Novel UHPLC-(+ESI)MS/MS Method for Determining Amygdalin, Prunasin and Total Cyanide in Almond Kernels and Hulls (Prunus dulcis)

Almonds contain cyanogenic glycosides (CNGs), prunasin and amygdalin, which generate hydrogen cyanide upon hydrolysis. Different extraction and analytical methods are currently used to measure CNGs or cyanide (CN), necessitating distinct samples and can lead to inconsistent or incomparable results. To address this, we describe a method that uses ultrasonic-assisted sample extraction. Amygdalin and prunasin are measured directly in the extract, whereas CN is measured in the extract after derivatization with cysteine ethyl ester to form a cyano-S-ethyl-O-cysteine (CNCysEt) conjugate. The amygdalin, prunasin, and CNCysEt are quantified using the same UHPLC-(+ESI)MS/MS method. This new approach measured total CN in ten common almond kernel and hull varieties. The limit of quantitation ranged from 7.78 μg L^-1 (amygdalin), 51.36 μg L^-1 (prunasin), and 7.80 μg L^-1 (CNCysEt; kernel) and 25.02 μg L^-1 (CNCysEt; hull). This is the first time CNGs and CN levels are reported for almond hulls. Average total CN levels in hulls (<3 mg kg^-1) were significantly lower than levels in kernels (<20 mg kg^-1). Based on these findings, the hulls from California sweet almond varieties may be considered for use in human food products without additional processing to reduce CNG levels.