Trichothecene mycotoxins occur in cereal grains and are produced by different Fusarium species, which may develop in the field, principally in wheat, maize, barley and oats. Trichothecene glucosylation can be included among naturally occurring mechanisms in cereals that lead to a reduction of native mycotoxin accumulation in grains. Although toxicological data are scarce, these modified forms may represent a potential food safety concern because they are not detectable by standard approaches and may be converted back to the parent toxin during digestion or food processing [1]. With respect to type-A trichothecenes, the recently issued Recommendation No. 165/2013/EC of the European Commission, setting indicative maximum permitted levels for T-2 toxin (T-2) and HT-2 toxin (HT-2), also takes into account the increasing knowledge made available on T-2/HT-2 glucosides stating that 'attention should be paid to the occurrence of masked forms, in particular their glycosylated-conjugates'. The increasing instrumental availability and technological advances in LC-MS, often allowing compound identification without the need for reference standards, have had a strong impact on the know how about formation and characterization of modified mycotoxins. Detection of known or "novel" trichothecene-related compounds in fungal cultures, plant material or processed foods can provide insights in detoxification and metabolisms of trichothecenes. Furthermore, the direct determination of free and conjugated forms might enable a more accurate evaluation of the risk of exposure. Recent advances in applications of LC-MS techniques for chemical characterization and quantitative determination of type-A trichothecene glucosyl derivatives will be reviewed and discussed. High-resolution mass spectrometry (HRMS), based on Orbitrap technology, has been applied to investigate on the presence of T-2 and HT-2 glucoside derivatives in naturally contaminated cereals (including wheat, oats and barley) and Fusarium fungal cultures. Molecular structure details obtained by measuring exact masses of main characteristic fragments, with high mass accuracy led to the identification of a monoglucoside derivative of T-2 toxin and two monoglucoside derivatives of HT-2 toxin. The analysis of their fragmentation patterns provided evidence for glucosylation at C-3 position for T-2 toxin and at C-3 or C-4 position for HT-2 toxin [2]. Two mono-glucosyl derivatives of neosolaniol (NEO) and one mono-glucoside derivative of diacetoxyscirpenol (DAS) have been identified and characterized by liquid chromatography tandem mass spectrometry (LC-MS/MS). These compounds were detected either in fungal cultures or in cereal samples naturally contaminated with the parent toxins [3]. Furthermore, a preliminary screening for the presence of these modified forms of mycotoxins, carried out on naturally contaminated cereal samples (i.e. wheat, oats and barley) showed a widespread occurrence of type-A trichothecene glucosides in cereal grains naturally contaminated with the relevant unconjugated toxins. Further insights on chemical structure of naturally occurring type-A trichothecenes glucosides were obtained by the combined use of MS/MS and ion mobility mass spectrometry (IMS) techniques. A chemically synthesized T-2 toxin-?-glucoside and a T-2 toxin-?-glucoside obtained by Blastobotrys muscicola cultures were characterized and compared with T-2 toxin-glucoside found in naturally contaminated oats and wheat samples. The study revealed the presence of the ?-linked form of T-2 toxin-glucoside in naturally contaminated plants, showing MS behavior identical to the yeast biotransformation product [4]. The availability of a reference standard made possible the collection of a first survey data aimed at obtaining more comprehensive information on the co-occurrence and contents of T-2 and HT-2 toxins and their glucosylated derivatives in naturally contaminated barley samples [5]. Different barley cultivars originating from a Northern Italian area were analysed by LC-HRMS in our laboratory for the presence of T-2, HT-2 and relevant glucosyl derivatives. The glucosyl derivative of HT-2 was detected at levels up to 163 ?g/kg in 17 of the 18 analysed unprocessed barley grains, whereas the monoglucosyl derivative of T-2 toxin was detected in only a few samples and at low ?g/kg levels. The ratio between glucosylated toxins (sum of T-2 and HT-2 glucosides) and native toxins (sum of T-2 and HT-2) ranged from 2% to 283%. A subset of nine different samples was subjected to micro-maltation in order to carry out a preliminary investigation on the fate of T-2, HT-2 and relevant glucosides along the malting process. Total mycotoxin reduction (sum of native and glicosylated forms) from cleaned barley to malt was observed at rates ranging from 4% to 87%.
