GB2135059A

GB2135059A - A method for non-destructively grading fruits and other foodstuffs

Info

Publication number: GB2135059A
Application number: GB08401058A
Authority: GB
Inventors: Koichi Akimoto
Original assignee: Gifu University NUC
Current assignee: Gifu University NUC
Priority date: 1983-01-26
Filing date: 1984-01-14
Publication date: 1984-08-22
Also published as: GB2135059B; CA1212145A; DE3402303A1; GB8401058D0

Abstract

Fruit is non-destructively graded having regard to the intensity of nuclear magnetic resonance signals relating to sugars and/or organic acids contained therein; signals may be obtained for each of a group of fruits in turn. Water contained in the fruit may be used as an internal standard. Other foodstuffs may be tested similarly, e.g. vegetables, eggs, flesh, fish, grain. and living plants and beasts.

Description

SPECIFICATION A method for non-destructively grading fruits The present invention relates to a method for non-destructively grading fruits.

In the invention the quantitative measurement of a component such as the sugar content or the acidity of fruits is non-destructively effected by nuclear magnetic resonance to give an indication of quality thereof against a standard. The standard may be predetermined external standard or in the case where there is use of nuclear magnetic resonance for measuring components contained in foods having known percentage water content there will be no necessity to provide additional reference material for comparison with measured results.

Almost all conventional methods for measuring the sugar content or the acidity of fruits as an indication of quality, particularly of the taste thereof, are effected by destructive inspections, so that fruits which have been used for the quality inspection cannot be further used for merchandise, and hence the quality of the batch of fruit must be extrapolated from the sampling inspection. However, the taste of fruits depends strongly on the natural conditions, and varies individually even under similar natural conditions, so that the measured sugar content or the measured acidity can be remarkably different even between individual fruits picked from the same plant.

Consumers have usually bought a few fruits as a result of individual selection and are deeply influenced by the taste of individual fruits brought in that way. So when the consumer is disappointed by the taste of one of a group of fruits which he believed to be as good, the reputation of the whole group with regard to quality is lost.

A satisfactory way of standardising the quality of fruits with respect to taste is by referring to the sugar content or the acidity thereof, and we have now developed non-destructuve means for individually testing the whole group of fruits in a short time without damaging them.

In the prior art, some non-destructive testing methods have been provided for indirectly measuring or estimating the quality of fruits in respect to the taste, but the accuracy thereof is too low to sufficiently restore the reputation of the fruit quality control which is apt to be lost as a result of sampling inspection. Consequently, a genuine non-destructive method for measuring the sugar content or the organic acidity of fruits so as to facilitate the direct and quantitative estimation of the quality has not yet been established.

Among these conventional methods for non-destructively grading fruits, for instance, an optical method for non-destructively grading fruits wherein the taste is indirectly estimated from the ripeness of fruits by measuring the pigment content in the process of discoloration in response to the ripeness from green to yellow, red or others with the use of visual light or infrared ray has the defect that the measuring accuracy is extremely low and that the information is obtained only from the surface of fruits. The other method for measuring the sugar content or the acidity, the indication of taste by the infrared absorption analysis, is extremely difficult of achievement and in terms of equipment because of the nature of the fruit, which is made up of a complex of various components including a lot of water.

There is a non-destructuve fruit grading method provided for estimating the quality of fruits by detecting the number and distribution of seeds in the fruit with the use of X-ray or other radiations; the high accuracy of the estimation of the quality cannot be expected, because this method is effected on the basis of statistical correlation.

Moreover, regarding the non-destructive dynamic fruit grading method provided for estimating the ripeness of fruits by the variation of peculiar number of oscillation in response to the ripeness, it is difficult to obtain the high accuracy of estimation because the method is affected by the size, the flesh density and the like. On the other hand, the non-destructive electrical method conventionally proposed for measuring the electrical property, for instance, the direct current resistance, the high frequency resistance or the high frequency capacitance in relation to the ripeness of fruits is difficult to be theoretically investigated and further has too low accuracy of measurement so far as the conventionally proposed methods are concerned, so that the certainty enough to estimate the quality of fruits has not yet been attained.

For ideally realizing the above mentioned method for non-destructively grading fruits, it is expected to practically use the measuring method effected by utilizing the nuclear magnetic resonance phenomenon, so as to industrially facilitate the rapid individual test of the whole group of fruits.

