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

Abstract

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 µg kg⁻¹ FB₁ and of 100, 200 and 300 µg 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 µg kg⁻¹ for FB₁ and 17 µg 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 µg kg⁻¹ (FB₁ + FB₂) in masa flour and 960 µg kg⁻¹ in tortilla chips. Over 30% of masa flours originating from Mexico exceeded the European Union maximum permitted level.

Keywords:

• high-performance liquid chromatography
• clean-up – affinity columns
• fumonisins
• cereals

Acknowledgements

This work was supported by EC KBBE-2007-222690-2 MYCORED. Dr W.P. Reyes-Velázquez, Universidad de Guadalajara (UDG), Jalisco, México, is acknowledged for providing masa flour samples from Mexico. The valuable technical assistance of Roberto Schena is also acknowledged.