Selenium speciation in Agaricus bisporus and Lentinula edodes mushroom proteins using multi-dimensional chromatography coupled to inductively coupled plasma mass spectrometry

In this study, selenium species from Se containing proteins in mushrooms (Agaricus bisporus and Lentinula edodes) were investigated with size-exclusion liquid chromatography coupled to UV and inductively coupled plasma mass spectrometry (ICP-MS). Different protein extraction protocols were investigated. Variability of the fractionation patterns with three extraction media (0.1 M NaOH, 30 mM Tris–HCl, and enzymatic digestions) was evaluated for both mushroom types. A 24 h Tris–HCl extraction followed by acetone addition was found to be optimal for protein precipitation. Presumably protein bound selenoamino acids were released using enzymes (proteinase K, protease XIV and trypsin). The selenium speciation of the proteolytic extract of the water soluble proteins fraction was carried out by using reversed-phase ion-pairing high performance liquid chromatography (RP-HPIPC) coupled on-line to ICP-MS for selenium specific detection. Selenocystine, selenomethionine, methylselenocysteine and inorganic selenium were established in both samples utilizing retention time standards and standard additions to the sample.