In this connection, by the above measuring method effected by utilizing the nuclear magnetic resonance phenomenon which has a recent tendency of utilization for the quantitative analysis of very little components contained in a target, the target is usually submitted to the measurement in a form of water solution, so as to obtain large nuclear magnetic resonance signals formed by activating the molecular motion in the target. However, fruits which necessitate the individual test of the whole group thereof contain individually a large amount of water in fleshes thereof, although surfaces thereof present the solid state.So that sufficiently large nuclear magnetic resonance signals enough to facilitate the measurement thereof can be obtained, and hence this measuring method effected by utilizing the nuclear magnetic resonance phenomenon can be recognized to be the most suitable to the method for non-destructively grading fruits.

In the above mentioned quantitative measurement of contained components under the utilization of nuclear magnetic resonance phenomenon, as is well known, atomic nuclears consisting in each of component compounds of the target, which is disposed in a high frequency magnetic field superposed on a static magnetic field, generate the nuclear magnetic resonance signals at respectively inherent frequencies in response to the difference of chemical circumstances in which each component compounds are respectively disposed, even if these atomic nuclears belong to the same kind. So that, the quantitative analysis of each component compounds can be achieved by measuring the magnitudes of the nuclear magnetic resonance signals at each resonance frequencies respectively.

In this connection, it is general for the above mentioned atomic nuclear to be measured to employ hydrogen atomic nuclear 1H having mass number 1, carbon atomic nuclear 13C having mass number 1 3 and oxygen atomic nuclear 170 having mass number 17, which are universally contained in various kinds of component compound.

The resonance frequencies presented by the same atomic nuclear respectively with regard to each component compounds, which contain universally the atomic nuclear concerned, are different from each other in response to the chemical circumstances which are different also from each other with regard to each component compounds. So that, it is usual to represent the respective resonance frequencies of each component compounds respectively by shift amounts of resonance frequencies, namely, so-called chemical shifts of each component compounds from that represented by the standard substance containing the atomic nuclear concerned in common.It is preferably for the standard substance standardized with respect to these chemical shifts, to emply a substance which has very little mutal reaction against the target disposed and measured together therewith and presents a single resonance frequency clearly apart from those presented by usual compounds consisting in the target. It is conventionally general to employ tetramethylsilane (TMS) for this standard substance.

In this connection, the manner of measurement effected by utilizing the nuclear magnetic resonance phenomenon will be explained by referring to an outlined arrangement of the measuring apparatus concerned as shown in Fig. 1. In the configuration as shown in Fig. 1, a pair of electromagnets B disposed opposite to each other is controlled by a lock-on controller K to form a static magnetic field Ho having an intensity of, for instance, 23,500 Gauss.A pair of sweeping coils C coupled with the pair of electromagnets B is driven by a magnetic field modulator N, so as to superpose a low frequency alternate magnetic field Hm having an appropriate sweep frequency Vm. The target A of, for instance, fruit or the like is disposed in a magnetic circumstance consisting of this superposed magnetic field Ho + Hm and then a transmitter coil D surrounding the target A is driven by a transmitter I comprised in an RF unit G, so as to apply a high frequency alternate magnetic field having a frequency v5 on the target A in further superposition on the superposed magnetic field Ho + Hm.The frequency v5 of this high frequency alternate magnetic field is set up, for instance, at 100 MHz when the nuclear magnetic resonance should be caused in the hydrogen nuclear 1H.

In this situation, the frequency vm of the low frequency alternate magnetic field Hm applied by the coil C is swept. As a result, when the superposed magnetic field frequency V5 + vm coincides with the resonance frequency of the atomic nuclear to be measured, an alternative magnetic field having a frequency obtained by adding the amount of the chemical shift, which is inherent to the concerned atomic nuclear contained in the component compound of the target A, to the superposed magnetic field frequency v5 + vm is catched by a receiving coil E, and hence an induced current is generated in the receiving coil E.

This induced current is detected by a detector provided in a receiver H comprised in the RF unit G. In this situation of the receiver H and the transmitter I which are comprised in the RF unit G, the receiving frequency and the transmitting frequency are swept in synchronism under the control of a revolution indicator F. A transmitted signal derive from the RF unit G is applied to an NMR signal detector J, and then the amount of the chemical shift, which is inherent to the component compound contained in the atomic nuclear to be measured, and the nuclear magnetic resonance signal concerned are compared with the similar amounts obtained with regard to the standard substance, and, as a result, the kind and the content of the component compound concerned can be calculated.

