Mechanisms of sulfide components expression and structural determination of substrate precursor in jumbo Leek (Allium ampeloprasum L.)

Abstract

The characteristics of sulfide precursor/components in the bulb of Allium ampeloprasum L. (jumbo leek) were compared with those in other Allium species : A. cepa L. (onion), A. sativum L., and A. ampeloprasum L. (broadleaf wild leek). Sulfide components from jumbo leek were analyzed by gas chromatography/mass spectrometry (GC-MS) using spectral analysis. The contents of sulfides from jumbo leek were dimethyl disulfide (M-SS-M ; 1.7mg/kg wet wt), methyl propenyl disulfide (M-SS-Pe ; 15.7mg/kg), propyl propenyl disulfide (P-SS-Pe ; 7.5mg/kg), dimethyl trisulfide (M-SSS-M ; 21.5 mg/kg), methyl propyl trisulfide (M-SSS-P ; lO.Omg/kg), and methyl propenyl trisulfide (M-SSS-Pe ; 14.0 mg/kg). The composition of alk(en)yl cysteine sulfoxide (alk(en)yl CSO) from jumbo leek was S-methyl cysteine sulfoxide (MCSO ; 4.1 ±0.5 mg/kg wet wt), S-propyl cysteine sulfoxide (PCSO ; 0.1 ±0.3mg/kg) and S-propenyl cysteine sulfoxide (PeCSO ; 2.4 ±0.4 mg/kg). The total content was the same as those of A. cepa L. and A. ampeloprasum L. Moreover, N- (τ-glutamyl)-S-(E-l- propenyl) cysteine (Glu-PEC, 87 mg/kg wet wt) which is a alk(en)yl cysteine precursor from jumbo leek, was detected. Therefore, the lower odor producing mechanism in jumbo leek was determined to be the same as that in leek. That is, the substrate precursor Glu-PEC is converted to S-E-l- propenyl cysteine (PEC) by τ-glutamyl transpeptidase. Then, PEC is oxidized to PeCSO, a substrate for allienase. PeCSO, another naturally present alk(en)yl CSO, is converted to S-alk(en)yl acid by allinase(C-S lyase), followed by sulfide production via formation of the dialkyl thiosulfinates.