Behaviour of Aspergillus flavus in Bambara groundnut (Vigna subterranea (L.) Verdc) as affected by milling, fermentation or roasting during storage

Abstract

Fungal contamination and mycotoxin accumulation in agricultural products are influenced markedly by processing and storage conditions. This study aimed at determining the growth of Aspergillus flavus and aflatoxin production in Bambara groundnut flour processed by milling, lactic acid bacteria (Lactobacillus plantarum) fermentation or roasting at 140 °C for 20 min and stored for up to 10 weeks at 25 ± 2 °C and 75 ± 2% relative humidity. It also studied the behaviour of A. flavus in maize-bambara composite flour. Processed and irradiated flour samples were inoculated with 2 × 10⁷ spores/ml of A. flavus and stored. Samples were withdrawn weekly and analyzed for viable populations of A. flavus, concentrations of AFB₁, AFB₂, AFG₁ and AFG₂ using HPLC-Fluorescence detection method, and changes in water activity values. The population of A. flavus significantly (p ≤ 0.05) decreased in roasted Bambara groundnut flour from 7.18 to 2.00 Log₁₀ CFU/g over the storage period, and in fermented Bambara groundnut flour from 6.72 to 2.67 Log₁₀ CFU/g after 7 weeks of storage and beyond was not detected. Significant (p ≤ 0.05) decrease in the concentration of AFB₁ from 0.36 to 0.26 μg/kg and AFG₁ from 0.15 to 0.07 μg/kg was also recorded in roasted Bambara groundnut flour over the storage period. Conversely, AFB₁ concentration in the composite flour significantly (p ≤ 0.05) increased from 1.17 to 2.05 μg/kg over the storage period. Lactic acid bacteria fermentation, roasting and compositing markedly influenced the growth of A. flavus and aflatoxin production in Bambara groundnut and maize flours during storage.

Keywords: Aflatoxins; Bambara groundnut; HPLC; Lactobacillus plantarum; Maize.