The Natural Inorganic Bromide Content of Edible Mushrooms

Among the wild-growing mushrooms used by the food industry are two species of dried boletes, i.e. Boletus edulis (Steinpilze) and Suillus luteus (Butterpilze), which are essential ingredients of various popular soups and sauces.Methyl bromide fumigation is often applied to protect these raw commodities against insect infestation during storage and transport. Consequently, there are legal prescriptions for the inorganic bromide residues incurred by this practice.In this paper, it is demonstrated that the natural bromide content of the said boletes is directly dependent on soil levels and, therefore, subject to considerable variation. Although most European collections analysed contained only a few mg/kg, boletes from Southern Brazil had levels in the range of the legal limits for residues associated with methyl bromide fumigation, e. g. S. luteus ( Butterpilze) often had a natural bromide content of 200 mg/kg. This means that in practice it is not possible to distinguish between fumigated and non-fumigated boletes by measuring the bromide content. A determination of the chloride/bromide ratio was not helpful either. The only valid approach was the determination of N-methylated amino acids, but this is hardly suitable for routine purposes. Finally, the bromide content of 79 species of edible mushrooms from the Swiss market was investigated with reassuringly low results.Analytical details are given for the simultaneous gas chromatography determination of chloride and bromide, both in mushroom and in soil samples.