The problem of water content determination in products containing lactose
- Publication Type
- Lecture
- Authors
- Isengard, H.-D., Merkh, G.
- Year of publication
- 2014
- Conference name
- 8th International Conference on Water in Food
- Conference location
- Timisoara, Rumänien
- Conference date
- 25.-27.05.2014
THE PROBLEM OF WATER CONTENT DETERMINATION IN PRODUCTS CONTAINING LACTOSE
Heinz-Dieter ISENGARD, Georg MERKH
University of Hohenheim, Institute of Food Science and Biotechnology,
Stuttgart, Germany
The water content of pure lactose (any isomer) can be determined both by drying as by Karl Fischer titration. The water of crystallisation of α‑lactose as lactose monohydrate is released only at relatively high temperatures. This fact may lead to serious problems when the water content of products containing lactose is to be determined. In some cases, the determination of water content by drying becomes even impossible. With the Karl Fischer titration combined with gas extraction it is possible to make such a situation visible. The sample water (and possibly other volatile substances) is driven by a dry air stream from the vial containing the sample into the Karl Fischer titration cell, where water is determined selectively. The vial can be heated using constant temperature or a temperature ramp. The detection rate of water and the total water detected are monitored. This technique allows in critical situations to show that the “lactose water” is only detected at temperatures at which the degradation of substances in the sample has already begun. This overlapping proves that a correct water determination by drying is impossible for such a product. No temperature exists where on the one hand the water of lactose is completely released and on the other hand the matrix does not release water produced by degradation. Baby food is presented as practical example for such a situation. As the Karl Fischer titration does not use such high temperatures, it is the method of choice in these cases. It is remarkable that, neglecting this fact and against scientific evidence, an official method to determine moisture of milk powder by drying has been established and still exists.