The standard substance used in the content measurement effected by utilizing the nuclear magnetic resonance phenomenon as mentioned above is conventionally provided by mixing or coexisting the aforesaid tetramethylsilane in the target, or by the separate measurement apart from the target. However, in the non-destructuve measurement of the solid state substance, the standard substance used as the inner standard is required to be dis posed together with the target within the same position, so that the measurement is affected by many limitations.On the other hand, with respect to the standard substance used as the outer standard, it is required to make the same magnetic circumstances between the target and the standard substances, or, when these magnetic circumstances are different from each other, to correct the difference, so as to facilitate the comparison between the respective measured results. Consequently, the conventional standard substance has a defect that the measuring apparatus is imposed with the excessively high accuracy of measurement.

An object of the present invention is to remove the above mentioned conventional defects and hence to provide a method for nondestructively grading fruits wherein the quality of fruits, particularly the sugar content or the acidity as the indication of taste thereof is comparatively readily and certainly measured in direct, and further the individual examination of the whole group of fruits can be comparatively speedily and industrially effected.

Another object of the present invention is to provide a method for non-destructively measuring a solid state substance having water content such as fruits and the like under the utilization of nuclear magnetic resonance phenomenon, particularly wherein the measurement can be extremely simply and certainly effected by setting up the standard substance within the solid state substance itself provided for the target without the use of the outer standard substance separated from the target.

The feature of the method for non-destructively grading fruits is that, by virture of utilizing the nuclear magnetic resonance (NMR) phenomenon which is presented in the high frequency alternate magnetic field by the atomic nuclear having the spin quantum number I being not zero among various kinds of atomic nuclears originating the sugar and the organic acid which dominates the taste of fruits, the sugar or the organic acid of fruits is non-destructively quantified and then compared with the standard values thereof, so as to facilitate the individual gradation based on the taste of fruits.In other words, the method for non-destructively grading fruits according to the present invention is characterized in that a fruit is disposed in the alternate magnetic field as the target to be measured, the intensity of the nuclear magnetic resonance signal of the atomic nuclear, which has the spin quantum nubmer being not zero with respect to at least either one of the sugar and the organic acid contained in fruits, being measured, the resultant measured value being compared with the predetermined standard value of quality.

The method for non-destructively grading fruits according to the present invention is further characterized in that, when the component content of the solid state substance having known water content is non-destructively measured on the basis of nuclear magnetic resonance phenomenon, the nuclear magnetic resonance spectrum presented by the component contained in the solid state substance is compared with the water contained therein as the standard substance having the known nuclear magnetic resonance spectrum, so as to obtain the content of the component concerned.

For the better understanding of the invention, reference is made to the accompanying drawing, in which: Figure 1 is a block diagram showing an example of configuration of the apparatus for measuring the nuclear magnetic resonance, so as to effect the method according to the present invention, as mentioned above.

Through the drawing, A is a target (fruit), B is an electromagnetic (parmanent magnet), C is a magnetic field modulating coil, D is a high frequency alternate magnetic field coil, E is a nuclear magnetic resonance signal detecting coil, F is a revolution indicator, G is an RF unit, H is a detector (receiver), I is a transmitter, J is an NMR signal detector, K is a lock on controller, L is an oscilloscope, M is a recorder, and N is a magnetic field modulating circuit.

The quality of fruits as merchandise is estimated principally with respect to the shape, the size, the appearance represented by the gloss and the taste of flesh, and particularly the quality regarding the appearance can be non-destructively and individually examined on the whole through the industrial process effected by the aforesaid conventional method for non-destructively grading fruits.

However, the taste of flesh which substantially dominates the quality of fruits is difficult to be individually and certainly estimated without the direct measurement of the sugar content or the acidity which is regarded as the universal indication of fruits.

The sugar content or the acidity of fruits can be estimated through the measurement of the content of the sugar or the organic acid contained in the flesh thereof. On the other hand, by the measuring method effected by utilizing the nuclear magnetic resonance phenomenon which has a recent tendency of utilization for the quantitative analysis of very little components contained in a target, the target is usually submitted to the measurement in a form of water solution, so as to obtain large nuclear magnetic resonance signals formed by activating the molecular motion in the target. However, fruits which necessitate the individual test of the whole group thereof contain individually a large amount of water in fleshes thereof, although surfaces thereof present the solid state.So that, sufficiently large nuclear magnetic reso nance signals enough to facilitate the measurement thereof can be obtained.