Glucosyl derivatives of type-A trichohecenes: mass spectrometric characterization of plant and fungal metabolites, and natural occurrence in cereals
B Ciasca;A Visconti;M Pascale
2015
Abstract
Trichothecene mycotoxins occur in cereal grains and are produced by different Fusarium species, which may develop in the field, principally in wheat, maize, barley and oats. Trichothecene glucosylation can be included among naturally occurring mechanisms in cereals that lead to a reduction of native mycotoxin accumulation in grains. Although toxicological data are scarce, these modified forms may represent a potential food safety concern because they are not detectable by standard approaches and may be converted back to the parent toxin during digestion or food processing [1]. With respect to type-A trichothecenes, the recently issued Recommendation No. 165/2013/EC of the European Commission, setting indicative maximum permitted levels for T-2 toxin (T-2) and HT-2 toxin (HT-2), also takes into account the increasing knowledge made available on T-2/HT-2 glucosides stating that 'attention should be paid to the occurrence of masked forms, in particular their glycosylated-conjugates'. The increasing instrumental availability and technological advances in LC-MS, often allowing compound identification without the need for reference standards, have had a strong impact on the know how about formation and characterization of modified mycotoxins. Detection of known or "novel" trichothecene-related compounds in fungal cultures, plant material or processed foods can provide insights in detoxification and metabolisms of trichothecenes. Furthermore, the direct determination of free and conjugated forms might enable a more accurate evaluation of the risk of exposure. Recent advances in applications of LC-MS techniques for chemical characterization and quantitative determination of type-A trichothecene glucosyl derivatives will be reviewed and discussed. High-resolution mass spectrometry (HRMS), based on Orbitrap technology, has been applied to investigate on the presence of T-2 and HT-2 glucoside derivatives in naturally contaminated cereals (including wheat, oats and barley) and Fusarium fungal cultures. Molecular structure details obtained by measuring exact masses of main characteristic fragments, with high mass accuracy led to the identification of a monoglucoside derivative of T-2 toxin and two monoglucoside derivatives of HT-2 toxin. The analysis of their fragmentation patterns provided evidence for glucosylation at C-3 position for T-2 toxin and at C-3 or C-4 position for HT-2 toxin [2]. Two mono-glucosyl derivatives of neosolaniol (NEO) and one mono-glucoside derivative of diacetoxyscirpenol (DAS) have been identified and characterized by liquid chromatography tandem mass spectrometry (LC-MS/MS). These compounds were detected either in fungal cultures or in cereal samples naturally contaminated with the parent toxins [3]. Furthermore, a preliminary screening for the presence of these modified forms of mycotoxins, carried out on naturally contaminated cereal samples (i.e. wheat, oats and barley) showed a widespread occurrence of type-A trichothecene glucosides in cereal grains naturally contaminated with the relevant unconjugated toxins. Further insights on chemical structure of naturally occurring type-A trichothecenes glucosides were obtained by the combined use of MS/MS and ion mobility mass spectrometry (IMS) techniques. A chemically synthesized T-2 toxin-?-glucoside and a T-2 toxin-?-glucoside obtained by Blastobotrys muscicola cultures were characterized and compared with T-2 toxin-glucoside found in naturally contaminated oats and wheat samples. The study revealed the presence of the ?-linked form of T-2 toxin-glucoside in naturally contaminated plants, showing MS behavior identical to the yeast biotransformation product [4]. The availability of a reference standard made possible the collection of a first survey data aimed at obtaining more comprehensive information on the co-occurrence and contents of T-2 and HT-2 toxins and their glucosylated derivatives in naturally contaminated barley samples [5]. Different barley cultivars originating from a Northern Italian area were analysed by LC-HRMS in our laboratory for the presence of T-2, HT-2 and relevant glucosyl derivatives. The glucosyl derivative of HT-2 was detected at levels up to 163 ?g/kg in 17 of the 18 analysed unprocessed barley grains, whereas the monoglucosyl derivative of T-2 toxin was detected in only a few samples and at low ?g/kg levels. The ratio between glucosylated toxins (sum of T-2 and HT-2 glucosides) and native toxins (sum of T-2 and HT-2) ranged from 2% to 283%. A subset of nine different samples was subjected to micro-maltation in order to carry out a preliminary investigation on the fate of T-2, HT-2 and relevant glucosides along the malting process. Total mycotoxin reduction (sum of native and glicosylated forms) from cleaned barley to malt was observed at rates ranging from 4% to 87%.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
