FI86480B - FOERFARANDE FOER KVANTITATIV BESTAEMNING AV UREA FRAON MJOELK ELLER EN MJOELKPRODUKT. - Google Patents

Description

5 1 86480

The present invention relates to a method for the quantitative determination of urea in milk or milk products. The present invention relates to a method for the quantitative determination of urea in milk or milk products.

Milk is an important source of protein in the diet. Prote-10 gins are produced in the cow’s metabolism and are excreted into the cow’s blood and also into the milk. The protein content of milk in the Nordic countries is usually around 3.2-4.0%, although in many other countries it remains lower, often below 3%. However, due to the importance of protein, it has already supplanted fat in some 15 countries as the main criterion for the price paid to producers.

Cows get the nitrogen they need for their protein synthesis from food. During the grazing season, the nitrogen intake is usually naturally sufficient, but in winter, when the cows are inside the feed fed to them, the nitrogen intake and with it the protein content of the milk tend to decrease. To compensate for this, in addition to feed, the cows have been given urea, which helps to keep the protein content of the milk at or even above the grazing season.

However, urea given to a cow has the property that it is not completely consumed for protein synthesis but part of it is transferred as such to milk. Small amounts of urea 30 are also produced in the cow's own metabolism, but the resulting urea content of the milk is usually at most 0.001%. On the other hand, as a result of the addition of urea to the feed, the urea content of the milk can increase 10 times the natural level, ie by a maximum of the order of 35 0.01%. However, such a high urea content is a sign of overdosing, which no longer promotes protein production but can instead be detrimental to the health of the cow and the amount of milk produced through it.

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For the above reasons, there is a need to measure the urea content of milk or milk products. Such monitoring makes it possible to optimize the amount of urea administered to the cows in terms of feeding costs, the state of health of the cows and milk production and thus to avoid a rise in the urea content in the milk to a harmfully high level.

To date, quantitative determinations of urea in liquid-10 samples have been made colorimetrically. Such an determination is made by staining the sample with a suitable chemical and measuring the intensity of the color with a colorimeter. However, such assays are in practice cumbersome and cannot be conveniently performed in large batches. Sample preparation, addition of reagents, and analysis are mostly slow manual, and the cost of reagents and labor raises the cost of the method.

It is an object of the present invention to provide a new method for the quantitative determination of urea in milk or milk products, in which the above-mentioned disadvantages of the known method are avoided. The invention is characterized in that an infrared absorption spectrum covering at least peaks in the wavelength range (dimension 25 1 / cm) of about 1650-1730 is measured from a sample of milk or milk products, and that urea is determined by eliminating its carbon-oxygen bond at about 1651 of which at least a possible error effect of the peaks in the wavenumber range of aldehydes and / or ketones in the wavenumber range of about 1700-1730.

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The determination of urea according to the invention is simple and fast and does not require the addition of any reagent to the test samples. The results obtained are sufficiently accurate up to an error of the order of 0,0005% and the method is particularly suitable for long series of determinations. In terms of cost, the method is substantially cheaper than the known colorimetric determination of urea.

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The utility of the infrared assay for urea according to the invention is also based on the fact that the milk does not contain close relatives of urea whose absorption peaks are close to those of the urea carbon-oxygen bond and which could thus seriously interfere with the assay. Closest to said urea absorption peak are said peaks in the wavenumber range of about 1700-1730 for aldehydes and ketones present in milk. The most abundant of these substances is acetone (absorption peak at 1715), which can be as high as 5% in milk in the case of acetonemia. Other aldehydes and ketones found in milk (wavelengths of absorption peaks in parentheses), which are formed not only as a result of the disease state but also as a result of the natural metabolism of the cow, are e.g. benzaldehyde (1703), formaldehyde, acetaldehyde, hexanal, nonanal (1728), 2-butanone (1717), diacetyl, 2-pentanone (1717), 2-hexanone, 2-heptanone and 2-nonanones (1719). Although the absorption peaks of said compounds are clearly separated from the peaks of the urea carbon-oxygen bond, they overlap slightly with the latter due to the spread of the peaks, so that the resulting minor error must be taken into account in the quantification.

The urea assay is also affected by a peak at about 1748 for the carbon-oxygen double bond of the ester group of the 25 fats in the milk and a peak at about 1547 for the peptide bond of the proteins in the milk.

If the sample contains fats and / or proteins, in an accurate quantitative determination, the infrared absorption spectrum 30 must be measured in at least the wavelength range of about 1540-1760, so that said peaks are visible and their error effect on the urea peak at about 1651 can be eliminated in the calculation.

35 Many different methods are known for measuring the fat content of milk, and one of these is the measurement of the absorption peak by the infrared technique caused by the carbon-oxygen double bond of the ester group of fats. Measurement results have been needed as a basis for * 86480 si to pay the producer for milk. However, prior to the present invention, infra-red technology has not measured urea, which is excreted in milk directly from cows' feeding and the determination of which is required mainly to determine the correct feeding.

