Monitoring of Cyanide Content in Cassava Roots and Flour Using Picrate Kits

At the Australian National University in Canberra, Australia we developed a simple picrate kit called Kit A to determine the total cyanide content of cassava roots (Egan et al., 1998; Bradbury et al., 1999). The stepwise procedure to be followed is found in Protocol A. A second kit called Kit B2 is for the determination of total cyanide in cassava flour and other cassava products. The procedure used is given in Protocol B2.

Each kit allows 100 analyses to be made. They are available free of charge to health workers and agriculturalists in developing countries. We developed a simple method for the preparation from cassava sap of the enzyme linamarase, (Haque and Bradbury, 1999a) and also the preparation of linamarin from very young cassava leaves (Haque and Bradbury, 2004). Both linamarase and linamarin are needed for the operation of kits A and B2.

We developed methods to determine the total cyanide content of all cyanogenic plants and foods using the picrate method and the acid hydrolysis method and applied these to a range of cyanogenic plants and foods. The acid hydrolysis method is generally applicable to all plants, but is much more difficult to use and is less accurate and reproducible than the picrate method, which is the method of choice for plants of importance for human food (Haque and Bradbury, 2002).

We have increased the sensitivity of the method tenfold by using a smaller (1x1cm) picrate paper, elution of the paper with 0.5mL water instead of 5mL as with the normal method and use of micro cells in the spectrometer (Bradbury, 2009).