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

摘要

The synthesis of partially hydrolyzed fumonisins (PHFB_1 and PHFB_2) and hydrolyzed fumonisins (HFB_1 and HFB_2) by chemical hydrolysis of pure fumonisins (FB_1 and FB_2) 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 FB_1 and FB_2 were identified, namely PHFB_(1a) and PHFB_1b and PHFB_2a and PHFB_2b. Reaction yields were 21% for PHFB_1 (sum of the two isomers), 52% for HFB_1, 31% for PHFB_2 (sum of the two isomers) and 30% for HFB_2. 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 B_1 and B_2. 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 ofmaize kernels and four samples ofmaize-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 FB_1 and FB_2), from 10 to 210 μg/kg for partially hydrolyzed fumonisins (sum of PHFB_1 and PHFB_2) and from 30 to 200 μg/kg for hydrolyzed fumonisins (sum of HFB_1 and HFB_2). This is the first report of the isolation of PHFB_2 and the co-occurrence of FB_1, FB_2, PHFB_1, PHFB_2, HFB_1 and HFB_2 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.