Method for continuously determining lactose, protein and fat content of milk

Abstract

The invention relates to a method for determining the lactose content # imgabs0 #, the protein content # imgabs1 # and the fat content # imgabs2 #, in particular in a continuous manner, of a flowable medium, in particular milk, milk replacer and / or milk product, comprising the following method steps: ascertaining the frequency-dependent relative permittivity of the medium in the frequency range of the frequency spectrum, the upper limit of the spectrum is 50 GHz, in particular 25 GHz, preferably 14 GHz, and the lower limit of the spectrum is 10 MHz, in particular 50 MHz, preferably 85 MHz; and-calculating a lactose content # imgabs3 #, a protein content # imgabs4 # and a fat content # imgabs5 # on the basis of the ascertained relative permittivity and on the basis of a lactose reference, a protein reference and a fat reference. The invention further relates to a measuring assembly.

Description

Technical Field

[0001] The present invention relates to a method for continuously determining, in particular, the lactose content of a flowable medium, in particular milk, milk substitutes and / or dairy products , protein content and fat content , and to a measuring assembly for determining the lactose content of a flowable medium, in particular milk, milk substitutes and / or dairy products , protein content and fat content . Background Art

[0002] Physical variables of the dielectric constant and loss factor of a medium in a production line can be determined by means of microwaves. From these two variables, which are measured at one or more different frequencies, conclusions can be drawn about application-specific parameters, such as the proportion of water in a mixture of water and other non-polar or weakly polar components or the solids content in a liquid medium.

[0003] The established transmission / reflection measurement is described in L.F. Chen, C.K. Ong, C.P. Neo, V.V. Varadan, V.K. Varadan - "Microwave Electronics, Measurement and Materials Characterization" (John Wiley & Sons Ltd., 2004). For this purpose, microwave signals are interfaced at two different positions at the medium in a container or measuring tube, the scattering parameters (transmission and optionally reflection) are measured between these interface structures, and the physical properties of the mentioned medium are calculated from the measured scattering parameters.

[0004] WO 2018 / 121927 A1 teaches a measuring assembly for analyzing the properties of a flowing medium by means of microwaves. In addition to microwave antennas, the measuring assembly has an electrically insulating lining layer on the inner peripheral surface of the measuring tube. This lining layer forms a dielectric waveguide through which at least part of the microwave signal can travel from the first microwave antenna to the second microwave antenna. One application of such a measuring assembly is to determine the proportion of solids in a liquid medium being conveyed. WO 2021 / 099152 A1 teaches a microwave antenna having a front part in contact with the medium, through which an excitation signal is transmitted into the medium.

[0005] Milk and any (intermediate) products obtained therefrom can be described as a mixture of different components, mainly consisting of water, milk fat, and other solids, where the other solids essentially include proteins, carbohydrates (especially including lactose), and small amounts of minerals.

[0006] During the processing chain from raw milk to finished milk, the proportions of these components are important parameters for using open-loop and closed-loop control to control the process, for process and quality control, and for balancing product flows. The common practice is to use standard methods for determining the proportions using laboratory samples. This means that only a few samples can be evaluated, and the analysis results are obtained with a considerable delay after the sampling process. Although process-oriented spectroscopic analysis in the infrared range with automatic sampling can be carried out, firstly, this method is very costly, and secondly, it is only based on a small number of samples obtained at relatively long time intervals. Therefore, the applicability of this analysis in process control is limited.

[0007] DE102017131269A1 discloses a method for continuously determining the fat content of milk with different solid contents using a Coriolis flowmeter and a microwave sensor. These types of measuring devices can be integrated into the milk processing process. The disadvantage of the disclosed technical solution is that the solids cannot be separated to accurately determine the protein and lactose contents. Summary of the Invention

[0008] The object of the present invention is to remedy this.

[0009] This object is achieved by the method according to claim 1 and by the measuring assembly according to claim 13.

