Method for detecting fat content in milk product based on impedance and admittance

Abstract

The invention discloses a method for detecting fat content in a milk product based on impedance and admittance. The method comprises the following steps: placing a to-be-detected sample in a sample tank provided with two metal electrodes which are distributed in parallel, wherein the to-be-detected sample completely covers an effective detection area between the two metal electrodes; wherein the sample to be detected is a milk product; an excitation voltage signal is applied between the two metal electrodes under a constant temperature condition, and a detection signal between the two metal electrodes is collected, so that the impedance Z and the admittance Y of the to-be-detected sample are obtained, and then the fat content in the to-be-detected sample is obtained according to a standard curve. According to the method, the change curve of the fat content in the milk along with impedance and admittance is constructed within a certain frequency range, rapid and accurate detection of the fat content in the milk is achieved, meanwhile, the operation difficulty is simplified through the detection method, the detection time is shortened, and the detection efficiency and safety are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of fat content detection, and in particular relates to a method for detecting the fat content in milk products based on impedance and admittance. Background Art

[0002] Milk is rich in milk fat and essential fatty acids, including linoleic acid, linolenic acid and arachidonic acid, which not only increase the nutritional value, but also provide good flavor characteristics, so it is widely loved by consumers. However, with the rapid development of the dairy industry, the quality control of milk (including raw milk and product milk) has become a focus, especially the detection of the content of various nutrients in milk to ensure the uniformity of nutrition and quality of milk. Milk fat content is an important indicator for evaluating the nutritional value, quality characteristics and safety of milk, and can also be used to analyze the production status of dairy cows. Therefore, it is necessary to quickly and accurately detect the milk fat content in milk to control product quality and stabilize the dairy market.

[0003] At present, the commonly used methods for detecting fat content in milk mainly include alkaline hydrolysis, Gerber's method, gas chromatography, high performance liquid chromatography and infrared spectroscopy. Among them, alkaline hydrolysis and Gerber's method are both national standard detection methods. The former has high accuracy but a long cycle, while the latter is convenient and rapid to detect, but difficult to operate. Gas chromatography, high performance liquid chromatography and infrared spectroscopy are new detection methods with high accuracy, repeatability and precision. However, the chromatography method requires saponification and methylation of fat before detection, which is a complex process, time-consuming and requires many consumables. The spectroscopic method does not require complex pretreatment operations, but there are problems such as overlapping absorption peaks, limited sensitivity and reduced accuracy.

[0004] In recent years, the detection of component changes based on electrical parameters of food has become a research hotspot. Due to the differences in the physical and chemical properties of proteins, fats, minerals, etc., they show different changes in electrical properties such as impedance, capacitance and conductivity. Therefore, based on the differences in electrical properties caused by changes in fat content in milk at different frequencies, a simple, accurate and sensitive fat content detection method was developed. Summary of the invention

[0005] The main purpose of the present invention is to provide a method for detecting fat content in milk products based on impedance and admittance, so as to overcome the shortcomings of the prior art.

[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes: The embodiment of the present invention provides a method for detecting fat content in milk products based on impedance and admittance, which comprises: The sample to be tested is placed between two sample slots provided with parallel metal electrodes, and the sample to be tested completely covers the effective detection area between the two metal electrodes; wherein the sample to be tested is a milk product; Under constant temperature conditions, an excitation voltage signal is applied between the two metal electrodes, and a detection signal between the two metal electrodes is collected to obtain the impedance of the sample to be tested. Z and admittance Y, and then calculate the fat content Φ in the sample to be tested according to formula (1): Φ=0.02Z 2 -16.49Y+C Formula (1) The value range of C in formula (1) is 0.023~1.256. Z The unit of is Ω, and the unit of Y is S.

