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

Abstract

The invention relates to a method for determining, in particular in a continuous manner, the lactose content a, protein content b, and fat content c of a flowable medium, in particular milk, a milk substitute, and / or a milk product, having the steps of: - ascertaining the frequency-based relative permittivity of the medium over a frequency range of a frequency spectrum, wherein the frequency spectrum has an upper limit of 50 GHz, in particular 25 GHz, preferably 14 GHz, and the frequency spectrum has a lower limit of 10 MHz, in particular 50 MHz, preferably 85 MHz; and - calculating the lactose content a, protein content b, and fat content c 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 additionally relates to a measuring assembly.

Description

[0001] Method for the continuous determination of lactose, protein and fat content of milk

[0002] The invention relates to a method for, in particular continuously, determining a lactose content a, protein content b and fat content c of a flowable medium, in particular milk, a milk substitute and / or a milk product, and to a measuring arrangement for determining a lactose content a, protein content b and fat content c of a flowable medium, in particular milk, a milk substitute and / or a milk product.

[0003] Microwaves can be used to determine the physical quantities of permittivity and loss factor of a medium in a process line. These two quantities – measured either at one or across many different frequencies – can be used to draw conclusions about application-specific parameters, such as the water content in a mixture of water and other non-polar or slightly polar components, or the solid content in a liquid medium.

[0004] The established transmission-Z-reflection measurement is described in LF Chen, CK Ong, CP Neo, VV Varadan, VK Varadan - “Microwave Electronics, Measurement and Materials Characterization”, John Wiley & Sons Ltd., 2004. For this purpose, the microwave signal is coupled to the medium in a container or measuring tube at two different positions, the scattering parameters (transmission and, if applicable, reflection) between these coupling structures are measured, and the measured scattering parameters are used to calculate the physical properties of the medium.

[0005] WO 2018 / 121927 A1 teaches a measuring arrangement for analyzing the properties of a flowing medium using microwaves. In addition to the microwave antennas, the measuring arrangement comprises an electrically insulating lining layer on the inner surface of the measuring tube. This lining layer forms a dielectric waveguide through which a microwave signal can be transmitted, at least in part, from a first microwave antenna to a second microwave antenna. One application for such a measuring arrangement is the determination of solids content in the liquid medium being conveyed. WO 2021 / 099152 A1 teaches a microwave antenna having a front section in contact with the medium, through which the excitation signal is emitted into the medium.

[0006] Milk and its (intermediate) products can be described as a mixture of different components, consisting mainly of water, milk fat and other solids, with the other solids essentially comprising proteins, carbohydrates (including in particular lactose) and, in small quantities, minerals.

[0007] Throughout the processing chain, from raw milk to the finished dairy product, the proportions of these components are important parameters for process control, process and quality control, and product flow balancing. It is common practice to determine these proportions using laboratory samples according to standard procedures. This means that only a small number of samples can be evaluated, and analytical results are only available with a significant delay after sampling. While process-related spectroscopic analysis in the infrared range with automated sampling is possible, it is, firstly, very cost-intensive and, secondly, only based on the small volume of samples taken at comparatively long time intervals. Such an analysis is therefore only of limited suitability for process control.

[0008] DE102017131269A1 discloses a method for continuously determining the fat content of milk with varying solids content using a Coriolis flowmeter and a microwave sensor. These types of measuring devices can be integrated into milk processing processes. A disadvantage of the disclosed solution is that it is not possible to separate the solids for the precise determination of the protein and lactose content.

[0009] The invention is based on the object of providing a remedy.

[0010] The object is achieved by the method according to claim 1 and the measuring arrangement according to claim 13.

[0011] The method according to the invention for, in particular continuously, determining a lactose content a, protein content b and fat content c of a, in particular flowable, medium, in particular milk, a milk substitute and / or a milk product, comprising the method steps:

[0012] - determining a frequency-dependent relative permittivity of the medium over a frequency range of a frequency spectrum, wherein the frequency spectrum has an upper limit of 50 GHz, in particular 25 GHz and preferably 14 GHz, wherein the frequency spectrum has a lower limit of 10 MHz, in particular 50 MHz and preferably 85 MHz; and

[0013] - Calculate the lactose content a, protein content b and fat content c based on the determined relative permittivity and depending on a lactose reference, a protein reference and a fat reference.

[0014] By providing the lactose, protein, and fat references and incorporating them into the calculation of the individual solid fractions, the lactose contribution can be distinguished and measured from the protein contribution despite very similar density and permittivity. The method according to the invention is suitable, for example, for use in a microwave sensor designed to determine the solid fraction in a flowable, aqueous medium.

