Meat freshness measuring apparatus

Abstract: A meat freshness measuring apparatus measures freshness of meat by detecting changes in a pigment contained in the meat. For this purpose, the meat (2) is exposed to rays of light of different wavelengths applied from a light source (1), and the rays obtained from the meat are separated to spectra for the respective wavelengths, which are received by a photoelectric conversion element (4). Spectrum data for each wavelength is amplified and then the amplified data is converted to a digital signal by an A/D converter (7), whereby the digital signal is stored in a RAM (12). Based on the stored spectrum data and using a prescribed equation of calculation, a content of the pigment in the meat is calculated and outputted by a CPU (10).

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates generally to meat freshness measuring apparatus. More particularly, the present invention relates to a meat freshness measuring apparatus for exposing meat to light from a light source and analyzing a specific pigment component representing freshness in the meat based on light reflected or transmitted from the meat. Description of the Background Art Freshness of beef or other meat is an important factor in quality control in a circulation process, or in suitable supply according to transactions or purposes of use, etc, and there have been proposed various methods or apparatus for measuring the freshness. One of such apparatus is a meat freshness measuring apparatus described in Japanese Patent Laying-Open No. 1-156664. According to this Japanese Patent Document, it was made clear by studies of Saito et al (Transactions of the Japanese Society of Scientific Fisheries, Vol. 24, pp. 749-750: 1957) and Uchiyama, Ehira et al (Transactions of the Japanese Society of Scientific Fisheries, Vol. 36, pp. 177-187, 977-992: 1970) that a composition ratio of nucleic acid compounds contained in beef or other animal meat has a close relation with freshness. More specifically stated, since ATP (adenosine triphosphate) in beef or other animal meat decomposes, after the death, in the order of ATP ―> ADP (adenosine triphosphate) ―> AMP (adenosine monophosphate) ―> IMP (inosinic acid) ―> Hx R (inosine) ―> Hx (buxanthine), the following K value is used as an index of freshness. K value (%) = (H x R + Hx) / (ATP + ADP + AMP + IMP + H x R + Hx) x 100. In addition, it was found as a result of the study by Watanabe et al (Papers on Polymers, Vol. 41, pp. 233-248: 1984) that ATP and ADP decompose rapidly after the death, and that there is a very small quantity of AMP. Thus, it was found that there is no practical problem if the terms of ATP, ADP and AMP are omitted from the above-mentioned expression of K value. The K value has been conventionally measured by various methods such as a column chromatographic method (Kato et al, Transactions of the Japanese Society of Scientific Fisheries, Vol. 39, pp. 1039-1044: 1973), an oxygen method (Uda et al, Japanese Patent Publication No. 59-130200), and a sensor method (Watanabe et al, Japanese Patent Publication No. 59-107256, or Arai et al, Japanese Patent Publication No. 59-232097). Another method conventionally used is a spectral method utilizing reflected or transmitted light, in which conditions of a meat pigment can be directly detected. Thus, this method is useful for determining what influence handling and processing of meat exert on stability of the meat pigment. As for this method, application of laser beam may be considered. However, measuring apparatus using this method are suited for use in laboratories but not suited for practical use in meat processing factories. An improved apparatus for color grading fish fillets is disclosed in EP-A-0221642. With this apparatus it is possible to illuminate a sample of fish or other meat and measuring the intensity of the resultant reflected light at certain wavelengths at which haemoglobin displays peculiar absorption characteristics. The apparatus ratios these measured intensities and compares the ratios with stored sets of values representing ratios of intensities of reflection at these wavelengths which would be expected for flesh of various color grades. The apparatus displays the color grade associated with the closest set of values. However, this measuring method is not able to detect absolute values of a meat property (such as concentration of a pigment). The classification is dependent upon predetermined values of color grade ratios to which the measured intensity values of reflected light from the sample are compared to. Further, the grading method is only able to differentiate between three different categories corresponding to different meat properties. Thus, there is an urgent need for an improved