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 FB_1. 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).

Keywords:

• protein-bound fumonisin
• total-bound fumonisin
• hydrolysed fumonisin
• breakfast cereals
• tortilla chips
• corn chips
• liquid chromatography

Acknowledgements

Work was conducted under the Agricultural Policy Framework. The authors are grateful to R. M. Eppley, US Food and Drug Administration, for HFB₁. They thank the Natural Sciences and Engineering Research Council of Canada (NSERC) for a visiting fellowship (J. W. Park).