Amino acid composition of some Tanzanian wild mushrooms
Introduction
Worldwide the nutritive and medicinal values of mushrooms have long been recognized (Cochran, 1978), as some of the edible mushroom species also possess pharmacological properties (Zimmerman, 2002). Mushrooms are also among the best sources of other essential nutrients, such as chromium. Previous studies (Gruen & Wong, 1982; Suzuki & Oshima, 1976; Zakhary, Abu-Bakr, El-Mahoy, & El-Tabey, 1983) have indicated that edible mushroom species are highly nutritious, their nutritional value comparing favourably with that of meat, eggs and milk. Additionally, several edible mushroom species act as sources of physiological agents for medicinal applications, possessing antitumour, cardiovascular, antiviral, antibacterial and other activities. Thus, Ganoderma lucidum, included in the studies we are hereby reporting, possesses potent anti-HIV activity (Chang & Mshigeni, 2001).
Despite the nutritional, medicinal, and physiological properties, almost all mushroom species growing wildly in tropical Africa, and particularly in Tanzania, have not been investigated for their constituent secondary metabolites or for their amino acid composition that would be a reliable indicator of the nutritional value. Apparently, even the biology of most of the wildly occurring Tanzanian mushroom species has not yet been sufficiently documented. For example, recently it was revealed that, out of 27 mushroom species of the genus Lactarius collected from various parts of Tanzania, 15 were hitherto scientifically not described (Karhula, Harkonen, Saarimaki, Verbeken, & Mwasumbi, 1998).
In Tanzania and most African countries, the use of some wild mushroom species in traditional medicines has been documented (Chang & Mshigeni, 2001; Karhula et al., 1998). Thus, in some rural areas of Tanzania, a mushroom soup is provided to mothers after childbirth in order to promote quick recovery of the mother, while other mushroom species are used as medicines for stomach and heart diseases. A few polypores, such as Ganoderma species, are used in the treatment of sick cows while some puffball mushrooms are traditionally used for wound healing in the Kilimanjaro region of Tanzania.
Although there are many edible wild mushroom species growing in Tanzania, their consumption is mainly confined to some rural communities, most of them being eaten only in the rainy season when they are abundantly available. Drying of fresh mushrooms is applied in some rural communities in order to preserve them for future use. In recent times, mushrooms have begun to assume greater importance in the diets of many urban dwellers in Tanzania and, as a consequence, the mushroom-farming business, using spores from domesticated as well as wild mushroom species, has begun to emerge in some suburbs of Dar es Salaam and other major towns (Chuwa, 1997; Mtowa, 1999). So far, few studies on the nutritive value of local edible mushrooms have appeared (Mamiro, 2002; Mashandete, 1998; Ndekya, 2002). Nevertheless, these studies have not determined the amino acid contents of wild mushroom species occurring in Tanzania. The determination of the amino acid content of these nutritional resources was conceived in order to establish a preliminary guide for assessing their relative nutritive qualities and thus provide a basis for taping the nutritive potential of these natural resources in efforts towards abating nutritional deficiencies in developing countries. Results from these studies are discussed in this paper.
Section snippets
Mushroom materials
Fruiting bodies (pileus + stipe) of mushrooms were either harvested or bought from various parts of Tanzania, including Mafinga, Mbeya, Kwamngumi forest reserve in the East Usambara Mountains, and at Ununio on the outskirts of Dar es Salaam city. The collections were done from December to May during 1999–2002; this period corresponds to the rainy season. The mushrooms were subsequently identified by Mr. L.B. Mwasumbi of the Herbarium, Department of Botany of the University of Dar es Salaam,
Results
The percentage composition of amino acids in the analysed mushroom species is summarized in Table 1, which reveals that, a total of 16 amino acids was recorded in the mushroom species investigated in this study. The mushroom species contained different types of amino acids in varying numbers, ranging from 6 to 15. The mushroom species that contained the least number of amino acids were G. lucidum and the Inonotus sp., which had six amino acids each, while Boletus pruinatus contained the
Discussion
These results clearly indicate the potential of wild mushroom species for their use as sources of essential amino acids. For example, of the 10 mushroom species that were investigated in this study, five were found to contain from 2 to 7 of the eight essential amino acids in different proportions. This is a 25% to 88% occurrence rate of the essential amino acids in the various mushroom species. Thus, the amino acid composition of some of the mushroom species, such as Boletinus cavipes (seven
Acknowledgements
This study was financially supported by Sida/SAREC as part of the research support to the Faculty of Science at the University of Dar es Salaam, which also covered the M.Sc. fellowship of V.A.N. We are very thankful to Sida/SAREC for this support. Contribution to this research within the MIRT/RSA Program that is carried out at the University of Dar es Salaam in collaboration with Hampton University in Virginia, USA, and funded by the US NIH is gratefully acknowledged. We thank Mr. L.B. Mwasumbi
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