Effect of initial moisture content and relative humidity on the accumulation of aflatoxin in maize grains (Zea Mays) during storage

Abstract

Maize grains conditioned to an initial moisture content of 10.5% and 13.5% were inoculated with a known quantity (50:50) of standard cultures of Aspergillus flavus (ATCC 15517) and Aspergillus parasiticus (ATCC 28285). The effects of initial moisture content and of varying relative humidities on the accumulation of aflatoxin in intact and damaged maize grains were studied over a period of four weeks during storage. The growth of the organism and accumulation of aflatoxins were quantified by the spread plate method and HPLC techniques respectively. Results showed that grains conditioned to a moisture level of 10.5% contained no fungal growth at 70% RH, in both intact and damaged grains, which had equilibrated at a moisture level of 11.3%. However, grains conditioned to a moisture level of 13.5% and stored at 70% RH showed a growth of 3 CFU/10g both in intact and damaged grains, at the end of the first week. The accumulation of aflatoxin B1 was higher in damaged grains than in intact ones (34.0 > 12.0 ng/g). Grains conditioned to a moisture level of 10.5%, when stored at 80% RH, showed a fungal growth of 3 and 4 CFU/10g and aflatoxin B1 levels of 55 and 160 ng/g for intact and damaged ones, respectively. Grains stored at 90% RH, showed no significant difference in the accumulation of aflatoxin B1 at the end of second week in both intact (50 ng/g) and damaged (60.0 ng/g) gains at p=0.05. These results suggest that maize grains dried to moisture levels lower than 11% (on wet weight basis) can be stored for longer periods of time under local environmental conditions (25±3°C,70-75%RH) devoid of fungal growth and accumulation of aflatoxin.