Use of liquid chromatography-high-resolution mass spectrometry for isolation and characterization of hydrolyzed fumonisins and relevant analysis in maize-based products

Abstract

The synthesis of partially hydrolyzed fumonisins (PHFB1 and PHFB2) and hydrolyzed fumonisins (HFB1 and HFB2) by chemical hydrolysis of pure fumonisins (FB1 and FB2) is reported together with the isolation and characterization by liquid chromatography-high-resolution mass spectrometry (LC-HRMS). Two structural isomers of partially hydrolyzed forms of FB1 and FB2 were identified, namely PHFB(1a) and PHFB(1b) and PHFB(2a) and PHFB(2b). Reaction yields were 21% for PHFB1 (sum of the two isomers), 52% for HFB1, 31% for PHFB2 (sum of the two isomers) and 30% for HFB2. Purity of each isolated compound was >98%. An LC-HRMS method for the simultaneous determination of fumonisins and their partially and totally hydrolyzed derivatives was applied to 24 naturally contaminated samples of maize and maize-based products. The majority of samples (18 out of 24) were contaminated with fumonisins B1 and B2. Fumonisins co-occurred with both partially hydrolyzed and hydrolyzed fumonisins in four nixtamalized samples (three masa flours and one tortilla chips). Co-occurrence of fumonisins with partially hydrolyzed fumonisins was also recorded in one sample of maize kernels and four samples of maize-based products (i.e. maize meal, cous-cous, corn-cakes and cornflakes). Mycotoxins levels ranged from 60 to 5700 µg/kg for fumonisins (sum of FB1 and FB2), from 10 to 210 µg/kg for partially hydrolyzed fumonisins (sum of PHFB1 and PHFB2) and from 30 to 200 µg/kg for hydrolyzed fumonisins (sum of HFB1 and HFB2). This is the first report of the isolation of PHFB2 and the co-occurrence of FB1, FB2, PHFB1, PHFB2, HFB1 and HFB2 in maize products. Considering the growing use of nixtamalized and maize-based products, the monitoring of fumonisins and their partially and totally hydrolyzed forms in these products may represent an important contributing factor in evaluating the relevant human risk exposure.

Keywords: (partially) hydrolyzed fumonisins; fumonisins; high-resolution mass spectrometry; maize; maize products.