[0015] The reference, within the meaning of the invention, is a mathematical quantity that describes the basic contribution of the respective component to the determined relative permittivity. The reference can comprise a mathematical function of the relative permittivity or its real or imaginary part as a function of frequency. The mathematical quantity can also be a frequency-dependent vector.

[0016] Advantageous embodiments of the invention are the subject of the subclaims.

[0017] One embodiment provides that only the real part of the relative permittivity is used to determine the lactose content a, protein content b and fat content c.

[0018] It has been found that the contributions of the individual components of lactose, protein and fat are more pronounced in the real part than in the imaginary part.

[0019] One embodiment provides that only the imaginary part of the relative permittivity is used to determine the lactose content a, protein content b and fat content c.

[0020] As an alternative to determining the proportions depending on the real part of the relative permittivity, the imaginary part of the relative permittivity can also be used to determine the individual proportions of lactose, protein and fat.

[0021] One embodiment provides that the procedure includes the following procedural steps:

[0022] - Measuring or providing the electrical conductivity of the medium,

[0023] - Compensating the imaginary part of the relative permittivity depending on the measured or provided conductivity.

[0024] The imaginary part of the real permittivity describes a loss term that arises from the constant repolarization of the molecules in the medium. This loss term is composed of polarization and conductivity losses. Conductivity losses are particularly evident at low frequencies, so conductivity compensation of the imaginary part is necessary for media with high conductivity (e.g., milk). The conductivity component can be calculated using the following equation:

[0025] <7

[0026] £ "' l = 2nf E0

[0027] Electrical conductivity can be determined using a conductivity sensor. This can be part of the measuring system and thus integrated into the process line, or it can be designed as an external handheld device with which the conductivity of a sample of the medium is determined or can be determined. Alternatively, the electrical conductivity of the medium can also be specified by the user.

[0028] One embodiment provides that the milk is modeled as a four-component system in the calculation, with the components including fat, lactose, proteins and water.

[0029] One embodiment provides that the water content of the medium is between 55, in particular 80 and 95 wt%.

[0030] One embodiment provides that the procedure includes the following procedural step:

[0031] - Establishing a working point, wherein the working point defines a water content or fixed water content range, wherein at least the lactose reference, the protein reference and / or the fat reference of different working points differ.

[0032] The operating point is determined by the user. The advantage of taking the expected water content into account is the resulting greater accuracy in determining the individual components. An operating point, as defined by the invention, encompasses precisely one specific water content, which is known or assumed by the user, or a water content range that encompasses a multitude of water contents.

[0033] One embodiment provides that the lactose reference, the protein reference and the fat reference can be linearized at the specified operating point.

[0034] One embodiment provides that the procedure includes the following procedural step:

[0035] - Measuring a temperature of the medium, whereby the temperature of the medium is used to calculate the lactose content a, protein content b and fat content c and in particular to compensate the imaginary part of the permittivity by means of the measured or provided conductivity.

[0036] In practice, relative permittivity depends on temperature and measurement frequency. Temperature measurement, which takes into account the temperature dependence of the medium properties, enables the desired accuracy.

[0037] One embodiment provides that the lactose, protein, and fat references are each temperature-dependent. One embodiment provides that the lactose reference has a frequency-dependent

[0038] Lactose vector l, wherein the protein reference comprises a frequency-dependent protein vector p, wherein the fat reference comprises a frequency-dependent fat vector / .

[0039] One embodiment provides that the lactose content a, protein content b and fat content c is determined / can be determined using the equation where for A it holds that where the basis vectors v l t v2and v3from an orthogonalization procedure of the

[0040] Lactose vector l, protein vector p and fat vector f, where M represents the determined relative permittivity, for which it is assumed that M = a - l + b ■ p + c ■ f .

[0041] The matrix can comprise the vector products of the basis vectors and the corresponding component vector, or alternatively can already be present as a parameter matrix, ie with vector products already executed in the measurement arrangement.

[0042] The basis vectors can also be stored as equations that describe the frequency-dependent behavior of the relative permittivity, or the real part or the imaginary part.

[0043] The measuring arrangement according to the invention for determining a lactose content a, protein content b and fat content c of a flowable medium, in particular milk, a milk substitute and / or a milk product, comprises:

[0044] - a measuring tube for guiding the medium;

[0045] - at least one microwave antenna, wherein the at least one microwave antenna is arranged on the measuring tube; - converter electronics configured to carry out the method according to the invention.

