RU2196985C2 - Method determining composition of milk - Google Patents

Abstract

FIELD: measurement technology, equipment for optical analysis of multicomponent finely divided media, in particular. SUBSTANCE: method includes illumination of sample of milk by three coherent monochromatic radiation sources with different wave lengths. Radiation scattered back is recorded by detector, its signal is converted and fractions of fat and protein in total mass are computed by empirical formulas. Sample of milk is illuminated in turn and detector is set at angle of 30-40 degrees to direction of drop of intensity of scattered back radiation I $\genfrac{}{}{0ex}{}{\text{p}}{\text{λ1}}$ , I $\genfrac{}{}{0ex}{}{\text{p}}{\text{λ2}}$ , I $\genfrac{}{}{0ex}{}{\text{p}}{\text{λ3}}$ . Signals U₁,U₂,U₃ are converted to digital form, then content of salts of heavy metals is additionally found by illumination of sample of milk along normal to surface by coherent monochromatic radiation in visible region of spectrum with wave length λ₄ different from radiation wave lengths of three sources. Spectrum of radiation scattered back in visible and near ultraviolet ranges ( (λ_а-λ_b) ) is recorded. Gradient of relative intensity

is calculated in advance. After this its value is compared with a priory set value N and, if Δ₄≥N, then judgment on presence of impurities in the form of salts of heavy metals in milk is made. Concentration of impurities is found by deviation of maximum of peak of laser radiation with wave length λ₁ scattered back. Fractions of fat and protein in total mass are computed by empirical formulas with use of coefficients obtained beforehand and correction for concentration of salts of heavy metals proportional to

, where

is maximum of intensity of peak of radiation scattered back in wave range λ_x1-λ_x2. EFFECT: widened application field of method thanks to possibility of simultaneous determination of concentration of salts of heavy metals, fat and protein in milk, raised efficiency of ecological control over milk products. 3 dwg, 1 tbl

Description

 The invention relates to measuring technique, in particular to devices for optical analysis of multicomponent fine media, and can be used for automatic express analysis of the concentration of medium components and the concentration of heavy metal salts in its composition, for example, for certification tests of milk by nutritional parameters, i.e. fat concentration and protein, as well as the content in it of salts of heavy metals: lead, cadmium, zinc, mercury, arsenic.

A known method for determining the content of fat and protein in milk, comprising irradiating a controlled sample of each component with an electromagnetic flux, measuring the total scattering indicatrix of the component, determining by calculation the optimal scattering angles for each component, and then establishing the content of each component in the milk sample from the radiation intensity scattered at optimal angles [1]. The advantage of the method is the ability to simultaneously determine the concentration of fat and protein in milk without preliminary dilution of the sample, sufficiently high accuracy, comparable with the accuracy of the control methods of the chemical type (Rose-Gottlieb, Kjeldahl, Heroer). However, the method has certain disadvantages:
- reduced accuracy in determining fat and protein due to seasonal fluctuations in the optical properties of milk and its degree of homogenization;
- the high complexity of calibration associated with the need to register the scattering indicatrix from each of the components;
- the difficulty in determining the optimal angles for each component by calculation using data obtained experimentally;
- sufficiently large dimensions of any variant of the device that implements the method, due to the registration of scattering from the milk sample forward;
- a decrease in accuracy due to registration of the absolute value of the intensity of the scattered light flux at the optimal angles of the scattering indicatrix;
- the impossibility of determining the concentration of salts of heavy metals in the composition of milk, since their presence does not introduce significant disturbances in the structure of the scattering indicatrix.

 The atomic emission method for the determination of heavy metal salts in the composition of liquid dairy products [2] provides for the excitation of the emission spectrum of a previously prepared sample using an arc, spark discharge or plasma torch, which ensures the transition of atoms, ions from an excited state to a lower energy state with the corresponding radiation and subsequent analysis of radiation spectra. Despite the possibilities of the method to determine up to 35 chemical elements, it requires complex preparation of a controlled sample and does not allow determining the concentration of components of a multicomponent medium, in particular milk, which contains salts of heavy metals.

