Relationship between S-Alk(en)yl-L-cysteine Sulfoxides and Green Pigmentation of Garlic (Allium sativum L.)

The effects of 3 S-alk(en)yl-L-cysteine sulfoxides (alliin, isoalliin, and methiin) on garlic greening were investigated using actual garlic as well as a model system. The intensity of greening was positively but weakly proportional to the content of isoalliin (S-trans-1-propenyl-L-cysteine sulfoxide) in actual garlic, whereas the content of alliin (S-allyl-L-cysteine sulfoxide) and methiin (S-methyl-L-cysteine sulfoxide) did not appear to influence greening. In a semi-defined greening model system, which contained different combinations of L-cysteine sulfoxides and thiosulfinate-less fresh garlic water extract, the intensity of greening was proportional to the isoalliin concentration. In the model system, alliin enhanced the intensity of greening up to a certain concentration, and beyond which, it reduced greening progressively and generated a more yellowish tint with increasing alliin content. Methiin, however, affected garlic greening negatively in the model system, and the intensity of greening decreased progressively as the content of methiin increased. Using purified natural L-cysteine sulfoxides, both alliin and methiin were newly found to have specific influences on garlic greening.