[0046] One embodiment provides that the measuring arrangement also includes:

[0047] - at least two microwave antennas, wherein the at least two microwave antennas are arranged on the measuring tube, wherein a first microwave antenna of the at least two microwave antennas has at least a first measuring range, wherein a second microwave antenna of the at least two microwave antennas has at least a second measuring range, wherein the first measuring range and the second measuring range together cover a frequency range of 10 MHz to 50 GHz, in particular 50 MHz to 25 GHz and preferably 85 MHz to 14 GHz.

[0048] One embodiment provides that the converter electronics comprises an electronic memory, wherein the fat reference and a frequency-dependent fat vector are stored in the memory.

[0049] The invention is explained in more detail with reference to the following figures. They show:

[0050] Fig. 1 : a first embodiment of the method according to the invention;

[0051] Fig. 2 : a second embodiment of the method according to the invention;

[0052] Fig. 3 : the real part of the relative permittivity as a function of frequency for a lactose reference, a protein reference and a fat reference; and

[0053] Fig. 4 : an embodiment of the measuring arrangement according to the invention.

[0054] Fig. 1 shows a first embodiment of the method according to the invention, which can be carried out or is to be carried out using a measuring arrangement with a microwave antenna. In a first method step 1.1, an operating point is determined. The operating point defines the water content of the medium to be monitored or the water content range in which the water content is to be expected for the medium. For milk, milk substitutes, dairy products and milk substitutes, a water content between 55, in particular 80 and 95 wt% is assumed. The operating point can be determined by the operator of the measuring arrangement on a corresponding display of the measuring arrangement on site or via a central monitoring unit that is connected to the measuring arrangement either contactlessly or via a cable.

[0055] In a second method step 11.1, a frequency-dependent relative permittivity of the medium is determined over a frequency range of a frequency spectrum. In the specific embodiment, the real part of the relative permittivity is determined and used to determine the individual components in the medium. The frequency spectrum has an upper limit of 50 GHz, in particular 25 GHz and preferably 14 GHz, and a lower limit of 10 MHz, in particular 50 MHz and preferably 85 MHz. This is done using a microwave sensor. The microwave sensor is configured to transmit a microwave signal into the medium and, after it has interacted with the medium, to measure it again. Based on the measured microwave signal, the real part of the relative permittivity for the frequency band of the microwave signal is determined.

[0056] In a third method step 111.1, the temperature of the medium is measured. A temperature sensor, which is part of the measuring system, can be provided for this purpose. Alternatively, the temperature of the medium can be determined using a temperature sensor separate from the measuring system. In this case, the current temperature of the medium is provided to the converter electronics.

[0057] In a fourth process step IV, 1, the determined real part of the relative permittivity is corrected or compensated depending on the measured temperature. Alternatively, the provided lactose, protein, and / or fat references can be temperature-dependent.

[0058] In a fifth process step V,1, the lactose content a, the protein content b, and the fat content c are calculated based on the determined real part and as a function of a provided lactose reference, a protein reference, and a fat reference. For modeling, a four-component system is assumed for the milk, the milk substitute, the milk product, and / or the milk substitute. The components are fat, lactose, proteins, and water. To achieve the highest possible accuracy in determining the individual proportions, it is essential that the lactose reference, the protein reference, and / or the fat reference are adapted to the respective operating point. This means that the lactose reference, the protein reference, and the fat reference are linearizable at the respective operating point. According to the design, the lactose reference is a frequency-dependent lactose vector l.The same applies to the protein reference, which comprises a frequency-dependent protein vector p, and the fat reference, which accordingly comprises a frequency-dependent fat vector f.

[0059] Using the lactose vector l, the protein vector p and the fat vector f, the lactose content a, protein content b and fat content c can be determined according to:

[0060] For A, the following applies: is, with the basis vectors v l t v2 and v3, which result from an orthogonalization procedure (e.g.

[0061] The Gram-Schmidt orthogonalization method) of the lactose vector l, the protein vector p, and the fat vector / results. The matrix A serves to transform the vectors l, p, and / into the orthogonal system. The vector M represents the determined relative permittivity, for which it is assumed that M = a - l + b - p + c - f.

[0062] Alternatively, the individual references can also be stored as mathematical functions.

[0063] Fig. 2 shows a second embodiment of the method according to the invention, which can be implemented or is to be implemented using a measuring system with a microwave antenna. In a first method step 1, 2, an operating point is determined. The operating point defines the water content of the medium to be monitored or the water content range within which the water content is expected for the medium. The operating point can be determined by the operator of the measuring system on a corresponding display of the measuring system on site or via a central monitoring unit that is connected to the measuring system either contactlessly or via a cable.

