Enzyme immunoassay for tenuazonic acid in apple and tomato products

Comprehensive review on patulin and Alternaria toxins in fruit and derived products

Mycotoxins are toxic secondary metabolites produced by certain fungi, which can contaminate various food commodities, including fruits and their derived products. Patulin and Alternaria toxins are among the most commonly encountered mycotoxins in fruit and their derived products. In this review, the sources, toxicity, and regulations related to these mycotoxins, as well as their detection and mitigation strategies are widely discussed. Patulin is a mycotoxin produced mainly by the fungal genera Penicillium, Aspergillus, and Byssochlamys. Alternaria toxins, produced by fungi in the Alternaria genus, are another common group of mycotoxins found in fruits and fruit products. The most prevalent Alternaria toxins are alternariol (AOH) and alternariol monomethyl ether (AME). These mycotoxins are of concern due to their potential negative effects on human health. Ingesting fruits contaminated with these mycotoxins can cause acute and chronic health problems. Detection of patulin and Alternaria toxins in fruit and their derived products can be challenging due to their low concentrations and the complexity of the food matrices. Common analytical methods, good agricultural practices, and contamination monitoring of these mycotoxins are important for safe consumption of fruits and derived products. And Future research will continue to explore new methods for detecting and managing these mycotoxins, with the ultimate goal of ensuring the safety and quality of fruits and derived product supply.

Rapid and sensitive detection of tenuazonic acid in agricultural by-products based on gold nano-flower lateral flow

Tenuazonic acid (TA) is a highly toxic mycotoxin mainly generated by the fungi of Alternaria genus and widely contaminates agricultural by-products. Given the threat of TA to food-security, it is very important to develop rapid and sensitive detection methods for TA monitoring. In this study, gold nano-particles (AuNP) with average diameter near 17.25 nm were prepared, and the developed AuNP-based strip has an assay time of 15 min with visual limit of detection (LOD) of 12.5 ng/ml and threshold of 100 ng/ml. To further improve sensitivity, multi-branched gold nano-flowers (AuNF) with average diameter near 50 nm were prepared and characterized by UV-VIS and TEM, and the established AuNF-based strip has visual LOD of 0.78 ng/ml and threshold of 50 ng/ml within 15 min. Both assays were applied to determine TA in apple juice and tomato ketchup, and the results were consistent with that of UHPLC-MS/MS. Thus, these assays could be applied for rapid determination of trace TA in real samples.

Recent Advances in Alternaria Phytotoxins: A Review of Their Occurrence, Structure, Bioactivity and Biosynthesis

Alternaria is a ubiquitous fungal genus in many ecosystems, consisting of species and strains that can be saprophytic, endophytic, or pathogenic to plants or animals, including humans. Alternaria species can produce a variety of secondary metabolites (SMs), especially low molecular weight toxins. Based on the characteristics of host plant susceptibility or resistance to the toxin, Alternaria phytotoxins are classified into host-selective toxins (HSTs) and non-host-selective toxins (NHSTs). These Alternaria toxins exhibit a variety of biological activities such as phytotoxic, cytotoxic, and antimicrobial properties. Generally, HSTs are toxic to host plants and can cause severe economic losses. Some NHSTs such as alternariol, altenariol methyl-ether, and altertoxins also show high cytotoxic and mutagenic activities in the exposed human or other vertebrate species. Thus, Alternaria toxins are meaningful for drug and pesticide development. For example, AAL-toxin, maculosin, tentoxin, and tenuazonic acid have potential to be developed as bioherbicides due to their excellent herbicidal activity. Like altersolanol A, bostrycin, and brefeldin A, they exhibit anticancer activity, and ATX V shows high activity to inhibit the HIV-1 virus. This review focuses on the classification, chemical structure, occurrence, bioactivity, and biosynthesis of the major Alternaria phytotoxins, including 30 HSTs and 50 NHSTs discovered to date.

