The analysis of pressed powdered dairy samples (whole and skimmed milk powder, milk protein, whey powder, cheese powder, infant formulas, etc.) by XRF spectrometry faces two major challenges: the inherent small-scale heterogeneity from many of those materials and the high fat content that may be present.
For some products, like infant formula, a high degree of small-scale heterogeneity may be caused by the manufacturing process, namely the mixing of skimmed milk powder with different oils/fats and mineral premixes. Additionally, if samples with a high fat content (> 10%) are to be pressed into pellets, they cannot be subjected to pressures larger than 2-4 ton, otherwise the fat will be extruded out of the sample, differentially mobilizing elements within the pellet and making an accurate and reproducible measurement impossible.
On the other hand, some samples with very low fat content may need higher pressures to form stable pellets. The use of different pelletizing pressures for a same application may render unpredictable analytical errors, especially with such low-density samples.
Malvern Panalytical has developed a novel approach for the reliable and consistent preparation of pressed powdered dairy samples. This approach minimizes heterogeneities, providing a truly representative sample and immobilizes the fat content allowing a unified pressing process, producing stable and consistent pressed pellets for a wide range of samples. This solution is valuable in a large number of industries including dairy product manufacturers, ingredient and food manufacturers, suppliers, analytical and research labs.
Materials and methods
In this study, commercially available infant formula with 26 % fat was firstly combined with PANblend-1 before being homogenized in a mixer-mill (Retsch™ MM400). Samples were prepared using 4.5 g of infant formula with 0.5 g of PANblend-1 and homogenized for 90 s at 20 Hz, using a 25 ml ZrO2 vessel and one 20 mm ZrO2 mixing ball. The homogenized powders were then pressed into 35 mm diameter pellets using a manually operated hydraulic press applying 100 kN of force for 30 s.
Ten pellets of infant formula were prepared according to this procedure. For comparison, ten pressed pellets of the same infant formula were prepared without PANblend-1 and without homogenization, by pressing them into 35 mm tablets using a manually operated hydraulic press employing a force of 30 kN for 30 s. Elemental analysis was performed with an Epsilon 4 benchtop EDXRF spectrometer using the same measurement conditions and time for both sets of samples.
One of the major advantages of the method demonstrated here is the outstanding increase in the sample preparation repeatability of the results, the consequence of a thorough sample homogenization and immobilization of fat during pressing.
In Table 1, those results can be observed for a commercial sample of infant formula with high fat content prepared with the new methodology and using the PANblend-1 additive. Comparison results are obtained from standard preparation without homogenization and low-pressure pressing.
All measured elements in the samples prepared with PANblend-1 presented a smaller spread of the results, as indicated by lower standard deviation (SD) values. The sample preparation repeatability for calcium showed an impressive 8.2 times improvement in relation to a standard preparation. The spread on the chlorine results improved by 6.3 times, potassium by almost 4 times, phosphorus and sulfur both by more than 2 times. Notice that absolute concentration values are slightly different between the two sets of samples due to the dilution effect.
Table 1. Sample preparation repeatability results for a commercial sample of infant formula (26 % fat) and improvement factors when using the PANblend-1 method
It was demonstrated that a new methodology of sample preparation for dairy powders provides unparalleled sample preparation repeatability, contributing to more accurate analytical results. A total analytical solution for the dairy industry can be provided by Malvern Panalytical, including a customized approach to sample preparation and all the expertise required for optimal analysis.