Non-invasive detection method for sweet potatoes using infrared light

Abstract

This invention provides a detection method that enables the early, individual, non-destructive, and rapid identification of infected sweet potatoes, thereby preventing the spread of infection among sweet potatoes. [Solution] The surface of the sweet potato to be detected is irradiated with infrared light in the wavelength range of 9.33 μm ± 0.5 μm. The presence or absence of tissue changes inside the sweet potato is estimated from the change in the amount of infrared light transmitted through the sweet potato, and sweet potatoes that have developed at least one of the following diseases, basal rot, dry rot, or soft rot, are detected from the decrease in the amount of infrared light transmitted.

Description

Technical Field

[0005]

[0001] The present invention relates to a non-invasive detection method for sweet potatoes using infrared light, and particularly to a detection method for early detection of basal rot disease and the like using a transmission image using light of a specific wavelength of infrared rays.

Background Art

[0002] Quality evaluation techniques for fruits and root vegetables using light rays can quickly and non-destructively evaluate the quality of agricultural products. Techniques for light irradiation and comparison of its transmission amount have been widely used in recent years to detect internal states, appearance abnormalities, etc. of fruits and root vegetables. For example, near-infrared spectroscopy, image processing techniques, etc. are utilized for evaluating quality characteristics such as sugar content, acidity, internal cavities, internal disorders, decay, etc. in fruits and root vegetables.

[0003] Here, pathogen infections such as basal rot disease are regarded as a problem in sweet potatoes. Basal rot disease occurs by being infected with pathogens (filamentous fungi) present on the soil or the surface of plants. Particularly, it causes great damage to crops of the Solanaceae and Cucurbitaceae families. As a countermeasure against basal rot disease, for example, a method of killing and repelling slugs from the field has been proposed (see Patent Document 1). Patent Document 1 mainly focuses on efforts to improve the cultivation soil of sweet potatoes.

[0004] Also, a method of detecting gas components released from harvested sweet potatoes has been proposed (see Patent Document 2). In Patent Document 2, molecules such as 4-methyl-1 released from sweet potatoes are detected by an odor sensor. <​​​​​​​​​​​​​​​​​​​​​

[0006] Currently, there are no known examples of direct detection of pathogens in quality assessment techniques for fruits and root vegetables using light. Furthermore, pathogen testing techniques for diseases such as basal rot are currently limited. Therefore, post-harvest inspection of fruits and root vegetables relies on sampling and destructive testing, which is time-consuming.

[0007] While the gas detection technology proposed in the aforementioned Patent Document 2 can detect the presence or absence of sweet potatoes infected with basal rot or other diseases after harvest, it is not easy to immediately identify infected sweet potatoes. Therefore, there is a need for the development of efficient and accurate inspection technology.

[0008] This invention was made to solve the above problems and provides a detection method that can prevent the spread of infection in sweet potatoes by individually identifying infected sweet potatoes early, non-destructively, and rapidly. [Means for solving the problem]

[0009] In other words, the non-invasive sweet potato detection method of this embodiment is characterized by irradiating the surface of the sweet potato to be detected with infrared light in the wavelength range of 9.33 μm ± 0.5 μm, and detecting the sweet potato that has developed a lesion based on the amount of infrared light transmitted through the sweet potato.

[0010] Furthermore, in a non-invasive detection method for sweet potatoes, the method may include a light source unit equipped with a light source that emits infrared rays, a holding unit that holds the sweet potatoes to be detected, a detection unit that detects transmitted light that has passed through the sweet potatoes held in the holding unit after being emitted from the light source unit, and a control unit that estimates the disease of the sweet potatoes from the transmitted light detected by the detection unit, wherein the control unit may detect the diseased sweet potatoes from changes in the transmitted light.

[0011] Furthermore, in a non-invasive detection method for sweet potatoes, the control unit may generate a transmission image based on the amount of infrared light transmitted, and the control unit may detect the location of the lesion in the sweet potato from the transmission image.