[0007] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention successfully realizes the rapid and accurate detection of the fat content in milk by constructing the variation law of the fat content in milk products with impedance and admittance within a certain frequency range. At the same time, the method adopted by the present invention does not require special pretreatment of the raw materials and does not add additional toxic reagents, which effectively simplifies the operation difficulty, shortens the detection time, and improves the detection efficiency and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0009] Figure 1 It is a curve diagram of the relationship between the fat content in milk products and the impedance and admittance fitting functions in a typical embodiment of the present invention; Figure 2 It is a schematic diagram of a device for detecting fat content in milk in Example 1 of the present invention. DETAILED DESCRIPTION

[0010] In view of the defects of the prior art, the inventors of this case were able to propose the technical solution of the present invention after long-term research and extensive practice, and were very pleasantly surprised to find that within a certain frequency range, there is a certain variation pattern between the fat content in milk and the impedance and admittance. Based on this, a method for detecting the fat content in milk based on the electrical properties of the raw materials was established, which not only simplified the operation difficulty, but also shortened the detection time, and improved the detection efficiency, accuracy and safety.

[0011] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0012] Specifically, as one aspect of the technical solution of the present invention, a method for detecting fat content in milk products based on impedance and admittance includes: The sample to be tested is placed in a sample slot provided with two parallel metal electrodes, and the sample to be tested completely covers the effective detection area between the two metal electrodes; wherein the sample to be tested is a milk product; Under constant temperature conditions, an excitation voltage signal is applied between the two metal electrodes, and a detection signal between the two metal electrodes is collected to obtain the impedance of the sample to be tested. Z and admittance Y, and then calculate the fat content Φ in the sample to be tested according to formula (1): Φ=0.02Z 2 -16.49Y+C Formula (1) The value range of C in formula (1) is 0.023~1.256. Z The unit of is Ω, and the unit of Y is S.

[0013] The relationship curve of the fat content in the milk product and the impedance and admittance fitting function in the present invention is as follows: Figure 1 shown.

[0014] In some preferred embodiments, the waveform of the excitation voltage signal is a sine wave, the peak-to-peak value of the level is 500-1500 mV, and the frequency is 15-100 kHz.

[0015] In some preferred embodiments, the sample slot and the two metal electrodes are disposed in a housing, and the two metal electrodes are electrically connected to an LCR tester, and the LCR tester is used to apply an excitation voltage signal and collect a detection signal between the two metal electrodes.

[0016] Furthermore, the sample tank is an insulating cylinder and is coaxially arranged at the center of the shell; the metal electrodes are cylindrical and are coaxially arranged on two surfaces of the insulating cylinder.

[0017] Furthermore, a circulating constant temperature medium can be introduced into the interior of the housing, at least for heating, cooling or controlling the temperature of the sample tank, and the temperature range is 20-30°C.

[0018] Furthermore, the metal electrode has a diameter of 10-40 mm and a thickness of 1-20 mm.

[0019] Furthermore, the inner diameter of the sample tank is 20-60 mm, and the depth is 10-60 mm.

[0020] In some preferred embodiments, the method specifically comprises: A standard milk product with a known fat content is taken, and the standard milk product is prepared into a series of milk standard solutions with a fat content between 0.1 and 5.0 g / 100 g; the series of milk standard solutions are tested under the same test conditions as the test sample, an excitation voltage signal is applied by an LCR tester, and a test signal between the two metal electrodes is collected to obtain the impedance and admittance values ​​of the standard solution; The relationship between the fat content of the standard solution and the impedance and admittance is determined to obtain formula (1).

[0021] In some preferred embodiments, the fat content detection range Φ of the method is 0.15~4.90 g / 100g.

[0022] In some preferred embodiments, the milk product includes any one of skim milk, fresh milk, and whole milk, but is not limited thereto.

[0023] In some more specific embodiments, the method for detecting fat content in milk products based on impedance and admittance comprises: S1. Provide a device for detecting the fat content in milk products: including: a shell, metal electrodes, a sample slot, and an LCR tester; the shell can be passed through a circulating constant temperature medium; the sample slot is embedded in the shell, the center of which contains parallel metal electrodes and is connected to the LCR tester.

