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 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. Materials Kernels of apricots (Wachauer Marille from Austria harvested 2008) and sour cherries (from gardens in Vienna, Austria, harvested 2008). 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 30°C 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. Correspondence to: Ao.Univ.Prof. Dr. Ingrid Steiner Institute of Chemical Engineering Getreidemarkt 9, A-1060 Vienna, Austria Tel: /16002, Fax: / Results 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. Grinding conditionsHCN (mg/kg) 30 s, interruptions 10 s3100 ± s, without interruptions2749 ± s, interruptions 10 s3517 ± s, without interruptions2510 ± s, without interruptions2903 ± s, without interruptions, charge ± s, without interruptions, charge ± s, without interruptions, charge 2 kernels stored 24 h at 30°C 1095 ± 214 Table 1. Kernels of sour cherries – Content of HCN equivalents for different grinding conditions Grinding conditionsHCN (mg/kg) 20 s, without interruptions159 ± s, without interruptions18,9 ± 4,3 60 s, without interruptions3,3 ± 2,8 Table 2. Kernels of apricots - content of HCN equivalents for different grinding conditions Fig.2. Particle size of grinded (60 s) apricot kernels Acknowledgement We gratefully thank Dr.Gerd Mauschitz for measuring the particle size. Fig.1. Formation of sodium isopurpurate after reaction of picric acid with HCN Fig.3. Decontamination of kernels „Wachauer Marille“ (apricot) Sour cherries