CN111175297A - Method for measuring content of vitamin C in fruits and vegetables by combining iodine turbidity method with infrared camera - Google Patents
Method for measuring content of vitamin C in fruits and vegetables by combining iodine turbidity method with infrared camera Download PDFInfo
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Abstract
The invention belongs to vitamin C content, and discloses a method for measuring the vitamin C content in fruits and vegetables by combining an iodine turbidity method with an infrared camera, which is characterized in that on the basis of redox reaction between vitamin C and iodine, the infrared camera is used for measuring the residual iodine content after the reaction by a turbidity measuring method to obtain the vitamin C content; infrared light emitted by the infrared light-emitting LED penetrates through the iodine suspension, is absorbed and scattered, and then is captured by the infrared camera to form a digital image, and color components capable of representing the concentration of vitamin C are obtained after processing; and fitting the different color components obtained by the camera with corresponding vitamin C with different concentrations to obtain an expression with higher fitting degree for measuring the vitamin C with unknown concentration. The iodine turbidimetry, the infrared camera and the image processing technology are combined for determining the vitamin C, a novel vitamin C measuring method is provided, the advantages of simplicity in operation, miniaturization and the like are achieved, and the application field of image detection is widened.
Description
Technical Field
The invention belongs to the technical field of vitamin C content determination, and particularly relates to a method for measuring the vitamin C content in fruits and vegetables by combining an iodine turbidity method and an infrared camera.
Background
Currently, the closest prior art: vitamin C is a colorless crystal, soluble in water. Since vitamin C has a function of preventing scurvy, it is also called ascorbic acid in medicine. Vitamin C participates in sugar metabolism and oxidation-reduction process in vivo; participating in the generation of intercellular substance, reducing capillary fragility, and accelerating blood coagulation; participate in detoxification function and increase resistance to infection; promoting folic acid to form tetrahydrofolic acid and increasing the absorption of iron in intestinal tract; has antihistaminic effect. Most plants and animals are able to synthesize vitamin C according to their own needs. However, vitamin C cannot be synthesized due to the deficiency of gulonolactone oxidase in the human body. Thus, vitamin C in the human body is mainly supplemented by fruits, vegetables and medicines. Therefore, the accurate determination of the vitamin C content is of great importance to the health and health of the diet.
At present, various methods are used for measuring the content of vitamin C, and the national standard method (GB 12392-90: the method for measuring the total ascorbic acid in vegetables, fruits and products thereof) stipulates a fluorescence method and a 2, 4-dinitrophenylhydrazine colorimetric method for measuring the ascorbic acid, and is suitable for measuring the total ascorbic acid in the vegetables, fruits and products thereof, wherein the fluorescence method in the national standard method needs a fluorescence photometer, and the 2, 4-dinitrophenylhydrazine colorimetric method needs an ultraviolet photometer. Other detection methods also include liquid chromatography (HPLC), fluorescence spectroscopy, visible spectrophotometry, and electrochemical methods. The detection speed of the liquid chromatography and the fluorescence spectrometry is high, the result is reliable, but the needed chromatographic instrument or spectroscopic instrument is expensive, and the operation is relatively complex. The electrochemical method is easy to miniaturize and has high sensitivity, but reaction products can pollute the electrode after multiple measurements, and the electrode needs to be replaced frequently. In recent years, new methods such as resonance rayleigh scattering, flow injection chemiluminescence have been developed. The resonance Rayleigh scattering method is carried out by using ironReacting potassium cyanide with vitamin C to generate potassium ferrocyanide, and reacting with Zn2+The reaction generates nano zinc potassium, then the shape and the diameter of the nano particles are observed by a transmission electron microscope to measure the content of the vitamin C, and the vitamin C is measured by a flow injection chemiluminescence method. However, these methods require expensive instruments such as an electron microscope and a photomultiplier tube, and are complicated to operate. The method for measuring the vitamin C by using the visible light spectrophotometry is based on a color development reaction, Fe (III) is quantitatively reduced to Fe (II) through the vitamin C, the Fe (II) reacts with phenanthroline to generate a stable orange-red complex, and the absorbance at a specific wavelength is measured to measure the concentration of the vitamin C. The result is reliable in the range of 0-8ug/L, is often used for detecting vitamin C, is widely used and is used for comparison verification.
In recent years, the development of computer image processing technology and imaging technology has led to the widespread use of cameras and image methods in various fields. In soil detection, the RGB value of the digital image and the soil index derived from the digital image can be used for determining the content of iron oxide and fine particles in soil. Iron and residual chlorine in the water were measured using a digital camera using N, N' -diethylphenylenediamine. And obtaining image information by using a common camera in combination with an image processing technology, and determining turbidity, nitrite, ammonia nitrogen, sulfide, phosphate and the like of water. The detection method combining the digital camera and the image processing technology has the advantages of simple design, convenience in operation, visual result and the like, and the feasibility of the application of the digital camera and the image processing technology in the field of trace analysis is verified. At present, no image processing method and technology is applied to measure the content of vitamin C in fruits and vegetables.
In summary, the problems of the prior art are as follows: the existing method for measuring the content of the vitamin C has the disadvantages of expensive price of required instruments and relatively complex operation; the reaction products contaminate the electrodes after multiple measurements.