 The method of atomic absorption spectroscopy [3] consists in measuring the absorption of the resonance line by the free atoms of the determined heavy metal salt in an unexcited state when optical radiation passes through the atomic vapor of the element being determined, obtained using an air-acetylene or nitrogen-acetylene flame. The advantage of the method is high selectivity, the ability to simultaneously determine several salts of heavy metals, good accuracy. However, in addition to the complexity of the hardware implementation, the sample preparation procedure, the method also does not allow simultaneous control of individual components of a multicomponent mixture in the express analysis mode, in particular, the content of fat and protein in milk.

The closest in technical essence and the achieved results to the invention is a method for determining protein and fat in milk, including lighting a milk sample with three coherent monochromatic radiation sources with three different wavelengths, registering the backscattered radiation by the receiver, converting the signal and calculating the mass fraction of fat and protein according to empirical formulas [4]. The method has several significant advantages in determining the concentration of fat and protein in milk:
- provides high accuracy and stability of readings due to the introduction of three radiation sources and as a result of taking into account information about the degree of homogenization, seasonal changes and features of technological processes of various milk processing enterprises;
- simplifies the calibration process of the device that implements the method, due to the use, when calibrating, not of individual components (fat or protein), but of a sample with a known fat and protein content, measured by control methods;
- reduces the overall dimensions of any constructive solution of the method due to registration of radiation scattered back in a thin layer of the product;
- provides the ability to control fat and protein directly in the technological container.

 A significant disadvantage of the prototype method is the impossibility of simultaneous with the measurement of the concentration of fat and protein control the presence of salts of heavy metals in milk. This problem is currently relevant both for environmental services, services of the Ministry of Emergencies, certification laboratories, and laboratories of large farms, since currently from 12 to 15% of dairy products do not meet the requirements of standards for quality indicators.

 The objective of the invention is to expand the scope of the method by simultaneously determining the concentration of salts of heavy metals, fat and protein in milk, increasing the effectiveness of environmental control of dairy products.

 Each distinguishing feature is closely related to the goal.

, сравнивают его значение с заданной величиной N и при Δ₄≥N судят о наличии примесей в виде солей тяжелых металлов в молоке, определяют концентрацию примеси по отношению максимума пика рассеянного излучения в спектральной области λ_x1-λ_x2 и интенсивности рассеянного назад излучения лазера с длиной волны λ1, причем вычисления массовой доли жира и белка по эмпирическим формулам осуществляют с использованием полученных ранее коэффициентов и поправки на концентрацию солей тяжелых металлов, пропорциональной

Указанные признаки являются существенными и взаимосвязанными между собой причинно-следственной связью с образованием совокупности существенных признаков, необходимых и достаточных для достижения указанного результата, поскольку наличие их позволяет использовать способ как для определения концентрации жира и белка в молоке, так и для определения наличия и концентрации солей тяжелых металлов в составе жидких молочных продуктов, расширяет его область применения при решении экологических и сертификационных задач путем экспресс-анализа молока как сырого, так и взятого на различных этапах технологического процесса.This goal is achieved by a method characterized in that the milk sample is illuminated alternately, the receiver is set at an angle of 30-40 ^o to the direction of decrease in the intensity of the backscattered radiation I $\genfrac{}{}{0ex}{}{\text{p}}{\text{λ1}}$ , I $\genfrac{}{}{0ex}{}{\text{p}}{\text{λ2}}$ , I $\genfrac{}{}{0ex}{}{\text{p}}{\text{λ3}}$ , and the signal is converted into digital form, respectively, U ₁ , U ₂ , U ₃ , then additionally find the content of salts of heavy metals, illuminating the sample normal to the surface with coherent monochromatic radiation in the visible region of the spectrum with a wavelength λ4 different from the radiation wavelengths of three sources , and register the spectrum of radiation scattered back in the visible and near infrared ranges λ _a -λ _b , the relative intensity gradient is preliminarily calculated

, compare its value with a given value of N and, for Δ ₄ ≥N, evaluate the presence of impurities in the form of salts of heavy metals in milk, determine the concentration of the impurity by the ratio of the peak of scattered radiation in the spectral region λ _x1 -λ _x2 and the intensity of the backscattered laser radiation with wavelength λ1, and the calculation of the mass fraction of fat and protein according to empirical formulas is carried out using the previously obtained coefficients and corrections for the concentration of salts of heavy metals, proportional to

These signs are essential and interconnected causally with the formation of a combination of essential signs necessary and sufficient to achieve the specified result, since their presence allows you to use the method both to determine the concentration of fat and protein in milk, and to determine the presence and concentration of salts heavy metals in the composition of liquid dairy products, expanding its scope in solving environmental and certification problems by express analysis and as a raw milk, and taken at different stages of the process.