In view of the above fact, the method for non-destructively grading fruits according to the present invention is arranged in a manner such that the non-destructive individual test of the whole group of fruits can be certainly and readily effected by measuring the content or the density of sugar or organic acid contained in flesh of fruits under the utilization of nuclear magnetic resonance phenomenon and then estimating the quality of each of the group of fruits through the comparison between the resultant measured values and the usual standard value.In this connection, the aforesaid non-destructive individual test of fruits does not consist only of the so-called non-destructive method whereby fruits is not mechanically or chemically destroyed at all, but also of the method wherein fruits are submitted to the examination after cut off in a shape being suitable to merchandise, so as to facilitate the provision thereof for sale after the examination.

In the above mentioned quantitative measurement of contained components under the utilization of nuclear magnetic resonance phenomenon, as is well known, atomic nuclears consisting in each of component compounds of the target, which is disposed in a high frequency magnetic field superposed on a static magnetic field, resonates to the high frequency magnetic field at respectively inherent frequencies in response to the difference of chemical circumstances in which each component compounds are respectively disposed, even if those atomic nuclears belong to the same kind, namely, at the so-called Larmor frequency which is the frequency of precession caused around the direction of the static magnetic field when the whole spin quantum number is not zero.The spectrum of the resultant resonant magnetic field is varied in response to respective kind of the component compound and respective intensity of the static magnetic field. This resultant resonant magnetic field is detected and then the amplitude of the nuclear magnetic resonance signal generated at the resonant frequency is measured through the operational process thereof.

As a result, the component compound contained the target as the compound effecting the nuclear magnetic resonance of the atomic nuclear thereof can be specified, because the amplitude of the nuclear magnetic resonance signal is proportional to the amount of atomic nuclears presenting the nuclear magnetic resonance. The spectrum of this nuclear magnetic resonance signal is called as the nuclear magnetic resonance spectrum, that is, the NMR spectrum.As an atomic nuclear adopted for the target to be measured, it is usual to adopt hydrogen atomic nuclear 1H having quantum number 1, carbon atomic nuclear 13C having quantum number 1 3 and oxygen atomic nuclear 170 having quantum number 1 7. The nuclear magnetic resonance spectra presented by these atomic nuclears are called as 'H NMR spectrum, '3C-NMR spectrum and 170 NMR spectrum respectively.

On the other hand, the target substances including fruits, which are objects to be measured according to the present invention, are usually mixtures of various component compounds, so that for the quantitative analysis of each component compounds contained in the target substance, such as the sugar or the organic acid contained in fruits, the resonance frequency of the nuclear magnetic resonance signal which can be submitted to the measurement is previously determined with regard to the atomic nuclear to be measured in each component compounds, as well as the relation between the intensity of nuclear magnetic resonance signal at each resonant frequencies and the content of each component compounds is previously prepared, so as to set up the necessary calibration curve.

The resonant frequencies presented by the same atomic nuclear with regard to each component compounds respectively differ from each other as mentioned earlier, in response to different chemical circumstances corresponding to each component compounds respectively, so that the shift amount of the resonant frequency of each component compounds from that presented by the standard substance contain in the same atomic nuclear, that is, the so-called chemical shift is usually employed for representing the respective resonant frequency.

As the standard substance used for the standard with respect to the chemical shift, it is preferable to select an substance which is scarcely effected by the interaction between the target substance disposed and measured together therewith and presents a single resonant frequency clearly apart from those presented by usual compounds consisting in the target to be measured. It is general that tetramethylsilane (TMS) is employed for this standard substance.

In the measuring arrangement as shown in Fig. 1, when the target A is a fruit and the component compound thereof is the sugar or the organic acid, the measured values thereof based on the nuclear magnetic resonance phenomenon can be obtained as mentioned later.

However, by referring to the numerous result measured by the inventor, the measured values of the sugar content or the acidity obtained under the utilization of nuclear magnetic resonance phenomenon and those obtained by the conventional method has a certain deviation from each other, at a constant ratio, although being very small. So that, the above measured values are required to be calibrated to usual sugar content or usual acidity by introducing specified coefficients.

