RU2794943C2 - Method for detecting non-dairy fat in milk - Google Patents

Abstract

FIELD: food industry; food analysis.

SUBSTANCE: in the method for detecting non-dairy fat in milk, when replacing milk fat from 10% or more, a milk sample is placed in a tray with an optical path length of not more than 3 mm, after centrifuging the sample, the transmission of electromagnetic radiation in the IR-A region of the spectrum is measured, and the transmission profile is compared along the height of the tray with the reference, and based on the presence of at least one additional peak on the measured profile compared to the reference, the presence of non-milk fat is judged.

EFFECT: invention allows to reduce the detection time of non-dairy fat, increase the sensitivity of the method, expand the range of detectable additives used for milk adulteration, and simultaneously determine the presence of several types of fats.

1 cl, 9 dwg, 7 ex

Description

Technical field

The invention relates to the food industry, mainly in the processing of milk and can be used for express detection of adulteration of milk by the presence of non-dairy fat in it.

State of the art

Recently, additives of vegetable and animal fats are increasingly used to falsify milk: palm, coconut, soy, beef, but the most widely used are the so-called milk fat substitutes, which are a mixture of vegetable fats subjected to modification, which expands the possibility of falsification and complicates the task. by their definition. In this connection, there is a need for a universal express method for quality control of milk for non-dairy fat additives of various origins.

Today, there are known methods for detecting adulteration of milk with non-dairy fats, based on various physicochemical properties of non-dairy fats. These include the determination of the fatty acid composition and the composition of the sterol fraction, which are established by the chromatographic method. The standardized method for identifying the fatty phase of dairy products is the method for determining sterols by gas-liquid chromatography (GOST 31979-2012 “Milk and dairy products”).

According to the state standard, milk should contain only milk fat (GOST 31449-2013 Raw cow's milk. Specifications). The presence of other fats is not allowed even in a minimal amount, therefore, a fast, affordable, qualitative, and not quantitative, method for detecting non-dairy fat in milk is needed to make a decision about its falsification.

A method is known (RF patent RU 2743840, C1, 2020.08), based on determining the presence of non-dairy fat in milk by the color of fluorescent radiation. It is based on the fundamental property of the luminescence of many organic substances in ultraviolet rays. Milk fat fluoresces in various shades of yellow under ultraviolet rays, and vegetable fats - violet-blue. The listed methods are complex, require special equipment, long-term sample preparation, low sensitivity, milk must contain at least 20 percent non-milk fat, and most importantly, the result is influenced by the nature of the origin of milk (region, seasonality, animal feeding ration), which leads to difficulties selection of a reference sample.

Recently, optical methods have become widespread. A known method for determining fats of non-dairy origin in milk fat (RU 2279071 C2, IPC G01J 33/03 2006.01), including the allocation of the fat fraction by thermostating at a temperature of 58-60°C for 8-12 and measuring the transmission at a wavelength of 430-450 nm in a cuvette with an optical path of 5 mm, determination of the optical density of the test sample and calculation of the quantitative content of non-milk fat using the formula:

where _Dmf is the optical density of milk fat, _Dcm is the optical density of the mixture, _Dnf is the optical density of non-dairy fat.

The need for information on the value of the optical density of the fat with which the dairy product was adulterated, as well as the changing value of the optical density of milk fat, which strongly depends on the temperature of the sample, the seasonality of sampling, the diet of animals, significantly complicates, and in many cases limits the implementation of the method.

A known method for determining the content of non-dairy fat, namely palm oil in milk (RU 2629839 C1, IPC G01N 33/04 2006.01), which includes the separation of the fat fraction by extracting fat from a milk sample with ethyl alcohol with a strength of 96 ± 4%, mixing, sonication , separation of the resulting suspension into fractions by centrifugation at a rotation speed of 3000 rpm (depending on the radius of the laboratory centrifuge, it can correspond to centrifugal acceleration from 1100 to 1400 g) for 5 minutes, registration of the scattered radiation of the fat fraction with laser radiation of 630-700 nm, determination of the size of colloidal formations by dynamic light scattering and calculation of the content of palm fat in milk from their size

This method is very time consuming and determines only one type of vegetable fat (palm oil) from the list of milk fats used for falsification, while the measurement reproducibility strongly depends on such parameters as the sample temperature, the time interval elapsed from the formation of the fat fraction of milk in an organic solvent to measurement, light scattering angle.

