Determination of naturally-occurring formaldehyde in raw and cooked Shiitake mushrooms by spectrophotometry and liquid chromatography-mass spectrometry.

The initial objective was to check samples of Shiitake mushrooms for potential contamination with formaldehyde. A small number of UK retail samples were analysed using a spectrophotometric method and were found to produce formaldehyde concentrations ranging from 110-240 mg kg(-1). A more specific method, based on a derivative that could be measured and characterized by LC-MS, confirmed these results. A secondary objective tested the hypothesis that the formaldehyde might be of natural origin. Samples of UK and Chinese Shiitake, verified as being produced without any formaldehyde treatments, were found to produce similar levels of formaldehyde ranging from 100-320 mg kg(-1). Frying for 6 min significantly reduced formaldehyde concentrations, whereas storage for up to 10 days had no effect on the concentrations. The relatively harsh analytical conditions used may have produced some of the formaldehyde measured during extraction, from a number of chemical precursors.