The determination of urea according to the invention may be a sample taken directly from whole milk. The infrared absorption spectrum then shows, in addition to the peak in urea wavelength of about 1651, close peaks in the aldehydes, ketones, fats and proteins contained in the milk, the effect of which on the urea peak must be taken into account. The determination with whole milk is facilitated if the milk is homogenized before measuring the infrared spectrum so that the size of the fat particles of 15 to 7 μπι: η is reduced to between 1 and 2 μπι.

The quantification of urea can also be performed on skimmed milk, in which case the fat peak of the spectrum is substantially lost. The urea determination according to the invention is also possible for other milk components or products made from milk.

The accompanying drawings show infrared absorption spectra measured on a MATTSSON FTIR spectrometer-25 in the wavelength range of about 1000-2400 such that Figure 1 is a spectrum measured from 2% urea solution, Figure 2 is a spectrum measured from about 3.4% fat whole milk, and Figure 3 is spectrum measured from skimmed milk (fat content 0,02-0,05%).

It should be noted that an arrangement has been used in the spectra according to the figures, in which the effect of the background water 35 has been eliminated, whereby the spectra have been made more pronounced. However, this fact is not relevant to the invention.

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The urea spectrum of Figure 1 shows an absorption peak at about 1651 for the urea C = 0 bond. This peak is the basis for the urea assays according to the invention, although the measurement of such a solution containing substantially only urea 5 is not within the scope of the present invention.

The whole milk spectrum of Figure 2 shows an absorption peak at 1748 of the C = O bond of the fat ester group, denoted by reference numeral 1, and an absorption peak at about 1709 of the C = 0 bond of aldehydes and ketones, denoted by reference numeral 2, urea C = The absorption peak at about 1651 of the 0 bond, indicated by reference numeral 3, and the absorption peak at about 1547 of the CN bond 15, denoted by reference number 4. According to the invention, urea can be quantified from peak 3 of the spectrum by taking into account peaks 1, 2 and 4 error effect.

The spectrum of skimmed (low-fat) milk according to Fig. 3 shows the above-mentioned peaks 1, 2, 3 and 4, however, so that the peak 1 caused by fat is small compared to the spectrum of Fig. 2. The determination of urea takes place at the urea peak 3, taking into account the error effect caused by said other silicon peaks 25, 2 and 4.

As can be seen from the figures, the measured wavenumber range of 1000-2400 is in fact unnecessarily wide for the invention. In routine work, the measurement of whole milk (Figure 2) could be limited to the wavelength range of about 1540-1760 and the measurement of skimmed milk (Figure 3) to a possibly even narrower range, e.g. about 1540-1730.

Using a DAILAB IR-2000 spectrometer, the amount of urea 35 can be quantified from said urea peak by the equation y = 8.370x3 + 0.346x2 + 6.951x - 0.006 O <λ r. n 6 DOM O '! where y = urea concentration and x = absorbance.

The above equation applies as such in the case 5 that there are no other interfering peaks in the vicinity of the urea peak. However, when the milk or milk product, depending on the situation, has to take into account the error caused by said absorption peaks 1, 2, 4 of urea 3, 2, 4 and 3 in the urea peaks 3, this is done by linear corrections, multiplying the concentrations given by the former peaks by certain coefficients and subtracted from the concentration value obtained from the urea peak. The following table shows the coefficients describing the effect of the peaks of said substances on each other.

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Table

Fat Ketones + Urea Protein _aldehydes_ 20 Fat 1.00 0.125 0.025

Ketones and 0.003 1.00 0.275 0.075 aldehydes

Urea 0.080 0.240 1.00 0.144

Protein 0.030 0.070 0.240 1.00 25

It can be seen from the table that for the determination of urea, the correction factor for the fat peak is 0.125, the correction factor for the aldehyde and ketone peak is 0.275 and the correction factor for the protein peak is 0.240.

However, it should be noted that the invention is not limited to the above-mentioned calculation method, as there are other calculation methods, the principles of which are known to a person skilled in the art. Furthermore, it is clear to a person skilled in the art that the applications of the invention may otherwise vary within the framework defined in the appended claims.

Claims (5)

7 86480 A method for the quantitative determination of urea in milk or milk products, characterized in that an infrared absorption spectrum covering at least peaks in the wavelength range of about 1650-1730 (1 / cm) is measured from a sample of milk or milk products and urea is determined by its carbon-oxygen bond. from a peak at about 1651 by eliminating at least the possible error effect of peaks at about 1700-10 1730 in the carbon-oxygen bond range of aldehydes and / or ketones. A method according to claim 1, characterized in that the infrared absorption spectrum is measured in at least a wavelength range of about 1540-1760, comprising, in addition to any aldehyde and ketone carbon-oxygen bond peaks, a carbon-oxygen double bond wavelength peptide bond of about 1748 peak of about 1547, and that any error of these peaks on the peak at about 1651 at the urea carbon-oxygen bond wavelength is eliminated. Method according to Claim 2, characterized in that the urea is determined from a sample of whole milk. 25 Process according to Claim 3, characterized in that the urea is determined from milk which has been homogenized in order to reduce the size of the fat particles. Process according to Claim 1 or 2, characterized in that the urea is determined from skimmed milk. β 86480