Development of a powder formulation of Aspergillus parasiticus for dry inoculation of peanut kernels

摘要

The aim of this study was to develop a method for the dry inoculation of Aspergillus parasiticus on peanut kernels for post-harvest studies. Inoculum powder was prepared by adding sterile kaolin powder to A. parasiticus spores developed on filter papers soaked with spore suspension prepared with Czapek medium (5% agar), which were dried at room temperature. Concentrations were adjusted to 5 x 10(5) and 1 x 10(6) spores g-1 of kaolin. Varied amounts of the powder inoculum were then used to inoculate 1 kg of peanut kernels. Inoculation was performed by mixing the powder inoculum with the peanut kernels in plastic bags until the kernels were completely covered. The effectiveness of this inoculation method was compared with the common inoculation methods of immersion in aqueous spore suspensions and contamination through contact with fungal colonies growing on culture medium. Fungal growth assay was performed on PDA saline medium, and near-infrared radiation measurements were used to determine peanut kernel moisture content. The dry inoculation technique was effective in inoculating peanut kernels with A. parasiticus, especially at concentrations of 3 x 10(6) and 4 x 10(6) spores g-1 per 1 kg of peanut kernels. In contrast to usual methods of inoculation, the dry inoculation technique does not increase the moisture content of inoculated peanut kernels. Thus, the physical state of the peanut kernel remains intact.