The difficulty of solving the technical problems is as follows: in the vitamin C measurement method discussed above, the measurement of vitamin C in a vitamin C sample, or in vegetables, fruits and products thereof, requires a complex process including adding a substance to generate a color reaction to generate a colored substance, or other reactions to generate nanoparticles, or adding a catalyst and other substances to react to generate a luminescent substance, and then can be combined with professional instruments such as a spectrophotometer, a chromatograph and the like to perform detection. In addition, the reaction principles and processes of different measurement methods are different, so that the simplification of the measurement process, the simplification of the instrument design and the reduction of the instrument cost have important practical significance for the vitamin C measurement.
The significance of solving the technical problems is as follows: the vitamin C measurement process is complex, and a professional instrument is needed, so that the measurement process is simplified, a new measurement method is provided by combining an image processing technology and the data processing capacity of a computer, the design of a measurement instrument is simplified, the measurement precision is improved, and the method has important practical significance. The invention provides a turbidity method for forming turbid liquid after iodine reaction based on vitamin C, which is combined with an infrared camera and an image processing technology for measuring the vitamin C, simplifies the design of instruments, provides a new vitamin C measuring method, has the advantages of simple operation, miniaturization and the like, and widens the application field of image detection.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a method for measuring the content of vitamin C in fruits and vegetables by combining an iodine turbidity method and an infrared camera.
The method for measuring the vitamin C content in the fruits and vegetables by combining the iodine turbidity method with the infrared camera is realized by determining the residual iodine amount after reaction by using the infrared camera through a turbidity measuring method on the basis of the redox reaction between the vitamin C and iodine; infrared light emitted by the infrared light-emitting LED penetrates through the iodine suspension, is absorbed and scattered, and then is captured by the infrared camera to form a digital image, and color components capable of representing the concentration of vitamin C are obtained after processing; fitting different color components obtained by the camera with corresponding vitamin C with different concentrations to obtain an expression with higher fitting degree for measuring the vitamin C with position concentration.
Further, the method for measuring the content of vitamin C in the fruits and vegetables by combining the iodine turbidity method with the infrared camera comprises the following steps:
the method comprises the steps that firstly, an infrared camera is used for shooting an image of light which penetrates through an iodine suspension, vitamin C and iodine are added into an iodine ethanol solution to perform oxidation-reduction reaction, and the iodine left after the reaction forms the iodine suspension;
secondly, obtaining an RGB value corresponding to the image by analyzing the image obtained by the camera, calculating to obtain a gray value and a logarithmic value of the gray value of the image, and converting the RGB color space into a CIE-Lab color space to obtain a corresponding Lab value;
and thirdly, obtaining a relational expression of the vitamin C concentration with high correlation degree and the L, the gray value and the logarithm of the gray value by analyzing the relation between the vitamin C and the color classification RGB value, the Lab value, the gray value and the logarithm of the gray value.
Further, the iodine turbidity method is combined with a method for measuring the content of vitamin C in the fruits and vegetables by an infrared camera to obtain a camera image, and the camera working parameters are set and the image is processed to obtain an RGB value, a Lab value and a gray value corresponding to the solution; obtaining a frame of image, obtaining an average value of RGB values of 3500 pixel points comprising six LED light source images in a central rectangular area of the image to obtain RGB values corresponding to a turbidity solution, and converting the RGB values into a Lab color space from the RGB color space to obtain a Lab value corresponding to the turbidity solution; wherein L represents the brightness of the transmitted light of the solution, a represents the range from red to green, b represents the range from yellow to blue, the value range of L is from 0 to 100, and the value ranges of a and b are from +127 to-128. The conversion of the RGB color space to the Lab color space employs an approximate conversion algorithm. And calculating by the RGB value to obtain the corresponding gray value and the logarithmic value of the gray.
Further, the method for measuring the content of vitamin C in the fruits and vegetables by combining the iodine turbidity method with the infrared camera comprises the following steps:
first, the RGB color space is converted to the XYZ color space:
then, the XYZ color space is converted to the Lab color space, resulting in the color component Lab:
acquiring the corresponding gray value of the RGB value:
grayscale＝R×0.299+G×0.587+B×0.114
further, the method for measuring the content of vitamin C in the fruits and vegetables by combining the iodine turbidity method and the infrared camera further comprises the following steps: sample solution: sampling 10g of fruit tissue such as tomato or cucumber, mashing, putting into an FSH-2A adjustable high-speed homogenizer, further mashing cells, and stirring the sample; adding kaolin for bleaching, diluting to 100ml with 0.25mol/L acetic acid, centrifuging in a centrifuge, and collecting the upper clear solution.
Further, the method for measuring the content of vitamin C in the fruits and vegetables by combining the iodine turbidity method and the infrared camera further comprises the following steps: adding 10mL of vitamin C solution with concentration into 1mL of iodoethanol solution to prepare required suspension; the mixed suspension was transferred to a cuvette and placed in an experimental setup for measurement. Acquiring an image of the suspension within 30 seconds, and automatically calculating an RGB value, a Lab value, a gray value and a logarithmic value of the gray value of the image by software; before measurement, the measurement device needs to be preheated for 20 minutes; fitting the vitamin C concentration sequence and corresponding Lab values, RGB values, gray values and logarithmic values of gray levels to obtain a relational expression between the vitamin C concentration sequence and the corresponding Lab values, RGB values, gray values and gray levels; the measurement of the actual sample adopts L, gray scale and logarithm of gray scale with higher fitting degree and consistency.
