Analysis of heat-processed corn foods for fumonisins and bound fumonisins

Abstract

Thirty retail samples of heat-processed corn foods, i.e. corn flakes, corn-based breakfast cereals, tortilla chips and corn chips, were analysed for fumonisins — fumonisin B1 (FB1), fumonisin B2 (FB2) and hydrolysed FB1 (HFB1) — as well as for protein- and total-bound FB1. Bound (hidden) fumonisins cannot be detected by conventional analysis. Improved methods for the determination of bound FB1 were developed. The protein-bound FB1 was extracted with 1% sodium dodecylsulfate (SDS) solution. The SDS, which interfered with high-performance liquid chromatography (HPLC) analysis, was then separated from protein-bound FB1 by complexing with methylene blue followed by solvent extraction and hydrolysis with 2 N KOH. To measure total-bound FB1, the sample itself was hydrolysed with KOH. In both cases, clean-up was accomplished on an OASIS polymeric solid-phase extraction column and the bound fumonisins were determined by HPLC measurement of HFB1. Fourteen of 15 samples of corn flakes and other corn-based breakfast cereals analysed contained detectable levels of FB1 with a mean in positive samples of 67 ng g−1 (13–237 ng g−1). Two samples also had detectable levels of FB2 (21–23 ng g−1). Bound FB1 was found in all samples; the mean protein-bound FB1 measured was 58 ng g−1 (22–176 ng g−1) and the mean total-bound FB1 measured was 106 ng g−1 (28–418 ng g−1), reported as FB1 equivalents after correction for recoveries of HFB1. There was an average of about 1.3 times more FB1 in the bound form compared with extractable FB1, and this was about twice as much as protein-bound FB1. Seven of the 15 samples of alkali-processed corn-based foods, such as tortilla chips and corn chips, contained FB1 and three contained HFB1 with means in measurable positive samples of 78 (48–134) and 29 (13–47) ng g−1, respectively. Five of these alkali-processed corn foods contained bound FB1; the mean measurable protein-bound FB1 was 42 ng g−1 (39–46 ng g−1) and the mean measurable total-bound FB1 was 100 ng g−1(54–209 ng g−1). HFB1 derived from bound FB1 in selected samples was confirmed by HPLC with mass spectrometry (MS).