Folie 1

1
Determination of cyanide compounds in kernels of
stone-fruits

Ingrid Steiner and Anatol Desser
Vienna University of Technology, Institute of
Chemical Engineering, Division of Natural
Products and Food Chemistry, Getreidemarkt 9,
A-1060 Vienna, Austria
Results
Introduction Kernels from stone-fruits can be
used as a source of fat and protein, but their
utilisation is connected with various technical
and toxicological problems so that these kernels
are normally burnt. One of these problems is the
occurrence of cyanogenic compounds which is
determined by the content of amygdalin. Amygdalin
is decomposed by the enzyme emulsion inside the
matrix into cyanogenic acid, benzaldehyde and
glucose. Furthermore free cyanogenic acid is
stored in cells of the stone. The Austrian food
law and the EC regulation recommend 50 mg HCN /
kg in foods (e.g. nougat and marzipan)
corresponding to 846,1 mg amygdalin.


Grinding conditions HCN (mg/kg)
30 s, interruptions 10 s 3100 1233
30 s, without interruptions 2749 955
40 s, interruptions 10 s 3517 2775
40 s, without interruptions 2510 961
50 s, without interruptions 2903 759
120 s, without interruptions, charge 1 2764 191
120 s, without interruptions, charge 2 1797 257
120 s, without interruptions, charge 2kernels stored 24 h at 30C 1095 214
Materials Kernels of apricots (Wachauer Marille
from Austria harvested 2008) and sour cherries
(from gardens in Vienna, Austria, harvested 2008).
Table 1. Kernels of sour cherries Content of
HCN equivalents for different grinding
conditions
Wachauer Marille (apricot)
Grinding conditions HCN (mg/kg)
20 s, without interruptions 159 189
40 s, without interruptions 18,9 4,3
60 s, without interruptions 3,3 2,8
Methods Grinded kernels were mixed with buffer
(pH 5) and a yellow picrate paper was attached
inside the vial without contact with the liquid
phase. The vial was tightly closed and left
standing at 30C for 24 hours. In the presence of
cyanide substances HCN is set free and the colour
of the picrate paper changes from yellow to red
according to the amount of HCN. After extraction
of the paper with water the solution is analyzed
by measuring the absorbance at 510 nm. Blank
values and the calibration graph were determined
in the same way. For this method it is important
that the sample is grinded well because all cells
and vacuoles have to be destroyed so that all
cyanogenic glucosides can react with the enzymes.
On the other hand the sample loses HCN while
grinded which influences the results in a fatal
way. The ideal time of grinding (maximum release
and minimum loss of cyanogenic glucosides) for 10
sour cherry kernels is approx. 120s.
Table 2. Kernels of apricots - content of HCN
equivalents for different grinding conditions

Sour cherries
Fig.1. Formation of sodium isopurpurate after
reaction of picric acid with HCN
Conclusion The results show that it is not easy
to find the best conditions for preparation of
the kernels to analyze HCN contamination. So the
next working steps should find out the optimal
processes not only for apricot kernels but also
for kernels of cherries, plums and peaches in
correlation with the particle size. A possibility
to accelerate the release of HCN from the samples
might be the addition of immobilised
enzymes. Storage of the kernels at higher
temperatures results in lower residues of HCN so
that it can be assumed that heat treatment and
storage of grinded kernels increases the loss of
HCN. Furthermore the residual amounts of HCN in
grinded and original kernels after storage at
different temperatures will be tested to check
the possibility for use in food and feed industry
under consideration of legal limits.
Fig.2. Particle size of grinded (60 s) apricot
kernels
Correspondence to Ao.Univ.Prof. Dr. Ingrid
Steiner Institute of Chemical Engineering Getreide
markt 9, A-1060 Vienna, Austria Tel
43-1-58801/16002, Fax [phone] Emaili
steiner_at_mail.zserv.tuwien.ac.at http//www.vt.tuwi
en.ac.at/
Fig.3. Decontamination of kernels
Acknowledgement We gratefully thank Dr.Gerd
Mauschitz for measuring the particle size.