In this connection, the above mentioned manner for deriving the nuclear magnetic resonance (NMR) signals is called as the magnetic field modulation frequency sweeping method, and according thereto, the contents of the sugar, the organic acid and the like component compounds contained in the target to be measured can be quantitatively measured in response to the amplitude of the derived NMR signal. In addition, the identification of the kinds of sugar, organic acid and the like component compounds can be effected, as mentioned above, on the basis of the chemical shift deviated from the measured value regarding the standard substance, for instance, aforesaid tetramethylsilane (TMS) which is measured together with the target A, that is, the standardized difference of the nuclear magnetic resonance frequency between the target and the standard substance.

Next, the measured results of the sugar content or the acidity of fruits according to the method for non-destructively grading fruits of the present invention will be described hereinafter.

Fruits as suitable for the non-destructive gradation effected under the utilization of nuclear magnetic resonance phenomenon according to the present invention are, for intance, citrus fruits, grape, water melon, peach, pear, melon, persimmon, apple, strawberry, kiwi fruits and the like.

sugars as suitable for the target to be quantitatively measured are typical sugars, that is, glucose, fructose, sucrose and the like.

Furthermore, organic acids as suitable for the target to be quantitatively measured are citric acid, malic acid, tartaric acid and the like. In this connection, although fruits to be measured by the method of the present invention is not required to be restricted to raw fruits immediately after harvested, extremely parched fruits are not suitable. On the other hand, the nuclear magnetic resonance measuring apparatus provided for the method for non-destructively grading fruit according to the present invention as arranged, for instance, as mentioned above is industrially suitable to be used in a situation where it is partially included in a conventional fruit grading apparatus as a new tester.

Measured Example 1 For the target to be measured, Unshu mandarin was selected. With respect to the sugar and the organic acid thereof the 13C-NMR spectrum was measured. Regarding the sugar, contents of sucrose, fructose and glucose were respectively measured, while, regarding the organic acid, content of citric acid was measured. On the basis of those measured data, with respect to each component of these sugars and acid, a linear equation for the calibration between the intensities of the nuclear magnetic resonance signals and the contents of these components which were measured by the conventional method was prepared.

The value of chemical shift of the nuclear magnetic resonance utilized for the measurement of the aforesaid '3C-NMR spectrum, which was measured with the standard substance of tetramethylsilane (TMS), was 73.0 ppm regarding sucrose, 103.3 ppm regarding fructose, 74.5 ppm regarding glucose and 175.2 ppm regarding citric acid. The correlation coefficient between the intensity of nuclear magnetic resonance signal and the content, which was obtained according to the above mentioned linear equation for the calibration, was 0.8-0.9. In this connection, for the standard substance, tetramethylsilane (TMS), which was enclosed in a capillary tube together with heavy acetone used for the inner lock and was nearly disposed around a fruit rotated as the target, was used for the internal standard.

After the correlation coefficient was set up according to the linear equation of the calibration between the intensity of the nuclear magnetic resonance signal and the content, the unknown 13C-NMR spectrum of sugar and organic acid contained in Satsuma mandarim (Citrus Unshiu Marc,) was measured similarly as mentioned above. Respective contents of sucrose, fructose, glucose and citric acid could be very simply and readily obtained from the intensity of the nuclear magnetic resonance signal which was calibrated according to the above linear equation for the calibration similarly as mentioned above. The result of grading of Satsuma mandarin adopted as the target, which was effected by estimating the quality thereof with the use of the above resultant component content as the indication thereof, was extremely excellent as mentioned later.

Measured Example 2 With respect to the same target as in the above example 1, 1H-NMR spectrum was measured, and then contents of sucrose, glucose and citric acid were obtained through the similar process as mentioned above.

The chemical shift value of the nuclear magnetic resonance signal used for measuring the 1H NMR spectrum was, under the use of the TMS standard similarly as mentioned above, 5.33'-'5.38 ppm regarding sucrose, 5.14-5.19 ppm and 3.39 ppm regarding glucose and 3.14 ppm regarding citric acid.

The accuracy of the 1H-NMR spectrum measurement was 0.82-0.89 as expressed with the use of the correlation coefficient similarly as mentioned above.

Measured Example 3 With respect to Delaware grape berries adopted for the target to be measured, 13C NMR spectrum was measured, so as to obtain the contents of glucose and fructose contained therein. The accuracy of this 13C-NMR spectrum measurement was 0.90-0.99 as expressed with the use of multiple correlation coefficient. The value of chemical shift utilized for this '3C-NMR spectrum measurement was, under the use of TMS standard similarly as mentioned above, 97.7 ppm, 82.3 ppm, 74.5 ppm and 67.5 ppm regarding glucose and 103.3 ppm, 99.7 ppm, 72.8 ppm, 65.7 ppm, 65.0 ppm and 62.4 ppm regarding fructose, these measured results being respectively calibrated according to the multiple regression equation.