где

- интенсивности рассеянного излучения от дополнительного источника излучения с длиной волны λ4, измеренные на длинах волн λ_a и λ_b.The method is as follows. The controlled product is illuminated alternately with three coherent monochromatic radiation sources with three different wavelengths, the receiver is set at an angle of 30-40 ^o to the direction of the intensity of the backscattered radiation I $\genfrac{}{}{0ex}{}{\text{p}}{\text{λ1}}$ , I $\genfrac{}{}{0ex}{}{\text{p}}{\text{λ2}}$ , I $\genfrac{}{}{0ex}{}{\text{p}}{\text{λ3}}$ , and the signal is converted into digital form, respectively, U ₁ , U ₂ , U ₃ , then additionally find the content of salts of heavy metals, illuminating the sample normal to the surface with coherent monochromatic radiation in the visible region of the spectrum with a wavelength λ4 different from the radiation wavelengths of three sources and register the spectrum of radiation scattered back in the visible and near infrared ranges λ _a -λ _b , the relative intensity gradient is preliminarily calculated:

Where

- the intensities of the scattered radiation from an additional radiation source with a wavelength of λ4, measured at wavelengths λ _a and λ _b .

The gradient value is compared with a given value of N and, for N≤Δ _4, the presence of impurities in the form of heavy metal salts in milk is judged, the concentration of impurities is determined by the ratio of the peak of scattered radiation in the spectral region λ _x1 -λ _x and the intensity of the backscattered laser radiation with a length waves λ1.

Calculations of the mass fraction of fat and protein using empirical formulas of the form typical for multiparameter sensors:
Cj ⁱ = α ₁ lnU ₁ + α ₂ lnU ₂ + α ₃ lnU ₃ + α ₄ δ ₁
Cb ⁱ = α ₅ lnU ₁ + α ₆ lnU ₂ + α ₇ lnU ₃ + α ₈ δ ₂ , (2)
where δ ₁ is a small correction associated with seasonal changes in the composition of milk or with the features of technological processes;
δ ₂ is a small correction associated with the presence of impurities in milk.

α _{1, 2, 3, 4, 5, 6, 7} — calibration coefficients determined experimentally during the calibration process.

When Δ ₄ ≥N, α ₄ = α ₈ = 1.

в спектральной области λ_x1-λ_x2, расположенной внутри диапазона λ_a-λ_b. Затем рассчитывают отношение

к интенсивности рассеянного излучения с длиной волны λ1 I $\genfrac{}{}{0ex}{}{\text{p}}{\text{λ1}}$ , то есть

.If Δ ₄ ≤N, then the concentration of salts of heavy metals is more than the maximum permissible values. In this case, determine the maximum peak of the scattered radiation from an additional source with a wavelength

in the spectral region λ _x1 -λ _x2 located within the range λ _a -λ _b . Then calculate the ratio

to the intensity of scattered radiation with a wavelength of λ1 I $\genfrac{}{}{0ex}{}{\text{p}}{\text{λ1}}$ , i.e

.

где F - функция, установленная эмпирическим путем.The concentration of salts of heavy metals in liquid dairy products With _STM is determined by the dependence:

where F is a function established empirically.

с увеличением концентрации солей тяжелых металлов связано с эффектом примесного тушения [5].Intensity change

with an increase in the concentration of salts of heavy metals is associated with the effect of impurity quenching [5].

.The concentration of fat and protein is determined by the formula (2), where α ₄ ≠ α ₈ ≠ 1, and previously determined experimentally;
δ ₁ - a small correction associated with seasonal changes in the composition of milk or with the features of technological processes;
δ ₂ - small correction, depending on the ratio

.

 The invention is illustrated in FIG. 1, 2, 3.

