Determination of water content in lactose by Karl Fischer titration - Interlaboratory collaborative study

Publikations-Art

Zeitschriftenbeitrag

Autoren

Isengard, H.-D.; Haschka, E.; Merkh, G.

Erscheinungsjahr

2011

Veröffentlicht in

Bulletin of the International Dairy Federation

Herausgeber

International Dairy Federation/Fédération internationale du lait

Verlag

International Dairy Federation , Brüssel

Band/Volume

450/

ISBN / ISSN / eISSN

0250-5118

Seite (von - bis)

1-14

Abstract

Lactose is a very important product in the dairy industry, but also for the pharmaceutical sector. The determination of the water content and the water activity are important to assess its microbiological, technical and commercial quality.

The method used most often for determining moisture content in milk products is gravimetric oven drying at 102 ± 2 °C until approximate mass constancy is reached. This method measures only the loss in mass by evaporation of all substances volatile under the conditions applied. No distinction is made between water and other volatile compounds. On the other hand, strongly bound water may not be detected.

Lactose exists essentially in three forms: α‑lactose with 5% of water of crystallization (lactose monohydrate), anhydrous β‑lactose and lactose in amorphous form. Commercial and technical lactose powder can be a mixture of all of these three forms. At drying temperatures of about 102 °C the water of crystallization is only partly determined [1]. Thus, incorrect results for the water content of lactose are obtained [1, 3] with the international standard for moisture determination in dried milk [2].

To determine the water content alone, a fast and simple method based on the Karl Fischer titration (KFT) was developed and tested in an international ring test. The method was proposed as an international standard to be adopted by the International Dairy Federation (IDF) and the International Organization for Standardization (ISO) [4].

[1] Rückold, S., Grobecker, K.H. & Isengard, H.‑D. Determination of the contents of water and moisture in milk powder. Fresenius J. Anal. Chem. 368: 522‑527 (2000).

[2] ISO 5537 | IDF 26 (2004). Dried milk – Determination of moisture content (Reference method).

[3] Isengard, H.‑D. Water determination – Scientific and economic dimensions. Food Chemistry 106:
1393‑1398 (2008).

[4] ISO 12779 | IDF 227 (2011). Lactose – Determination of water content – Karl Fischer method.