Comparison of methods and optimisation of the analysis of fumonisins B1 and B2 in masa flour, an alkaline cooked corn product

A comparison study of different extraction and clean-up procedures for the liquid chromatographic analysis of fumonisins B1 (FB1) and B2 (FB2) in corn masa flour was performed. The procedures included extraction (heat or room temperature) with acidic conditions or EDTA-containing solvents, and clean-up by immunoaffinity or C18 solid-phase extraction columns. Thereafter an analytical method was optimised using extraction with an acidic mixture of methanol-acetonitrile-citrate/phosphate buffer, clean-up through the immunoaffinity column and determination of fumonisins by liquid chromatography with automated pre-column derivatisation with o-phthaldialdehyde reagent. Recovery experiments performed on yellow, white and blue masa flours at spiking levels of 400, 800 and 1200 mu g kg-1 FB1 and of 100, 200 and 300 mu g kg-1 FB2 gave overall mean recoveries of 99% (+/- 6%) for FB1 and 88% (+/- 6%) for FB2. Good recoveries (higher than 90% for both FB1 and FB2) were also obtained with corn tortilla chips. The limits of quantification of the method (signal-to-noise ratio of 10) were 25 mu g kg-1 for FB1 and 17 mu g kg-1 for FB2. The method was tested on different commercial corn masa flours as well as on white and yellow corn tortilla chips, showing fumonisin contamination levels (FB1 + FB2) up to 1800 mu g kg-1 (FB1 + FB2) in masa flour and 960 mu g kg-1 in tortilla chips. Over 30% of masa flours originating from Mexico exceeded the European Union maximum permitted level.