Selenium and Aflatoxins in Brazil Nuts

Abstract

Brazil nuts (Bertholletia excelsa H.B.K.) are considered a high nutritious food. Apart from carbohydrates, lipids, sulphur proteins and minerals, Brazil nuts are known to be rich in selenium Se (Barclay et al., 1995; Coutinho et al., 2002, Souza et al., 2004, Pacheco and Scussel, 2007). Despite of that, when their shell are cracked either when pods fall on the ground, or during pod opening for nut extraction (done by an axe) and exposed to high moisture and temperature of the tropical forest, fungi may grow, leading to nut spoilage. If fungi are toxigenic they may produce aflatoxins (AFLs). Se has been reported to be an antioxidant and studies have reported differences on its levels in Brazil nuts from the two Amazon regions being the Eastern nuts richer in Se than the Westerns (Chang et al., 1995; Pacheco and Scussel, 2007). Its content may vary when grown in different soils of the Amazon basin. The aflatoxigenic Aspergillus species of A. flavus and parasiticus are intimately related to agricultural crops, including tree nuts and their growth are influenced by environmental conditions. Although Brazil nuts have tested positive for A. flavus, less is known about its populations on Brazil nuts, how they grow and vary among the two Amazon regions, in the different stages of nut collection prior reaching the factory and how the processing affect them (Castrillon and Purchio, 1988; Freire et al., 2000; Candlish et al, 2001, Caldas et al., 2002). However, AFLs have been reported contaminating Brazil nuts. Their pods are harvested after they fall onto the forest soil. They stay directly in contact with the soil for several days or weeks prior to collection. It is during that time that pods may get contaminated with Aspergillus sp. and so with AFLs. Post harvesting operations are expected to have major influence on further contamination of the nuts (Bayman, 2002; Campos/Pas, 2004). For fungi growth and for their normal maintenance, a number of metals are required in different amounts. Many microorganisms are known to be able to use Se (i.e., selenite, selenate of other forms) in their metabolism (Roux et al., 2001; Fleet-Stalder et al., 2000). Se has been added to the media as sodium selenite (Na2SeO3), to understand its effect in different concentrations on fungi behaviour. The inhibitory action of Se on the growth rate of various fungi such as Aspergillus, Penicillum and Fusarium was reported by several authors (Ramadan et al., 1983, Ragab, et al., 1986, Zohri et al., 1997, Li et al, 2003). When it was used in Czapek Dox agar medium to evaluate the A. parasiticus behavior concerning morphological growth and toxin production, it was observed that fungus growth decreased by the increasing of the Se concentration (Zohri et al., 1997). In an