The invention also aims to provide a measuring device for implementing the method for measuring the content of vitamin C in fruits and vegetables by combining the iodine turbidity method with an infrared camera, wherein the measuring device comprises: the device comprises a USB interface, an infrared camera, a 850nm narrow-band filter, an LED constant-current driving circuit, an infrared light source, a sample cell, an acrylic box and a reaction cup;
the computer passes through the USB interface and is connected with infrared camera, and LED constant current drive circuit's power supply is +5V and the ground end of the USB interface of infrared camera board through the wire connection, installs the 850nm narrow-band filter on the infrared camera, and LED constant current drive circuit passes through the wire and infrared LED connects, and sample cell is placed to ya keli box central point, has placed the cell on the sample cell.
Furthermore, the infrared light source consists of six 850nm infrared LEDs and is driven by a constant current circuit.
Further, after a reference voltage generated by the U2 of the constant current driving circuit is buffered by the U1A, the reference voltage is compared with a sampling voltage on the sampling resistor R6, and the Q1 is controlled to realize LED constant current driving; adjusting W1 to change the working current of the LED; the circuit is powered by the USB interface.
The invention also aims to provide application of the method for measuring the vitamin C content in the fruits and vegetables by combining the iodine turbidity method with the infrared camera in vitamin C content measurement.
In summary, the advantages and positive effects of the invention are: the invention designs a measuring device and processing software of an iodine suspension, which are used for acquiring images and corresponding color components of the iodine suspension. Through actual determination of the vitamin C content in the tomatoes and the nectarines and comparison with a spectrophotometry, the method has higher accuracy in comparison with the measurement of a standard solution, and has higher consistency in comparison with the measurement of an actual fruit and vegetable sample. Practice proves that the method can be used for measuring the vitamin C, and the range is 0-5 mug/ml.
The invention utilizes an infrared camera to shoot an image of light which penetrates through iodine suspension, wherein the iodine suspension is formed by adding vitamin C into an iodine ethanol solution, the vitamin C and iodine undergo redox reaction, and the residual iodine after the reaction. The method comprises the steps of obtaining an RGB value corresponding to an image by analyzing the image acquired by a camera, calculating to obtain a logarithmic value of a gray value and a gray level of the image, converting the RGB color space to a CIE-Lab color space to obtain a corresponding Lab value, obtaining a relational expression of a vitamin C concentration with high correlation degree and L, the gray value and the logarithmic gray value by analyzing the relationship between the vitamin C and a color classification RGB value, the Lab value, the gray value and the logarithm of the gray value, and using the relational expression for measuring the vitamin C in an actual sample. The principle of vitamin C detection is shown in FIG. 2. The iodine turbidimetry, the infrared camera and the image processing technology are combined for determining the vitamin C, a novel vitamin C measuring method is provided, the advantages of simplicity in operation, miniaturization and the like are achieved, and the application field of image detection is widened.
Drawings
FIG. 1 is a flow chart of a method for measuring the vitamin C content in fruits and vegetables by combining an iodine turbidity method and an infrared camera provided by the embodiment of the invention.
Fig. 2 is a schematic diagram of a principle for measuring vitamin C based on an infrared camera and a turbidity method provided by the embodiment of the invention.
FIG. 3 is a structural diagram of a measuring device provided in an embodiment of the present invention;
in the figure: 1. a USB interface; 2. an infrared camera; 3. a 850nm narrow-band filter; 4. an LED constant current driving circuit; 5. an infrared light source; 6. a sample cell; 7. an acrylic box; 8. a cuvette.
Fig. 4 is a schematic diagram of an LED constant current driving circuit according to an embodiment of the present invention.
FIG. 5 is a graph showing RGB color components versus vitamin C concentration according to an embodiment of the present invention.
FIG. 6 is a schematic diagram of Lab color component versus vitamin C concentration provided by an embodiment of the present invention.
FIG. 7 is a graph of gray scale values and log scale values versus vitamin C concentration provided by an example of the present invention.
FIG. 8 is a graph showing the relationship between L, log-grams (logarithmic values of gray scale) and vitamin C concentration according to an embodiment of the present invention.
FIG. 9 is a graph showing the fitting results of L, grayscale (gray scale), log-grayscale (log of gray scale) and vitamin C concentration provided by an embodiment of the present invention.
FIG. 10 is a schematic diagram showing comparison between the actual density value and L, gray scale, logarithm of gray scale, and spectrophotometric measurement values, according to an embodiment of the present invention.
Fig. 11 is a diagram illustrating a comparison result between the spectrophotometry provided by the embodiment of the present invention and the method provided by the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Aiming at the problems in the prior art, the invention provides a method for measuring the content of vitamin C in fruits and vegetables by combining an iodine turbidity method and an infrared camera, and the invention is described in detail by combining the attached drawings.