Next, with respect to the data of contents of sugar and organic acid cntained in fruits, which data are obtained on the basis of the measurement of nuclear magnetic resonance spectrum according to the present invention as mentioned above and the hit rate of the quality estimation of fruits by referring to the grading based on these data, the results of the investigation thereof will be described.

Generally speaking, tastes of vegetables and fruits have deep relations with the contents thereof, particularly, those of fruits are mostly affected by the contents of sugar and organic acid contained therein. For example, with respect to aforesaid Satsuma mandarin, the following relation between the taste and the contents of sugar namely the total sugars and organic acids has been clarified by the estimation of the measured results according to the present invention.

A group of testees consisting of thirty consumers and thirty persons concerned to mandarin production tasted Satsuma mandarins harvested respectively in four production districts. The manner of tasting such that three of four segments of mandarins harvested in each district were alloted in each dishes respectively. Testees tasted these segments of mandarins in random sampling manner. The results of tasting were reported according to seven step gradation regarding the fancy, that is, from "very delicious" to "very unsavory", as well as according to seven step gradation regarding the mellowness and the sourness, that is, for "very mellow" to "very sour".

Thus, the relation between these results and the contents of sugar and organic acid contained in the same samples which were measured by the conventional methods was analysed. In this connection, the analysis of sugar and organic acid was effected by employing the high speed liquid chromatography.

According to the result of the above mentioned analysis, it is clarified that the generally preferred taste of fruits is the taste of fruits having the content more than 1 2.0% of sugar and the content 0.8-1.2% of organic acid, that is, having the content ratio 10-1 5 which is expressed by the ratio of contents between sugar and organic acid. In addition, the linear relation is recognized between the content of sugar and the degree of fancy, the larger the former being, the higher the latter is. On the other hand, the content of organic acid affects the degree of fancy in relation to the content of sugar.Moreover, the step of estimation regarding the degree of fancy is varied in the case that the content of sugar presents a difference of 1.4-1.8% and that the content of organic acid presents a difference of 0.4-0.5%.

The contents of sugar and organic acid contained in Unshu mandarin as the target are distributed respectively within ranges of 8.0-14.0% and 0.53-1.49%, so that the allowable error of the measured values with respect to the maximum content becomes 10.0% regarding sugar and 26.8% regarding organic acid.

On the other hand, the accuracy of measurement by the method for grading fruits according to the present invention, in the situation where the multiple regression equation is adopted as an estimating equation used for the operational process of the measured results, can be sufficiently held within the range of allowable error, so that, under the consideration of the aforesaid result of taste estimation, the result of nuclear magnetic resonance spectrum measurement according to the present invention can be practically submitted to the estimation of the taste of fruits.

Consequently, as mentioned above, by referring to the minimum difference of contents of sugar and organic acid which difference causes the variation of the estimation steps of the degree of fancy regarding mandarin, the taste estimation is prepared with three steps by 2.0% step regarding the content of sugar and by 0.4% step regarding the content of organic acid. In this situation, with respect to mandarins, the contents of sugar of which belong to each steps of -10.0%, 10.0-12.0% and 12.0- respectively and the contents of organic acid of which belong to each steps of -0.8%, 0.8-1.2% and 1.2%respectively, the taste estimation was effected by the similar method as mentioned above.

According to the result of this taste estimation, the measured result obtained by the fruit grading method of the present invention is clarified to facilitate the expression of the degree of fancy for mandarin.

It was clarified also that the higher degrees of fancy in the above mentioned result of the estimation of the degree of fancy could be obtained for the content more than 12.0% of sugar and for the content 0.8-1.2% of organic acid regarding the mandarin producers, while the content more than 12.0% of sugar and for the content less than 0.8% of organic acid regarding the usual male consumers and for the content 10.0-12.0% of sugar and for the content 0.8-1.2% of organic acid regarding the usual female consumers.

