Evaluation of Small-Scale Extrusion for Aflatoxin Decontamination of Maize in Kenya

2020-07-24T12:43:16Z (GMT) by Margaret Leah Hegwood

Aflatoxins, secondary metabolites produced by the molds Aspergilllus flavus and A. parasiticus, are estimated to affect upwards of 25% of the world’s global food supply. For Low and Middle-Income Countries like Kenya, a combination of trade, economic, and health challenges related to aflatoxin contamination present a serious threat to food and national security. One option for reducing aflatoxin risks in countries like Kenya is deploying small-scale, reprocessing technologies that degrade aflatoxin in contaminated food products. One potential technology for reprocessing is small-scale extrusion (60 pph) like the TechnoChem Mini-Extruder™.

First, to understand the extent of aflatoxin contamination in Kenyan maize, two field work trials were conducted in Uasin Gishu County, Kenya. Aflatoxin levels from each sample were analyzed and compared to a variety of agro-economic variables (e.g. farm size) using a stepwise multiple linear regression. Upon analysis, only 5% of maize samples collected during field work tested positive for unsafe levels of aflatoxin ( >10 ppb). Thus, the resulting regression model is highly biased towards predicting low aflatoxin levels. Such bias makes any inferences to predict high aflatoxin levels in maize largely inconclusive. The inherent heterogeneity of aflatoxin and the history of wide-spread contamination in Kenya further supports the conclusion that more studies are needed to understand the true extent of aflatoxin contamination in Uasin Gishu maize.

Second, to test the effectiveness of small-scale extrusion on aflatoxin degradation in maize, contaminated samples were processed at varying motor frequencies (15, 38, and 50 hz) and moisture contents (35, 40, 45 %wb). Moisture content is significant (p-value < 0.05) in aflatoxin degradation. Total aflatoxin degradation varied between 11 and 83% depending on processing conditions. Maximum degradation occurred at 40 %wb product moisture with a residence time of 265.1 s and an effective shear rate of 56.5 1/s. Thermal degradation is considered negligible due to low temperature increases. Consequently, all degradation is attributed to shear forces inside the extruder. Shear rates were approximated using the Harper model with moisture content and residence time being the most significant factors affecting shear effects on aflatoxin degradation. Although significant aflatoxin degradation occurred in the extruder, further studies are necessary to understand the role of processing parameters on aflatoxin degradation before small-scale extrusion can be confirmed as a viable reprocessing technology.