FI87837C - Method for quantitative determination of fat from an emulsion containing fat particles - Google Patents

Description

1 87837

The present invention relates to a method for the quantitative determination of fat absorption from an emulsion containing fat particles. on the basis of a specific absorption peak by eliminating the possible error effect of the other components of the emulsion.

The main target of quantitative fat determinations 15 is milk and milk products. The natural fat content of milk is usually between 3.0 and 5.5%, but in different dairy products the fat content can vary from almost 0 to more than 40%. The measurement of fat content is needed as a basis for the price to be paid to the milk producer and, in addition, for quality control of 20 milk products.

Determination of the fat content of milk is possible by traditional chemical means, examples of which are the so-called Gerber and Röse-Gottlieb methods. However, infrared absorption is currently used in routine assays, although chemical methods are still needed to calibrate IR analyzers. The most commonly used IR assays have an absorption peak at a wavelength of about 1750 (1 / cm) (at a wavelength of about 5.7 .mu.m) of the carbon-oxygen double bonds of the triglyceride moiety contained in the fat molecule. This ·. in addition, the method described in EP 0012492 is based on an absorption peak at a wavelength of about 2870 (1 / cm) (at a wavelength of about 3.5 .mu.m) of the carbon-hydrogen bonds contained in the fat molecule.

: λ 35

A disadvantage of using a carbon-oxygen double bond in IR assays is that the absorption peak is not dependent on the size of the fat molecules, as a result of which, for example, the variation of milk fat composition in different seasons and different feeding of cows causes assay errors. Furthermore, the use of said dressing is out of the question in the case of fermented milk products, since the lactic acid present interferes with the determination. The use of a carbon-hydrogen bond as a basis for the assay avoids the former disadvantage, as the amount of said bonds in the fat molecule is directly proportional to the size of the molecule. On the other hand, when using a C-H bond, the contribution of other substances containing C-H bonds in the milk, mainly proteins and lactose, to the absorption peak must be taken into account. This is achieved by measuring the IR absorption peaks characteristic of said other substances in addition to the absorption peak of the C-H bond and by calculating the correction to the absorption peak of the C-H bond to reach the target fat concentration.

However, the use of the absorption peak of the C-H bond is associated with disadvantages which mean a deterioration e.g. compared to the older C = 0 double bond method.

The 20 C-H absorption peak is located in the infrared spectrum of milk in a rather awkward place on the slope of a strong water absorption peak from which it is difficult to separate. In addition, the composition of milk, i.e. when the amounts of fat proteins, lactose, minerals, etc. components vary in the proportion of water in the sample to be determined, it is not always known exactly, which causes an uncontrollable error in the results, which is repeated in the corrections calculated for proteins and lactose. Another source of error that particularly hinders the use of the C-H bond is scattering alongside IR absorption in the sample. Caused by fat particles. scattering strongly affects the signals to be recorded and thus interferes with the fat determination when the wavelength of the absorption peak corresponds to or is smaller than the diameter of the particles. When the diameter of the fat particles in raw 35 milk is in the order of 0.5-5 μπι, it follows that scattering strongly interferes with the absorption of the CH bond at 3.5 μια, unless the fat particles can be reduced to a diameter well below 3.5 μηι: η before fat - 3 87837 determinations in the homogenisation of milk. Thus, the above-mentioned EP 0012492 discloses that the average diameter of the fat particles should not exceed 2 μπι, and IR-ana-5 lysers generally used for milk fat determinations are equipped with a homogenizer to break the fat particles to said size. However, with the analyzers in continuous use, the performance of the homogenizer deteriorates slightly, so that over time more and more poorly homogenized milk samples containing fat particles with a diameter of more than 2 μιη are added to the measuring cuvette, giving erroneous results. The problem could be partially alleviated, for example, by homogenizing the sample several times, but this would reduce the capacity of the analyzer to such an extent that the solution is not usable. The determination based on the C = 0 absorption peak is less disturbed by scattering even in deficiently homogenized samples, as the peak is located at a clearly higher wavelength of 5.7 μιη, where the absorbance curve, which describes the fat concentration as a function of absorption, is clearly more direct.

It is an object of the present invention to provide a new method for the quantitative determination of fat by an infrared absorption technique in which the above-mentioned disadvantages associated with the use of a C-H bond are avoided. The method according to the invention is characterized in that the determination takes place from an absorption peak at a wavelength of about 1440 (1 / cm) of the carbon-carbon bonds of the fat molecules.

The absorption peak of the C-C bond to be used according to the invention at a wavelength of about 1440, which corresponds to a wavelength of about 1440.

