CYANOGENIC GLUCOSIDE PATTERNS IN SWEET AND BITTER ALMONDS
When an almond (Prunus dulcis (Mill.) D. A. Webb) kernel containing cyanogenic glucosides (prunasin or amygdalin) is disintegrated, the glucosides will typically be hydrolyzed by amygdalin hydrolase, prunasin hydrolase, and mandelonitrile lyase with concomitant release of glucose, benzaldehyde, and hydrogen cyanide (HCN). Benzaldehyde and HCN, in low amounts, provide the characteristic almond taste and flavour. Because of the toxicity of HCN, low cyanogenic glucoside content in the kernel is a prime breeding target. Biochemical analyses of different almond tissues were carried out to investigate their ability to synthesize and degrade prunasin and amygdalin. The analyses were carried out during the entire growth season, from almond tree flowering to kernel ripening using the following tissues: leaves, petioles, and the fruit (endosperm and cotyledon). Four different genotypes were investigated: Ramillete (SkSk: sweet), Marcona (Sksk: sweet), Garrigues (Sksk: slightly bitter) and S3067 (sksk: bitter). LC-MS analysis from all different tissues in the four genotypes revealed that amygdalin is present in high concentrations in the bitter kernel, substantiating previous reports. UDPG-mandelonitrile glucosyltransferase activity was detected in the vegetative part of the tree (leaves), and in fruit tissues (endosperm and in the cotyledon) of the homozygous genotypes. UDPG-prunasin glucosyltransferase activity was detected in all four genotypes and the activity was restricted to the cotyledons. The similar activity levels of the biosynthetic enzymes measured in sweet and bitter genotypes suggest that the catabolism of prunasin or amygdalin determines whether an almond kernel becomes sweet or bitter.
Sánchez-Pérez, R., Lindberg Møller, B., Olsen, C.E. and Dicenta, F. 2009. CYANOGENIC GLUCOSIDE PATTERNS IN SWEET AND BITTER ALMONDS. Acta Hort. (ISHS) 814:481-486
prunasin, amygdalin, UDPG-glucosyltransferase, Prunus dulcis, bitterness