Acid number

from Wikipedia, the free encyclopedia

The acid number (AN) is a chemical quantity used to characterize acidic components in fats or oils. It describes the mass of potassium hydroxide (in mg ) that is necessary to neutralize the free fatty acids contained in 1 g of fat . In addition to fatty acids , any mineral acids that may be present can also be recorded. However, the acids bound as glycerides (= fatty acid esters) are not recorded as is the case with the saponification number .


The higher the acid number, the inferior the fat or oil. The determined free fatty acids provide information about degradation processes or pretreatment. The oxidation stability of the oils decreases as the acid number increases. According to the guiding principles for edible oils and fats, the acid number for native and unrefined ones may be <4.0, for refined ones up to 0.6.


According to EN ISO 660 (version from 2009), proceed as follows. The sample is dissolved in a suitable solvent (mixture) and the acids present are titrated with an ethanolic or methanolic solution of potassium hydroxide (ethanolic or methanolic standard solutions, 0.1 mol / l and 0.5 mol / l). A suitable solvent is ethanol (anhydrous or 96%) or 2-propanol . Other possible solvents are diethyl ether , peroxide-free, tert-butyl methyl ether , petroleum ether (boiling range 40 ° C to 60 ° C) or toluene . Phenolphthalein is used to determine the endpoint . If the fats are too colored for this indicator, alkali blue or thymolphthalein must be used.

Individual evidence

  1. ^ Siegfried Hauptmann : Organic Chemistry , 2nd revised edition, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig, 1985, p. 654, ISBN 3-342-00280-8 .
  2. ^ The German Food Book and the German Food Book Commission: Guidelines for Edible Fats and Edible Oils