As shown in fig. 1, the method for measuring the content of vitamin C in fruits and vegetables by combining an iodine turbidity method and an infrared camera provided by the embodiment of the invention comprises the following steps:
s101: an infrared camera is used for shooting an image of light after the light penetrates through the iodine suspension, vitamin C and iodine are subjected to redox reaction by adding the vitamin C into an iodine ethanol solution, and the iodine remained after the reaction forms the iodine suspension.
S102: the method comprises the steps of obtaining an RGB value corresponding to an image by analyzing the image obtained by a camera, calculating to obtain a gray value and a logarithmic value of the gray value of the image, and converting the RGB color space into a CIE-Lab color space to obtain a corresponding Lab value.
S103: by analyzing the relationship between the vitamin C and the color classification RGB value, Lab value, gray value and logarithm of the gray value, the relational expression of the vitamin C concentration with high correlation degree and the L, gray value and logarithm gray value is obtained.
The technical solution of the present invention is further described below with reference to the accompanying drawings.
The invention utilizes an infrared camera to shoot an image of light which penetrates through iodine suspension, wherein the iodine suspension is formed by adding vitamin C into an iodine ethanol solution, the vitamin C and iodine undergo redox reaction, and the residual iodine after the reaction. The method comprises the steps of obtaining an RGB value corresponding to an image by analyzing the image acquired by a camera, calculating to obtain a logarithmic value of a gray value and a gray level of the image, converting the RGB color space to a CIE-Lab color space to obtain a corresponding Lab value, obtaining a relational expression of a vitamin C concentration with high correlation degree and L, the gray value and the logarithmic gray value by analyzing the relationship between the vitamin C and a color classification RGB value, the Lab value, the gray value and the logarithm of the gray value, and using the relational expression for measuring the vitamin C in an actual sample. The principle of vitamin C detection is shown in FIG. 2. The iodine turbidimetry, the infrared camera and the image processing technology are combined for determining the vitamin C, a novel vitamin C measuring method is provided, the advantages of simplicity in operation, miniaturization and the like are achieved, and the application field of image detection is widened.
1. Experimental part
1.1 measuring device
The experimental setup is shown in fig. 3. The device comprises a USB interface 1, an infrared camera 2, a 850nm narrow-band filter 3, an LED constant-current driving circuit 4, an infrared light source 5, a sample pool 6, an acrylic box 7 and a cuvette 8.
The computer passes through USB interface 1 and is connected with infrared camera 2, and infrared camera 2 passes through the wire and is connected with LED constant current drive circuit 4, installs 850nm narrow frequency filter 3 on the infrared camera 2, and LED constant current drive circuit 4 passes through wire infrared light source 5 and connects, and 7 central point in ya keli box puts and places sample cell 6, has placed the cell 8 on the sample cell 6.
The sampling area is sealed by the shading box and isolated from the external light, so that the influence of the external light on sampling is avoided. The infrared light source consists of six 850nm infrared LEDs and is driven by a constant current circuit. Although the images formed by the light rays emitted by the LED light sources after passing through the suspension are not uniform, the measurement error can be eliminated by calculating the average value of the whole imaging area. Compared with a single LED, the image sampling area is enlarged, and the uneven distribution of the suspended iodine is reduced. When infrared light emitted by the light source passes through the turbid liquid, the infrared light is absorbed and scattered by the suspended matters, and the absorption and scattering degrees of the suspended matters to light are different due to different concentrations of vitamin C and turbidity of the turbid liquid formed after reaction, so that the light and shade degrees of the images acquired by the infrared camera are different.
1.2 constant current drive circuit
The infrared LED is driven by a constant current circuit, and the principle is shown in fig. 4. After the reference voltage generated by the U2 is buffered by the U1A, the reference voltage is compared with the sampling voltage on the sampling resistor R6, and the Q1 is controlled to realize the constant-current driving of the LED. Adjusting W1 may change the operating current of the LED. The circuit is powered by the USB interface. After the circuit is powered on, the circuit must be preheated for 20 minutes before measurement can be carried out.
1.3 Infrared camera
The digital camera used for measurement is a commercially available common infrared camera, and consists of an optical lens, a CMOS image sensor, a control chip and the like, the model is KS1.3A142 (Shenzhen Jinshenxiang technology, Inc.), and the maximum resolution of the camera is 1280 x 960. A850 nm narrow-band optical filter is additionally arranged on the lens, so that the focal length can be manually adjusted. The image acquired by the infrared camera is a single-channel image similar to a gray image, and the color interference of the test solution is avoided. In the experimental device, the upper computer software can change the configuration of the camera and adjust the gray effect of the image through the adjustment of the hue, the saturation and the white balance. The selection of other infrared cameras is all right, the camera is required to be capable of manually adjusting the focal length, parameters such as automatic exposure and automatic brightness can be forbidden, the exposure degree can be manually adjusted, and the parameter consistency in the measuring process is guaranteed.
The CMOS photosensitive element used for the digital camera is a semiconductor element used for recording light change. Each pixel of the camera corresponds to a photo-detection element. When light emitted by the light source passes through turbid liquid, the light is filtered by the 850nm optical filter and then projected onto the image sensor to generate an analog signal, and the analog signal is processed by the camera integrated signal processing chip and then transmitted to the upper computer software through the USB port to be processed. The signal processing part integrated with the camera directly converts the electric signals into image data, avoids analog-to-digital conversion and signal processing processes required by development of other instruments, and can also visualize the vitamin C concentration measurement process.
