Extrusion cooking may lower aflatoxins in peanuts

By Nathan Gray

- Last updated on GMT

Related tags Aflatoxin

Levels of aflatoxins in peanut meal may be reduced by up to 84 per cent, using an extrusion cooking process, according to new research.

The study, published in LWT - Food Science and Technology,​ explored the feasibility of degrading aflatoxins in contaminated peanut meal by extruding in the presence of calcium chloride with lysine and methylamine.

The researchers, led by Firibu Saalia from the University of Ghana, found that lysine “showed comparable efficacy with methylamine in mediating aflatoxin reduction during extrusion cooking.”

Aflatoxins are naturally occurring toxins that are known to contaminate corn, peanuts and other food crops including nuts. They are known to be toxic to humans and are among the most carcinogenic substances known.

High-level aflatoxin exposure produces an acute hepatic necrosis and can lead to liver cancer. However, humans have an a very high tolerance to aflatoxin exposure and rarely suffer acute aflatoxicosis.

Despite a high tolerance, it is seen as important to reduce aflatoxin levels in foods. Several methods have been suggested to reduce the risk of exposure to the toxin through contaminated food. Saalia and colleagues explained that a chemical method is “particularly attractive because of their rapid execution.”

Previous studies have shown the most effective chemical agents for the degradation of aflatoxins to be nitrogen bases – especially ammonia and methylamine.

However, the authors noted that the efficacies of such reagents in reducing aflatoxins depend on treatment variables, such as temperature, time, and moisture.

Treatments that provide high temperatures and pressures similar to or higher than autoclaving (as in extrusion cooking) have shown some promising results. Research has shown that the aflatoxin B1 may be reduced by over 97 per cent in peanut cake by mixing with a combination of methylamine and calcium hydroxide and extruding, whilst with ammonium hydroxide has also shown good success in reducing aflatoxins.

“It is hypothesized that extrusion cooking of contaminated peanut meal in the presence of lysine might have the potential to reduce aflatoxin levels, similar to that reported for methylamine and ammonium hydroxide,”​ said the authors.

A previous preliminary study found lysine and methylamine to show comparable efficacies in degrading aflatoxins in aqueous phosphate buffers. However in the presence of a food matrix, aflatoxins may bind to the macromolecules and be protected from structural degradation during processing.

Study details

The researchers determined the efficacies of methylamine and lysine, the role of pH, and the influence of calcium chloride, on aflatoxin degradation in partially defatted roasted peanut meal during extrusion.

The authors reported that feed moisture, pH, and temperature of the extruder barrel were the most influential variables in reducing aflatoxins.

They added that extrusion of moistened peanut meal at pH 7.5 (without an added nucleophile) resulted in over a 60 per cent reduction in aflatoxins.

Saalia and co-workers found increasing the pH to 9.5, in addition to nucleophiles (lysine, methylamine) improved reduction in aflatoxins.

Under these conditions, extrusion cooking reduced aflatoxins in the peanut meal by 84 per cent (from an initial 417.72 micrograms per kg to 66.87 micrograms per kg).

The authors added that the binding of aflatoxins to the molecules in the peanut meal, and their subsequent protection from destruction during extrusion cooking may be reduced via the addition of calcium chloride.

Source: LWT - Food Science and Technology
Published online ahead of print, doi: 10.1016/j.lwt.2011.02.012
“Reduction of aflatoxins in peanut meal by extrusion cooking in the presence of nucleophiles”
Authors: F.K. Saalia, R.D. Phillips

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