QUANTIFICATION OF ALK(EN)YL-L-CYSTEINE SULFOXIDES AND RELATED AMINO-ACIDS IN ALLIUMS BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

A liquid chromatographic technique was developed for the quantification of alk(en)yl-L-cysteine sulfoxides (ACSO) and selected amino acids (presumed to be involved in ACSO biosynthesis) in extracts of plant tissues. The method is based on fluorescent detection of 9-fluorenylmethyl chloroformate-derivatized ACSO adducts. On the basis of the sampling scheme used, conservative estimates of detection limits were 5 pmol of ACSO adduct, equivalent to less than or equal to 2.5 mg/100 g of fresh weight (g fw). Methyl-L-cysteine sulfoxide (MCSO) and 2-propenyl-L-cysteine sulfoxide (2-PECSO) were present in garlic (Allium sativum) cloves (16:84 w/w) with total ACSO levels of 300-500 mg/100 g fw. Some garlic cloves also contained lesser amounts of 1-propenyl-L-cysteine sulfoxide (1-PECSO). Pungent onion (Allium cepa) and leek (Allium porrum cv. Titan) bulbs contained MCSO and 1-PECSO (14:86 and 27:73 w/w, respectively) with total ACSO content of 100-200 mg/100 g fw. Cabbage (Brassica oleracea) leaves contained only MCSO at about 80 mg/100 g fw. None of the examined tissues contained the n-propyl-L-cysteine sulfoxide within the limits of detection, or less than or equal to 0.68-2.4% of the total ACSO in all samples. Of the amino acids quantified, glutamic acid (9-69 mg/100 g fw) was substantially more abundant than valine and glycine (up to 5 mg/100 g fw). Cysteine was also present in moderate amounts but was not quantified because of uncertainties in the extent of oxidation taking place during sample handling and analysis.