1.4 Upper computer software design
The designed upper computer software is used for acquiring the camera image, setting the camera working parameters and processing the image to obtain the RGB value, Lab value, gray value and the like corresponding to the solution. The software is based on a Visual Studio platform and is developed by combining a C # language with a Camera _ NET control. The Camera selection is used for selecting an experimental Camera, and the Camera settings are used for setting the Camera, so that the settings of brightness, white balance, hue, saturation, exposure and the like of the Camera can be adjusted, and the setting parameters of the Camera at the last time can be automatically saved. The Snapshot a frame obtains a frame of image, and the average value of RGB values of 3500 pixel points in a rectangular region in the center of the frame of image, wherein the 3500 pixel points comprise six LED light source images. Thus, the RGB value corresponding to the turbidity solution is obtained, and then the RGB color space is converted into the Lab color space, so that the Lab value corresponding to the turbidity solution is obtained. Where L represents the luminance (luminescence) of the transmitted light of the solution, a represents a range from red to green, and b represents a range from yellow to blue. The range of L is from 0 to 100, and the ranges of a and b are from +127 to-128. The conversion from the RGB color space to the Lab color space adopts an approximate conversion algorithm:
first, the RGB color space is converted to the XYZ color space:
then, the XYZ color space is converted to the Lab color space, resulting in the color component Lab:
acquiring the corresponding gray value of the RGB value:
grayscale＝R×0.299+G×0.587+Bx0.114 (5)
1.5 reagents and materials used in the experiment
Sucrose, fructose, glucose, alumina, ammonium chloride, ferrous sulfate, copper sulfate, anhydrous calcium chloride, sodium chloride, ferric sulfate, magnesium chloride, vitamin C (ascorbic acid), vitamin B1, vitamin B2, L-methionine, L-tryptophan, L-lysine, L-cysteine, acetic acid, and kaolin, available from the national pharmaceutical group Chemicals Co., Ltd (https:// www.reagent.com.cn), were used in the experiments. Vitamin E was purchased from Shanghai Ruichu Biotechnology, Inc., and all reagents used were analytical grade and were used without further purification. Deionized water used in the experimental procedure was purchased from Shanghai Jing pure Water technology, Inc. Iodine ethanol solution: 0.7g of iodine is added into 30mL of 95% ethanol, the dissolution is accelerated by using an adjustable high-speed homogenizer, the mixture is transferred into a 50mL volumetric flask, and 95% ethanol is added to 50mL to prepare 50mL of iodine ethanol solution. Vitamin C standard solution: vitamin C is easily oxidized in aqueous solutions, but is stable in acidic solutions. Thus, 200mg of vitamin C was added to 200mL of 0.25mol/L acetic acid solution to prepare 200mL of 1mg/L vitamin C solution. Other vitamin C standard solutions of different concentrations were prepared by dilution.
Actual sample solution: sampling 10g of fruit tissue such as tomato or cucumber, mashing, putting into an FSH-2A adjustable high-speed homogenizer, further mincing cells, and stirring the sample. Adding kaolin for bleaching to prevent pigment influence, diluting with 0.25mol/L acetic acid to 100ml, centrifuging in a centrifuge, and collecting the upper clear solution.
2 principle of measuring vitamin C by iodine turbidity method
The solubility of iodine in ethanol decreases significantly with decreasing ethanol concentration. Vitamin C solution is added into iodine ethanol solution, and due to the fact that the addition of the vitamin C solution causes reduction of ethanol, the solubility of iodine is obviously reduced, and iodine suspension is formed. The iodine simple substance is reduced into iodine ions, and the iodine ions promote the dissolution of iodine to form trivalent iodine ions so as to reduce the turbidity of the iodine suspension:
C6HBO6+I2＝C6H8O6 ++2I- (6)
when light passes through the suspension, the suspended particles can block the propagation of the light in the medium. The extent to which the propagation of light is affected by the suspended matter depends on factors such as the size and shape of the particles in solution and the wavelength of the incident light. In addition to scattering effects, the intensity of the transmitted light is absorbed and attenuated by the particles, both according to beer-lambert law:
I＝I0e-[αa+αb]xc(8)
ln I＝ln I0-(αa+αb)xc (9)
wherein I is the transmitted light intensity, I0is the incident light intensity, x is the distance light travels through the medium, c is the particle concentration, α a is the absorption coefficient, α b is the scattering coefficient.
The invention obtains suspension with different turbidities by mixing the iodine ethanol solution and the vitamin C solution with different concentrations. When light passes through turbid liquid with different turbidity, the light after absorption and scattering is acquired by the infrared camera. When 850nm infrared light is used as a light source, the influence of soluble particles in the suspension can be ignored, and the concentration of vitamin C can be obtained by analyzing an infrared image of the iodine suspension.
