Chapter 14 - Cyanogenic Glycosides in Nuts and Seeds

Abstract

Many plant species actively synthesize and accumulate cyanide-containing compounds. These cyanogenic plants have the ability to release hydrogen cyanide (HCN) up to toxic thresholds in response to cell disintegration. This chapter examines cyanogenic nuts and seeds. The concentrations of cyanide-containing compounds in nuts and seeds vary widely; however, in some species, such as Prunus amygdalus (almonds), P. armeniaca (apricots), and Phaseolus lunatus (lima bean), they can reach toxic thresholds. Most cyanogenic glycosides are derived from the five hydrophobic protein amino acids, tyrosine, phenylalanine, valine, leucine, and isoleucine. In the course of the biosynthetic pathway the specific amino acids are hydroxylated to N-hydroxylamino acids, aldoximes, and then to nitriles serving as intermediates. Because HCN generally is toxic to all eukaryotes, including the plant itself, the accumulation of this toxin as an inactive precursor is essential to prevent autotoxicity. Although potentially toxic, cyanogenic nuts and seeds are often characterized by exceptionally high nutritive values. All of the economically most important cyanogenic nuts and seeds (i.e., almonds, macadamia nuts, lima beans, and flaxseed) contain health-promoting compositions of fatty acids, minerals, vitamins, and carbohydrates. Taking into consideration the possible health risk arising from consumption of inappropriately processed plant materials or the selection of highly cyanogenic crop plant genotypes, cyanogenic nuts and seeds represent excellent food sources.