Olfactory Perception of Cysteine-S-Conjugates from Fruits and Vegetables

Volatile sulfur compounds have a low odor threshold, and their presence at microgram per kilogram levels in fruits and vegetables influences odor quality. Sensory analysis demonstrates that naturally occurring, odorless cysteine-S-conjugates such as S-(R/S)-3-(1-hexanol)-L-cysteine in wine, S-(1-propyl)-L-cysteine in onion, and &((R/S)-2-heptyl)-L-cysteine in bell pepper are transformed into volatile thiols in the mouth by microflora. The time delay in smelling these volatile thiols was 20-30 s, and persistent perception of their odor occurred for 3 min. The cysteine-S-conjugates are transformed in free thiol by anaerobes. The mouth acts as a reactor, adding another dimension to odor perception, and saliva modulates flavors by trapping free thiols.