[0024] S2, inject the milk product to be tested into the sample tank and fill the effective detection area between the parallel metal electrodes. Under constant temperature conditions, apply an excitation voltage signal of a certain frequency between the parallel metal electrodes through an LCR tester, and collect the detection signal to obtain the impedance Z and admittance Y of the milk product to be tested. According to the relationship Φ=0.02Z 2 -16.49Y+C to obtain the fat content Φ of the milk, wherein the value range of C is 0.023~1.256, and the detection range of the method is 0.15~4.90 g / 100g.

[0025] In some embodiments, the parallel metal electrodes have a diameter of 10-40 mm and a thickness of 1-20 mm.

[0026] In some embodiments, the sample tank has an inner diameter of 20 to 60 mm and a depth of 10 to 60 mm.

[0027] In some embodiments, the excitation voltage signal has a waveform of a sine wave, a peak-to-peak value of 500-1500 mV, and a frequency of 15-100 kHz.

[0028] In some embodiments, the material of the parallel metal electrodes includes but is not limited to copper, platinum, stainless steel, etc.

[0029] In some embodiments, the material of the sample tank includes but is not limited to epoxy resin, nylon, organic glass, polycarbonate, etc., and the shell must be wrapped around the outside of the sample tank.

[0030] In some embodiments, a constant temperature medium may be introduced into the shell to increase, decrease and control the temperature of the sample tank, and the medium includes but is not limited to water, oil, etc. The temperature range of the constant temperature condition is 20-30°C.

[0031] In some embodiments, the milk product is skim milk, fresh milk, whole milk, etc.

[0032] The technical solution of the present invention is further described in detail below in conjunction with several preferred embodiments and drawings. This embodiment is implemented on the premise of the technical solution of the invention, and a detailed implementation method and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

[0033] Calculation of relative deviation (%) of the test results of different methods in the present invention: Let the test result of this implementation method be Y a , the control method test result is Y b , then the relative deviation (%) = (Y a -Y b ) / Y c ×100, where Y c is the average of the two test results.

[0034] Unless otherwise specified, the experimental materials used in the following examples can be purchased from conventional biochemical reagent companies.

[0035] Example 1 A method for detecting fat content in whole milk comprises the following steps: S1. A device for detecting fat content in milk (e.g. Figure 1 As shown in the figure, it includes: stainless steel shell, platinum electrode, epoxy resin sample tank, and LCR tester. The stainless steel shell is a rectangular parallelepiped with a length × width × height of 180 × 180 × 140 mm, and 25 ℃ pure water is passed into the interior to maintain a constant temperature; an epoxy resin sample tank is provided in the center of the shell, with an inner diameter of 40 mm and a depth of 30 mm; a parallel columnar platinum electrode with a diameter of 20 mm and a thickness of 3 mm is provided in the sample tank. The electrodes are connected to the LCR tester to generate and receive detection signals.

[0036] S2. Inject the whole milk sample to be tested into the epoxy resin sample tank so that it fills the effective detection area between the parallel platinum electrodes. At 25°C, apply a 50 kHz excitation voltage sine wave signal between the platinum electrodes, and the voltage level "peak-to-peak" value is 1000 mV. Collect the detection signal to obtain the impedance Z and admittance Y of the sample.

[0037] Take commercially available milk with a fat content of 5.0 g / 100g (the milk fat content measured by the third method in GB 5009.6-2016 - alkaline hydrolysis method), dilute with water to prepare standard solutions with fat contents of 0.1, 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0 g / 100g. According to steps S1 and S2, the relationship between impedance Z and admittance Y under different fat contents is measured, thereby obtaining the relationship Φ=0.02Z 2 -16.49Y+0.036, where Φ is the fat content of milk, and the detection range is 0.85~4.90 g / 100g.

[0038] Substitute the impedance Z and admittance Y measured by the sample to be tested into the relationship to calculate the fat content Φ of the sample to be tested.

