Decontaminate aflatoxin in peanut meal using extrusion cooking.

As you know, aflatoxin is a naturally occurring mycotoxin produced by two types of mold: Aspergillus flavus and Aspergillus parasiticus. Aspergillus flavus is common and is most often found when certain grains are grown under stressful conditions such as drought. The mold occurs in soil, decaying vegetation, hay and grains undergoing microbiological deterioration. It invades organic substrates when the conditions are favorable for its growth. Favorable conditions include high moisture content and high temperatures. At least 13 different types of aflatoxin are produced in nature. Aflatoxin B1 is considered among the most toxic.

The presence of Aspergillus flavus does not always indicate harmful levels of aflatoxin. But it does mean that the potential for aflatoxin production is present. Aflatoxins in peanuts are not easily destroyed under normal processing conditions. But scientists at the University of Georgia were able to destroy somewhat more than 60% of the toxin in artificially contaminated peanut meal after considering protein-bound species. The apparent destruction was up to 90%. While this was not as dramatic as they would have liked, it did show promise. Investigators are continuing to study various aspects of the process, including scaling it up to a larger extruder that may give them longer residence times and more vigorous conditions.

The role of lysine and other nucleophiles was complex, depending on pH and other processing conditions. Generally pH had a greater role than added nucleophile. Scientists certainly could not claim this process is ready for industrial adoption yet. They must wait for additional findings to decide if it is going to be sufficiently effective for further consideration.

The scientists used extrusion cooking to decontaminate aflatoxins in peanut meal by mediating starch as a plasticizer and using lysine as a nucleophile. Researchers experimented with cornstarch (0%, 25%, 50%), nucleophiles (none, methylamine, lysine) and feed moisture (20%, 30%, 40%). Partially defatted peanut meal was autoclaved. Then it was mixed with cornstarch in the ratios specified by an experimental design.

All treatments were adjusted to pH 8 and extruded. A commercial extruder was equipped with a 5-mm circular die and a screw with a 1:5 compression ratio. Researchers ran the extruder at a constant screw speed of 135 rpm and set temperatures of 150 C at zones two and three in the system. The scientists monitored certain extrusion process parameters including throughput, torque and extrudate moisture content.

Aflatoxin levels were measured before and after extrusion. The scientists determined aflatoxin degradation, and they correlated this information with the extrusion process parameters. Cornstarch had a significant effect on the degradation of aflatoxin B1, particularly at lower moisture levels.

On the other hand, the presence of nucleophiles did not have a similar effect. At 40% moisture, however, the percent of degraded aflatoxin B1 was significantly affected by the presence of nucleophiles. The presence of lysine at high moisture levels showed a relatively high level of degradation. This points to a promising direction in detoxification efforts.

Further information. F.K. Saalia; University of Georgia Department of Food Science and Technology, Griffin, GA 30223; phone: [phone]; email: [e-mail].