[0012] Furthermore, in the non-invasive detection method for sweet potatoes, the lesions may be defined as basal rot, dry rot, or soft rot. [Effects of the Invention]

[0013] The present invention provides a non-invasive detection method for sweet potatoes, which involves irradiating the surface of the sweet potato to be detected with infrared light in the wavelength range of 9.33 μm ± 0.5 μm and detecting diseased sweet potatoes by measuring the amount of infrared light transmitted through the sweet potato. This method allows for the early, non-destructive, and rapid identification of diseased sweet potatoes, thereby preventing the spread of infection among sweet potatoes. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram of the apparatus configuration for implementing the non-invasive sweet potato detection method of the embodiment. [Figure 2] (A) First schematic diagram, (B) Second schematic diagram, and (C) Third schematic diagram illustrate the generation of transparent images. [Figure 3] This is a graph of absorbance when irradiated with light in the short wavelength range. [Figure 4] This is a graph of absorbance when irradiated with light in the long wavelength range. [Modes for carrying out the invention]

[0015] Sweet potatoes (Ipomoea batatas) are known to develop diseases such as basal rot and dry rot when infected with certain filamentous fungi (e.g., Diaporthe destruens), and soft rot when infected with certain rod-shaped bacteria (e.g., Pectobacterium carotovorum). Inside infected sweet potatoes, the tissue changes, rots, emits a foul odor, and becomes unusable for consumption or as seed potatoes. In the early stages of infection with diseases such as basal rot, it is very difficult to visually detect the disease from the outside of the sweet potato. By the time it becomes visible, the disease has progressed considerably, and the infection has spread not only to the initially infected sweet potato but also to other sweet potatoes in storage. As a result, during the ripening period after harvest, the infection spreads from infected sweet potatoes to surrounding ones, leading to significant financial losses.

[0016] Conventionally, to confirm the onset of sweet potato basal rot disease or the like, it was necessary to extract a part of sweet potatoes from the whole, cut them, and examine the cross-sections. Therefore, the accuracy of inspection and separation of infected sweet potatoes was not sufficient, and sweet potatoes in the early stage of infection that were not extracted were overlooked. Also, in the method of cutting and inspecting sweet potatoes, both normal (non-infected) sweet potatoes and infected sweet potatoes are cut, so normal sweet potatoes are also discarded for inspection, resulting in a large loss during inspection.

[0017] In view of the actual situation of sweet potato production areas and producers, it is necessary to be able to individually and at an early stage detect sweet potatoes infected with basal rot disease or the like. Furthermore, a method that can quickly detect without damaging (non-invasive) sweet potatoes is desired.

[0018] Therefore, as a non-invasive inspection method for sweet potatoes each time detection is performed, as a result of attempting to improve the appearance inspection method using light rays (electromagnetic waves), it was found that it is possible to distinguish between normal (non-infected) sweet potatoes and infected sweet potatoes based on the difference in the amount of infrared rays (far-infrared rays) transmitted in a wavelength region of a predetermined area.

[0019] In the non-invasive detection method for sweet potatoes of the embodiment, infrared rays (far-infrared rays) in a wavelength region of 9.33 μm ± 0.5 μm are irradiated onto the surface of the sweet potato. Then, the amount of infrared rays transmitted through the sweet potato (which can also be calculated as the absorption amount or absorption rate) is measured. Due to the irradiation of infrared rays in this wavelength region, a significant difference in the amount of infrared rays transmitted occurs between normal (non-infected) sweet potatoes and infected sweet potatoes. Utilizing this characteristic, it is possible to detect infected sweet potatoes without damaging (non-invasively) sweet potatoes with lesions caused by infection, and furthermore, to individually inspect all sweet potatoes.

[0020] The tissue of sweet potato is mainly composed of cellulose and the like. When a sweet potato is infected with a filamentous fungus such as the basal rot pathogen, the filamentous fungus produces chitin that does not originally exist in the sweet potato as it grows. Therefore, as a result of exploring the absorption wavelength of infrared rays at the lesion site of the sweet potato, it was found that infrared rays in the wavelength range of 9.33 μm ± 0.5 μm are effective for discriminating the presence or absence of chitin in the sweet potato. The embodiment detects a substance that does not originally exist in the sweet potato through the transmittance (absorption rate) of infrared rays and discriminates the presence or absence of infection.