[Determination of seven Alternaria toxins in infant milk powder by solid phase extraction coupled with ultra-performance liquid chromatography-tandem mass spectrometry]

Alternaria toxin is a general term for a class of toxic metabolites produced by Alternaria, which widely exists in soil, grain, vegetables, and fruits. This mycotoxin is extremely harmful to human health. It is well known that infant milk powder containing vegetable oil is easily contaminated by Alternaria alternata. Alternaria toxins have thus become an increasingly important focus in food. Rapid and accurate detection of Alternaria toxin residues in food is of great significance for food safety. This requires pretreatment to purify the target toxins and maximize the accuracy and precision of the analysis. In this study, a rapid method based on online solid phase extraction/purification and ultra-performance liquid chromatography-tandem mass spectrometry (online SPE UPLC MS/MS) was established to detect seven Alternaria toxins (alternariol monomethyl ether, altenuene, tenuazonic acid, alternariol, tentoxin, altenusin, and altertoxin Ⅰ) in infant milk powder. First, the mass spectrometry and chromatographic conditions were optimized. A BEH-C18 column (50 mm×2.1 mm, 1.7 μm) was selected, with 0.1% formic acid aqueous solution-acetonitrile as the mobile phase. Then, the extraction conditions (extraction agent ratio and extraction method) and the solid phase extraction process (extraction column, type and volume of the eluent, and pH of the sample loading solution) were optimized. One gram of milk powder (accurate to 0.01 g) was weighed into a 50 mL tip and bottom plug centrifuge tube. Acetonitrile-water (84∶16, v/v) was set as the extraction agent for the first two cycles, and acetonitrile-methanol-water (45∶10∶45, v/v/v) was set as the third extraction agent. Horizontal shaking for 30 min was the best extraction method. The sample was centrifuged at 9500 r/min for 10 min, and the supernatant extracted many times was mixed and blown with nitrogen at 40 ℃. The sample was redissolved in first-order water (pH 5.5), purified on an HLB column, and successively activated with 6 mL methanol and 6 mL first-order water (pH 5.5). The solution was then loaded onto the column, and the SPE was adjusted to ensure that the water sample flowed through the column at the rate of 1 mL/min so that the column did not dry up during the analysis process before the end of sample loading. The column was rinsed with 12 mL of first-order water. After leaching, the negative pressure filtration was continued for approximately 5 min, followed by elution with 10 mL methanol, and the eluted solution was directly tested after passing through a 0.22 μm filter membrane, without concentration. The analytes were determined by electrospray ionization (ESI) with alternating positive and negative ions. Under the optimal analysis conditions, the linear relationships of the seven Alternaria toxins were good in the mass concentration range of 0.5-200 μg/L, with coefficients of determination (R2)>0.9903. The limits of detection and limits of quantification were 0.15-0.64 μg/kg and 0.54-2.24 μg/kg, respectively. The recoveries of the seven Alternaria toxins were 79.1%-114.3%, and the relative standard deviations were less than 8.87% at different concentrations. The method was applied to the determination and analysis of 60 samples of infant milk powder, and the results showed that no toxin was found in stage one or stage two of the milk powder. Only one sample of the stage three of milk powder was detected, which was tentoxin, and the content was 4.97 μg/kg. The developed method is accurate, rapid, simple, sensitive, repeatable, and stable. It can be used for the practical determination of seven Alternaria toxins in infant milk powder.

Biosynthesis and biological function of secondary metabolites of the rice blast fungus Pyricularia oryzae