[0039] The fat content in 8 portions of whole milk was detected by this embodiment and the third method in GB 5009.6-2016, the alkaline hydrolysis method. As shown in Table 1, the relative standard deviation of the detection results of the method in this embodiment is always less than 2%, indicating that the method in this embodiment has high stability. Compared with the method in GB 5009.6-2016, the relative deviation of the detection results is always less than ±4%, and the accuracy is high. In addition, the detection time of the detection method in this embodiment is 10 minutes, which is much lower than the average detection time of 40 minutes of the third method in GB 5009.6-2016, the alkaline hydrolysis method, and the detection cycle is shorter.

[0040] Table 1

[0041] Example 2 A method for detecting fat content in skim milk comprises the following steps: S1. The steps are the same as those in Example 1, except that the shell is a cylindrical copper-zinc alloy shell with a diameter of 180 mm and water flowing inside for temperature control; the sample tank is made of plexiglass with an inner diameter and a depth of 60 mm; the electrode is a stainless steel electrode with a diameter of 30 mm and a thickness of 5 mm.

[0042] S2. Inject the skim milk sample to be tested into the organic glass sample tank so that it fills the effective detection area between the parallel stainless steel electrodes. At 24°C, apply a 15 kHz excitation voltage sine wave signal between the stainless steel electrodes, and the voltage level "peak-to-peak" value is 1500 mV. Collect the detection signal to obtain the impedance Z and admittance Y of the sample.

[0043] Take commercially available milk with a fat content of 3.0 g / 100g (the milk fat content measured by the third method in GB 5009.6-2016 - alkaline hydrolysis method), dilute with water to prepare standard solutions with fat contents of 0.1, 0.2, 0.5, 1.0, 2.0, and 3.0 g / 100g. According to steps S1 and S2, the relationship between impedance Z and admittance Y under different fat contents is measured, thereby obtaining the relationship Φ=0.02Z 2 -16.49Y+0.883, where Φ is the fat content of milk, and the detection range is 0.15~1.25 g / 100g.

[0044] Substitute the impedance Z and admittance Y measured by the sample to be tested into the relationship to calculate the fat content Φ of the sample to be tested.

[0045] The fat content in 8 portions of skim milk was detected by using this embodiment and the third method in GB 5009.6-2016, the alkaline hydrolysis method. As shown in Table 2, the relative standard deviation of the detection results of the method in this embodiment is always less than 3%, indicating that the method in this embodiment has high stability. In addition, compared with the method in GB 5009.6-2016, the relative deviation of the detection results is always less than ±3%, and the accuracy is high. In addition, the detection time of the detection method in this embodiment is 10 minutes, which is much lower than the average detection time of 40 minutes of the third method in GB 5009.6-2016, the alkaline hydrolysis method, and the detection cycle is shorter.

[0046] Table 2

[0047] Embodiment 3 A method for detecting fat content in fresh milk comprises the following steps: S1. The steps are the same as those in Example 1, except that the sample tank is made of polycarbonate, with an inner diameter and a depth of 20 mm and 10 mm respectively; the electrode is a titanium electrode, with a diameter of 10 mm and a thickness of 1 mm.

[0048] S2. Inject the fresh milk sample to be tested into the polycarbonate sample tank so that it fills the effective detection area between the parallel titanium electrodes. At 30°C, apply a 100 kHz excitation voltage sine wave signal between the titanium electrodes, and the voltage level "peak-to-peak" value is 500 mV. Collect the detection signal to obtain the impedance Z and admittance Y of the sample.

[0049] Take commercially available milk with a fat content of 5.0 g / 100g (the milk fat content measured by the third method in GB 5009.6-2016 - alkaline hydrolysis method), dilute with water to prepare standard solutions with fat contents of 0.1, 0.2, 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0 g / 100g. According to steps S1 and S2, the relationship between impedance Z and admittance Y under different fat contents is measured, thereby obtaining the relationship Φ=0.02Z 2 -16.49Y+1.179, where Φ is the fat content of milk, and the detection range is 0.73~3.85 g / 100g.

[0050] Substitute the impedance Z and admittance Y measured by the sample to be tested into the relationship to calculate the fat content Φ of the sample to be tested.