[0021] FIG. 1 is a schematic diagram of an example of an apparatus for implementing a non-invasive detection method for sweet potatoes according to an embodiment. The detection apparatus 1 is provided with a light source unit 20, a holding unit 30, and a detection unit 40, and the light source unit 20 and the detection unit 40 are connected to a control unit 10. The detection method according to the embodiment is a method that utilizes infrared spectroscopic analysis, and the device configurations of an infrared spectroscopic analyzer, particularly a Fourier transform infrared spectroscopic analyzer (FTIR: Fourier Transform Infrared Spectroscopy), are applied to the light source unit 20, the detection unit 40, and the control unit 10.

[0022] The light source unit 20 includes a light source that irradiates infrared rays and irradiates infrared rays in the wavelength range of 9.33 μm ± 0.5 μm. Different from the case of an infrared spectroscopic analyzer, a configuration for irradiating infrared rays in various wavelength bands outside the above-mentioned range can be omitted. Alternatively, it is possible to separate and irradiate only the infrared rays in the above-mentioned range from a wide wavelength band by spectroscopic means such as an optical slit.

[0023] The holding unit 30 is a mounting table, various members such as a clamp, etc., for holding the sweet potato that is the detection target. The sweet potato is held in the longitudinal direction or around the body (direction orthogonal to the longitudinal direction) of the sweet potato.

[0024] The detection unit 40 detects the transmitted light obtained by the infrared rays irradiated from the light source unit 20 passing through the sweet potato held by the holding unit 30. A detector mounted on an infrared spectroscopic analyzer or the like is used for the detection unit 40.

[0025] The control unit 10 estimates the disease of sweet potatoes from the transmitted light detected by the detection unit 40 and detects the diseased sweet potatoes from the changes in the transmitted light. The control unit 10 is a known personal computer (PC), tablet terminal, smartphone, or other type of electronic computer (computing resource). Alternatively, the control unit 10 may be configured as a dedicated device. Hardware-wise, the control unit 10 is composed of computing elements (CPU, GPU), ROM, RAM, memory, input / output buffers (I / O), etc. Other components include main memory and LSI. Software-wise, programs for spectroscopic measurement and analysis loaded into the main memory are implemented. In the illustration, a monitor 19 is connected to the control unit 10 as an external output device.

[0026] As shown in the schematic diagram in Figure 1, the sweet potato 35 to be detected is held (fixed) in the holding unit 30. Infrared light in the wavelength range of 9.33 μm ± 0.5 μm is irradiated from the light source unit 20, and the transmitted infrared light that has passed through the sweet potato 35 is detected by the detection unit 40. When irradiating a normal (uninfected) sweet potato, the absorption of infrared light in the aforementioned wavelength range is small, and the amount transmitted is larger compared to an infected sweet potato. In contrast, when irradiating a sweet potato infected with filamentous fungi, etc., the absorption of infrared light in the aforementioned wavelength range is larger compared to a normal sweet potato due to changes in the internal components of the sweet potato, and the amount transmitted decreases. Based on this trend in transmittance, the control unit 10 estimates the lesion of the sweet potato from the transmitted light of the currently held sweet potato and determines whether or not it is infected.

[0027] Therefore, there is no need to cut or peel the sweet potatoes to be detected (non-invasive), all of the sweet potatoes can be inspected, and only those infected and showing lesions can be accurately separated from all the inspected sweet potatoes. In particular, since it is an optical detection method that does not rely on the odor emitted from the sweet potatoes, the detection sensitivity is improved. Furthermore, by increasing the number of light source units 20 and detection units 40, infrared spectroscopic analysis of sweet potatoes being transported on a conveyor belt, for example, becomes possible.

[0028] Figure 2 is a schematic diagram illustrating another form of infrared transmission measurement. Specifically, it is an example where the control unit 10 generates a transmission image for each sweet potato to be detected. In Figure 2(A), the light source unit 20 moves along the longitudinal direction (long axis) of the sweet potato 35, scanning for infrared irradiation and detection. Also, as shown in Figure 2(B), the light source unit 20 moves along a direction perpendicular to the longitudinal direction (long axis) of the sweet potato 35, scanning for infrared irradiation and detection in that direction. For illustrative purposes, the holding unit 30 is omitted in Figure 2.