[0064] In a second method step 11,2, a frequency-dependent relative permittivity of the medium is determined over a frequency range of a frequency spectrum. In the specific embodiment, the imaginary part of the relative permittivity is determined and used to determine the individual components in the medium. The frequency spectrum has an upper limit of 50 GHz, in particular 25 GHz and preferably 14 GHz, and a lower limit of 10 MHz, in particular 50 MHz and preferably 85 MHz. The imaginary part is determined using a microwave sensor. The microwave sensor is configured to transmit a microwave signal into the medium and, after it has interacted with the medium, to measure it again. Based on the measured microwave signal, the imaginary part of the relative permittivity for the frequency band of the microwave signal is determined.

[0065] In a third method step 111,2, the temperature of the medium is measured. A temperature sensor, which is part of the measuring system, can be provided for this purpose. Alternatively, the temperature of the medium can be determined using a temperature sensor separate from the measuring system. In this case, the current temperature of the medium is provided to the converter electronics.

[0066] In a fourth process step VI, 2, the electrical conductivity of the medium is measured. A conductivity sensor, which is part of the measuring system, can be provided for this purpose. Alternatively, the conductivity of the medium can be determined using a conductivity sensor separate from the measuring system. In this case, the current conductivity in the medium is provided to the converter electronics.

[0067] In a fifth process step V,2, the determined imaginary part of the relative permittivity is corrected or compensated for as a function of temperature and conductivity. Alternatively, the provided lactose, protein, and / or fat references can be temperature- and / or conductivity-dependent.

[0068] In a sixth process step VI, 2, the lactose content a, the protein content b and the fat content c are calculated based on the determined imaginary part and depending on a provided lactose reference, a protein reference and a fat reference.

[0069] Fig. 3 shows the real part of the relative permittivity as a function of frequency for a protein reference 201, a lactose reference 202, and a fat reference 203. The individual references are each derived from the difference between two reference measurements of different reference media, which 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 essentially identical.

[0070] For Protein Reference 201, the lactose and fat content of the two reference media are essentially identical. For the Protein Reference 201 shown, 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 and 92 wt%. The curve of Protein Reference 201 is parabolic in some sections and has a minimum at approximately 5 GHz.

[0071] For Lactose Reference 202, the protein and fat content of the two reference media are essentially identical. For the Lactose Reference 202 shown, 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 and 92 wt%. The curve of Lactose Reference 202 is parabolic and has a minimum at approximately 8 GHz.

[0072] For the fat reference 203, the lactose and protein contents of the two reference media are essentially identical. For the fat reference 203 shown, 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 and 86 wt%. The profile of the fat reference 203 is essentially linear in sections. Fig. 4 shows an embodiment of the measuring arrangement 100 according to the invention for determining a lactose content a, protein content b, and fat content c of a flowable medium, in particular milk, a milk substitute, and / or a milk product. The measuring arrangement 100 comprises a measuring tube 101 for guiding the medium and two oppositely arranged microwave antennas 116, 118. The microwave antenna 116 is configured to feed a microwave signal into the medium when the medium is present in the measuring 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, an additional microwave antenna pair can be provided. In this case, the two measuring ranges of the two microwave antenna pairs together cover the frequency range from 10 MHz to 50 GHz, in particular from 50 MHz to 25 GHz, and preferably from 85 MHz to 14 GHz.

[0073] 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 a converter electronics unit 102, which is configured to carry out the method according to the invention. The converter electronics unit 102 can be mechanically connected to the microwave antenna. If the determination of the individual components takes place on-site in the converter electronics unit 102, the converter electronics unit 102 has an electronic memory unit 103 in which the fat reference and a frequency-dependent fat vector f are stored. Alternatively, the determination of the individual components can take place in a higher-level processing unit that communicates with the converter electronics unit 102 via a wired or wireless connection.

[0074] In addition to the microwave antennas, the measuring arrangement includes a temperature sensor 104, which is arranged in a lateral opening of the measuring tube 101 and positioned such that it is in contact with the medium when the medium is present. Alternatively, the temperature of the medium can also be determined via a temperature sensor arranged on the outer surface of the measuring tube and not in contact with the medium. The temperature sensor 104 is electrically connected to the transmitter electronics 102 and is configured to provide current measured temperature values ​​to the transmitter electronics 102.

[0075] The measuring arrangement 100 further comprises a conductivity sensor 105, which, like the temperature sensor 104, is arranged in a lateral opening of the measuring tube 101 and is configured to determine the electrical conductivity of the medium. The conductivity sensor 105 can be configured to be in contact with the medium or not. The conductivity sensor 105 is electrically connected to the converter electronics 102 and is configured to provide the converter electronics 102 with measured electrical conductivity values.

