Effect of reducing agents on oxidation-reduction potential and the outgrowth of Clostridium botulinum type E spores.

Oxidation-reduction potential (Eh) levels were measured and standardized to pH (Eh7) for Trypticase soy broth containing various concentrations of reducing agents. Prereduced Trypticase soy broth with no added reducing agents exhibited a potential of -141 mV. Ascorbic acid at 0.2 to 0.005% and sodium thioglycolate at concentrations below 0.05% produced an Eh7 higher than the prereduced Trypticase soy broth containing no added reducing agents. The addition of cysteine hydrochloride,2-mercaptoethanol, and sodium formaldehyde sulfoxylate to prereduced Trypticase soy broth resulted in a reduction of Eh7 compared to the system without added reducing agents. The order of relative reducing intensity (from highest to lowest) for the reducing agents when comparing molar concentration was: sodium formaldehyde sulfoxylate,2-mercaptoethanol, cysteine hydrochloride, sodium thioglycolate, and ascorbic acid. Optimal growth of the test organism occurred at low Eh7 and low concentration of the reducing agents. A direct correlation existed between growth of the test organism and -Eh7 x -log concentration of the reducing agent.