Rapid moisture measurement with microwave resonance technology in infant formulas

Georg Merkh, Marion Dambacher, Heinz Dieter Isengard
Besides breast milk, infant formula is the only other milk product that the medical community considers nutritionally acceptable for infants under the age of one year.
Water content is a very important value for the quality especially for the physical, microbial and shelf-life properties of a product. Accurate and rapid measuring of water or moisture content is the basis for producing dried powdered food like infant formula. For this purpose different methods, for example NIR spectroscopy or microwave resonance technology, can be used.
Microwave resonance technology is a non-destructive, non-chemical and very fast method to determine moisture in various kinds of food. For measuring moisture, a low-energy microwave field is generated which shows a sensor specific resonance. Solid products and water molecules that are brought into the microwave field influence the resonance frequency and the resonance bandwidth. Because of their dipole property, the free water molecules permanently realign with the alternating field and so absorb energy. Frequency shift and attenuation of the resonance are measured and converted into a moisture value that is independent of varying product density. To achieve accurate results with this method it is important to calibrate correctly with an adequate reference method. This was done by different methods like oven drying, volumetric Karl-Fischer-Titration and an automatic Karl-Fischer-Titration heating oven. Depending on the kind of infant formula it is possible to calibrate the microwave resonance device with these different methods.
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