Drying and processing protocols affect the quantification of cyanogenic glucosides in forage sorghum.
BACKGROUND
Cyanogenic glucosides are common bioactive products that break down to release toxic hydrogen cyanide (HCN) when combined with specific β-glucosidases. In forage sorghum, high concentrations of the cyanogenic glucoside dhurrin lead to reduced productivity and sometimes death of grazing animals, especially in times of drought, when the dhurrin content of stunted crops is often higher. The aim of this study was to develop harvesting protocols suitable for sampling in remote areas.


RESULTS
Dhurrin concentration in air- and oven-dried leaves was the same as in fresh leaves, with no subsequent losses during storage. Dhurrin concentration was halved when leaves were freeze-dried, although activity of the endogenous dhurrinase was preserved. Direct measurement of dhurrin concentration in methanolic extracts using liquid chromatography/mass spectrometry (LC/MS) gave similar results to methods that captured evolved cyanide. A single freezing event was as effective as fine grinding in facilitating complete conversion of dhurrin to cyanide.


CONCLUSIONS
Direct measurement of dhurrin using LC/MS is accurate but expensive and not appropriate for fieldwork. Air drying provides an accurate, low-cost method for preparing tissue for dhurrin analysis, so long as the specific β-glucosidase is added. It is recommended that comparative studies like the one presented here be extended to other cyanogenic species.
School of Biological Science, Monash University, Melbourne 3800, Victoria, Australia. ros.gleadow@monash.edu
Roslyn M
RM
Gleadow
Morten E
ME
Møldrup
Natalie H
NH
O'Donnell
Peter N
PN
Stuart
D000383:Agriculture / Q000379:methods*; D000821:Animal Feed / Q000032:analysis*; D000822:Animal Husbandry / Q000379:methods*; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004795:Enzyme Stability; D059022:Food Safety; D005517:Foodborne Diseases / Q000517:prevention & control / Q000662:veterinary; D006027:Glycosides / Q000032:analysis* / Q000378:metabolism; D006856:Hydrogen Cyanide / Q000032:analysis / Q000737:chemistry / Q000506:poisoning; D007202:Indicators and Reagents / Q000737:chemistry; D009570:Nitriles / Q000032:analysis* / Q000378:metabolism; D010936:Plant Extracts / Q000737:chemistry; D018515:Plant Leaves / Q000737:chemistry* / Q000254:growth & development / Q000378:metabolism; D010939:Plant Poisoning / Q000517:prevention & control / Q000662:veterinary; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism; D045868:Sorghum / Q000737:chemistry* / Q000254:growth & development / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization; D001617:beta-Glucosidase / Q000737:chemistry / Q000378:metabolism
D006027:Glycosides; D007202:Indicators and Reagents; D009570:Nitriles; D010936:Plant Extracts; D010940:Plant Proteins; C007173:cyanogenic glycosides; D006856:Hydrogen Cyanide; C411650:Dhr1 protein, Sorghum; D001617:beta-Glucosidase; C011220:dhurrin