[0010] A method according to the present invention for continuously determining, in particular, the lactose content , protein content and fat content of a flowable medium - in particular milk, milk substitutes, and / or dairy products - comprises the following method steps:

[0011] - Determining the frequency-dependent relative permittivity of the medium across a frequency range of a spectrum,

[0012] where the upper limit of the spectrum is 50 GHz, in particular 25 GHz, and preferably 14 GHz,

[0013] where the lower limit of the spectrum is 10 MHz, in particular 50 MHz, and preferably 85 MHz; and

[0014] - Calculating the lactose content , protein content and fat content .

[0015] By providing lactose, protein, and fat references and including them in the calculation of the respective components of the solids, the contribution of lactose can be distinguished from the contribution of protein and the contributions of lactose and protein can be measured, even though the density and dielectric constant are very similar.

[0016] The method according to the invention is suitable for use, for example, in a microwave sensor designed to determine the solids content of a flowable aqueous medium.

[0017] In the context of the present invention, a reference is a mathematical variable that describes the fundamental contribution of each component to a relatively defined dielectric constant. The reference can include a mathematical function of the frequency-based relative dielectric constant or its real or imaginary part. The mathematical variable can also be a frequency-dependent vector.

[0018] Advantageous embodiments of the invention are the subject of the dependent claims.

[0019] One embodiment provides that in determining the lactose content , protein content and fat content , only the real part of the relative dielectric constant is included.

[0020] It has been found that the contributions of the individual lactose, protein, and fat components are more pronounced in the real part than in the imaginary part.

[0021] One embodiment provides that in determining the lactose content , protein content and fat content , only the imaginary part of the relative dielectric constant is included.

[0022] As an alternative to determining the ratio based on the real part of the relative dielectric constant, the imaginary part of the relative dielectric constant can also be used to determine the individual lactose, protein, and fat ratios.

[0023] One embodiment provides that the method comprises the following method steps:

[0024] - Measuring or providing the conductivity of the medium;

[0025] - Compensating the imaginary part of the relative dielectric constant based on the measured or provided conductivity.

[0026] The imaginary part of the true dielectric constant describes the loss term resulting from the continuous repolarization of the molecules in the dielectric. This loss term consists of polarization loss and conductivity loss. Conductivity loss is particularly evident at low frequencies. Therefore, for dielectrics with high conductivity (e.g., milk), conductivity compensation must be performed on the imaginary part. The proportion of conductivity can be calculated using the following equation:

[0027]

[0028] The conductivity can be determined using a conductivity sensor. This can be part of a measurement assembly and thus integrated into the production line, or it can be designed as an external handheld device with which the conductivity of a sample of the dielectric can be determined or by which it can be determined. Alternatively, the conductivity of the dielectric can also be predefined by the user.

[0029] One embodiment provides that in the calculation, milk is modeled as a four-component system,

[0030] where the components include fat, lactose, protein, and water.

[0031] One embodiment provides that the water content of the dielectric is between 55 wt.% - especially 80 wt.% - and 95 wt.%.

[0032] One embodiment provides that the method includes the following method steps:

[0033] - Specify an operating point,

[0034] where the operating point specifies the water content or a fixed water content range,

[0035] where for different operating points, at least the lactose reference, protein reference, and / or fat reference are different.

[0036] The operating point is specified by the user. The advantage of considering the expected water content is the higher accuracy that can thus be achieved in determining the individual proportions. In the context of the present invention, the operating point includes exactly one specific water content known or assumed by the user, or a water content range including multiple water contents.

[0037] One embodiment provides that the lactose reference, protein reference, and fat reference can be linearized at the specified operating point.

[0038] One embodiment provides that the method includes the following method steps:

[0039] - Measure the temperature of the dielectric,

[0040] where in calculating the lactose content 、protein content and fat content When, and in particular when compensating for the imaginary part of the dielectric constant by means of the measured or provided conductivity, the temperature of the medium is included.

[0041] In practice, the relative dielectric constant depends on the temperature and the measurement frequency. The desired accuracy is achieved by temperature measurements that take into account the temperature dependence of the medium properties.

[0042] One embodiment provides that the lactose, protein, and fat references are each temperature-dependent.

[0043] One embodiment provides that the lactose reference includes a frequency-dependent lactose vector ,

[0044] wherein the protein reference includes a frequency-dependent protein vector ,

[0045] wherein the fat reference includes a frequency-dependent fat vector .

