 12, and the waveform generating circuit 13 are for generating a 90-degree selective pulse.

Using the above-described MRI apparatus, the present inventors place a watermelon 15 approximately in the center of the bore of the main coil 1, and set the longitudinal relaxation time (T1) of hydrogen nuclei contained in water molecules in the central region of the watermelon. ) And transverse relaxation time (T2) were measured. At this time, in the stimulated echo method (STEAM method), a method of obtaining an NMR signal while changing the echo time TE and the repetition time TR (see FIG. 3) was employed. This procedure is as follows.

Since the watermelon 15 is placed in a static magnetic field in the z-axis direction, the macroscopic magnetic moment formed by the hydrogen nucleus spin of the fruit juice of the watermelon 15 is initially due to the rotation of the axis parallel to the z-axis. Doing a differential movement. First, in order to limit the slice area in the z-axis direction, while applying a gradient magnetic field a in the z-axis direction, under the control of the control signal processing computer 8, the synthesizer 11, the modulator 12, the waveform generation circuit 1
3 and the selectivity 90 created by the transmitting amplifier 10
A degree pulse is applied. By this operation, only the spin on the specific slice plane orthogonal to the z-axis changes the direction by 90 degrees. Subsequently, if the same operation is performed while applying a gradient magnetic field d in the x-axis direction and a gradient magnetic field f in the y-axis direction, only the magnetic moment in the cubic region where three orthogonal slices overlap is reduced to 27.
The spin in the region where the two slices of the three slices overlap by 0 degree will be rotated by 180 degrees.

After time Te / 2 has elapsed after the selection operation for the three axes is performed, an echo signal called stimulated echo (Stimulated Echo) can be obtained. At this time, since there is no transverse magnetization in the region rotated by 180 degrees, no nuclear magnetic resonance signal is ideally generated. Therefore, the stimulated echo signal observed outside is only from a cubic region where three orthogonal slices overlap, and slice selection can be performed so that this region matches the region where the sugar content is to be evaluated. For example, it is possible to evaluate only a specific area. However, in practice, a large number of echo signals other than stimulated echo signals are generated. To prevent this, magnetic field gradients b, c, and e having arbitrary strengths are added at time Te and Tm in FIG. Was added. If the intensity of the stimulated echo signal obtained in the above sequence is I, I can be described as the following equation (2). I @ exp (-Te / T2) .exp (-Tm / T1). [1-exp (-Tr / T1) ... (2)

In order to investigate the influence of the temperature, the present inventors preliminarily adjusted the temperature to each of 5 ° C., 10 ° C., 15 ° C., 20 ° C., and 25 ° C. (5 in total). ) Is used as a sample, and 3 × 3 × 3 at the center of the sample is used.
The longitudinal relaxation time (T1) and the transverse relaxation time (T2) of hydrogen nuclei contained in water molecules in a (cm) cubic region were measured. At this time, the ratio (T1 / T2) of the measured values of the longitudinal relaxation time (T1) and the lateral relaxation time (T2) was also measured.

On the other hand, the sugar content of the watermelon was measured using a refraction type refractometer after the measurement of each relaxation time was completed and the sample was broken to take out the central measurement region. For 25 samples, the multiple regression line between the measured value (observed value) by the refraction refractometer, the longitudinal relaxation time (T1), the transverse relaxation time (T2), and the ratio (T1 / T2) of these two relaxation times was obtained. As a result, it was confirmed that there was a relationship as shown in the following equation (3). The “sugar content” on the right side of the equation (3) is a predicted value obtained from the longitudinal relaxation time (T1), the lateral relaxation time (T2), and the ratio of the two relaxation times (T1 / T2). Sugar content = -10.35 x longitudinal relaxation time (T1)-5.3 x lateral relaxation time (T2)-8.5 x relaxation time ratio + 20.5 ... (3)

As described above, the vertical relaxation time (T1) and the horizontal relaxation time (T2) have different temperature dependences. That is, the longitudinal relaxation time (T1) has a particularly large temperature dependency as compared with the transverse relaxation time (T2), and varies from about 40 ms to 50 ms per 1 ° C., but the transverse relaxation time (T2) is substantially temperature dependent. Is not shown (see FIG. 1).
reference). Therefore, the vertical relaxation time (T1) and the horizontal relaxation time (T
The ratio (T1 / T2) of 2) is an index indicating the temperature. The present invention has succeeded in eliminating the influence of temperature by incorporating the above-mentioned principle and incorporating the ratio of the two relaxation times (T1 / T2) into a formula for predicting the sugar content.

According to the above procedure, the present inventors measured the sugar content value (predicted value) predicted by the formula (3) and the refraction type refractometer for 30 separately prepared samples (watermelon). The relationship between the measured sugar content values (observed values) was investigated. The result is shown in FIG. Then, when the correlation coefficient between the predicted value and the actually measured value was obtained from the results of FIG. 4, it was confirmed that a high value of 0.96 was obtained.

On the other hand, when the predicted value of the sugar content was measured using the same sample according to the above equation (1), it was confirmed that the correlation coefficient between the observed value and the predicted value was only 0.48. From these facts, it was proved that according to the method of the present invention, the sugar content of watermelon can be measured nondestructively in a short time without being affected by the temperature of the sample.

[0033]

The present invention is configured as described above.
A method has been realized in which the internal quality such as the sugar content of a fruit can be evaluated nondestructively and quickly without being affected by the temperature of the fruit. In addition, when this method is applied to a shipment line of a fruit producer or a stock inspection line of a fruit and vegetable distributor, it is extremely useful in optimizing the timing of product shipment by classifying fruits and judging the degree of maturity. Yes, its effects are highly expected.

[Brief description of the drawings]

FIG. 1 is a longitudinal relaxation time (T1) and a lateral relaxation time (T2).
4 is a graph showing the temperature dependence of the present invention.

FIG. 2 shows an MRI configured to carry out the method of the invention.
It is a block diagram of an example of a device.

FIG. 3 is a timing chart when the device shown in FIG. 2 is applied.

FIG. 4 is a graph showing the relationship between the sugar content (predicted value) of watermelon predicted by the method of the present invention and the sugar content (observed value) measured by an optical refractometer from fruit juice actually squeezed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main coil 2 Gradient magnetic field coil 3 Probe coil 4 Matching network 5 Preamplifier 6 Duplexer 7 Receiver 8 Control signal processing computer 9 Gradient amplifier 10 Transmission amplifier 11 Synthesizer 12 Modulator 13 Waveform generation circuit 15 Watermelon

Claims (3)

[Claims] 1. A certain region in a fruit is selected, and longitudinal relaxation time (T1) and transverse relaxation time (T2) of a nucleus of a certain atom present in the region are measured by nuclear magnetic resonance. A non-destructive evaluation of the internal quality of the fruit based on each relaxation time and the ratio of the two relaxation times. 2. The evaluation method according to claim 1, wherein the fruit is a watermelon. 3. The evaluation method according to claim 1, wherein the sugar content is evaluated.