Fat and other nutritional values can easily be determined by NIR analysis. However a proper sample preparation beforehand
is essential for a correct result.
The fat content is one of the most important parameters for the quality control of food and feed. On the one hand, the fat
content contributes greatly to the nutritional value of a product; on the other hand, some fats (e.g. milk fat or cocoa fat)
are quite expensive components and should therefore be used economically.
Fat Analysis Methods
There are various methods of quantitative fat analysis. Which method is applied depends on the sample material, the required
accuracy and the time frame. Solvent extraction according to Soxhlet and Weibull-Stoldt are two of the classic methods but
need a separate step to determine the fat content.
In addition to the above mentioned classic extraction methods Near Infrared (NIR) Spectroscopy has established itself as an
alternative. This method not only allows for the determination of the fat content within seconds, but also of further important
parameters such as protein, humidity, and carbohydrates. Moreover, NIR spectroscopy is carried out without the use of chemicals
and can be applied close to the production process. For quantitative NIR analysis, inhomogeneous samples will yield inaccurate
results. If the concentration of fat is not distributed homogeneously, the results can vary greatly, depending on the part
of the sample which was analyzed. To avoid this, it is important to carry out reproducible size reduction of the sample before
it is measured in the spectrometer.
Size Reduction of Samples with a High Fat Content
To determine the fat content by NIR, it is necessary to prepare the sample beforehand. During the preparation process care
must be taken that the fat content is not altered in any way. If size reduction is improperly conducted, then a loss of fat
is unavoidable. Incorrect accessory configuration and operating parameters will inevitably lead to the loss of fat content;
the residues will remain inside the grinding chamber and tools. The sample must then be rejected and the mill must be cleaned.
The RETSCH Knife Mill Grindomix GM 300 (Figure 1) is preferably used for materials with a high fat content such as fish pellets,
meat, sausages, or cheese. This mill grinds and homogenizes sample amounts of up to 4.5 liters through cutting and/or impact
effects in a liquid-tight container. The final fineness and the degree of homogenization are determined by the variable speed.
The mill provides reliable operation, reproducible results, and can be equipped with heavy-metal-free grinding tools. Figure
2 shows three ground dog food samples and a corresponding NIR spectrum. It takes only 1 min at 2500 rpm to grind 500 g of
this sample to homogeneity in the GM 300. Within a few seconds it is possible to obtain a NIR spectrum which allows a reliable
quantitative statement on the fat content of the sample.
Accurate and reproducible results are essential for proper sample preparation. This can be assured by using the correct equipment,
which gently but effectively homogenizes the sample.
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