Production and quality control of maize with a low aflatoxin content during the rainy season in Thailand

Previous studies conducted by the Department of Agriculture in Thailand strongly indicate that aflatoxin contamination of maize was primarily a post-harvest problem in the major rainy season crop. In Phase 1 of the UK-Thai Project, carried out in 1984, it was decided to test the effectiveness of introducing mechanical drying into the existing maize marketing chain at "local merchant" and "regional merchant" levels. It was found that although drying systems that completed drying to 14% moisture content within 48 hours could prevent further aflatoxin contamination, they could not produce maize with a low aflatoxin content. The reason for this was provided by the control survey, based on samples collected from the marketing chain, which showed that the aflatoxin content of freshly shelled maize at the local merchants averaged 45 ppb while maize at the regional merchants averaged over 100 ppb. The lowest aflatoxin content was found in maize entering farmers'stores, which had a post-harvest history of about one week and averaged only 21 ppb in aflatoxin content. Phase 2 of the project, carried out in 1985, used only freshly harvested, freshly shelled maize in 35 drying trials conducted in two provinces. The trials were on a 3-tonne scale using a reverse-flow, single stage batch system. These trials successfully produced maize averaging only 5 ppb in aflatoxin content which is much lower (P0.01) than the controls which averaged 75 ppb at the local merchants and over 100 ppb at the regional merchants. Twenty of the trials dried maize to 14% moisture content, no part exceeding 15%, and this maize was successfully stored for two months with no increase in aflatoxin content. Fifteen batches were partially dried to 16% moisture content, no part exceeding 16.5%, and these were stored for one week with only a marginal increase in aflatoxin content.