Immunological detection of molds, including mycotoxin producers, in foods

Ruth K Yong, Purdue University

Abstract

The enzyme-linked immunosorbent assay (ELISA) was developed to detect aflatoxin and other mycotoxin-producing molds, and a combination of spoilage molds (Aspergillus versicolor, Cladosporium herbarum, Fusarium poae, Geotrichum candidum, Mucor circinelloides, and Penicillium chrysogenum). The assays had sensitivities of 0.1 $\mu$g/mL for A. parasiticus, 0.5 $\mu$g/mL for F. moniliforme, and 0.1 $\mu$g/mL for the six molds. The A. parasiticus antibody detected A. parasiticus and phenotypically similar A. flavus, A. oryzae, and A. soyae. The F. moniliforme antibody detected all Fusarium species tested, and two Monascus species. The cocktail antibody recognized all six mold genera plus eight others. No yeasts were detected. Low and high levels of aflatoxin corresponded with low and high ELISA readings for naturally contaminated corn; however ELISA and mycotoxin levels did not correspond to viable counts. When mold antigens were added to corn and other foods, A. parasiticus was detected at 0.1 $\mu$g/mL; F. moniliforme was detected at 0.5 $\mu$g/mL; and the six molds were detected at 0.5 $\mu$g/mL. When 10$\sp2$ spores/mL of A. parasiticus were inoculated into corn, they were detected by days 10 and 4 at 15 and 21$\sp\circ$C when less than 1.5 ppb and 1 ppb of aflatoxin were present, respectively. When peanuts were inoculated with 10$\sp2$ spores/mL of A. parasiticus, mold antigens were detected by days 4 and 2 at 15 and 21$\sp\circ$C, respectively, but no aflatoxins were present. When corn samples were inoculated with 10$\sp2$ spores/mL of F. moniliforme, mold antigens were detected by day 2 at 21$\sp\circ$C when 0.6 ppm levels of fumonisin was detected. In a survey of commercial food products, the mixed antibody detected mold antigens in 45 of 49 retail food products; 25 of the 49 retail products contained low levels of A. flavus/parasiticus antigens; and 32 of the 49 retail products were positive for Fusarium antigens but fungal counts ranged from $<$10 (est.) to 10$\sp3$ cfu/g, $<$10 (est.) to 10$\sp2$ cfu/g (est.) and $<$10 (est.) to 10 cfu/g, respectively. Mold counts did not correspond with ELISA because it detected both viable and nonviable cells. When extracellular and mycelial antigens were partially purified and characterized, they contained carbohydrate and protein, which after protease addition, showed significantly reduced ELISA activity. Galactosyl residues and $\beta$ linkages were immunodominant for A. parasiticus.

Degree

Ph.D.

Advisors

Cousin, Purdue University.

Subject Area

Food science

COinS