[0076] The previous description of the illustrated embodiment refers to a transmission measurement method in which the microwave signal is generated with a microwave antenna and measured by another microwave antenna, usually positioned opposite. Alternatively, the illustrated embodiment can also be operated 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 undergoing interaction with the medium. The second microwave antenna 118 is also configured to radiate a microwave signal into the medium and to measure the microwave signal undergoing interaction with the medium.

[0077] The second microwave antenna 118 is not necessarily 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. The two measurement ranges together cover a frequency range from 10 MHz to 50 GHz, in particular 50 MHz to 25 GHz, and preferably 85 MHz to 14 GHz.

[0078] LIST OF REFERENCE SYMBOLS

[0079] 100 measuring arrangement

[0080] 101 Measuring tube 102 Converter electronics

[0081] 103 storage

[0082] 104 Temperature sensor

[0083] 105 Conductivity sensor

[0084] 106 Process connection 116 first microwave antenna

[0085] 118 second microwave antenna

[0086] 201 Protein Reference

[0087] 202 Lactose reference

[0088] 203 Fat reference

Claims

PATENT CLAIMS 1. A method for, in particular continuously, determining a lactose content a, protein content b and fat content c of a flowable medium, in particular milk, a milk substitute and / or a milk product, comprising the method steps: - determining a frequency-dependent relative permittivity of the medium over a frequency range of a frequency spectrum, wherein the frequency spectrum has an upper limit of 50 GHz, in particular 25 GHz and preferably 14 GHz, wherein the frequency spectrum has a lower limit of 10 MHz, in particular 50 MHz and preferably 85 MHz; and - Calculate the lactose content a, protein content b and fat content c based on the determined relative permittivity and depending on a lactose reference, a protein reference and a fat reference.

2. Method according to claim 1, wherein only the real part of the relative permittivity is used to determine the lactose content a, protein content b and fat content c.

3. Method according to claim 1, wherein only the imaginary part of the relative permittivity is used to determine the lactose content a, protein content b and fat content c.

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

5. Method according to one of the preceding claims, wherein in the calculation the milk is modelled as a four-component system, the components comprising fat, lactose, proteins and water.

6. The method according to claim 5, wherein the water content of the medium is between 55, in particular 80 and 95 wt%.

7. Method according to one of the preceding claims, comprising: - Establishing a working point, wherein the working point defines a water content or fixed water content range, wherein at least the lactose reference, the protein reference and / or the fat reference of different working points differ.

8. The method according to claim 7, wherein the lactose reference, the protein reference and the fat reference are linearizable at the specified operating point.

9. Method according to one of the preceding claims, comprising: - Measuring a temperature of the medium, whereby the temperature of the medium is used in the calculation of the lactose content a, protein content b and fat content c and in particular in the compensation of the imaginary part of the permittivity by means of the measured or determined conductivity.

10. The method according to claim 9, wherein the lactose, protein and fat references are each temperature dependent.

11. The method according to any one of the preceding claims, wherein the lactose reference comprises a frequency-dependent lactose vector l, wherein the protein reference comprises a frequency-dependent protein vector p, wherein the fat reference comprises a frequency-dependent fat vector / .

12. The method according to claim 11, wherein the lactose content a, protein content b and fat content c is determined / determinable by means of the equation where for A it holds that where the basis vectors v l t v2and v3from an orthogonalization procedure of the Lactose vector l, protein vector p and fat vector f, where M represents the determined relative permittivity, for which it is assumed that M = a - l + b ■ p + c ■ f .

13. Measuring arrangement (100) for determining a lactose content a, protein content b and fat content c of a flowable medium, in particular milk, a milk substitute and / or a milk product, comprising: - a measuring tube (101) for guiding the medium; - at least one microwave antenna (116), wherein the at least one microwave antenna (116, 118) is arranged on the measuring tube (101); - converter electronics (102) which are configured to carry out the method according to one of the preceding claims.

14. Measuring arrangement (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 a first microwave antenna (116) of the at least two microwave antennas (116, 118) has at least a first measuring range, wherein a second microwave antenna (118) of the at least two microwave antennas (116, 118) has at least a second measuring range, wherein the first measuring range and the second measuring range together cover a frequency range from 10 MHz to 50 GHz, in particular 50 MHz to 25 GHz and preferably 85 MHz to 14 GHz.

15. Measuring arrangement (100) according to claim 13 or 14, wherein the converter electronics (102) comprises an electronic memory (103), wherein the lactose vector l, the protein vector p, and the fat vector f are stored in the memory.

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