Microwave drying and disinfestation of Brazil nut seeds

• Contamination of Brazil nut seeds by aflatoxin-producing fungal strains was investigated.
• Aflatoxigenic potential was found for 40% of the strains from inside of the seed coat.
• Dielectric properties of the Brazil nut shell and the kernel were studied.
• Microwave heating reduces both the water activity and moisture content of the seeds.
• Microwave dielectric heating is a disinfestation process for contaminated nuts.

Fungal contamination of Brazil nuts can cause health problems, which limits their worldwide consumption and leads to economic restrictions for the producing regions. In this study the contamination of Brazil nut seeds by aflatoxin-producing fungal strains was investigated. It was observed that of the 31 strains isolated from the inside of the seed coat, 39% showed aflatoxigenic potential, indicating a high level of contamination by microorganisms which produce aflatoxins, which have strong carcinogenic and hepatotoxic activity. The moisture content and water activity are determining factors for fungal growth. Measurements of the dielectric properties at microwave frequencies of the Brazil nut shell and the kernel reveals that the shell has a higher loss tangent (0.12) at 30 °C relative to the kernel (0.06) and high values for the penetration depth of both shell (20 cm) and kernel (35 cm) that are related to their chemical composition. Microwave heating was employed leading to reductions in the moisture content (46.4%) and water activity (20%). Furthermore, the effectiveness of microwave dielectric heating as a disinfestation process for contaminated nuts was investigated, showing that colonization inside the shell decreased by 61.67% and on the kernel by 81.75%, without damaging the organoleptic properties of the Brazil nut seeds.