[0029] As shown in the figure, the results of the transmission (light absorption rate) measurements in the longitudinal direction and the direction perpendicular to it of the sweet potato 35 are analyzed by the control unit 10 and combined in three dimensions. This generates a transmission image 36 (tomographic image) of the sweet potato 35 as shown in Figure 2(C). In the transmission image 36 in the figure, the normal area 37 and the lesion area 38 are shown. The processing method used in known diagnostic imaging equipment such as X-ray CT is applied when generating the transmission image 36 (tomographic image). The generation of the transmission image 36 makes it possible to analyze the lesion area in the sweet potato, which can be used to predict areas that are prone to infection in the sweet potato.

[0030] By using the detection device 1 to implement the non-invasive detection method for sweet potatoes according to this embodiment, it becomes easy to detect and separate sweet potatoes that have developed lesions such as basal rot, dry rot, and soft rot. Furthermore, the inspection is non-invasive and does not damage the sweet potatoes, resulting in less loss during inspection. [Examples]

[0031] To understand the pathological changes in sweet potatoes caused by infection, three types of sweet potatoes were prepared: normal (uninfected) sweet potatoes (Group I: so-called control), sweet potatoes infected with basal rot in the early stages of disease (Group II), and sweet potatoes infected with dry rot in the early stages of disease (Group III). Since the sweet potatoes in Groups II and III were in the early stages of disease, it was difficult to distinguish them from normal sweet potatoes (Group I) by visual inspection of their appearance.

[0032] Using a Fourier transform infrared spectrometer (FTIR), the absorbance (synonymous with transmittance) of each group of sweet potato cross-sections (the portion containing vascular bundles) was continuously irradiated with infrared light ranging from approximately 1000 nm to approximately 14000 nm. Figure 3 shows the graph for irradiation with infrared light ranging from approximately 2500 nm to approximately 3500 nm. From this graph, the absorbance of each group showed a nearly identical trend, and no characteristic wavelengths that distinguished each group were found.

[0033] Next, we explored the far-infrared range, including the longer wavelength side. Figure 4 shows a graph of irradiation with infrared light from approximately 6000 nm to 14000 nm. From this graph, a difference in absorbance was observed between normal sweet potatoes (Group I) and diseased groups (Groups II and III) in the wavelength range of 8000 nm to 11000 nm. Further analysis of this wavelength range revealed that the distinction between normal sweet potatoes (Group I) and diseased sweet potatoes was most pronounced around 9300 nm. Therefore, we are confident that the wavelength range of 9.33 μm ± 0.5 μm is effective in distinguishing between normal (uninfected) sweet potatoes and sweet potatoes in the early stages of disease due to basal rot.

[0034] The difference in absorbance between normal sweet potatoes (Group I) and those that are not is thought to be due to the influence of components not normally present in sweet potatoes. The causative fungi of basal rot (filamentous fungi, etc.) produce chitin, which is not normally present in sweet potatoes, to form the cell wall of the fungus. Therefore, it is thought that the produced chitin absorbed infrared light in a specific range. In the examples, irradiation was performed on the cut surface of the sweet potatoes to prioritize the detection of the effective wavelength band. Of course, it is thought that the effectiveness would not be affected even if the skin was left on.

[0035] Based on the results of absorbance measurements using a series of infrared spectroscopic analyses, the wavelength range of 9.33 μm ± 0.5 μm is effective in distinguishing between normal (uninfected) sweet potatoes and sweet potatoes in the early stages of basal rot infection. Therefore, for example, in detection device 1 shown in Figure 1, infrared irradiation in this wavelength range can be used to easily detect and separate sweet potatoes that have developed lesions. Furthermore, even when the presence or absence of lesions cannot be determined by visual inspection, it is possible to distinguish them and exclude the affected sweet potatoes. [Explanation of Symbols]

[0036] 1. Detection device 10 Control Unit 20 Light source section 30 Holding part 35 Sweet Potato 36. Transmission image (tomographic image) 37 Normal site 38. Lesion site 40 Detection unit

Claims

[Claim 1] A non-invasive method for detecting sweet potatoes using infrared light, characterized by irradiating the surface of the sweet potato to be detected with infrared light in the wavelength range of 9.33 μm ± 0.5 μm, and detecting sweet potatoes that have developed at least one of the following diseases: basal rot, dry rot, or soft rot, based on the amount of infrared light transmitted through the sweet potato.

Images