Rapid Risk Assessment of the Detection of Listeria Monocytogenes in Enoki Mushrooms

This rapid assessment has been requested to inform a decision by FSA Policy whether a temporary overarching risk management response to the commodity (enoki mushrooms) is necessary. Cultivated enoki mushrooms are deprived of light and grown in a CO2-rich environment. Commercially grown enoki mushrooms are grown in hard wood sawdust that is impregnated with the spores. The sawdust is usually good for four or five crops of mushrooms. The mushrooms are encouraged to grow long and thin by placing glass tubes over them. This produces a pale white mushroom with long, slender stems, up to five inches in length, and small caps. Whilst specific practices may vary, generally the initial growing environment is humid with a temperature between 22°C – 25°C, followed by lowering the temperature to 7°C – 12°C whilst maintaining humidity. It is this change in temperature that causes the mycelium to form fruiting bodies that grow into mature mushrooms which are harvested after about 90 days (Pereira et al., 2023). The species Flammulina filiformis, known and sold in different regions as “enoki”/“enokitake” Japan, “jingu” (China), “futu” (India), “paengi beoseot” (Korea), “nám kim cham” (Vietnam) also grows wild throughout a broad natural range on the rotting wood of a range of common trees, although wild-growing mushrooms appear quite different. The majority of enoki mushrooms on sale appear to be commercially cultivated and fresh rather than wild mushrooms. It is unknown if wild enoki mushrooms present a similar L. monocytogenes risk to cultivated mushrooms. Listeria spp., including L. monocytogenes, can be present in the soil (Linke et al., 2014), and are common in natural and urban environments (Orsi and Wiedmann, 2016). Contamination and proliferation is possible during cultivation but also during harvesting and packing (uncertainty).