BIOGENESIS OF OFF-ODOR IN BROCCOLI STORAGE UNDER LOW-OXYGEN ATMOSPHERE

Broccoli was stored for 10 days at 0 degrees C under modified atmosphere containing the following initial percentages of O-2/CO2: (A) 1.1%/3%; (B) 18%/11%. Weight and color retention was better under modified atmosphere than in air, but under anaerobic condition broccoli produced severe off-flavor. In the headspace of low oxygen stored broccoli, methanethiol, dimethyl sulfide, and dimethyl disulfide were identified using GC/MS. A possible enzymatic pathway for the production of these compounds was investigated. In a cell-free system of fresh broccoli, methanethiol formation occurred in response to L-methionine and S-methylcysteine; dimethyl sulfide was formed from S-methylmethionine. An increase in free amino acids was observed in broccoli under anaerobic conditions and control; free sulfur-containing amino acids calculated were 10.4 and 2.2 mu g/g, respectively. These findings suggest that broccoli has the enzymatic capacity to produce volatile sulfur compounds, which are contributors to the objectionable odor, but precursors, free sulfur-containing amino acids, seem to arise preferably in broccoli storage under low oxygen atmosphere.