## 4 Results and Discussion
As a result, at  
Figure 3: Concentration dependence of droplet radius \(r\) on the weight percent of added palm fat \(C_{palm}\) in spreads B1-PO0 (black), B2-PO1 (red), B2-PO2 (green), B2-PO3 (blue). such concentrations, we observe a decrease in the scattering intensity, a decrease in the average droplet size, and an increase in the average error of the measured size, which is evident in Figure 3.  
The fitting of data in Figure 3 in the range of 0-65% PO with a second-order polynomial gives the expression:  
\[r=A_{0}+A_{1}C_{palm}(\%)+A_{2}C_{palm}^{2}(\%), \tag{6}\]  
here, \(A_{0}\) = 390.22 \(\pm\) 21.65, \(A_{1}\) = 1.7239 \(\pm\) 1.3058, \(A_{2}\) = 0.04301 \(\pm\) 0.0178. From the expression (6), the content of palm fat in the spread is defined as  
\[C_{palm}(\%)=-20.04+\sqrt{401.63+23.25(r(nm)-390.22)}, \tag{7}\]  
Here, \(C_{palm}(\%)\) is the content of palm fat, \(r\) is the average drop radius in nanometers. The difference between the coefficients for B1-PO0 spread in Formulas (6) and (7) and those given in the preliminary report [24] is associated with more stringent control criteria for ACF-distorting factors during data processing. As a result of the violation of regularity (6) at \(C_{palm}>65\%\), a direct determination of the concentration of palm fat in a spread can only be carried out when \(C_{palm}\) is less than this concentration. To determine the content of palm fat in the spread of unknown composition over the entire range of possible concentrations, one can use the following procedure. A researcher measures the \(r\) value in two samples prepared as follows. The first one is the sample of the spread tested, and the second one is the sample of the mixture of the spread tested with pure butter in a 1:1 ratio. If in the second sample, the \(r\) value will decrease compared to the \(r\) of the first sample, the initial content of palm fat lies in the range of 0-65% and can be determined directly from the curve in Figure 3. If the \(r\)-value increases in the second sample relative to the \(r\) of the first one, it means that the spread tested contains more than 65% of the palm fat. In this case, the palm fat content \(C_{palm}\) (%) in the spread tested can be determined as follows. One can calculate \(C_{palm}\) (%) of the first sample from \(r\) value for the first sample by (7) and curve in Figure 3 and multiply it by 2. In this way, it is possible to retrieve the actual palm fat content in a spread sample with any palm fat content. Thus, by measuring the drop size in the spread emulsion in ethyl alcohol, one can determine the percentage of palm fat in it and hence the percentage of butter fat. The method works clearly and quickly. The error in determining the palm oil content with the DLS method is the sum of the error of the curve in Figure 3 (dependence (6)) and the error in measuring the size of the droplets of the tested spread emulsion. In our case, this total average error over all measurements was 10%. However, the error in determining the curve can be significantly reduced by collecting statistics and brought to 1-2%. The accuracy of particle or droplet size measurement by DLS in a monodisperse suspension depends on sample purity and laser stability; it is usually no worse than 2%. Therefore, the main source of errors in this method of determining the vegetable oil content are deviations in the process of sample preparation. With reliable standardization of such a process, the error in determining the content of palm oil can be reduced to 5%. This method of determining oil adulteration can be successfully supplemented by simple measurements of the luminescence spectrum of the butter or spread [27]. The luminescent method is not physically related to the DLS method but complements it well, although it can also be used independently. The luminescence spectra of butter B2 spreads with PO1 and PO2, obtained upon excitation by radiation with a wavelength of 266 nm, are shown in Figure 4a,b, respectively.