On the other hand, in the result of the similar estimation of the degree of fancy for Persimmon (Diospyros Kaki L. cv. Fuyu) as mentioned above, the taste of persimmon could be represented by the content of sugar only, and the contents of sugar of persimmons harvested in each production districts were distributed within the range 9.8-17.8%. This distribution range of the content of sugar contained in persimmon was prepared, similarly as in the above case of mandarin, with four steps less than 12.0%, 12.0-14.0%, 14.0-16.0% and more than 16.0%. The estimation of the degree of fancy for persimmons, the results of measurement of which according to the present invention belonged to each of these steps, was effected similarly as in the above case of mandarin.

According to the investigation of relation between the result of the above estimation of the degree of fancy and the measured result of the content of sugar, it was clarified that the expression of the content of sugar which coincided to the degree of fancy of the usual consumers could be effected by the method for grading fruits according to the present invention.

Next, another aspect of the fruit grading method of the present invention will be described hereinafter.

In a situation where the water content of a solid state substance containing water is known, or, a little differs from each other within the same lot thereof, and hence a sampled value thereof practically measured for a few samples indiscriminately selected from the same lot can be applied to the whole lot, the component content can be extremely simply and certainly calculated, as shown in examples as described later, from the intensity of the nuclear magnetic resonance signal based on the contained water and that based on the other component, which is calibrated with the standard of the known water content.

In the solid state substance containing water such as fruits, the content of a little contained component, for instance, sugar and organic acid is extremely small in comparison with the water content thereof. However, when the component content, which is conventionally calculated with the conventional standard substance from the measured digital values of about 1 2 bits, is obtained from about 1 6 bit digital measured values by the so-called computer process, the content of a little contained component can be calculated with the same accuracy and certainty as hitherto.

The basic principle of the quantitative analysis effected by utilizing the nuclear magnetic resonance phenomenon is established on the basis of the fact that the intensity of the signal, which is generated, due to the effect of the nuclear magnetic resonance caused in the high frequency magnetic field, by the atomic nuclear having the nuclear spin quantum number being not zero among various kinds of atomic nuclears consisting in a fixed quantity of contained component to be measured, has the proportional relation with the number of atomic nuclears contained in the component of the target to be measured.In this principle, since the intensity of the nuclear magnetic resonance signal is affected by the measuring circumstance, the standard substance which has the known density is measured together with the target concerned, and then the quantitative analysis is effected on the basis of the relative ratio between those intensities of signal. In the fruit grading method of the present invention, the water contained in the target is used for the standard substance, so that the accuracy of the water content of the target directly affects the accuracy of the quantitative analysis of the component to be measured.

Accordingly, in a situation where the water content of the target is not accurately known, samples extracted indiscriminately from plural substances of the same kind which are produced on the same conditions as the target to be measured are accurately measured with respect to the water content thereof, and then it is required to estimate the water content of the target of the non-destructive measurement on the basis of those actually measured.

Examples of the practical measurement of component content of the water containing solid state substance according to the method of the present invention will be described hereinafter on the basis of the above investigation.

Measured Example 4 Generally speaking, the water content of early grown Satsuma mandarin of the same cultivar harvested in the same production district in the same season is scarcely dispersed.

For example, in the result of practical measurement of the water content of mandarin of Miyagawa early grown cultivar, which were collected into a packing house in a specified mandarin production district, the measured water content was 87.30 + 17% at the confidence rate 95%.

For the non-destructive quantitative analysis under the utilization of the nuclear magnetic resonance phenomenon with respect to the sugar content and the acidity of fifty mandarins of Miyagawa early grown cultivar which were collected into this packing house, the water component contained individually in each mandarin was respectively used as the standard substance, the mean value of water content of which was determined to 87.3%.

For the content measuring method according to the present invention, the calibration equation between the content of compound to be the object of the quantitative analysis and the relative intensity ratio of the nuclear mag netic resonance signal measured with the contained water used as the standard substance has been previously set up.In the result of comparation between the measured values of sugar content which were obtained by the quantitative analysis under the utilization of the nuclear magnetic resonance, with respect to the above mentioned mandarins, and the measured values of the sugar content and the acidity obtained thereafter by the quantitative analysis effected by the high speed liquid chromatography of the juice obtained by wringing and filtering the same mandarins, the preferable linear correspondence could be obtained between those measured values with the correlation of 0.990. In this connection, with respect to the accuracy of the quantitative analysis under the utilization of the nuclear magnetic resonance phenomenon, the error of the measured value thereof from that obtained by the high speed liquid chromatography is expressed as an rate + 2.49% at the confidence rate 95%.So that, the measured values obtained with the utilization of the nuclear magnetic resonance phenomenon under the above mentioned accuracy of measurement becomes 10.000 + 0.249% when the sugar content obtained by the high speed liquid chromatography is 10.000%, and the former becomes 0.900 + 0.022% when the latter is 0.900%.