зарегистрированный при освещении молока дополнительным источником когерентного монохроматического излучения с длиной волны λ4. В диапазоне длин волн λ_x1-λ_x2 наблюдается характеристический пик спектра с интенсивностью

.In FIG. 1 shows the scattering spectrum from milk in the absence of impurities in it in the visible and near infrared ranges

registered when illuminating milk with an additional source of coherent monochromatic radiation with a wavelength of λ4. In the wavelength range λ _x1 -λ _x2 there is a characteristic peak of the spectrum with an intensity

.

зарегистрированный при дополнительном освещении пробы молока по нормали к поверхности когерентным монохроматическим излучением в видимой области спектра с длиной волны λ4. Появление примесей такого рода сопровождается изменением интенсивности максимума пика рассеянного излучения

в спектральной области λ_x1-λ_x2, расположенной внутри диапазона λ_a-λ_b.Figure 2 shows the scattering spectrum from milk containing impurities in the form of salts of heavy metals, in the visible and near infrared range

detected by additional illumination of a milk sample along the normal to the surface by coherent monochromatic radiation in the visible region of the spectrum with a wavelength of λ4. The appearance of impurities of this kind is accompanied by a change in the intensity of the peak maximum of the scattered radiation

in the spectral region λ _x1 -λ _x2 located within the range λ _a -λ _b .

In FIG. Figure 3 shows the scattering spectra under illumination of milk with a fat content of C _f = 3.5% and protein C _p = 3.28% (curve 1-1) of the same milk with micro concentrations of lead salt Pb (CH ₃ COO) ₂ 0.09 mg / l (curve 1-2), 0.31 mg / l (curve 1-3);), 5.51 mg / l (curve 1-4).

 The invention meets the criterion of "industrial applicability", because it can be carried out using known means of production and existing technology.

 Example.

A cuvette with a sample of pure milk with a fat content of C _f = 3.53% and protein C _p = 3.28%, previously determined by the Rose-Gottlieb method, was illuminated along the normal to the surface alternately with three sources of coherent monochromatic radiation with wavelengths λ1 = 0 , 69 μm, λ2 = 0.83 μm, λ3 = 1.32 μm, using a prototype device [4], taken as a prototype. Intensities of backscattered radiation from sources with wavelengths λ1, λ2, λ3 - I $\genfrac{}{}{0ex}{}{\text{p}}{\text{λ1}}$ , I $\genfrac{}{}{0ex}{}{\text{p}}{\text{λ2}}$ , I $\genfrac{}{}{0ex}{}{\text{p}}{\text{λ3}}$ registered with a radiation receiver installed at an angle of 34 degrees to the direction of incidence, and after converting the signals from the radiation receivers into digital form, respectively, U ₁ = 0.6 (rel. units); U ₂ = 0.58 (rel. Units); U ₃ = 0.18 (rel. Units).

. Рассчитывали по полученным данным и при использовании результатов предварительной калибровки массовые доли жира и белка в пробе.Then, a cuvette with the same milk sample was illuminated normal to the surface with coherent monochromatic radiation in the visible spectrum with a wavelength of λ4 = 0.512 μm, the spectrum of radiation scattered backward was recorded (Fig. 3, curve 1-1) using the Jobin Yvon setup "in the range of λ _a -λ _b -0.5-0.75 μm and the relative intensity gradient was calculated

. The mass fractions of fat and protein in the sample were calculated from the data obtained and using the results of preliminary calibration.

To compare the intermediate results, the maximum of the scattered radiation peak was determined in the region of 0.65-0.7 μm - 2600 rel. and calculated the ratio I ^pmax 0.5-0.7 / U ₁ = 35.14 • 10 ² .

 The results of measurements and calculations are listed in the table.

Then, samples were also prepared from the same milk with microconcentrations of lead salt Pb (CH ₃ COO) ₂ and subjected to similar studies. The backscattered emission spectra are shown in FIG. 3 (curve 1-2 for a concentration of 0.09 mg / L; curve 1-3 for a concentration of 0.31 mg / L; curve 1-4 for a concentration of 5.51 mg / L ) The final and intermediate results are given in the table. The salt concentration was determined by the formula (3).