3 general operation procedure
The desired suspension was prepared by adding 10mL of a vitamin C solution to 1mL of an iodoethanol solution. The mixed suspension was transferred to a cuvette and placed in an experimental setup for measurement. The image of the suspension is required to be acquired within 30 seconds, and the RGB value, Lab value, gray value and logarithmic value of the gray level of the image are automatically calculated by software. The measuring device needs to be preheated for 20 minutes before measurement. And fitting the vitamin C concentration sequence and corresponding Lab values, RGB values, gray values and gray logarithmic values to obtain a relational expression between the vitamin C concentration sequence and the corresponding Lab values, RGB values, gray values and gray values. The measurement of the actual sample adopts L, gray scale and logarithm of gray scale with higher fitting degree and consistency.
4 results
In the experiment, the RGB value, Lab value, gray scale and logarithm value corresponding to different vitamin C concentrations are respectively measured. During the experiment, 17 parts of standard solution were made. The corresponding concentrations were 0, 0.5, 1, 1.5, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5. mu.g/mL. Each set of experiments contained a series of measurements of standard solutions, and 3 sets of experimental data were randomly selected and averaged to obtain a set of averaged data.
4.1 Experimental data and analysis
The invention obtains color component data (R, G, B, L, a and B), gray value and logarithmic value of gray level corresponding to suspension image through designed measuring device and analysis software. Fig. 5(a), fig. 5(B) and fig. 5(C) are R, G and the relationship between B value and vitamin C concentration. The infrared image is similar to the gray image in that the RGB values are theoretically equal, and the R, G, B value difference is caused by the adjustment of the camera parameters, so that the RGB values are not suitable for vitamin C measurement. FIGS. 6(a), 6(b) and 6(C) are graphs showing the relationship between L, a and b values and vitamin C concentration. The L value and the vitamin C concentration have approximate linear relation, and can be used for measuring the vitamin C concentration. Since different vitamin C concentrations may correspond to the same a and b values, the relationship between them cannot be expressed by a simple function, so the color classification a or b values cannot be used to measure the vitamin C concentration.
Fig. 7(a) and 7(b) show the relationship between the gray scale value and the logarithmic value of the gray scale value and the vitamin C concentration. The gray scale and the concentration of the vitamin C are in logarithmic relation, the logarithmic value of the gray scale and the concentration of the vitamin C are in linear relation, and the Lambert-beer laws (8) and (9) are met. Thus, the vitamin C concentration can be measured using gray scale values and logarithmic gray scale values.
FIG. 8 shows a comparison of L and log-grams (log-log of gray scale) after normalization. The log values of the gray scale and L have a similar functional relationship with vitamin C. In fact, when L is converted from the RGB color space to the CIE-Lab color space, the operations (2) to (5) approach logarithmic operations, so L has a similar tendency to log-graycale. Turbidity refers to the degree of obstruction of light by a solution, including scattering of light by suspended matter and absorption of light by solute molecules, and brightness refers to the brightness of an image. For a suspension, the turbidity determines the brightness of the solution image, while the gray scale refers to the brightness of the pixels in a black-and-white image, so the brightness L and gray scale of the solution image can represent the turbidity of the solution.
4.2 fitting results of vitamin C to L, grayscale (Gray) and log-grayscale (logarithmic values of Gray)
The above experiment results show that the L, gray scale logarithm value and the vitamin C concentration have high correlation, and after the L, gray scale logarithm value and the vitamin C concentration are fitted, the relational expression and the curve are shown in FIG. 9. The adjusted r-square sum relational expression is shown in table 1. Adj. R2The statistical index reflecting the degree of correlation between the variables is based on the deviation on the basis of the respective mean values of the two variables being the same, and is multiplied by two dispersion degrees to reflect the degree of correlation between the two variables, and is the square of the correlation coefficient between the expression value (measured data) and the estimation value (calculated by a fitting model). From the fitting result, the fitting degree of L, gray scale and gray scale logarithm values is high, wherein the fitting degree of the gray scale logarithm values is highest and is a linear relation, and the L, gray scale and gray scale logarithm values are recommended to be used as a measuring method.
TABLE 1L fitting expressions for gray scale, gray scale versus number for vitamin C and adj2
4.3 interference experiments
The effect of foreign substances such as sugars, metal ions, amino acids and vitamins etc. was tested in 4ug/ml vitamin C solution. The tolerance ratio for the maximum concentration of foreign substances causing a relative error of about 5% in the vitamin C concentration is listed in table 2. It was shown that very high concentrations of light metal ions Na could be tolerated+，Fe2+，Ca2+，Al3+，
Mg2+And saccharides, and heavy metal ions, such as Cu2+，Fe3+And partially reducing amino acidsE.g. lysine, cysteine, are only allowed to be present in low concentrations. However, common vegetables and fruits usually contain little or no heavy metal ions and amino acids, and therefore, the detection result is not influenced. The common reducing vitamins are only vitamin C and vitamin E, but most fruits and vegetables do not contain vitamin E, and the vitamin E is fat-soluble, insoluble in aqueous solution and removable by centrifugation.
