Efficacy and permanency of ammonia treatment in reducing aflatoxin levels in corn

Naturally contaminated yellow corn containing 12500 ng/g of aflatoxin B1 (AFB1) was ground and blended with non-contaminated corn to obtain various levels of AFB1 (7500, 6300, 400, 354, and 17 ng AFB1/g). All samples were exposed to ammonia treatment under various conditions for 60 min. Treatment variables included ammonia concentration, moisture level of the corn, temperature, and pressure applied. The moisture content of the corn (8%) was adjusted to 12% and 16%, respectively. Four ammonia treatments were conducted for each moisture level: (a) 1.5% and 2.0% gaseous NH3 at 40-45 degrees C and 55 psi; (b) aqueous NH4OH (2.0% as NH3) at 121 degrees C and 17 psi; (c) sequential treatment of (a) and (b); and (d) aqueous NH4OH (2.0% as NH3) at 25 degrees C and 55 psi. For the treatment with 2% gaseous NH3, the reduction in levels of AFB1 in samples containing 12% moisture ranged from 52.7 to 67.7%, while in samples containing 16% moisture, the reduction ranged from 79.4 to 93.1%. Treatment with NH4OH alone at elevated temperatures (b) or following gaseous NH3 treatment (c) resulted in a reduction of the AFB1 content by greater than 99%. Treatment with NH4OH at 25 degrees C (d) showed a lower efficiency in reducing AFB1 levels. The permanency of the process, i.e. reversion of inactivated AFB1 to the parent compound, was studied by exposing the ammonia-treated corn to HCl (pH = 2.0 at 37 degrees C for 2 h) to simulate stomach acidity. The results showed no significant reversion of aflatoxin (reversibility less than 0.05%). These findings suggest that at high temperature aqueous NH4OH or gaseous NH3 can be used effectively to reduce AFB1 in corn. The present study also revealed that the moisture level of the product and holding temperature were the crucial factors that influenced the efficacy of aflatoxin decontamination by ammoniation.