Determination of hydrolysed fumonisin B1 in alkali-processed corn foods.

Abstract

Treatment of fumonisin B1 (FB1)-contaminated corn with calcium hydroxide solution is known to cause large losses of FB1 and formation of the aminopentol AP1 by hydrolysis. Methodology was developed for determination of AP1 in foods manufactured from calcium hydroxide-processed corn. The ground food (tortilla chips, nacho chips, taco shells, or air-dried corn tortillas) was extracted with methanol-water (8:2) or methanol-acetonitrile-water (25:25:50), which also extracted FB1 and fumonisin B2 (FB2). Clean-up for fumonisin determination was carried out on a 1 ml strong anion exchange (SAX) solid phase extraction (SPE) column. The water wash from this column, containing AP1, was cleaned up on a 1 ml C-18 SPE column. AP1 and, separately, FB1 and FB2 were determined as their o-phthaldialdehyde-mercaptoethanol (OPA/MCE) and, in some cases, 4-fluoro-7-nitrobenzofurazan (NBD-F) derivatives by gradient reverse phase liquid chromatography with fluorescence detection. Recoveries of AP1, FB1 and FB2 from spiked samples were generally satisfactory, but FB1 and FB2 recoveries were low with some samples. Better recovery of FB1 with the methanol-acetonitrile-water (25:25:50) extraction solvent compared with methanol-water (8:2) was observed for naturally-contaminated samples. Detection limits were about 10 ng AP1 per g and 20 ng FB1 and FB2 per g with OPA/MCE derivatization, but there were interferences for FB2. Analysis of 31 samples of alkali-processed corn foods (including three known already to contain FB1) showed measurable levels of AP1 in nine samples, all < 100 ng/g and lower than the corresponding FB1 concentrations.