Mycotoxin levels in subsistence farming systems in South Africa

[摘要] ENGLISH ABSTRACT: Fusarium spp. and Aspergillus spp. are toxin-producing fungi associated with maize andgroundnut. Fusarium verticillioides produces fumonisins in maize, and Aspergillus flavusproduces aflatoxins in maize and groundnut kernels. Both toxins are responsible forcarcinogenesis in humans and animals. Contamination of maize and groundnut withmycotoxins is often most severe in rural areas where subsistence farmers are unaware of theirexistence and follow agricultural practices that might contribute to their production. Aquestionnaire was, therefore, compiled to investigate agricultural decisions in rural areas thatmay influence mycotoxin contamination of crops. During 2006 and 2007, maize andgroundnut samples were collected in the Eastern Cape, KwaZulu-Natal (KZN), Limpopo, andMpumalanga provinces. Mycotoxin levels were quantified using the ELISA technique, andthe incidence of Fusarium spp. in maize grain was determined by plating maize kernels out onFusarium selective medium. Fumonisin-producing Fusarium spp. were also quantified usingreal-time PCR (TaqMan). The incidence of A. flavus and A. parasiticus in groundnut wasdetermined by plating out kernels on potato dextrose agar. Fumonisin contamination levels inmaize samples ranged from 0-21.8 parts per million (ppm) and aflatoxin levels ranged from 0-49 parts per billion (ppb), depending on the region where samples were collected. Aflatoxinlevels in groundnut ranged from 0-160.1 ppb. Fusarium verticillioides was the most commonFusarium sp. in maize followed by F. subglutinans and F. proliferatum, respectively.Regression analyses showed a positive correlation between fumonisin-producing Fusariumspecies when determined by real-time PCR and fumonisin concentration (r2=0.866).Regression analyses further showed a highly significant positive correlation between A. flavusand aflatoxin contamination (r2=0.10235). Samples from northern KZN contained levels ofmycotoxins that were far in excess of the maximum levels set by the Food and DrugAdministration in the USA. In South Africa there are currently no regulations with regard tothe maximum allowable levels of fumonisin in human food. The high incidence of mycotoxincontamination of human food in subsistence farming systems indicates the need for awarenessprogrammes and further research.

[发布机构] Stellenbosch University