[0046] One embodiment provides that the lactose content , the protein content , and the fat content can be determined by means of / can be determined with the following equation:

[0047]

[0048] wherein the following applies to :

[0049]

[0050] wherein the basis vectors , , and are obtained from the orthogonalization process of the lactose vector , the protein vector , and the fat vector ,

[0051] wherein represents the determined relative dielectric constant, and for , it is assumed that .

[0052] The matrix can include the vector products of the basis vectors and the corresponding component vectors, or alternatively can already exist in the measurement component as a parameter matrix, i.e., the vector products have already been performed.

[0053] The basis vectors can also be stored as equations describing the frequency-dependent behavior of the relative dielectric constant, or more precisely the real or imaginary part.

[0054] A measuring assembly for determining the lactose content, protein content and fat content of a flowable medium, in particular milk, milk substitutes and / or dairy products, according to the invention , protein content and fat content comprises:

[0055] - a measuring tube for conducting the medium;

[0056] - at least one microwave antenna;

[0057] wherein at least one microwave antenna is arranged on the measuring tube;

[0058] - transducer electronics designed to carry out the method according to the invention.

[0059] One embodiment provides that the measuring assembly comprises:

[0060] - at least two microwave antennas,

[0061] wherein at least two microwave antennas are arranged on the measuring tube,

[0062] wherein the first microwave antenna of the at least two microwave antennas has at least a first measurement range,

[0063] wherein the second microwave antenna of the at least two microwave antennas has at least a second measurement range,

[0064] wherein the first measurement range and the second measurement range together cover a frequency range from 10 MHz to 50 GHz, in particular from 50 MHz to 25 GHz, and preferably from 85 MHz to 14 GHz.

[0065] One embodiment provides that the transducer electronics comprise an electronic memory,

[0066] wherein a lactose vector , protein vector and fat vector are stored in the memory. Description of the Drawings

[0067] The invention will be explained in more detail with reference to the following drawings, in which:

[0068] Figure 1 a first embodiment of the method according to the invention is shown;

[0069] Figure 2 a second embodiment of the method according to the invention is shown;

[0070] Figure 3shows the real part of the frequency-based relative permittivity for lactose reference, protein reference, and fat reference; and

[0071] Figure 4 shows an embodiment of a measurement assembly according to the present invention. Detailed Description

[0072] Figure 1 shows a first embodiment of a method according to the present invention, which can or is to be carried out by means of a measurement assembly having a microwave antenna. In a first method step I,1, an operating point is specified. The operating point specifies the water content of the medium to be monitored or the water content range in which the water content expected for the medium lies. For milk, milk substitutes, dairy products, and milk substitute products, a water content between 55 wt.% - especially 80 wt.% - and 95 wt.% is assumed. The operating point can be specified by the operator of the measurement assembly on-site or via a central monitoring unit that is connected to the measurement assembly either non-contactlessly or via a cable at a corresponding display of the measurement assembly.

[0073] In a second method step II,1, the frequency-dependent relative permittivity of the medium is determined across a frequency range of the spectrum. In a particular embodiment, the real part of the relative permittivity is determined and used to determine the respective proportions in the medium. The upper limit of the spectrum is 50 GHz, especially 25 GHz, and preferably 14 GHz, and the lower limit of the frequency is 10 MHz, especially 50 MHz, and preferably 85 MHz. This is carried out using a microwave sensor. The microwave sensor is designed to send a microwave signal into the medium and to measure the microwave signal again after the microwave signal has interacted with the medium. The measured microwave signal is used to determine the real part of the relative permittivity for the frequency band of the microwave signal.

[0074] In a third method step III,1, the temperature of the medium is measured. For this purpose, a temperature sensor can be provided, which is part of the measurement assembly. Alternatively, a temperature sensor separate from the measurement assembly can be used to determine the temperature of the medium. In this case, the current temperature of the medium is provided to the transducer electronics.

[0075] In a fourth method step IV,1, the real part of the determined relative permittivity is corrected or compensated based on the measured temperature. Alternatively, the provided lactose, protein, and / or fat reference can be temperature-dependent.