apparatus for measuring meat freshness, determining concentrations of different components contained in said meat. SUMMARY OF THE INVENTION Therefore, a principal object of the present invention is to provide a meat freshness measuring apparatus capable of measuring freshness of meat by spectral analysis on changes of a pigment (such as myoglobin) in the meat in real time utilizing reflected or transmitted light from the meat. Briefly stated, in the apparatus of the present invention, meat is exposed to rays of different wavelengths and the rays of the respective wavelengths from the meat are separated into spectra of the respective wavelengths. The rays of the spectra of the respective wavelengths are received and spectrum data is stored for each wavelength. Based on the spectrum data for each wavelength thus stored and a prescribed calculation equation, a content of a pigment in the meat is calculated and outputted. Consequently, according to the present invention, contents of pigments in meat are calculated according to spectrum data for each wavelength obtained from the meat. Thus, the apparatus can be small-sized and made light, which makes it possible to measure freshness of meat efficiently and in a handy manner in various places as required. The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic block diagram of an embodiment of the present invention. Fig. 2 is a graph showing spectra in specimens of refrigerated meat blocks in different three conditions. Fig. 3 is a graph showing absorption spectra of Mb, MbO and MMb. Fig. 4 is a graph showing a calibration curve of an absorbance A₅₂₅ of a wavelength 525nm and a content of Mb. Fig. 5 is a view showing a fiber probe. Fig. 6 is a diagram showing data stored in the RAM shown in Fig. 1. Fig. 7 is a diagram showing an example of spectrum data measured according to the embodiment of the invention. Figs. 8 to 10 are flow charts for explaining specific operations of the embodiment of the invention. Particularly, Fig. 8 represents a main routine; Fig. 9 represents a calibration subroutine; and Fig. 10 represents a spectrum measurement subroutine. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to Figs. 2, 3 and 4, description will be made of the general principles on which the present invention is based. A surface of a carcass refrigerated one night after slaughter presents a color inherent in oxymyoglobin (hereinafter referred to as MbO). An internal portion thereof cut by a knife presents a color inherent in myoglobin (hereinafter referred to as Mb). A surface of a carcass stocked for a very long period presents a color of metmyoglobin (hereinafter referred to as MMb). According to the present invention, freshness of meat is measured by analyzing spectral changes of Mb, MbO and MMb. Fig. 3 shows absorption spectra of Mb, MbO and MMb with absorption coefficients thereof being set in equal ranges. In this figure, 525nm represents an isosbestic point of Mb, MbO and MMb. Therefore, absorbance A₅₂₅ of a wavelength 525nm is as follows. A₅₂₅ = K₅₂₅ (C Mb + C MbO + C MMb ) · D (1) where K₅₂₅ : absorption coefficients of Mb, MbO, MMb at the wavelength 525nm C Mb : concentration of Mb C MbO : concentration of MbO C MMb : concentration of MMb D : optical path at the time of reflection spectrum measurement. First, C Mb will be obtained. A wavelength 474nm is an isosbestic point of MbO and MMb, and absorbance A₄₇₄ thereof is as follows. A₄₇₄ = K Mb ₄₇₄ · C Mb · D + K₄₇₄ · (C MbO + C MMb ) · D (2) From the equations (1) and (2), the following equation is obtained. K₄₇₄ · (A₅₂₅/D) - K₅₂₅ (A₄₇₄/D) = K₅₂₅ · K₄₇₄ · C Mb - K Mb ₄₇₄ · K₅₂₅ · C Mb Therefore, C Mb is obtained by the following equation. C Mb = (K₄₇₄ · A₅₂₅ - K₅₂₅ · A₄₇₄) / [(K₅₂₅ · K₄₇₄ - K Mb ₄₇₄ · K₅₂₅) · D] (3) Next, as for MbO, a wavelength 614nm represents an isosbestic point of Mb and MMb, and accordingly absorbance A₆₁₄ thereof is as follows. A₆₁₄ = K Mb ₆₁₄ · C MbO · D + K₆₁₄ (C Mb + C MMb ) · D (4) Therefore, in the same manner as in the case of Mb, from the equations (1) and (4), C MbO is obtained by the following equation. C MbO = (K₆₁₄ · A₅₂₅ - K₅₂₅ · A₆₁₄) / [(K₅₂₅ · K₆₁₄ - K MbO ₆₁₄ · K₅₂₅) · D] (5) As for MMb, a wavelength 572nm represents an isosbestic point of Mb and MbO and thus, in the same manner, C MMb is obtained by the following equation. C MMb = (K₅₇₂ · A₅₂₅ - K₅₂₅ · A₅₇₂) / [(K₅₂₅ · K₅₇₂ - K MMb ₅₇₂ · K₅₂₅) · D] (6) The above-mentioned wavelengths may be other values. For instance, the wavelength 474nm for Mb may be 370nm or 597nm; the wavelength 614nm for MbO may be 675nm or 460nm; and the wavelength 572nm for MMb may be 460nm, 507nm, 555nm or 597nm. In addition, from the equation (1), the following equation is obtained. C Mb + C MbO + C MMb = A₅₂₅ / [K₅₂₅ · D] (7) If a calibration