[0051] The fat content in 8 portions of fresh milk was detected by using this embodiment and the third method in GB 5009.6-2016, the alkaline hydrolysis method. As shown in Table 3, the relative standard deviation of the detection results of the method in this embodiment is always less than 3%, indicating that the method in this embodiment has high stability. In addition, compared with the method in GB 5009.6-2016, the relative deviation of the detection results is always less than ±3%, and the accuracy is high. In addition, the detection time of the detection method in this embodiment is 10 minutes, which is much lower than the average detection time of 40 minutes of the third method in GB 5009.6-2016, the alkaline hydrolysis method, and the detection cycle is shorter.

[0052] Table 3

[0053] Example 4 A method for detecting fat content in ultra-high temperature sterilized pure milk comprises the following steps: S1. The steps are the same as those in Example 1, except that the electrode is a copper electrode with a diameter of 40 mm and a thickness of 5 mm; the inner diameter and depth of the epoxy resin sample tank are 60 mm and 50 mm, respectively.

[0054] S2. Inject the ultra-high temperature sterilized pure milk sample to be tested into the epoxy resin sample tank so that it fills the effective detection area between the parallel copper electrodes. At 26 °C, apply an 80 kHz excitation voltage sine wave signal between the copper electrodes, and the voltage level "peak-to-peak" value is 800 mV. Collect the detection signal to obtain the impedance Z and admittance Y of the sample.

[0055] Take commercially available milk with a fat content of 5.0 g / 100g (the milk fat content measured by the third method in GB 5009.6-2016 - alkaline hydrolysis method), dilute with water to prepare standard solutions with fat contents of 0.1, 0.2, 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0 g / 100g. According to steps S1 and S2, the relationship between impedance Z and admittance Y under different fat contents is measured, thereby obtaining the relationship Φ=0.02Z 2 -16.49Y+0.268, where Φ is the fat content of milk, and the detection range is 1.15~4.90 g / 100g.

[0056] Substitute the impedance Z and admittance Y measured by the sample to be tested into the relationship to calculate the fat content Φ of the sample to be tested.

[0057] The fat content in 8 portions of ultra-high temperature sterilized pure milk was detected by using this embodiment and the third method in GB 5009.6-2016, the alkaline hydrolysis method. As shown in Table 4, the relative standard deviation of the detection results of the method in this embodiment is always less than 3%, indicating that the method in this embodiment has high stability. In addition, compared with the method described in GB 5009.6-2016, the relative deviation of the detection results is always less than ±3%, and the accuracy is high. In addition, the detection time of the detection method in this embodiment is 10 minutes, which is much lower than the average detection time of 40 minutes of the third method in GB5009.6-2016, the alkaline hydrolysis method, and the detection cycle is shorter.

[0058] Table 4

[0059] Comparative Example 1 A method for detecting fat content in whole milk comprises the following steps: S1. Steps are the same as those in Example 1.

[0060] S2. The steps are the same as those in Example 1, except that the frequency of the sinusoidal wave excitation voltage is 5 kHz, and the peak-to-peak value of the voltage level is 300 mV.

[0061] Take commercially available milk with a fat content of 5.0 g / 100g (the milk fat content measured by the third method in GB 5009.6-2016 - alkaline hydrolysis method), dilute with water to prepare standard solutions with fat contents of 0.1, 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0 g / 100g. According to steps S1 and S2, the relationship between impedance Z and admittance Y under different fat contents is measured, thereby obtaining the relationship Φ=0.02Z 2 -15.42Y+0.097, where Φ is the fat content of milk, and the detection range is 1.53~4.25 g / 100g.

[0062] Substitute the impedance Z and admittance Y measured by the sample to be tested into the relationship to calculate the fat content Φ of the sample to be tested.

[0063] The fat content in 8 portions of whole milk was tested by this comparative example and the third method in GB 5009.6-2016, the alkaline hydrolysis method. As shown in Table 5, the relative standard deviation of the test results of this comparative example method always varied in the range of 2% to 7%, indicating that the test stability of the method was insufficient, which may be related to the large fluctuations in impedance and admittance of the raw materials due to the low frequency. In addition, compared with the GB 5009.6-2016 method, the relative deviation of the test results always exceeded ±4%, and the accuracy of the test method decreased.

