Cepathiolactols and Cepathiolactones─Two Newly Discovered Families of Organosulfur Compounds Formed in Cut Onion

Isolation and structural characterization of two large families of organosulfur compounds spontaneously formed upon cutting of onion (Allium cepa) were carried out. The structures of these hitherto unknown species, trivially named cepathiolactols and cepathiolactones, were established based on NMR, MS, and IR data. It was found that cepathiolactols (CHOS₃ and CHO₂S₄; x = 7-12, y = 14-24) are 3,4-dimethyl-γ-thiolactols bearing various side chains linked via a disulfanyl moiety at position C-5. On the other hand, cepathiolactones were shown to be 3,4-dimethyl-γ-thiolactones structurally analogous to cepathiolactols. Sensory properties of cepathiolactols were also evaluated, along with testing their ability to participate in the formation of pink discoloration of processed onion.