TABLE 2 Effect of foreign substances (vitamin C concentration 4ug/ml)
| Foreign matter | Tolerance ratio | Foreign matter | Tolerance ratio |
| Na+，Cl+ | 2000 | Methionine | 750 |
| NH+，Cl+ | 1875 | Lysine | 0.075 |
| Cu2+，SO4 2+ | 0.025 | Tryptophan | 800 |
| Fe3+，SO4 2+ | 0.05 | sucrose | 3000 |
| Al3+，SO4 2+ | 1777.5 | Glucose | 1000 |
| Ca2+Cl+ | 1550 | Fructose | 2000 |
| Mg2+Cl+ | 1600 | VitaminB1 | 300 |
| Fe2+，SO4 2+ | 1725 | VitaminB2 | 200 |
| Cysteine | 0.05 | VitaminE | Insolubleinwater |
4.4 comparative experiments with spectrophotometry
Based on the above analysis results, a vitamin C concentration measurement method based on L, gray scale and logarithmic gray scale is proposed. To verify the accuracy and reliability of the method, vitamin C was measured in the standard solution and in the actual fruit samples and compared to spectrophotometry. The spectrophotometric method for comparison experiment is based on that vitamin C reduces ferric iron into ferrous iron, then mixes with 1, 10-phenanthroline for color development, and measures absorbance under 510nm wavelength. The spectrophotometer used for the comparative experiment was 721g visible spectrophotometer (Shanghai sperm analysis Instrument Co., Ltd.).
4.5 measurement results of comparative Standard solution
The vitamin C standard solutions of 1ug/ml, 1.5ug/ml, 2ug/ml, 2.5 ug/ml, 3ug/ml, 3.5ug/ml and 4ug/ml were measured by the method of the present invention and spectrophotometry, respectively. And (5) obtaining a p value through t test of an independent sample. In general, P<0.05 indicates that differences between the two methods should be considered. The results show that the measurement results of the L method, the gray scale logarithm method and the spectrophotometry method have no obvious difference compared with the standard vitamin C concentration. Table 3 shows the p-values and deviations (Std Dev) for the four methods2)。
TABLE 3L independent sample T test results and arithmetic mean error for gray scale, log of gray scale and spectrophotometer method
In table 3, method L is closer to the standard vitamin C concentration with higher accuracy. The L method, the gray scale method, and the logarithmic gray scale method can be used for the measurement of the concentration of vitamin C, and although the gray scale method and the logarithmic gray scale method are less accurate than other methods, the present invention suggests using the gray scale method or the logarithmic gray scale method because the conversion from RGB to Lab space is very time-consuming. The actual vitamin C concentration was compared with the concentrations determined by the four methods, and the results are shown in fig. 10.
4.6 comparative measurement of actual fruit samples
3 tomatoes and 3 nectarines were purchased from the market as test fruits and were treated to obtain actual samples. The method and spectrophotometry provided by the invention respectively determine 6 fruit samples, and the results are shown in table 4. The results of comparing the spectrophotometrically determined vitamin C concentrations with the proposed method are shown in fig. 11.
TABLE 4L measurement of vitamin C content of fruits and vegetables by Grayscale, Log-Grayscale and spectrophotometry
And respectively comparing and analyzing the three groups of data of L, gray scale and gray scale logarithm with a spectrophotometry by using a one-factor variance analysis method to obtain the probability P. P >0.05 indicates no significant difference between the two sets of data. The one-way anova P-values for the three sets of data are shown in table 5.
TABLE 5 comparison of one-way ANOVA to L, Gray Log, and spectrophotometry
In table 5, all P values are greater than 0.05, so there is no significant difference between the L, gray and logarithmic gray scale methods and spectrophotometry, demonstrating the feasibility of the proposed method. In addition, recovery tests were performed using standard addition methods and the results are shown in Table 6.
TABLE 6 test results of recovery with addition of a standard
The invention adopts the infrared camera and the iodine turbidity method to measure the vitamin C, can simplify the design of instruments, replaces the traditional optical instrument to measure the vitamin C content of fruits and vegetables, and provides a new idea for the measurement of the vitamin C. The vitamin C concentration in the suspension is obtained by adding a vitamin C solution into an iodine ethanol solution, forming a suspension of the residual iodine by using the redox reaction of the vitamin C and the iodine, and measuring the turbidity of the suspension by using an infrared camera. The designed measuring device and the designed image processing software can accurately acquire the color component corresponding to the suspension. Compared with a spectrophotometry method, the method has higher accuracy in measuring the standard solution, has no significant difference with the spectrophotometry method in measuring the vitamin C content in the fruits and the vegetables, and proves the effectiveness of the method.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (10)
1. A method for measuring the vitamin C content in fruits and vegetables by combining an iodine turbidity method and an infrared camera is characterized in that the method for measuring the vitamin C content in fruits and vegetables by combining the iodine turbidity method and the infrared camera is based on the redox reaction between vitamin C and iodine, and the infrared camera is used for measuring the residual iodine content after the reaction by a turbidity measuring method to obtain the vitamin C content; infrared light emitted by the infrared light-emitting LED penetrates through the iodine suspension, is absorbed and scattered, and then is captured by the infrared camera to form a digital image, and color components and gray components which can be used for representing the concentration of the vitamin C are obtained after processing; and fitting the different color component values and the gray values acquired by the camera with the corresponding vitamin C with different concentrations to obtain an expression with higher fitting degree for measuring the vitamin C with unknown concentration.
