Detecting Aspergillus parasiticus in cereals by an enzyme-linked immunosorbent assay

An enzyme-linked immunosorbent assay (ELISA) was used for the specific detection of Aspergillus parasiticus molds in artificially contaminated corn, rice, wheat and peanut, and also to detect naturally occurring aflatoxigenic molds in the same form cereals. After inoculation of Aspergillus parasiticus in the cereals, the growth of A. parasiticus was monitored by both plate count and ELISA, and the aflatoxin content was measured. Water activity (a_w) affected the fungal growth, aflatoxin production and degradation. The higher a_w level (a_w=0.98 vs. a_w=0.92) resulted in higher fungal growth rates and fungal masses in corn, rice and wheat, and the plate count and ELISA measurements were better correlated, with correlation coefficients of 0.94, 0.93, 0.96 and 0.86, respectively for corn, rice, wheat, and peanuts. Aflatoxin was also both produced sooner and degraded more rapidly at a_w=0.98. Although standard plate counting techniques detected A. parasiticus/A. flavus in 5 out of the 40 cereal samples bought from retail stores, ELISA did not give a positive result in any of them. After moisturization and incubation of these commercial samples at 28°C for 29 days, the incident rates of aflatoxigenic molds increased to 65% and 52% by plate count and ELISA, respectively.