curve of A₅₂₅ and the Mb content is prepared as shown in Fig. 4, the following equation (8) is obtained. Total Mb content = α · A₅₂₅ + β (8) A percentage of Mb is, from the equations (3) and (7), as follows. In the same manner, percentages of MbO and MMb are obtained as follows. MbO% = (1 -K₅₂₅/K MbO ₆₁₄·A₆₁₄/A₅₂₅) x 100 (10) MMb% = (1 -K₅₂₅/K MMb ₅₇₂·A₅₇₂/A₅₂₅) x 100 (11) According to the present invention, Mb%, MbO%, MMb% are measured on the basis of the above mentioned principles. In the following, a more detailed description will be made in connection with an embodiment. Fig. 1 is a schematic block diagram of an embodiment of the present invention. Referring first to Fig. 1, a construction of the embodiment will be described. A light source 1 irradiates an object 2 to be measured such as meat. Reflected or transmitted light from the object 2 enters spectroscopic means 3, where it is spectrally separated. A beam of a prescribed wavelength thus obtained is supplied to a photoelectric conversion element 4, where it is converted to an electric signal. The electric signal is amplified by an amplifier 5 and the amplified signal is supplied to a log amplifier 6, where it is converted to a light quantity signal. The light quantity signal is supplied to an A/D converter 7, where it is converted to a digital signal. The digital signal thus obtained is supplied as light quantity data of the prescribed wavelength to a CPU 10 through an I/O port 8 and an I/O bus. The CPU 10 is connected with a ROM 11, a RAM 12, a video RAM 13, and an operation unit 15 through the I/O bus. The ROM 11 stores in advance necessary programs for processing of the CPU 10 (such as programs based on the below-described flow charts as shown in Figs. 7 to 9). The RAM 12 stores various data necessary for processing of the CPU 10 as will be described in detail afterwards with reference to Fig. 5. The video RAM 13 temporarily stores data processed by the CPU 10 and displays the data on a CRT display 14. The operation unit 15 includes a calibration key 16, a spectrum measurement key 17 and an analysis prohibition indicator 18. The calibration key 16 is provided to give an instruction for obtaining a reference spectrum at the time of obtaining an absorption spectrum. The spectrum measurement key 17 is provided to instruct measurement of spectrum data. The analysis prohibition indicator 18 is provided to indicate that sampling data cannot be analyzed. The calibration key 16 and the spectrum measurement key 17 can individually provide instructions to the CPU 10. By operating those keys, operation as described below based on the flow charts shown in Figs. 9 and 10 is executed. A clock generator 9 is provided to supply clock pulses to the photoelectric conversion element 4, the A/D converter 7 and the I/O bus. Fig. 5 shows a fiber probe. The fiber probe 20 shown in Fig. 5 is provided to transmit the light from the light source 1 to the object 2 to be measured and to transmit the light reflected from the object 2 to the spectroscopic means 3. The fiber probe 2 includes a light transmitting fiber bundle 21 and a light receiving fiber bundle 22, which are joined together in an intermediate portion to form a fiber bundle 23. An end of the light transmitting fiber bundle 21 receives the light from the light source 1. An end of the fiber bundle 23 on the other side contacts the object 2. The light transmitted through the light transmitting fiber bundle 21 is reflected by the object 2 and is communicated to the spectroscopic means 3 through the light receiving fiber bundle 22. If the probe is of a transmission type, the transmitted light may be communicated to the spectroscopic means 3 through the light receiving bundle 22 without integrally forming the light transmitting fiber bundle 21 and the light receiving fiber bundle 22. Fig. 6 is a diagram showing data stored in the RAM shown in Fig. 1, and Fig. 7 is a graph showing an example of spectrum data measured in the embodiment of the present invention. In the above-described measurement apparatus shown in Fig. 1, the light from the light source 1 is applied to the object 2 through the light transmitting fiber bundle 21 of the fiber probe 20 shown in Fig. 5 and the reflected or transmitted light therefrom is directed to the spectroscopic means 3 through the light receiving fiber bundle 22, by which a spectrum is produced, and then it is converted to an electric signal by the photoelectric conversion element 4. The electric signal is amplified by the amplifier 5 and the signal thus amplified is converted to a light quantity signal by the log amplifier 6, whereby the light quanity signal is sampled by the A/D converter 7. Then, results E₁₁, E₁₂, E₁₃,... , E 1m of the sampling with respective wavelengths λ₁, λ₂, λ₃,..., λm are stored as spectrum data in an area 12a1 of the RAM 12 shown in Fig. 6. Distribution of those spectrum data is as shown in Fig. 7. Referring to Fig. 6, the data stored in the RAM 12 will be described. The RAM 12 includes areas 12a1, 12a2... 