Research On Initial Content Of Formaldehyde In Lentinus Edodes

In this paper, the effects of wood species in cultural media, variety, cultural modes, artificial factors such as formaldehyde added into media and/or soils, conditions of product storage, and drying methods on the contents of formaldehyde in shiitake mushroom(Lentinus edodes(Berk) Sing) were studied. The formaldehyde contents between shiitake mushrooms grew in wild wood and in PDA medium were compared. The major results were summarized bellow:1. It was proven by systematic trials that the formaldehyde in shiitake mushroom is probably the natural metabolite of itself. Formaldehyde can be detected in pure PDA medium cultured shiitake mushroom. Though the medium contained only 3.38mg/kg of formaldehyde, the mushroom fruit body could reach 20.45mg/kg. Formaldehyde in wild wood cultivated shiitake mushroom was also detected and could be as high as 66.19mg/kg. However, the formaldehyde in shiitake mushrooms grew on wild wood was lower than that in shiitake mushrooms grew on bag-media, indicating the effect of cultural media on the formaldehyde content in shiitake mushrooms.2. No significant effect of formaldehyde artificially added into media or covering soil was found on the content of formaldehyde in shiitake mushrooms. When diluted by 500times or higher, the formaldehyde added into media or covering soil will undergo evaporation and degradation during the cultural process, and finally exert little influence on the mushrooms harvested.3. There was no significant variation in formaldehyde contents among the six varieties of shiitake mushrooms, or mushrooms grew on cultural media with different wood species. The highest formaldehyde content was found in mushroom cultivated in white poplar based medium, and that was still no more than 22.54mg/kg. However, the cultivation modes did have significant effect on the formaldehyde content in shiitake mushroom. The formaldehyde content in mushroom cultivated with soil covering was highest, followed by that cultivated in shelf, and that in plastic shed was the lowest. These differences were attributed to the difference in ventilation condition and cultivation density.4. The storage conditions had influence on the formaldehyde content in shiitake mushroom. The mushrooms stored in sealed space had a growing content of formaldehyde. The content reached to 41.62mg/kg after 31 days of sealed storage. On the other hand, no significant changes in formaldehyde content in mushroom stored in open space was found.In summary, the background contents of formaldehyde in shiitake mushrooms under different cultivation or postharvest handling conditions, and detected with different extract condition were different. Under the testing conditions of this experiment, the formaldehyde contents in dried shiitake mushrooms ranged between 116.43mg/kg～247.28mg/kg, and that in fresh shiitake mushrooms ranged between 13.31mg/kg～52.11mg/kg. Since cultivation condition, harvest batches, and extracting condition will all affect the formaldehyde content in shiitake mushroom, it will only be meaningful to define a legal content limit after all the conditions were carefully defined.