The closest technical solution is a method for determining the content of vegetable fat in milk, based on the specific absorption of phospholipid membranes of milk fat in the UV range. (Kovalenko D.N. Falsification of milk and dairy products. "Milk processing", 2011, No. 3. p. 7-8), which includes the isolation of the fat fraction by extraction with hexane, followed by centrifugation at a rotation speed of 8000 rpm for 10 min., removal of the absorption spectrum in the range from 200 to 400 nm, and in the absence of a peak in the region of 200-250 nm, the presence of vegetable fat is judged. The method requires special sample preparation using highly toxic hexane, uniform heating of the cuvette to a certain temperature, in order to achieve maximum, uniform light transmission through the fat fraction. The method is implemented when replacing milk fat by more than 50%.

The main disadvantage of this method, like all of the above, is that they are not sensitive if the milk is falsified with a milk fat substitute (MMF), which is a mixture of modified vegetable fats, and this greatly complicates the task of determining them. Therefore, it is so important to have a high-quality, fast, uncomplicated method that allows you to determine the addition of all currently known fats, including FMF used to falsify milk.

Disclosure of the essence of the invention

The objective of the invention is to develop a high-quality express, not laborious method for detecting non-dairy fat in milk with high sensitivity when replacing milk starting from 10%.

As a result of solving the problem, the following technical results are achieved:

- reducing the time of detection of non-dairy fat in milk by reducing the number of sample preparation operations;

- reduction in the cost of the method due to the use of serial, standard manufactured equipment;

- increasing the sensitivity of the method, which allows to determine falsification when replacing milk fat from 10%, due to the simultaneous measurement of transmission over the entire height of the cuvette;

- expansion of the range of determined additives used for milk adulteration, including all currently known fats, including BMF, by identifying differences in physical properties, in particular, the density, size and shape of fat globules of milk and non-dairy fat after centrifugation ;

- the ability to simultaneously determine the presence of several types of fats (mixtures) used for adulteration of milk.

To achieve these technical results in the method for detecting non-dairy fat in milk, a milk sample is placed in a cuvette with an optical path length of not more than 3 mm, the sample is centrifuged, the transmission of electromagnetic radiation in the IR-A region of the spectrum is measured, a transmission profile is built along the height of the cuvette, compared with reference and by the presence of at least one additional peak on the measured profile compared to the reference, the presence of non-dairy fat is judged.

Brief description of the drawings

fig. 1 example is the change in the transmission function T% in the form of jumps (peaks) by the value of ΔT1 and ΔT2 when non-dairy fat is added.

fig. 2 is a diagram of a device for obtaining a transmission profile.

1 - Infrared light source

2 - Optical System

3 - Cuvette

4 - CCD matrix

5 - Processor

6 - Personal computer

fig. 3 schemes for obtaining transmission profiles for the following samples: 3a - reference milk sample, 3b - milk sample with the addition of non-milk fat.

fig. 4 reference transmission profile of natural milk.

fig. 5a, 5b, 5c transmission profiles of a milk sample with 25% replacement of milk fat with non-milk fat,

5a - the measurement was carried out in a cuvette with a long optical path of 2 mm,

5b - the measurement was carried out in a cuvette with a long optical path of 3 mm,

5c - the measurement was carried out in a cuvette with a long optical path of 1 mm;

fig. 6 transmission profile of a milk sample with 25% replacement of milk fat with non-dairy fat, from a source of electromagnetic radiation with a wavelength range of 900-920 nm.

fig. 7 transmission profile of a milk sample with 25% milk fat replacement for non-milk fat obtained with a centrifugal acceleration of 2800 g.

fig. 8 transmission profile of a milk sample with 10% milk fat replacement for non-milk fat.

In FIG. 9 shows an example of a transmission profile of a milk sample with 50% milk fat replacement for non-milk fat.

Implementation of the invention

The proposed method is implemented as follows: a milk sample is placed in a cuvette with an optical path length of not more than 3 mm, the sample is centrifuged, and the transmission value of the electromagnetic radiation of the IR-A region is measured. Based on the data obtained, a transmission profile is built along the cuvette height, compared with the reference one obtained by measuring the transmission profile of natural milk, and the presence of non-dairy fat is judged by the presence of at least one additional peak in the measured profile compared to the reference one. The peak is considered additional or new if the sharp change in the transmission function T% (on the y-axis) in the region of the fat fraction is greater than or equal to one percent ΔT≥1% (Fig. 1).

As a source of infrared radiation, you can use any known, with a wavelength range from 700 to 1400 nm. It is preferable to carry out measurements using radiation with a wavelength of 800 to 950 nm, it is even more preferable to use the range of 850-870 nm.

