Evaluation of the Botulism Hazard from Vacuum-packaged Enoki Mushrooms ( Flammulina velutipes ).

Flammulina velutipes , commonly known as the enoki or winter mushroom, is cultured aseptically in Japan and the United States and is vacuum-packaged in polyethylene film for retail sale. Because of the known potential hazard of botulism from agaric mushrooms that are packaged in plastic films, the safety of vacuum-packaged enokis was evaluated. Botulinal toxin was not detected by mouse assay in 148 packages from 14 independent lots when a rich medium containing trypticase-peptone-glucose-yeast extract, was added aseptically to the packages which were heat-shocked (60 or 80°C for 20 min) and incubated at 30 or 37°C. Botulinal toxin was produced when spores were added to the packages, but spoilage was evident prior to toxin formation. Toxin was not formed when the inoculated packages were kept refrigerated (6°C). The results indicate that fresh vacuum-packaged enoki mushrooms do not present a botulism hazard when cultured aseptically and stored refrigerated.