Efficacy and safety evaluation of ammonia treatment for reducing aflatoxin levels in corn.

Abstract

The efficacy and safety of ammoniation procedures for reducing aflatoxin hazards in corn were determined by exposing naturally incurred aflatoxin B₁ (AFB₁) contaminated corn (17, 354, and 7,500 ng AFB₁/g) to various ammoniation processes. Treatment with gaseous NH₃ or NH₄OH under appropriate conditions resulted in 93∼99% decrease in AFB₁ levels. No significant reversion of aflatoxin was observed (reversibility < 0.05%). Moisture content in corn and holding temperature were the crucial factors influencing the efficacy of ammoniation. ¹⁴C-AFB₁ spiked corn sample (1 μCi/kg, original AFB₁ = 7500 ng/g) was subjected to sequential isolation and separation procedures (CH₂Cl₂, and CH₃OH extraction, followed by acetic acid and NaOH treatment or Pronase E digestion) to determine the distribution of ammonia/aflatoxin reaction products. Approximately 12% of the added radioactivity was volatilized during ammoniation; 19 and 13% with CH₂Cl₂ and CH₃OH extraction, respectively; and 19% with acid-base treatment or Pronase digestion. The final matrix following either the acid-base treatment or Pronase digestion contained 37% of the added radioactivity. The above isolates were then tested using the Salmonella/microsomal mutagenicity assay (TA100). Purified AFB₁ showed positive response around 10 ng/plate. All isolates from ammonia treated and untreated aflatoxin-contaminated corn did not exhibit positive mutagenic potential. Further study provided the evidence of CH₂Cl₂ extractable "unknown interfering materials" in the corn which may bind with aflatoxin and/or block the mutagenic activity of aflatoxin. These substances were not separated from the aflatoxins by the TLC. Further studies are required using different sequential solvent fractionation processes and different procedures of the Ames test to evaluate this phenomenon. Male F-344 rats were fed diets containing ammonia-treated and untreated aflatoxin-contaminated and aflatoxin-free corn for 14 day period. Terminal liver tissues were analyzed for AFB₁-DNA adducts. No AFB₁-induced DNA adducts were detected in controls and animals fed diets containing 75 ng AFB₁/g and 20 ng AFB₁+ 237 ng ammonia/AFB₁ reaction products. These data confirm the efficacy and permanency of the ammonia process to reduce aflatoxin levels and evidence of safety through absence of AFB$\sb1$-DNA adducts in rat liver.