Optimized Formation, Extraction, and Determination of Sulforaphane in Broccoli by Liquid Chromatography with Diode Array Detection

A new method has been developed to determine sulforaphane in broccoli florets, stems, and leaves using liquid chromatography coupled to diode array detection. The hydrolysis reaction, required to convert glucoraphanin to its breakdown product, sulforaphane, and the extraction procedure, based on solvent extraction with methyl t-butyl ether followed by solid phase extraction with silica cartridges, were optimized for the three broccoli matrices; the resulting recovery values ranged from 92 to 102 % in all cases. A fast separation was performed on a C-18 analytical column with a mobile phase composed of ammonium formate (20 mM) in water and acetonitrile (55:45, v/v) in isocratic elution mode. This method was fully validated and was found to be selective, linear from 2.5 to 800 mg/kg, and precise (percent relative standard deviation values below 5 %). Moreover, the limits of detection and quantification were 0.8 and 2.5 mg/kg, respectively. Finally, the proposed method has been applied to the analysis of sulforaphane in broccoli samples of two different cultivars (Parthenon and Marathon).