Filamentous fungi have many secondary metabolism genes and produce a wide variety of secondary metabolites with complex and unique structures. However, the role of most secondary metabolites remains unclear. Moreover, most fungal secondary metabolism genes are silent or poorly expressed under laboratory conditions and are difficult to utilize. Pyricularia oryzae, the causal pathogen of rice blast disease, is a well-characterized plant pathogenic fungus. P. oryzae also has a large number of secondary metabolism genes and appears to be a suitable organism for analyzing secondary metabolites. However, in case of this fungus, biosynthetic genes for only four groups of secondary metabolites have been well characterized. Among two of the four groups of secondary metabolites, biosynthetic genes were identified by activating secondary metabolism. These secondary metabolites include melanin, a polyketide compound required for rice infection; tenuazonic acid, a well-known mycotoxin produced by various plant pathogenic fungi and biosynthesized by a unique nonribosomal peptide synthetase-polyketide synthase hybrid enzyme; nectriapyrones, antibacterial polyketide compounds produced mainly by symbiotic fungi, including plant pathogens and endophytes, and pyriculols, phytotoxic polyketide compounds. This review mainly focuses on the biosynthesis and biological functions of the four groups of P. oryzae secondary metabolites.

Simultaneous Detection of Seven Alternaria Toxins in Mixed Fruit Puree by Ultra-High-Performance Liquid Chromatography-Tandem Mass Spectrometry Coupled with a Modified QuEChERS

The presence of Alternaria toxins (ATs) in fruit purees may cause potential harm to the life and health of consumers. As time passes, ATs have become the key detection objects in this kind of food. Based on this, a novel and rapid method was established in this paper for the simultaneous detection of seven ATS (tenuazonic acid, alternariol, alternariol monomethyl ether, altenuene, tentoxin, altenusin, and altertoxin I) in mixed fruit purees using ultra-high performance liquid chromatography-tandem mass spectrometry. The sample was prepared using the modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) method to complete the extraction and clean-up steps in one procedure. In this QuEChERS method, sample was extracted with water and acetonitrile (1.5% formic acid), then salted out with NaCl, separated on an ACQUITY UPLC BEH C₁₈ with gradient elution by using acetonitrile and 0.1% formic acid aqueous as eluent, and detected by UPLC-MS/MS under positive (ESI⁺) and negative (ESI⁻) electrospray ionization and MRM models. Results showed that the seven ATs exhibited a good linearity in the concentration range of 0.5–200 ng/mL with R² > 0.9925, and the limits of detection (LODs) of the instrument were in the range of 0.18–0.53 μg/kg. The average recoveries ranged from 79.5% to 106.7%, with the relative standard deviations (RSDs) no more than 9.78% at spiked levels of 5, 10, and 20 μg/kg for seven ATs. The established method was applied to the determination and analysis of the seven ATs in 80 mixed fruit puree samples. The results showed that ATs were detected in 31 of the 80 samples, and the content of ATs ranged from 1.32 μg/kg to 54.89 μg/kg. Moreover, the content of TeA was the highest in the detected samples (23.32–54.89 μg/kg), while the detection rate of Ten (24/31 samples) was higher than the other ATs. Furthermore, the other five ATs had similar and lower levels of contamination. The method established in this paper is accurate, rapid, simple, sensitive, repeatable, and stable, and can be used for the practical determination of seven ATs in fruit puree or other similar samples. Moreover, this method could provide theory foundation for the establishment of limit standard of ATs and provide a reference for the development of similar detection standard methods in the future.

An enhanced open sandwich immunoassay by molecular evolution for noncompetitive detection of Alternaria mycotoxin tenuazonic acid

Open sandwich enzyme-linked immunosorbent assay (OS-ELISA), a novel noncompetitive immunoassay format, has shown great potential in rapid detection for small molecules compared with traditional competitive format. Here, an enhanced OS-ELISA towards the mycotoxin tenuazonic acid (TeA) was developed for the first time based on heavy chain variable region (V_H) and light chain variable region (V_L) from the hybridoma cells (3F10) producing anti-TeA monoclonal antibody (mAb). The established OS-ELISA exhibited a limit of detection of 0.08 ng/mL, and was 13 times more sensitive than mAb-based indirect competitive ELISA (ic-ELISA). The proposed assay was also applied to detect TeA contents in juice, flour and tomato ketchup samples with satisfactory recoveries of 87.6%-111.3%. Finally, the great accuracy of the established OS-ELISA method was validated by the standard ultra-performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS).