12ak... 12an, 12b, 12c1 to 12c4, 12d and 12e. Spectrum data the number of which is n are stored in the areas 12a1 to 12an. Average spectrum matrix data E ₁, E ₂... E m are stored in the area 12b. The total Mb content, respective percentages of Mb%, MbO%, MMb% analyzed by absorption spectra are stored in the areas 12c1 to 12c4. Measured calibration data is stored in the area 12d, and absorption spectrum data are stored in the area 12e. Figs. 8 to 10 are flow charts for explaining a specific operation of the embodiment of the present invention. Particularly, Fig. 8 represents a main routine; Fig. 9 represents a calibration subroutine; and Fig. 10 represents a spectrum measurement subroutine. Referring to Figs. 1 to 10, the specific operation of the embodiment will be described. First, in the main routine shown in Fig. 8, when measurement is started, the program proceeds to a calibration mode in step SP1, in which the calibration subroutine shown in Fig. 9 is executed. In the calibration mode, the top end of the fiber probe 20 shown in Fig. 5 is in contact with a material such as a reference white plate having a fixed reflectance with respect to a measured wavelength range in place of the object 2 to be measured. In the case of a probe of a transmission type, light from the light transmitting fiber bundle 21 may be directly applied to the light receiving fiber bundle 22. The CPU 10 waits for turn-on of the calibration key 16 in step SP11 shown in Fig. 9 and when it is determined that the calibration key 16 is on, the CPU 10 sets the number k of measurements to 1 in step SP12. Then, the CPU 10 executes the spectrum measurement subroutine in step SP13. In the spectrum measurement subroutine, the number i of measurements is set to 1 in step SP51 as shown in Fig. 10 so as to sample the first light quantity. In step SP52, a clock pulse corresponding to the wavelength λ₁ is generated from the clock generator 9. When this clock pulse is generated from the clock generator 9, the photoelectric conversion element 4 photoelectrically converts a spectral component corresponding to the wavelength λ₁ provided by the spectroscopic means 3 in step SP53. In step SP54, the amplifier 5 amplifies an output of the photoelectric conversion element 4 and the log amplifier 6 converts the output of the amplifier 5 to a light quantity signal. In step SP55, the A/D converter 7 converts the light quantity signal to a digital signal in response to the clock pulse supplied from the clock generator 9. The digital signal obtained by the A/D converter 7 is supplied to the CPU 10 from the I/O port 8 through the I/O bus. The CPU 10 accepts digital data E k1 corresponding to the wavelength λ₁ in step SP56, and stores the data E k1 in the area 12ak of the the RAM 12 in step SP57. The CPU 10 determines in step SP58 whether the number i is smaller than m. If it is determined that the number i is smaller than m, the CPU 10 returns to step SP52. In step SP52, a clock pulse corresponding to the wavelength λ₂ is generated from the clock generator 9. Subsequently, in the same manner as described above, the operation in steps SP53 to SP57 is executed, whereby the sampling data E k2 of the wavelength λ₂ is stored in the area 12ak of the RAM 12. The CPU 10 repeats this operation, whereby the spectrum data E k1 , E k2 ..E km having m wavelength components are stored in the storage area 12ak. Then, the CPU 10 returns to the calibration subroutine shown in Fig. 9. The CPU 10 stores, in step SP14, the spectrum data stored in the area 12ak into the area 12a1. Thus, if the initial condition set in step SP12 is k = 1, the measured spectrum data is stored in the area 12a1, and subsequently, each time the number k is set to 2, 3,..., n, the spectrum data is stored successively in the areas 12a2, 12a3,..., 12an. In step SP15, the initial condition is set to k = k + 1 and, in step SP16, it is determined whether k is smaller than n. If it is smaller than n, the CPU 10 returns to the above-mentioned step SP13. Thus, sampling for the spectral output from the object 2 is repeated m times in steps SP13 to SP16. In step SP17, the sampled spectrum data are averaged and the result is stored as calibration data in the area 12d. After that, the CPU 10 returns to step SP2 shown in Fig. 8. In step SP2, the top end of the fiber probe 20 shown in Fig. 5 is brought into contact with a specimen of meat as the object 2 to be measured. In step SP3, the CPU 10 sets the number i of measurements to 1, and the CPU 10 waits in step SP4 until the