Quantification of total cyanide content in kernels of stone fruits

Abstract

Many plants from the genus prunus deliver fruits which are popular food or pre product in many parts of the world. The kernels of those fruits vastly remain unprocessed and are disposed of, because of the high content of cyanogenic glycosides which refers to up to 2500 mg HCN per kg plant material. Therefore it is crucial to be aware of the total cyanide content and to apply appropriate methods of decontamination to allow industrial use. In this work the method of determination of total cyanide with picric acid was adapted for analysis of stone fruit kernels. The content of total cyanide was determined photometrically according to the reaction of HCN with picric acid to isopurpuric acid on a test strip and expressed in mg HCN per kg food sample. In the different stone fruit kernels (apricot, sort cherry and bitter almond) the content of total cyanide was determined to be in a range of 800 to 2400 mg/kg. In stone fruit kernels from sweet cultivars (sweet almond) no cyanide was determined. In products made from stone fruit kernels (roasted kernels, persipan) cyanide was determined to be in a range of 60-173 mg per kg food sample. In other products made from stone fruit kernels (marzipan, marzipan filling, chocolate) no cyanide was detected. Several methods of decontamination were tested: continuous flow and batch by water, batch by ethanol, heat and fermentation with ß-glucosidase. It was shown that satisfying decontamination can be achieved simply with cold water. The HCN content of apricot kernels was reduced by 80% in a 24h batch process using cold water. The results of this study indicate that stone fruit kernels and kernel products can be used in the food industry after an appropriate decontamination step. Furthermore it was shown that the method of determining the HCN content with picric acid on a test strip can be used for rapid analysis.