7.0 μπι, is located in the IR absorption spectrum at a substantially more advantageous point for analysis than the absorption peak of the C-H bond. When measuring milk or dairy products, the absorption of water: 35 is not disturbed and this makes it easier to read the absorbance of the peak. At the same time, the peak gives a more reliable assay result that does not depend on the amount of water in the sample. The wavelength of the absorption site of 7.0 μπ »is also clearly larger than the maximum diameter of the fat particles of about 5.0 μπι, which means that the method according to the invention is relatively insensitive to light scattering errors when measuring raw milk. The method thus gives a correct result, even if the homogenisation of the milk sample is incomplete or not carried out at all, although homogenisation of the sample to a mean particle size of less than 3,0 μπι is still recommended in order to obtain accurate results. A further significant advantage of the invention is that, due to the lower scattering, the ratio of the change in absorbance to the change in concentration is higher, especially at higher fat concentrations, than in the C-H absorption peak, which means correspondingly improved assay accuracy.

15

It should further be noted that compared to the use of a C = O absorption peak, the invention achieves the same advantage as C-H absorption, i.e. that the variation in the size of the fat molecules does not cause an error in the result obtained. When measuring milk or milk products, the effect of other components of milk containing C-C bonds, ie mainly proteins and lactose, on the C-C absorption peak must be compensated in the same way as in the C-H absorption assay. In these respects, the method according to the invention is thus substantially equivalent to the method in question. known method.

When measuring the absorption peak of a C-C bond, it is preferable to measure the absorption spectrum from a slightly wider range, e.g. the wavelength range n, regardless of the quality of the emulsion.

30 · 1380-1440, from which the required reference wavelength is obtained, ·: the absorbence of which is subtracted from the absorption peak obtained.

When the assay is for milk or a milk product, e.g. whole milk containing about 3.0-5.5% fat, the milk 35 is first heated to 40 ° C and mixed thoroughly to obtain the most representative sample possible for analysis. Homogenization is then performed, after which the sample is analyzed by measuring its IR absorption at the desired wavelengths. In this case, according to the invention, the characteristic absorption peak of the milk-containing protein at a wavelength of about 1550 and the characteristic absorption peak of the milk-containing lactose at about 1050 can be measured, whereby the proportion of proteins and lactose in the C-C bond at about 1440 Depending on the IR spectrometer used, it may then be advantageous to measure a continuous IR absorption spectrum from a sample in the wavenumber range of about 1050-1550.

10

Although the use of the invention for determining the fat content of milk or milk product has been discussed above, other fats, such as emulsions containing vegetable fats, can also be measured by the method according to the invention.

15 In practice, the determination of these fat contents may be simpler, as compensation for other components necessary for milk is no longer necessary.

In some cases, it may be advantageous to base the determination of the fat content of the emulsion simultaneously on several different absorption peaks due to the absorbent bonds at different wavelengths of the fat molecule. The idea is known in principle from U.S. Pat. No. 4,447,725, which uses 25 C = O bond absorption peaks and a C-H bond absorption peak.

According to the present invention, it is possible to proceed in such a way that, in addition to the absorption peak of the C-C bond at a wavelength of about 1440, the C = O-two of the ester groups of the fat molecule is measured. an absorption peak at a wavelength of about 1750 of the moss bond and / or an absorption peak at a wavelength of about 1160-1190 of the simple C-0 bond of the ester groups and / or an absorption peak at about 2870 of the C-H bond of the fatty molecule. 35 peak, the fat being determined on the basis of two or more absorption peaks in the spectrum. Most preferably, such an assay takes into account, in addition to the C-C absorption peak, the absorption peak of the C = O and / or C-O bond, however, <37837 so that the absorption peak of the C-C bond has the highest weight in the assay.

In the accompanying drawings 5, Figure 1 shows the infrared absorption spectrum of whole milk (fat content 3.4%) measured with a Mattsson FTIR spectrometer in the wavelength range of about 3.0-10 μπι (wavelength range of about 1000-3000), 10 Figure 2 shows the same spectrometer of the same whole milk the infrared absorption spectrum measured in the wavelength range of about 1000-3000, from which the effect of background water has been eliminated, Fig. 3 shows the IR absorption spectrum measured according to Fig. 2 from a milk sample with a fat content of less than 0.05%, and Fig. 4 graphically shows the dependence between absorbance and fat content on the absorption peaks of the CC bond, the C = O bond, and the CH bond.

20

The absorption spectrum according to Figure 1 shows the absorption peak of the CH bond at a wavelength of about 3.5 μιη (at a wavelength of about 2870), the absorption peak of a C = 0 double bond at a wavelength of about 5.7 μπι (at a wavenumber of about 1750), the CC bond - '25 its absorption peak at 3 wavelengths of about 7.0 μπι (at wavelength of about 1440) and the absorption peak of a simple C-0 bond at 4 wavelengths of about 8.4-8.6 μπι (at wavelength of about 1160-1190) . It is found that the absorption peak 1 of the C-H bond is located on the slope of a strong water absorption peak, .... 30 in contrast to the absorption peak 3 of the C-C bond used according to the invention, where there is no water-induced absorption.

In Figure 2, the absorption spectrum of which is measured from the same size. From the 35 milk samples as the spectrum of Figure 1, the same absorption peaks 1-4 generated by different bonds of the fat molecule are seen without the water-disturbed background effect. In addition, the curve includes an absorption peak of 7,87837 due to peptide binding of proteins at a wavelength of about 1550 and an absorption peak of 6 due to lactose at a wavelength of about 1050. In Figure 3, the absorption spectrum of which was measured from a have clearly decreased compared to the peaks in Figure 2, while peaks 5 and 6 for protein and lactose have remained essentially unchanged.