2. The method for measuring the vitamin C content in the fruits and vegetables by combining the iodine turbidity method with the infrared camera as claimed in claim 1, wherein the method for measuring the vitamin C content in the fruits and vegetables by combining the iodine turbidity method with the infrared camera comprises the following steps:
the method comprises the steps that firstly, an infrared camera is used for shooting an image of light which penetrates through an iodine suspension, vitamin C and iodine are added into an iodine ethanol solution to perform oxidation-reduction reaction, and the iodine left after the reaction forms the iodine suspension;
secondly, obtaining an RGB value corresponding to the image by analyzing the image obtained by the camera, calculating to obtain a gray value and a logarithmic value of the gray value of the image, and converting the RGB color space into a CIE-Lab color space to obtain a corresponding Lab value;
and thirdly, obtaining a relational expression of the vitamin C concentration with high correlation degree and the L, the gray value and the logarithm of the gray value by analyzing the relation between the vitamin C and the color classification RGB value, the Lab value, the gray value and the logarithm of the gray value.
3. The method for measuring the vitamin C content in the fruits and vegetables by combining the iodine turbidity method with the infrared camera as claimed in claim 2, wherein the method for measuring the vitamin C content in the fruits and vegetables by combining the iodine turbidity method with the infrared camera is used for obtaining a camera image, setting a camera working parameter and processing the image to obtain an RGB value, a Lab value and a gray value corresponding to a solution; obtaining a frame of image, obtaining an average value of RGB values of 3500 pixel points comprising six LED light source images in a central rectangular area of the image to obtain RGB values corresponding to a turbidity solution, and converting the RGB values into a Lab color space from the RGB color space to obtain a Lab value corresponding to the turbidity solution; wherein L represents the brightness of the transmitted light of the solution, a represents the range from red to green, b represents the range from yellow to blue, the value range of L is from 0 to 100, the value ranges of a and b are from +127 to-128, and the conversion from RGB color space to Lab color space adopts an approximate conversion algorithm.
4. The method for measuring the vitamin C content in the fruits and vegetables by combining the iodine turbidity method with the infrared camera as claimed in claim 3, wherein the method for measuring the vitamin C content in the fruits and vegetables by combining the iodine turbidity method with the infrared camera comprises the following steps:
first, the RGB color space is converted to the XYZ color space:
then, the XYZ color space is converted to the Lab color space, resulting in the color component Lab:
acquiring the corresponding gray value of the RGB value:
grayscale＝R×0.299+G×0.587+B×0.114。
5. the method for measuring the vitamin C content in the fruits and vegetables by combining the iodine turbidity method with the infrared camera as claimed in claim 1, wherein the method for measuring the vitamin C content in the fruits and vegetables by combining the iodine turbidity method with the infrared camera further comprises the following steps: sample solution: sampling 10g of fruit tissue such as tomato or cucumber, mashing, putting into an FSH-2A adjustable high-speed homogenizer, further mashing cells, and stirring the sample; adding kaolin for bleaching, diluting to 100ml with 0.25mol/L acetic acid, centrifuging in a centrifuge, and collecting the upper clear solution.
6. The method for measuring the vitamin C content in the fruits and vegetables by combining the iodine turbidity method with the infrared camera as claimed in claim 1, wherein the method for measuring the vitamin C content in the fruits and vegetables by combining the iodine turbidity method with the infrared camera further comprises the following steps: adding 10mL of vitamin C solution with concentration into 1mL of iodoethanol solution to prepare required suspension; transferring the mixed suspension into a cuvette, placing the cuvette into an experimental device for measurement, and requiring to obtain an image of the suspension within 30 seconds, wherein the RGB value, Lab value, gray value and logarithmic value of the gray value of the image are automatically calculated by software; before measurement, the measurement device needs to be preheated for 20 minutes; fitting the vitamin C concentration sequence and corresponding Lab values, RGB values, gray values and logarithmic values of gray levels to obtain a relational expression between the vitamin C concentration sequence and the corresponding Lab values, RGB values, gray values and gray levels; the measurement of the actual sample adopts L, gray scale and logarithm of gray scale with higher fitting degree and consistency.
7. A measuring device for implementing the method for measuring the content of vitamin C in fruits and vegetables by combining the iodine turbidity method with the infrared camera according to any one of claims 1-6, is characterized by comprising the following components: the device comprises a USB interface, an infrared camera, a 850nm narrow-band filter, an LED constant-current driving circuit, an infrared light source, a sample cell, an acrylic box and a reaction cup;
the computer passes through the USB interface and is connected with infrared camera, and infrared camera passes through the wire and is connected with LED constant current drive circuit, installs 850nm narrowband filter on the infrared camera, and LED constant current drive circuit passes through the wire and connects with infrared light source, and acrylic box central point puts and places the sample cell, places the cell on the sample cell.
8. The measurement device of claim 7, wherein the infrared light source consists of six 850nm infrared LEDs, driven by a constant current circuit.
9. The measuring device of claim 7, wherein a reference voltage generated by U2 of the constant current driving circuit is buffered by U1A, and then compared with a sampling voltage on a sampling resistor R6, and a Q1 is controlled to realize LED constant current driving; adjusting W1 to change the working current of the LED; the circuit is powered by the USB interface.
10. An application of the method for measuring the vitamin C content in fruits and vegetables by combining the iodine turbidity method and the infrared camera as claimed in any one of claims 1-6 in vitamin C content determination.
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