Fat and moisture analysis
- Fat and moisture in milk powder
- Fat and moisture in milk powder-based products
- Independent of particle size or color of milk powder
- Rapid and accurate, and superior to wet chemistry
Milk powders and milk powder-based products are extensively produced and sold. These products are used as a base for several kinds of “instant” milk drinks, as a base for bottled milk for weaning babies and as a simple storable form of milk for chocolate products, etc. in the confectionary industry.
Huge quantities of milk powders are also supplied to developing countries where acute food shortages are quite common. For customers with varied fat content requirements, producers normally deliver an entire product range of milk powders. As a result, these products have to be clearly measured for fat content. The water content is quantified and this should be less than approximately 4% for all products as too much water will lead to product deterioration.
The oil content of milk powders is traditionally measured by solvent extraction, but this method is relatively slow, time consuming and needs glassware, solvents, laboratory personnel and so on. The water is determined either by drying or by the Karl Fischer method, which even though provides a more accurate measurement, is again time consuming and requires laboratory personnel.
The minispec Method
This article describes the minispec method through an experiment conducted with a set of 40 samples of different products from a leading multinational food company. The fat contents of these samples range from 15% to 30% and water content ranges between 0% and 3% (both by weight). A “Spin Echo” technique was used to make the measurements, as shown in the following figure. The diagram demonstrates the time evolution of events first by a 90 degree radio frequency pulse and then by a 180 degree pulse.
The spin-echo pulse sequence showing measured points S1 and S2.
The amplitudes S1 and S2 represent the points at which the NMR signal amplitudes are determined. Where milk powder is concerned, the water has to be the “bound” water in a semi-liquid state, meaning that at S1 the amplitude represents the entire volume of liquid (fat and water) present in the sample. Conversely, this “bound” water also has a short “relaxation time” T2, meaning that the signal at S2 specifies only the oil content in the sample.
- S2/ weight α
- α moisture content per gram
- Sample volume: ~ 40 ml
- 10 MHz NMR system
- Tube diameter: ~ 40 mm
- Included in a package with aluminum block, tubes and calibration standards
- Suggested for semi-homogenized materials or seeds like rapeseed
- Sample volume: ~ 8 ml
- 20 MHz NMR system
- Tube diameter: ~ 18 mm or others
- Suggested for little amounts of seeds down to a single seed
Analysis of Fat and Water in Milk Powder Based Products. For fat the accuracy is +/- 0.06 with s. d. = 0.08, and for the moisture measurement an accuracy of +/-0.05 with s.d. = 0.1.
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