Measured Example 5 Generally speaking, the water content of spinach is largely varied in response to the weather, the temperature and other conditions when harvested. For this reason, as the result that the water content of five stumps of spinach, which had been indiscrimately extracted from fifty stumps thereof, was measured through the electric resistance type water content meter, the water content thereof was 92.7 + 3.1% at the confidence rate 95%.By referring to the result of comparison between the content of L-ascorbic acid which was obtained by the quantitative analysis with the utilization of the nuclear magnetic resonance phenomenon with respect to the aforesaid fifty stumps on the standard of the above water content and the measured value thereof obtained by the quantitative analysis effected through the hydrazin colorimetry with regard to the same stumps after ground down, the former was held within the range + 3.9% of the latter at the confidence rate 95%, so that the former could be regarded to be held within the practically allowable error range.In this connection, with regard to the measured value 40.10 mg% of the content of L-ascorbic acid through the hydrazine colorimetry, the measured value thereof through the quantitative analysis with the utilization of nuclear magnetic resonance phenomenon becomes 40-10 + 1.56 mg% at the confidence rate 95%.

As is apparent from the above described, according to the present invention, it becomes possible to effect the taste estimation based on the non-destructive examination of fruits which has not been conventionally realized, and further to attain the individual test of the whole group of fruits by the non-destructive measurement without any change of taste and with maintenance of commodity, and hence to avoid the conventional loss caused by abandonning the tested fruits.

In addition, it becomes possible also to effect numerically the quality expression relating to the taste of individual fruit, and further to standardize the quality of fruits with regard to the taste thereof which has been conventionally expected.

On the other hand, according to the other aspect of the present invention, for the nondestructive quantitative analysis under the utilization of nuclear magnetic resonance phenomenon with respect to the solid state substance having the known water content, the standard substance used for the calibration of the measured values is not looked for outside of the solid state substance, but inside thereof, that is, the water contained in that substance itself can be used for the standard substance. So that, the process of measurement can be extremely simplified in comparison with the conventional process. As a result, for the quantitative analysis of foodstuff, for instance, fruits, vegetables, fleshes, eggs, fishes, grains and further living bodies, for instance, beasts and plants, the practical use of the measuring method under the utilization of the nuclear magnetic resonance phenomenon can be expected.

Conclusively speaking, various remarkable effects can be attained according to the present invention.

Although the invention has been described with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example and that numerous changes in details of construction and the combination and arrangement of parts may be resorted to without departing from the scope of the invention.

Claims

1. A method for non-destructively grading fruits, comprising: obtaining measured values by measuring an intensity of a nuclear magnetic resonance signal of an atomic nucleus, spin quantum number of which is not zero, with respect to at least either one of the sugar and organic acid contained in the fruits, and comparing the measured values with a predetermined standard value representing quality of the fruits.

2. A method for non-destructively grading fruits as defined in claim 1, wherein said measured value is calibrated with respect to tetramethylsilane.

3. A method for non-destructively grading fruits as defined in claim 1, wherein said measured values are calibrated by a predetermined regression line.

4. A method for non-destructively grading fruit as defined in claim 1, wherein said measured values are calibrated by a predetermined equation of multiple regression.

5. A method for non-destructively grading fruits as defined in claim 1, wherein said measured values are calibrated by being multiplied with a predetermined coefficient 0.8-0.9.

6. A method for non-destructively grading fruits as defined in claim 1, wherein said measured values are calibrated by being regressively multiplied with a predetermined coefficient 0.9-0.99.

7. A method for non-destructively grading fruits having a known water content, comprising: measuring a nulcear magnetic resonance spectrum presented by components contained in the fruits, and comparing said nuclear magnetic resonance spectrum with a known nuclear magnetic resonance spectrum presented by water contained in the fruits, whereby the quality of the fruits can be estimated through the comparison with a standard determined.

8. A method for non-destructively grading fruits as defined in claim 7, whereby the quality of the fruits can be estimated through the comparison with a standard in respect to the water contained in the fruits.

9. Methods for the non-destructive testing of fruits substantially as herein described with reference to the accompanying drawing.