spectrum measurement key 17 is operated. When the spectrum measurement key 17 is operated, the CPU 10 executes the spectrum measurement subroutine in step SP5. In the spectrum measurement subroutine, steps SP51 to SP58 shown in Fig. 10 are executed in the same manner as described above. Through this spectrum measurement subroutine, the spectrum data of the respective wavelengths are measured, and the number i + 1 is set in step SP6. In step SP7, it is determined whether the number i of measurements is smaller than n, and if the number i is smaller than n, the CPU 10 returns to step SP3. Thus, steps SP3 to SP7 are repeated and the spectrum data for the respective wavelengths are measured n times. In step SP8, the measured spectrum data are averaged and subtraction is performed as to the calibration data C₁ to C m stored in the area 12d. Thus, the following equation: is performed, whereby the absorption spectrum data is stored in the area 12e. After that, the CPU 10 executes calculations of the above-mentioned equations (8), (9), (10) and (11), so as to obtain the entire Mb content, respective percentages of Mb%, MbO%, MMb% and to store those data in the areas 12c1 to 12c4. The CPU 10 displays the entire Mb content, Mb%, MbO%, MMb% stored in the areas 12c1 to 12c4 in step SP9, on the CRT display 14 through the video RAM 13. As described in the foregoing, according to the embodiment of the invention, meat to be tested is exposed to rays of different wavelengths and the rays of the respective different wavelengths obtained from the meat are received for spectrum analysis. Thus, data representing a pigment of the meat is calculated according to the spectrum pattern and prescribed calculation equations and the data is provided as output. Consequently, the apparatus can be made to have a small size and a light weight, and freshness of meat can be measured efficiently and in a handy manner in various places.

Claims: A meat freshness measuring apparatus for measuring freshness of meat by detecting changes in a pigment contained in the meat, comprising: light source means (1) for applying rays of light of different wavelengths to said meat; spectroscopic means (3) for spectrally separating the rays applied to said meat by said light source means and reflected or transmitted from said meat into spectra of the respective wavelengths; light receiving means (4) for receiving the rays of the respective wavelengths separated by said spectroscopic means; storage means (12) for storing spectrum data for each of the wavelengths received by said light receiving means; calculating means (10-13) for calculating contents of Mb, MbO and MMb as the content of the pigment in said meat according to (i) the spectrum data for each of the wavelengths stored in said storage means (12) and (ii) to a prescribed equation of calculation comprising an algorithm making use of isosbestic points of the absorption curves of Mb, MbO and MMb at selected wavelengths, the calculation means including a calibration mode for detecting a plurality of spectrum data as a reference for each wavelength, and a measurement mode for detecting a plurality of spectrum data provided by said light receiving means (4) and a means (SP9) for calculating contents of Mb, MbO and MMb as the content of said pigment; and output means (14) for providing the contents of Mb, MbO and MMb, respectively as the content of the pigment in said meat calculated by said calculating means. The meat freshness measuring apparatus in accordance with claim 1, further comprising: calibration mode selecting means (16) for selecting a calibration mode, said calculating means (10-13) including means (SP11 to SP14) responsive to the selection of the calibration mode by said calibration mode selecting means (16), for said detecting a plurality of spectrum data as a reference for each wavelength, for averaging the data for each wavelegth, and storing the averaged data as calibration data. The meat freshness measuring apparatus in accordance with claim 2, further comprising: measurement mode selecting means (17) for selecting a measurement mode, said calculating means (10-13) wherein said means (SP9) for calculating contents of Mb, MbO and MMb as the content of the pigment is also responsive to the selection of the measurement mode by said measurement mode selecting means, for said detecting a plurality of spectrum data for each wavelength provided from said light receiving means, averaging the spectrum data and subtracting said averaged data from said calibration data, said calculation being carried out according to said equation of calculation.

Inventors: KANDA MASAHIKO, KANDA, MASAHIKO
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1990
Main classification: G01N33
IPC codes: G01N33, G01N21