- спектр рассеянного излучения в области углов 30-40 градусов по отношению к падающему пучку;
λ_a-λ_b - диапазон длин волн в видимом и ближнем ИК диапазоне, где регистрируют спектр

;

- градиент относительной интенсивности, где

- интенсивности рассеянного излучения от дополнительного источника излучения с длиной волны λ4, измеренные на длинах волн λ_a и λ_b;
(λ_a и λ_b) - длина диапазона как разность длин волн начала и конца диапазона;
N - априорно заданная величина, соответствующая градиенту относительной интенсивности, при допустимой концентрации соли тяжелого металла в продукте;

- максимум интенсивности пика рассеянного излучения в диапазоне волн λ_x1-λ_x2, расположенном внутри диапазона λ_a-λ_b.Application designation list
METHOD FOR DETERMINING THE MILK COMPOSITION
λ1, λ2, λ3 — wavelengths of three sources of coherent monochromatic radiation;
I $\genfrac{}{}{0ex}{}{\text{p}}{\text{λ1}}$ , I $\genfrac{}{}{0ex}{}{\text{p}}{\text{λ2}}$ , I $\genfrac{}{}{0ex}{}{\text{p}}{\text{λ3}}$ - the intensity of the scattered radiation of each source;
U ₁ , U ₂ , U ₃ - signals of photodetectors after conversion to digital form;
λ4 is the wavelength of an additional coherent monochromatic radiation source in the visible region of the spectrum;

- the spectrum of scattered radiation in the region of angles 30-40 degrees with respect to the incident beam;
λ _a -λ _b - wavelength range in the visible and near IR range, where the spectrum is recorded

;

- gradient of relative intensity, where

- the intensities of the scattered radiation from an additional radiation source with a wavelength of λ4, measured at wavelengths λ _a and λ _b ;
(λ _a and λ _b ) is the length of the range as the difference between the wavelengths of the beginning and end of the range;
N is an a priori specified value corresponding to a gradient of relative intensity, with an allowable concentration of heavy metal salt in the product;

- the maximum intensity of the peak of scattered radiation in the wavelength range λ _x1 -λ _x2 located within the range λ _a -λ _b .

Sources of information
1. Copyright certificate of the USSR, 857869, IPC G 01 N 33/06, 1981

 2. Maistrenko V.N., Khamitov R.Z., Budnikov G.K. Environmental and analytical monitoring of supertoxicants. - M .: Chemistry, 1996.

 3. Britske M.E. Atomic absorption spectrochemical analysis. M .: Chemistry, 1982.

 4. RF patent 2110065, IPC G 01 N 33/04, 1998

 5. Suminov V.M., Mogilnaya T.Yu., Grebenyuk E.I. et al. Development of a laser optoelectronic device for express analysis of liquid dairy products. Scientific works, issue 2. 1999. MATI-RSTU named after K.E. Tsiolkovsky. - 5 sec.

Claims (1)

A method for determining the composition of milk, including illuminating a milk sample with three coherent monochromatic radiation sources with different wavelengths, registering the backscattered radiation with a receiver, converting the signal and calculating the mass fraction of fat and protein using empirical formulas, characterized in that the milk sample is illuminated alternately, the receiver is set under angle of 30-40 ^o C to the direction of fall of the intensity of the backscattered radiation I $\genfrac{}{}{0ex}{}{\text{p}}{\text{λ1}}$ , I $\genfrac{}{}{0ex}{}{\text{p}}{\text{λ2}}$ , I $\genfrac{}{}{0ex}{}{\text{p}}{\text{λ3}}$ and the signals are converted into digital form, respectively, U ₁ , U ₂ , U ₃ , then additionally find the content of salts of heavy metals by illuminating the sample normal to the surface with coherent monochromatic radiation in the visible region of the spectrum with a wavelength of λ ₄ different from the radiation wavelengths of three sources and recorded spectrum of radiation scattered back into the visible and near infrared range (λ _a -λ _b), a pre-calculated gradient relative intensity

, compare its values with an a priori set value of N and, for Δ ₄ ≥N, evaluate the presence of impurities in the form of salts of heavy metals in milk, determine the concentration of impurities from the ratio of the peak maximum of backscattered laser radiation with a wavelength of λ ₁ , moreover, the calculation of the mass fraction of fat and protein according to empirical formulas is carried out using previously obtained coefficients and corrections for the concentration of salts of heavy metals, proportional

where

- the maximum intensity of the peak of scattered radiation in the wavelength range λ _x1 -λ _x2 .

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