[0076] In a fifth method step V,1, the lactose content is calculated based on the determined real part and based on the provided lactose reference, protein reference, and fat reference 、protein content and fat content . For modeling purposes, a four-component system is assumed for milk, milk substitutes, dairy products, and / or milk replacers. These components are fat, lactose, protein, and water. In order to achieve the highest possible accuracy when determining the individual ratios, the lactose reference, protein reference, and / or fat reference must be adapted to each operating point. This means that the lactose reference, protein reference, and fat reference can be linearized at each operating point. According to this embodiment, the lactose reference is a frequency-dependent lactose vector . The same applies to the protein reference and the fat reference, where the protein reference includes a frequency-dependent protein vector , and the fat reference correspondingly includes a frequency-dependent fat vector .

[0077] Using the lactose vector , the protein vector , and the fat vector , the lactose content , the protein content , and the fat content can be determined according to the following formula

[0078]

[0079] The following formula applies to :

[0080]

[0081] where the basis vectors , , and are obtained from the orthogonalization process (e.g., the Gram-Schmidt orthogonalization process) of the lactose vector , the protein vector , and the fat vector . The matrix is used to transform the vectors , , and into an orthogonal system. The vector represents the determined relative permittivity, and for , it is assumed that .

[0082] Alternatively, the individual references can also be stored as mathematical functions.

[0083] Figure 2Shows a second embodiment of the method according to the invention, which can be or is to be carried out with the aid of a measuring assembly having a microwave antenna. In the first method step I,2, an operating point is specified. This operating point specifies the water content of the medium to be monitored or the water content range in which the water content expected for the medium lies. This operating point can be specified by the operator of the measuring assembly on site or via a central monitoring unit that is connected to the measuring assembly either non - contactlessly or via a cable on the corresponding display of the measuring assembly.

[0084] In the second method step II,2, the frequency - dependent relative permittivity of the medium is determined over a frequency range of the spectrum. In a particular embodiment, the imaginary part of the relative permittivity is determined and used to determine the individual proportions in the medium. The upper limit of the spectrum is 50 GHz, in particular 25 GHz, and preferably 14 GHz, and the lower limit of the frequency is 10 MHz, in particular 50 MHz, and preferably 85 MHz. A microwave sensor is used to determine the imaginary part. The microwave sensor is designed to send a microwave signal into the medium and to measure the microwave signal again after the microwave signal has interacted with the medium. The measured microwave signal is used to determine the imaginary part of the relative permittivity for the frequency band of the microwave signal.

[0085] In the third method step III,2, the temperature of the medium is measured. For this purpose, a temperature sensor can be provided, which is part of the measuring assembly. Alternatively, a temperature sensor separate from the measuring assembly can be used to determine the temperature of the medium. In this case, the current temperature of the medium is provided to the transducer electronics.

[0086] In the fourth method step VI,2, the conductivity of the medium is measured. For this purpose, a conductivity sensor can be provided, which is part of the measuring assembly. Alternatively, a conductivity sensor separate from the measuring assembly can be used to determine the conductivity of the medium. In this case, the current conductivity of the medium is provided to the transducer electronics.

[0087] In the fifth method step V,2, the imaginary part of the determined relative permittivity is corrected or compensated based on the temperature and conductivity. Alternatively, the provided lactose, protein and / or fat references can depend on the temperature and / or conductivity.

[0088] In the sixth method step VI,2, the lactose content is calculated based on the determined imaginary part and based on the provided lactose reference, protein reference and fat reference 、protein content and fat content .

[0089] Figure 3Shows the real part of the frequency-based relative permittivity for protein reference 201, lactose reference 202, and fat reference 203. Each reference is the difference between two reference measurements of different reference media, where the different reference media differ only in water content and one of the remaining three components (protein, lactose, and fat). This also means that two components of the reference media are substantially the same.

[0090] For protein reference 201, the lactose and fat contents of the two reference media are substantially the same. For the shown protein reference 201, there is a protein difference of approximately 4.5 wt.% between the two reference media. The water content of the two reference media is between 87 wt.% and 92 wt.%. The curve for protein reference 201 is partially parabolic, with the lowest point at approximately 5 GHz.