[0064] Table 5

[0065] Comparative Example 2 A method for detecting fat content in whole milk comprises the following steps: S1. Steps are the same as those in Example 1.

[0066] S2. The steps are the same as those in Example 1, except that the frequency of the sinusoidal wave excitation voltage is 150 kHz, and the peak-to-peak value of the voltage level is 2000 mV.

[0067] Take commercially available milk with a fat content of 5.0 g / 100g (the milk fat content measured by the third method in GB 5009.6-2016 - alkaline hydrolysis method), dilute with water to prepare standard solutions with fat contents of 0.1, 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0 g / 100g. According to steps S1 and S2, the relationship between impedance Z and admittance Y under different fat contents is measured, thereby obtaining the relationship Φ=0.02Z 2 -18.79Y+0.027, where Φ is the fat content of milk, and the detection range is 1.53~4.25 g / 100g.

[0068] Substitute the impedance Z and admittance Y measured by the sample to be tested into the relationship to calculate the fat content Φ of the sample to be tested.

[0069] The fat content in 8 portions of whole milk was tested by this comparative example and the third method in GB 5009.6-2016, the alkaline hydrolysis method. As shown in Table 6, the relative standard deviation of the test results of the comparative example method was always less than 2%, indicating that the method has high detection stability. However, compared with the GB 5009.6-2016 method, the relative deviation of the test results was always higher than ±4%, and the highest reached -7.94%, indicating that the accuracy of the method was insufficient, which may be related to the fact that the higher frequency increased the differences in the raw materials themselves, making it impossible for the impedance and admittance characteristics to accurately characterize the changes in the composition of the raw materials.

[0070] Table 6

[0071] Comparative Example 3 A method for detecting fat content in whole milk comprises the following steps: S1. The steps are the same as those in Example 1, except that the epoxy resin sample groove in the center of the shell has an inner diameter of 40 mm and a depth of 8 mm.

[0072] S2. The steps are the same as those in Example 1.

[0073] Take commercially available milk with a fat content of 5.0 g / 100g (the milk fat content measured by the third method in GB 5009.6-2016 - alkaline hydrolysis method), dilute with water to prepare standard solutions with fat contents of 0.1, 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0 g / 100g. According to steps S1 and S2, the relationship between impedance Z and admittance Y under different fat contents is measured, thereby obtaining the relationship Φ=0.02Z 2 -15.89Y+0.125, where Φ is the fat content of milk.

[0074] The impedance Z and admittance Y measured by the sample to be tested are substituted into the relationship to calculate the fat content Φ of the sample to be tested. The detection range of the method is 0.85~4.05 g / 100g.

[0075] The fat content in 8 portions of whole milk was detected by this comparative example and the third method in GB 5009.6-2016, the alkaline hydrolysis method. As shown in Table 7, the relative standard deviation of the detection results of the comparative example method was always less than 3%, indicating that the detection stability of the method was high. However, compared with the GB 5009.6-2016 method, the relative deviation of the detection results was always higher than ±3%, and the highest reached -6.65%, indicating that the accuracy of the method was insufficient, which may be related to the size of the spacing between the electrodes. The smaller the spacing, the smaller the sample loading, and the impedance and admittance characteristics could not accurately characterize the composition changes of the raw materials.

[0076] Table 7

[0077] Comparative Example 4 A method for detecting the fat content in whole milk comprises the following steps: S1. The steps are the same as those in Example 1, except that a parallel columnar platinum electrode with a diameter of 8 mm and a thickness of 3 mm is provided in the sample tank.

[0078] S2. The steps are the same as those in Example 1.