For centrifugation, any commonly used centrifugal acceleration g known to the person skilled in the art can be used. For example, from 1500 to 3000 g. It is preferable to use acceleration 2000-2300 g.

The method is based on the difference in the light transmission profiles of the IR-A region taken over the entire height of the cuvette of milk samples containing one or more fatty components in its composition after the application of centrifugal force due to differences in the distribution of fatty particles of the emulsion in accordance with their size, shape and density .

To obtain a transmission profile, a spectrophotometer with the ability to detect the intensity of transmitted light over the entire height of the cuvette and an infrared source illuminating the entire cuvette evenly (Fig. 2) can be used.

The graph of the light transmission profile, along the entire height of the cuvette, contains information about the components of milk after centrifugation. For natural milk, the IR-A transmission profile of the light region after centrifugation has a clear and defined curve (Fig. 3a), which does not depend on temperature, seasonality, animal feeding ration and the course of the curve can only change when non-dairy fat is added in the form of a transmission jump by the value of ΔT in the region of the fat fraction, which is reflected in the profile graph in the form of one or more additional peaks (Fig. 3b).

Below are examples of the invention.

Example 1

The proposed method was implemented on a milk sample with 25% milk fat replacement.

At the beginning of the experiment, a reference transmission profile is determined and built. To do this, a sample of natural milk is placed in a cuvette with an optical path length of 2 mm, centrifuged at a centrifugal load of 2000 g for 10 minutes. The transmission of electromagnetic radiation in the IR-A region of the spectrum is measured from a light source with a wavelength range of 850-870 nm, a reference transmission profile is built along the height of the cuvette (Fig. 4).

A sample of milk with 25% replacement of milk fat is placed in a cuvette with an optical path length of 2 mm, centrifuged at a centrifugal load of 2000 g for 10 minutes. The transmission of electromagnetic radiation in the IR-A region of the spectrum is measured from a light source with a wavelength range of 850-870 nm, a transmission profile is built along the height of the cuvette (Fig. 5a) and compared with the reference one (Fig. 4). The transmission profile of the sample with added non-milk fat has one additional peak in the transmission region of the fat fraction with ΔT=6%, in contrast to the reference profile, the presence of this additional peak is used to judge the presence of non-milk fat in milk.

Example 2

All as in example 1, but used a cuvette with an optical path length of 3 mm. The transmission profile of the sample is obtained (Fig. 5b), which has one additional peak in the transmission region of the fat fraction with ΔT=6%, in contrast to the reference profile (Fig. 4), therefore the presence of non-dairy fat in milk is judged.

Example 3

All as in example 1, but used a cuvette with an optical path length of 1 mm. A transmission profile of the sample is obtained (Fig. 5c), having one additional peak in the transmission region of the fat fraction with ΔT=10%, in contrast to the reference profile (Fig. 4), this is used to judge the addition of non-milk fat to milk.

Example 4

All as in example 1, but used a source of electromagnetic radiation with a wavelength range of 900-920 nm. A transmission profile of the sample (FIG. 6) is obtained, having one additional peak in the transmission region of the fat fraction with ΔT=2%, in contrast to the reference profile (FIG. 4), indicating the presence of non-dairy fat in milk.

Example 5

Everything is as in example 1, but centrifuged at a centrifugal load of 2800 g. A sample transmission profile is obtained (FIG. 7) having two additional peaks in the fat fraction transmission region with ΔT=1% and ΔT=14%, in contrast to the reference profile (FIG. 4). The presence of these two additional peaks in the transmission curve indicates the presence of non-dairy fat in the milk sample.

Example 6

All as in example 1, but used a sample of milk with 10% replacement of milk fat. A sample transmission profile is obtained (FIG. 8) having two additional peaks in the fat fraction transmission region with ΔT=6% and ΔT=10%. In contrast to the reference profile (Fig. 4), this is used to judge the presence of non-dairy fat in the milk sample.

Example 7

All as in Example 1, but a milk sample with 50% fat replacement was used. A transmission profile of the sample is obtained (Fig. 9) having two additional peaks in the transmission region of the fat fraction with ΔT=10% and ΔT=17%, in contrast to the reference profile (Fig. 4), this is used to judge the addition of non-dairy fat to milk.

Claims (1)

A method for detecting non-dairy fat in milk, which includes placing a milk sample in a cuvette with an optical path length of not more than 3 mm, centrifuging the sample, measuring the transmission of electromagnetic radiation in the IR-A region of the spectrum, building a transmission profile along the height of the cuvette, comparing it with a reference one, by the presence of at least one additional peak on the measured profile compared to the reference one is judged to be the presence of non-dairy fat.

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