Susceptibility of steeped and heat dried cowpea flour to fungal growth and aflatoxins production

Abstract

In vitro studies were carried out to determine the susceptibility of flours from steeped and heat dried cowpea to fungal growth and aflatoxins production. A 2 × 7 factorial experimental design with 2 levels of steeping time of cowpea grain in water (0 and 3 min steeping) and 7 levels of drying temperatures of the grains ranging from 35 to 120°C were used for flour production. Processed flours were used to prepare solid Cowpea Flours Agar media (CFA). Aflatoxigenic strain (Aspergillus flavus) was inoculated to these media and incubated at 30°C for 7 days. Yeast Extract Sucrose (YES) was used as control. Radial growth of colonies formed was measured and aflatoxins production was determined using High Performance Liquid Chromatography (HPLC). After incubation period, maximal growth of A. flavus colonies was observed in all CFA. The aflatoxin levels detected in CFA prepared with flour dried at 35 to 50°C ranged from 4.40 to 29.63 µg toxin /kg flour, while higher levels ranging from 27.45 to 75.00 µg toxin /kg flour were detected in CFA prepared with flours dried at 60 to120°C. The effect of steeping cowpea in water on aflatoxin production was dependent on drying temperatures. The average aflatoxin levels in CFA flours obtained from non steeped and steeped grains were 11.16 and 16.14 µg toxin /kg flour respectively and were statistically similar at P= 0.05 at 35 to 50°C drying temperatures. It was concluded that drying steeped or non steeped cowpea at temperatures less than 60oC exposes cowpea flour to minimal risk of aflatoxin contamination. Key words: Cowpeas flour, aflatoxins, drying temperature.