γ-Glutamyl peptides in the biosynthesis of S-alk(en)yl- l-cysteine sulphoxides (flavour precursors) in Allium

Abstract

Pulse-chase experiments with 35SO 4 2− fed for 10 min to leaves of Allium cepa (onion), A. sativum (garlic) and 4 A. siculum showed that label appeared in γ-glutamyl peptides within 15 min, reached a maximum amount at 1 hr and had decreased by 6 hr. Label was not detected in free S-alk(en)yl- l-cysteine sulphoxides (flavour precursors) until 6 hr after pulse feeding, and then increased steadily for at least 24hr and for onions until day 3. It is concluded that glutathione, and γ-glutamyl peptides are intermediates in the biosynthetic pathway to flavour precursors in Allium spp.