In Fig. 4, curve 7 shows the dependence of absorbance on the fat content of the sample at the absorption peak of the C-C bond, curve 8 shows the dependence of the absorbance on the fat content at the absorption peak of the C = 0 bond and curve 9 shows the dependence of the absorbance on the fat content at the absorption peak of the C-H bond. It can be seen that when using the absorption peak of the C-C bond according to the invention, the absorbance increases more strongly with the fat content than in the peaks of the C = 0 and C-H bonds, whereby a higher assay accuracy is achieved, especially at higher fat contents.

According to the basic idea of the invention, the fat content of milk is determined from the CC bond absorption peak at 1440 shown in Figures 2 and 3 by subtracting the absorption at a reference wavelength of about 1380 and calculating the fat content by the formula F = ax3 + bx2 + cx-d where F is fat content absorbance, and by making corrections to the still obtained result due to protein silicon 30 and lactose peak 6. When using a DaiLab IR-2000 spectrometer, the calculation formula - F = 11,3x3 + 9,0x2 + 6,7x 35 is given and the correction factors for protein and lactose are given in the following table: β 77837

Table _Fat_Protein_Lactose

Fat 1 0.020 0.015 5 Protein -0.007 1 -0.007

Lactose -0.005 -0.039 1

The effect of protein and lactose is taken into account by linear corrections, in which the absorbances of peaks 5 and 6 are multiplied by the factors in Table 10 and added from the C-C absorption peak to the fat content calculated by the above formula. According to the table, the absorbance of the protein peak is multiplied by 0.007 and the absorbance of the lactose peak by 0.005, and the values obtained are subtracted from the value calculated by the formula to arrive at the final fat content.

If, in addition to the CC bond absorption peak, absorption peaks due to other bonds of the fat molecule are used in the fat content determination, the fat content is calculated using the formula: F (-CC), (CO), (C = O), (CH) = kx F (CC) + 1 x F (CO) + mx F (C = O) + nx F (CH) 25 where F (CC), F (CO), F (C = O) and F (CH) are respectively. the fat concentrations calculated with the bonds, the calculation taking place in each case with the formula F = ax3 + bx2 + cx-d 30 where F denotes the quantitative amount of fat and x the absorbance of the peak in question.

k, 1, m and n are in the formula experimental constants, the sum of 35 of which should be about 1 and which can be varied to emphasize the contribution of different bonds in the determination. Practical experiments have shown that it is advantageous to weight the value F (C-C) calculated from the absorption peak of the C-C bond and to combine one or both of the quantities F (C = 0) and F (C-O).

It will be clear to a person skilled in the art that the various embodiments of the invention are not limited to the example given above, but may vary within the scope of the appended claims. In particular, it should be noted that the coefficients in the calculation formulas shown are device-specific values that change when switching to another spectrometer.

Claims (10)

10 R7 837 A method for the quantitative determination of fat from an emulsion containing fat particles, which method measures the infrared absorption of an emulsion sample and determines fat 5 by a specific absorption peak in the absorption spectrum by eliminating any from an absorption peak of about 1440 (1 / cm). 10 A method according to claim 1, characterized in that the infrared absorption spectrum of the emulsion is measured at least in the wavelength range of about 1380-1440. Method according to Claim 1 or 2, characterized in that the emulsion is milk or a milk product. Process according to Claim 3, characterized in that the emulsion is whole milk having a fat content of about 3.0 to 5.5%. A method according to claim 3 or 4, characterized in that the absorption peaks of the proteins and lactose at wavelengths of about 1550 and about 1050 are measured and on the basis of these the contribution of said substances to the absorption peak at wavelength of about 1440 is compensated. Method according to one of Claims 3 to 5, characterized in that the continuous infrared absorption spectrum is measured in the wavenumber range from about 1050 to 1550. Method according to one of Claims 3 to 6, characterized in that the milk is homogenized before measuring the infrared absorption spectrum so that the total size of the fat particles in the measuring step is substantially less than 3 μπι. n 87837 Process according to Claim 1 or 2, characterized in that the fat is determined from an emulsion containing vegetable fat. Method according to one of the preceding claims, characterized in that in addition to the absorption peak of the carbon-carbon bonds (CC) at a wavelength of about 1440, the absorption peak and / or the ester group of the carbon-oxygen double bond (C = 0) of the ester groups of the fat molecule are measured. An absorption peak at about 1160-1190 for a simple carbon-oxygen (CO) bond and / or an absorption peak at about 2870 for a hydrocarbon (CH) bond of a fat molecule, wherein the fat is determined from two or more absorption peaks in the spectrum. 15 Method according to Claim 9, characterized in that, in addition to the absorption peak of the carbon-carbon bonds, the absorption peak of the C = O and / or C-O bond is taken into account in the determination, provided that the assay is mainly based on the IR absorption of the carbon-carbon bonds. 12 8 7 8 37