A unit that measures the activity of the enzyme diastase. Diastase was the first enzyme to be discovered and is actually the group of amylases, enzymes that convert starches to sugars. One diastase unit is the amount of enzyme which will convert 0.01 gram of starch to the prescribed end-point in 1 hour at 40°C. Symbol DN. The diastatic index is usually measured by the Schade method¹ (now as modified by White and Pairent, and Hadorn and Zürcher), and the unit is also called the Schade unit or the Gothe unit.
The unit mainly occurs in tests of honey. To greatly oversimplify an exacting procedure, the honey is mixed with a starch solution and iodine added at intervals. As in the familiar school experiment, iodine turns the starch blue. Diastase converts the starch to sugar; the more starch converted to sugar, the less blue. The time needed for the solution to reach an absorbance of 0.235 (0.301 in the German standard) is noted. 300 divided by the time in minutes gives the DN number.
In recent years the Schade test has been replaced by a method using Phadebas tablets, which gives more consistent results.² The determinations are usually converted to Schade units.
A major use of the index is controlling the quality of honey. In Europe, for example, the minimum permitted DN for honey is 8 DN per gram. The Codex Alimentarius³ also recommends this level “for voluntary application by commercial partners”, and since honeys from certain species of flower naturally have much lower levels of diastase, for those “not less than 3 Schade Units”.
1. J. E. Schade, G. L. Marsh and J. E. Eckert.
Diastase activity and hydroxymethylfurfural in honey and their usefulness in detecting heat adulteration.
Food Research, vol 23, 446-463 (1958).
2. U. Siegenthaler.
Bestimmung der Amylase in Bienenhonig mit einem handelsublichen, farbmarkierten Substrat.
Mitt. Gebiete Lebensmitt. Hyg., vol 66, pages 393-399 (1975)
Honigdiastase, Gegenüberstellung verschiedener Bestimmungsmethoden.
Mitt. Gebiete Lebensmitt. Hyg., vol 75, pages 214-220 (1984)
3. Revised Codex Standard for Honey, 12-1981, Rev. 1 (1987), Rev 2 (2001).
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Last revised: 28 January 2005.