Science Snippets!

Extrusion-cooking is often used to process raw grain/meal into an array of different products. In the extrusion process, grain or meal are exposed to high temperatures, high pressure, and shearing forces. Mycotoxins are known potent toxins and can be detrimental to human and animal health. The level of mycotoxin contamination in cereal grain and other crops depends on infection rate and the local environment.

Aflatoxin (AF) is a family of mycotoxins and can be found in cereal crops. Aflatoxin consists of several classes: AFB1, AFB2, AFG1, and AFG2. Castells et al. (2006) designed an interesting study to see how extrusion-cooking would affect artificially contaminated rice meal. The authors were particularly interested in how the initial moisture content of the rice meal sample, the extrusion temperature, and the length of extrusion time would affect the AF content in rice meal samples. Rice meal samples were at 24, 27, or 30% moisture content. The samples were either exposed to 140, 170, or 200°C for 30, 40, 50, 60, or 70 seconds. The authors analyzed the resulting extruded meal on AFB1, AFB2, AFG1, and AFG2 by HPLC (high pressure liquid chromatography) against known AF standards.

Castells et al. (2006) found that, in general, an increase in time in the extrusion vessel and temperature resulted in a decrease in AF. Aflatoxin content was reduced from 51% to 95% due to the extrusion-cooking process. A processing time of between 50 and 60 seconds yielded the greatest reduction in aflatoxin.

The most optimum temperature was 170°C; AFB1 and AFB2 were surprisingly more reduced at 170°C than at 200°C. There was no difference in the reduction of AFG1 at 170 or 200°C. The lowest reductions in aflatoxin content were at 140°C, the lowest temperature used in this study. Castells et al. (2006) also found that the starting moisture content of the grain was important in reducing AFB2, AFG1, and AFG2. The higher starting moisture content (e.g. 27%) resulted in higher AF reduction; the authors believe this to be due to better heat transfer with higher moisture content. However, the starting moisture content did not affect AFB1 reduction.

We can conclude from this study that aflatoxin content can effectively be reduced by extrusion-cooking. This study showed that cooking rice meal at 170°C for 50 to 60 seconds yielded the greatest reduction in aflatoxin. However, some experimentation might be warranted for individual plant settings.

Reference:

Castells, M., S. Marín, C. Sanchis, and A. J. Ramos. 2006. Reduction of aflatoxins by extrusion-cooking of rice meal. J. Food Science. 71:C369-C377.