[0091] For lactose reference 202, the protein and fat contents of the two reference media are substantially the same. For the shown lactose reference 202, there is a lactose difference of approximately 15 wt.% between the two reference media. The water content of the two reference media is between 87 wt.% and 92 wt.%. The curve for lactose reference medium 202 is parabolic, with the lowest point at approximately 8 GHz.

[0092] For fat reference 203, the lactose and protein contents of the two reference media are substantially the same. For the shown fat reference 203, there is a fat difference of approximately 6.5 wt.% between the two reference media. The water content of the two reference media is between 80 wt.% and 86 wt.%. The curve for fat reference 203 is substantially linear in some parts.

[0093] Figure 4 Shows an embodiment of a measurement assembly 100 for determining the lactose content , protein content and fat content of a flowable medium - in particular milk, milk substitutes, and / or dairy products - according to the present invention. The measurement assembly 100 includes a measurement tube 101 for holding the medium and two microwave antennas 116, 118 arranged opposite each other. The microwave antenna 116 is configured to feed a microwave signal into the medium when the medium is present in the measurement tube. The microwave signal covers a frequency range from 10 MHz to 50 GHz, in particular from 50 MHz to 25 GHz, and preferably from 85 MHz to 14 GHz. Alternatively, a pair of additional microwave antennas can also be provided. In this case, the two measurement ranges of the two pairs of microwave antennas together cover a frequency range from 10 MHz to 50 GHz, in particular from 50 MHz to 25 GHz, and preferably from 85 MHz to 14 GHz.

[0094] The microwave antenna 118 is configured to measure the microwave signal transmitted into the medium by the microwave antenna 116. The measured microwave signal is provided to the transducer electronics 102, which is configured to perform the method according to the invention. The transducer electronics 102 can be mechanically connected to the microwave antenna. If the individual components are determined in-situ in the transducer electronics 102, the transducer electronics 102 has an electronic memory 103, in which the fat reference is stored as a frequency-dependent fat vector . Alternatively, the individual components can also be determined in a main computing unit that communicates with the transducer electronics 102 via a cable or wirelessly.

[0095] In addition to the microwave antenna, the measuring assembly also has a temperature sensor 104, which is arranged in a side opening of the measuring tube 101 and is positioned such that it is in contact with the medium when the medium is present. Alternatively, a temperature sensor arranged on the outer surface of the measuring tube and not in contact with the medium can also be used to determine the temperature of the medium. The temperature sensor 104 is electrically connected to the transducer electronics 102 and is configured to provide the current temperature measurement value to the transducer electronics 102.

[0096] Furthermore, the measuring assembly 100 includes a conductivity sensor 105, which is arranged in a side opening of the measuring tube 101 in a similar manner to the temperature sensor 104 and is designed to determine the conductivity of the medium. The conductivity sensor 105 can be designed such that it is in contact with the medium or not in contact with the medium. The conductivity sensor 105 is electrically connected to the transducer electronics 102 and is configured to provide the measured conductivity value to the transducer electronics 102.

[0097] The foregoing description of the illustrated embodiment relates to a transmission measurement method, in which a microwave signal is generated by a microwave antenna and measured by another microwave antenna that is typically positioned opposite the microwave antenna. Alternatively, the illustrated embodiment can also operate in reflection mode. In this case, the first microwave antenna 116 is configured to radiate a microwave signal into the medium and simultaneously measure the microwave signal interacting with the medium. The second microwave antenna 118 is also configured to radiate a microwave signal into the medium and measure the microwave signal interacting with the medium. In this case, the second microwave antenna 118 does not have to be arranged opposite the first microwave antenna 116. The microwave signal generated by the first microwave antenna 116 covers a first measurement range, while the second microwave antenna 118 covers a second measurement range. These two measurement ranges together cover a frequency range from 10 MHz to 50 GHz, in particular from 50 MHz to 25 GHz, and preferably from 85 MHz to 14 GHz.

