Elemental analysis of log-cultivated fruit bodies of G. lucidum revealed phosphorus, silica, sulfur, potassium, calcium, and magnesium to be the main mineral components. Iron, sodium, zinc, copper, manganese, and strontium were also detected in lower amounts, as were the heavy metals lead, cadmium,
and mercury (91). Freeze-dried fruit bodies of unidentified Ganoderma spp collected from the wild were reported to have a mineral content of 10.2% with potassium, calcium, and magnesium the major components (48). Significantly, no cadmium, mercury, or selenium was detected in these samples. There are several reports of heavy metal accumulation in mushroom fruit bodies (92-96). However, the evidence for greater accumulation in mushrooms collected in urban areas compared with domains considered to be "pollution-free'' is conflicting (94,97).
Regardless of the site of cultivation, there is a risk of contamination by heavy metals (e.g., Hg, Cd) from the environment, and of contamination by toxins from spoilage microbes and by pathogenic microbes (48,98). Natural products are not necessarily safe, and while the toxic dose of G. lucidum appears to be very high, the issue of contamination by heavy metals and microbial toxins must not be neglected (99). Food toxicology is a growing discipline, and this reflects a growing awareness of this possibility. Commercial preparations, therefore, must be tested, and a certificate of analysis containing information on heavy-metal and microbial content in relation to specified limits is needed.
Particular attention has been given to the germanium content of Ganoderma spp. Germanium was fifth highest in terms of concentration (489 Ag/g) among minerals detected in Ganoderma fruit bodies collected from nature (48). This mineral is also present in the order of parts per billion in many plant-based foods including ginseng, aloes, and garlic (100). Germanium is not an essential element but, at low doses, has been ascribed immuno-potentiating, antitumor, antioxidant, and antimutagenic activities (32,101103). However, although the germanium content of G. lucidum has often been used to promote G. lucidum-based products, there is no firm evidence linking this element with specific health benefits associated with the mushroom.
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