Untersuchung der Ursachen von Aromaveränderungen an einem ...

Zusammenfassung / Abstract
Analysis of odour improving changes to a medical, herbal formulation
during a storage period
Identification and genesis of unpleasant odour
by M. Lucas
Abstract:
The first ever study of the causes of changes in odour of an aqueous-alcoholic distillate
obtained from dried medical ethereal herbal plants was undertaken. The study
centered on the appearance and subsequent disappearance of a disturbing and unpleasant
odour during a maturing process of the distillate.
The odour is linked to the presence of hydrogen sulphide and methanthiol. Both
compounds occur immediately after the distillation in concentrations of 10-50 µg/l. It
was found that the minimum concentration at which the odour can be detected by
humans is 5 µg/l (threshold) of either compound.
The occurrence of the compounds can be explained by the thermic decomposition
during the distillation process of the amino acids L-cysteine and L-methionine, which
were found in the raw plant material.
The study mentions three paths of decomposition: decomposition in the presence of
an α–dicarbonyl compound, the break down in the presence of a base (ß-elimination)
and the intra-molecular break down under formation of a lacton.
It can be observed that the concentration of both disturbing and unpleasant odour
compounds decreased during the process of maturing. In addition, both compounds
could effectively be eliminated out of the headspace of the distillate by using charcoalfilters,
metallic copper or higher amounts of water.
The typical odour of the examined product is characterised by the compounds 1,8-
Cineol, Linalool and Eugenol. During the maturing period an increase in the concentration
of these or other coumpounds with a pleasant odour was shown not to occur.
The study describes the use of gaschromatography-olfactometry (GCO) and aroma
extract dilution analysis (AEDA) for the identification of olfactory relevant compounds
in the distillate. Changes in concentration of these selected odour compounds
between different olfactory states of the distillate is shown by objective, instrumental
analytical methods and confirms their contribution to the odour.
The advantages of headspace-sampling in the examination of volatile compounds as
opposed to other techniques to increase the concentration of these compounds or to
the liquid-injection of aroma extracts are described and explained.
A procedure is described which removes the sulphur containing compounds with
metallic copper.
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