[0098] List of reference numerals

[0099] 100 Measuring assembly

[0100] 101 Measuring tube

[0101] 102 Transducer electronics

[0102] 103 Memory

[0103] 104 Temperature sensor

[0104] 105 Conductivity sensor

[0105] 106 Process connection

[0106] 116 First microwave antenna

[0107] 118 Second microwave antenna

[0108] 201 Protein reference

[0109] 202 Lactose reference

[0110] 203 Fat reference

Claims

1. A method for continuously determining, in particular, the lactose content of a flowable medium, in particular milk, milk substitutes and / or dairy products , protein content and fat content , comprising the following method steps: - Determine the frequency-dependent relative permittivity of the medium across the frequency range of the spectrum, Among them, The upper limit of the spectrum is 50 GHz, particularly 25 GHz, and preferably 14 GHz, wherein the lower limit of the spectrum is 10 MHz, particularly 50 MHz, and preferably 85 MHz; and - Calculate the lactose content based on the determined relative permittivity and based on a lactose reference, a protein reference, and a fat reference , the protein content and the fat content .

2. The method according to claim 1, Among them, When determining the lactose content , protein content and fat content , only the real part of the relative permittivity is included.

3. The method according to claim 1, Among them, When determining the lactose content , protein content and fat content , only the imaginary part of the relative permittivity is included.

4. The method according to claim 3, comprising: - Measuring or providing the conductivity of the medium; - Compensating the imaginary part of the relative permittivity based on the measured or provided conductivity.

5. The method according to one of the preceding claims, Among them, In the calculation, milk is modeled as a four-component system, wherein the components include fat, lactose, protein, and water.

6. The method according to claim 5, Among them, The water content of the medium is between 55 wt.% - particularly 80 wt.% - and 95 wt.%.

7. The method according to any one of the preceding claims, comprising: - Designating an operating point, wherein the operating point designates the water content or a fixed water content range, wherein for different operating points, at least the lactose reference, the protein reference, and / or the fat reference are different.

8. The method according to claim 7, Among them, The lactose reference, the protein reference, and the fat reference can be linearized at the designated operating point.

9. The method according to any one of the preceding claims, comprising: - Measuring the temperature of the medium, Among them, when calculating the lactose content , protein content and fat content , and especially when compensating for the imaginary part of the dielectric constant by means of the measured or determined conductivity, the temperature of the medium is included.

10. The method according to claim 9, Among them, The lactose reference, protein reference, and fat reference are each temperature-dependent.

11. The method according to one of the preceding claims, Among them, The lactose reference includes a frequency-dependent lactose vector , Among them, the protein reference includes frequency-related protein vectors , Wherein, the fat reference includes a frequency-dependent fat vector .

12. The method according to claim 11, Among them, The lactose content , the protein content and the fat content can be determined by means of the following equation: wherein, the following formula is applicable to : Among them, the basis vectors , and are obtained by the orthogonalization process of the lactose vector , the protein vector and the fat vector . Among them, represents the determined relative permittivity. For , assume that .

13. A measuring assembly (100) for determining the lactose content , protein content and fat content of a flowable medium, in particular milk, milk substitutes and / or dairy products, comprising: - A measuring tube (101) for holding the medium; - At least one microwave antenna (116); wherein the at least one microwave antenna (116, 118) is arranged on the measuring tube (101); - Transducer electronics (102) designed to perform the method according to any one of the preceding claims.

14. The measuring assembly (100) according to claim 13, comprising: - At least two microwave antennas (116, 118), wherein the at least two microwave antennas (116, 118) are arranged on the measuring tube (101), wherein the first microwave antenna (116) of the at least two microwave antennas (116, 118) has at least a first measurement range, wherein the second microwave antenna (118) of the at least two microwave antennas (116, 118) has at least a second measurement range, wherein the first measurement range and the second measurement range together cover a frequency range from 10 MHz to 50 GHz, particularly 50 MHz to 25 GHz, and preferably 85 MHz to 14 GHz.

15. The measuring assembly (100) according to claim 13 or claim 14, Among them, The transducer electronic device (102) includes an electronic memory (103), Among them, the lactose vector , the protein vector and the fat vector are stored in the memory.

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