The reversible and irreversible emission of methanethiol (MT) and dimethyl disulfide (DMDS) from broccoli florets was demonstrated during anaerobic storage at 20 degrees C for up to 24 h. Reversible emission of MT and DMDS was feasible only in broccoli stored for between 0 and 12 h under entirely anaerobic condition. Beyond that, the emission was completely irreversible. This irreversible process was demonstrated through significant reductions in the chlorophyll fluorescence values and rate of carbon dioxide production and significant increase in the membrane permeability of induced broccoli tissues after exposure to air and incubation. Irreversible emission was also demonstrated through significant change in color from the characteristic bright green to olive green as well as the conversion of chlorophyll a to pheophytin a and chlorophyll a' contents of the induced florets after hot-water treatment. These findings suggest that the irreversible emission of MT and DMDS is a function of permanent membrane damage and loss of intracellular compartmentation in the broccoli tissues as a result of the anaerobic induction. The off-odor formation can still be reversed if the affected tissue is only temporarily impaired by anaerobic condition, thereby maintaining the quality of stored broccoli.