Methanethiol Formation in Disrupted Tissue Solution of Fresh Broccoli

Abstract

Factors for the formation of methanethiol using a disrupted broccoli tissue solution were investigated. A trace amount of methanethiol was detected in the headspace of a capped test tube containing the disrupted fresh tissue solution after incubation at 20 °C for 1 hr. When L-cysteine or reduced glutathione was added to the sample solution, a considerable amount of methanethiol was formed. In a molecular weight of below 10, 000 fraction of the fresh sample solution, a significant amount of methanethiol was formed by adding L-cysteine. However, in a disrupted tissue solution prepared from a heat-treated tissue, no detectable methanethiol was formed by adding L-cysteine.
We propose that methanethiol is a degradation product of methyl methanethiosulfinate (MMTSO) which is present in the disrupted fresh tissue solution. The concentration of the MMTSO is pH-dependent, being higher in basic than in acidic solutions. No MMTSO was detected in the disrupted tissue solution prepared from a heat-treated tissue. When L-cysteine was mixed with the fresh sample solution, MMTSO disappeared.
It was confirmed that MMTSO was formed by an enzymatic reaction in the disrupted fresh broccoli solution which reacts nonenzymatically with L-cysteine or reduced glutathione to produce methanethiol.