Abstract
Aflatoxins count to the most toxic known mycotoxins and are a threat to food safety especially in regions with a warm and humid climate. Contaminated food reaches consumers globally due to international trade, leading to stringent regulatory limits of aflatoxins in food. While the formation of aflatoxin (AF) B1 by the filamentous fungus Aspergillus flavus is well investigated, less is known about the formation kinetics of its precursors and further aflatoxins. In this study, autoclaved maize kernels were inoculated with A. flavus and incubated at 25 °C for up to 10 days. Aflatoxins and precursors were analyzed by a validated UHPLC-MS method. Additional to AFB1 and AFB2, AFM1 and AFM2 were detected, confirming the ability of the formation of M-group aflatoxins on cereals by A. flavus. The measured relative levels of AFB2, AFM1, and AFM2 on maize compared to the level of AFB1 (mean of days 5, 7, and 10 of incubation) were 3.3%, 1.5%, and 0.2%, respectively. The occurrence and kinetics of the measured aflatoxins and their precursors sterigmatocystin, O-methylsterigmatocystin, 11-hydroxy-O-methylsterigmatocystin, aspertoxin, and 11-hydroxyaspertoxin (group 1) as well as of dihydrosterigmatocystin and dihydro-O-methylsterigmatocystin (group 2) supported the so far postulated biosynthetic pathway. Remarkable high levels of O-methylsterigmatocystin and aspertoxin (17.4% and 4.9% compared to AFB1) were found, raising the question about the toxicological relevance of these intermediates. In conclusion, based on the study results, the monitoring of O-methylsterigmatocystin and aspertoxin as well as M-group aflatoxins in food is recommended.
Highlights
Aflatoxins (AFs) are secondary metabolites of filamentous fungi, especially produced by Aspergillus species like A. flavus, A. minisclerotigenes, and A. parasiticus, which count to the most serious fungal contaminants of food and feed (Coppock et al 2018)
The analytes AFB1, AFB2, AFG1, AFG2, AFM1, AFM2, ST, OMST, and AFL were identified by comparison of their retention times, accurate masses in MS spectra and MS/MS spectra with those of the reference compounds
Yogendrarajah et al (2015) reported low concentrations of ST compared to those of OMST and A FB1 as well, when analyzing the mycotoxin profile of a variety of A. flavus and A. parasiticus strains on malt extract agar by LC–MS/MS
Summary
Aflatoxins (AFs) are secondary metabolites of filamentous fungi, especially produced by Aspergillus species like A. flavus, A. minisclerotigenes, and A. parasiticus, which count to the most serious fungal contaminants of food and feed (Coppock et al 2018). Main sources of intake of B- and G-group AFs are contaminated maize, peanuts, tree nuts, and dried fruits (Taniwaki et al 2018). AFM1 and AFM2 have been considered until now mainly as hydroxylation products of AFB1 and AFB2, formed enzymatically in the liver of lactating dairy cows being fed with AFs contaminated feed (Min et al 2021). Little attention has been paid to limited older findings that M-/GM-group AFs can be produced by A. flavus and A. parasiticus on/in laboratory media (Ramachandra Pai et al 1975; Dutton et al 1985; Yabe et al 2012). AFM1 has already been found a few times in cereals like maize and Perl millet (Matumba et al 2015a; Abdallah et al 2017; Houissa et al 2019) as well as dried fruits like figs (Sulyok et al 2020)
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