ENZYME-LINKED-IMMUNOSORBENT-ASSAY OF TOTAL AFLATOXIN-BU, AFLATOXIN-B2, AND AFLATOXIN-G1 IN CORN - FOLLOW-UP COLLABORATIVE STUDY

A direct competitive enzyme-linked immunosorbent assay screening metho d for aflatoxins at 20 ng/g in corn was studied by 15 collaborating la boratories. Test samples of corn were extracted by blending with metha nol-water (8 + 2). The extracts were filtered and the filtrates were d iluted with buffer to a final methanol concentration of <30%. Each dil uted filtrate was applied to a test device containing a filter with im mobilized polyclonal antibodies specific to aflatoxins B1, B2, and G1. Aflatoxin B1-peroxidase conjugate was added, the test device was wash ed with water, and a mixture of hydrogen peroxide and tetramethylbenzi dine was added. A test sample was judged to contain greater-than-or-eq ual-to 20 ng aflatoxins/g when, after exactly 1 min, no color was obse rved on the filter; if a blue or gray color developed, the test sample was judged to contain <20 ng aflatoxins/g. All laboratories correctly identified naturally contaminated com test samples. Only one false po sitive was found for controls containing no aflatoxins. The correct re sponses for positive test samples spiked at levels of 10, 20, and 30 n g aflatoxins/g (the ratio of B1:B2:G1 was 15:1:3) were 67, 97, and 100 %, respectively. This method was adopted first action by AOAC INTERNAT IONAL as a change in method for 990.34 for screening for aflatoxins B1 , B2, and G1 in corn at total aflatoxin concentrations of greater-than -or-equal-to 20 ng/g.