[0079] Take commercially available milk with a fat content of 5.0 g / 100g (the milk fat content measured by the third method in GB 5009.6-2016 - alkaline hydrolysis method), dilute with water to prepare standard solutions with fat contents of 0.1, 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0 g / 100g. According to steps S1 and S2, the relationship between impedance Z and admittance Y under different fat contents is measured, thereby obtaining the relationship Φ=0.02Z 2 -18.56Y+0.232, where Φ is the fat content of milk, and the detection range is 1.05~3.95 g / 100g.

[0080] Substitute the impedance Z and admittance Y measured by the sample to be tested into the relationship to calculate the fat content Φ of the sample to be tested.

[0081] The fat content in 8 portions of whole milk was tested by this comparative example and the third method in GB 5009.6-2016, the alkaline hydrolysis method. As shown in Table 8, the relative standard deviation of the test results of this comparative example method was always less than 3%, indicating that the method has high detection stability. However, compared with the GB 5009.6-2016 method, the relative deviation of the test results was always higher than ±3%, and the highest reached -6.49%, indicating that the accuracy of the method was insufficient, which may be related to the size of the electrode plate, the reduced contact area between the electrode plate and the sample, the weakened effective effect of the electric field, and the inability of the impedance and admittance characteristics to accurately characterize the composition changes of the raw materials.

[0082] Table 8

[0083] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments with other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0084] It should be understood that the technical solution of the present invention is not limited to the above-mentioned specific implementation cases. Any technical deformation made according to the technical solution of the present invention without departing from the scope of protection of the purpose of the present invention and the claims shall fall within the protection scope of the present invention.

Claims

1. A method for detecting fat content in milk products based on impedance and admittance, characterized in that: include: The sample to be tested is placed in a sample slot provided with two parallel metal electrodes, and the sample to be tested completely covers the effective detection area between the two metal electrodes; wherein the sample to be tested is a milk product; Under constant temperature conditions, an excitation voltage signal is applied between the two metal electrodes, and a detection signal between the two metal electrodes is collected to obtain the impedance of the sample to be tested. Z and admittance Y, and then calculate the fat content Φ in the sample to be tested according to formula (1): Φ=0.02Z 2 -16.49Y+C Formula (1) The value range of C in formula (1) is 0.023~1.

256. Z The unit of is Ω, and the unit of Y is S.

2. The method according to claim 1, characterized in that: The waveform of the excitation voltage signal is a sine wave, the peak-to-peak value of the level is 500-1500 mV, and the frequency is 15-100 kHz.

3. The method according to claim 1, characterized in that: The sample slot and the two metal electrodes are both arranged in a shell. The two metal electrodes are electrically connected to an LCR tester. The LCR tester is used to apply an excitation voltage signal and collect a detection signal between the two metal electrodes.

4. The method according to claim 3, characterized in that: The sample tank is an insulating cylinder and is coaxially arranged at the center of the shell; the metal electrodes are cylindrical and are coaxially arranged on two surfaces of the insulating cylinder.

5. The method according to claim 3, characterized in that: A circulating constant temperature medium can be introduced into the interior of the shell, which is at least used to increase, decrease or control the temperature of the sample tank, and the temperature range is 20-30°C.

6. The method according to claim 4, characterized in that: The metal electrode has a diameter of 10-40 mm and a thickness of 1-20 mm.

7. The method according to claim 4, characterized in that: The inner diameter of the sample tank is 20-60 mm, and the depth is 10-60 mm.

8. The method according to claim 1, characterized in that Specifically include: A standard milk product with a known fat content is taken, and the standard milk product is prepared into a series of milk standard solutions with a fat content between 0.1 and 5.0 g / 100 g; the series of milk standard solutions are tested under the same test conditions as the test sample, an excitation voltage signal is applied by an LCR tester, and a test signal between the two metal electrodes is collected to obtain the impedance and admittance values ​​of the standard solution; The relationship between the fat content of the standard solution and the impedance and admittance is determined to obtain formula (1).

9. The method according to claim 1, characterized in that: The fat content detection range Φ of the method is 0.15~4.90 g / 100g.

10. The method according to claim 1, characterized in that: The milk product includes any one of skimmed milk, fresh milk and whole milk.

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