A high sensitive platinum-modified colloidal gold immunoassay for tenuazonic acid detection based on monoclonal IgG

Due to the threat of tenuazonic acid (TA) to public health, it is urgent to establish rapidly effective and sensitive assay methods for TA. In this study, a TA-specific IgG monoclonal antibody (McAb) with high affinity (Kaff was 1.72 × 10¹⁰ L/mol) was screened, and the developed icELISA for TA detection has IC₅₀ of 2.50 ng/mL and LOD of 0.17 ng/mL. Platinum-modified gold nanoparticle (Au@PtNP) was optimized as Au@Pt_0.4NP, and the resulted Au@Pt_0.4NP-McAb probe was designed to catalyze precipitation-type tetramethylbenzidine for visual detection of trace TA with visual LOD of 0.39 ng/mL. The sensitivity of this established Au@Pt_0.4NP-McAb strip was highly increased when compared with the existing colloidal gold strip. The developed strip was used to detect trace TA in apple juice and tomato ketchup which were consistent with the results from UHPLC-MS/MS. Therefore, this developed strip could be used for rapid detection of trace TA in real samples.

Enhanced Non-Toxic Immunodetection of Alternaria Mycotoxin Tenuazonic Acid Based on Ferritin-Displayed Anti-Idiotypic Nanobody-Nanoluciferase Multimers

The non-toxic immunoassay for mycotoxins is being paid more attention due to its advantages of higher safety and cost savings by using anti-idiotype antibodies to substitute toxins. In this study, with tenuazonic acid (TeA), a kind of highly toxic Alternaria mycotoxin as the target, an enhanced non-toxic immunoassay was developed based on the ferritin-displayed anti-idiotypic nanobody-nanoluciferase multimers. First, three specific β-type anti-idiotype nanobodies (AId-Nbs) bearing the internal image of TeA mycotoxin were selected from an immune phage display library. Then, the AId-Nb 2D with the best performance was exploited to generate a nanoluciferase (Nluc)-functionalized fusion monomer, by which a one-step non-toxic immunodetection format for TeA was established and proven to be effective. To further improve the affinity of the monomer, a ferritin display strategy was used to prepare 2D-Nluc fusion multimers. Finally, an enhanced bioluminescent enzyme immunoassay (BLEIA) was established in which the half maximal inhibitory concentration (IC₅₀) for TeA was 6.5 ng/mL with a 10.5-fold improvement of the 2D-based enzyme-linked immunosorbent assay (ELISA). The proposed assay exhibited high selectivities and good recoveries of 80.0-95.2%. The generated AId-Nb and ferritin-displayed AId-Nb-Nluc multimers were successfully extended to the application of TeA in food samples. This study brings a new strategy for production of multivalent AId-Nbs and non-toxic immunoassays for trace toxic contaminants.

Development of a chemiluminescence immunoassay for detection of tenuazonic acid mycotoxin in fruit juices with a specific camel polyclonal antibody

The natural mycotoxin tenuazonic acid (TeA) in foods is identified as the most toxic mycotoxin among the over 70 kinds of secondary toxic metabolites produced by Alternaria alternata. Some hapten-antibody-mediated immunoassays have been developed for TeA detection in food samples, but these methods show unsatisfactory sensitivity and specificity. In this study, a rationally designed hapten for TeA mycotoxin generated with computer-assisted modeling was prepared to produce a highly specific camel polyclonal antibody, and an indirect competitive chemiluminescence enzyme immunoassay (icCLEIA) was established with a limit of detection of 0.2 ng mL-1 under optimized conditions. The cross-reactivity results showed that several analogs and some common mycotoxins had negligible recognition by the anti-TeA polyclonal antibody. The average recoveries spiked in fruit juices were determined to be 92.7% with an acceptable coefficient of variation, and good correlations between icCLEIA and liquid chromatography tandem mass spectrometry (LC-MS/MS) results were obtained in spiked samples. This developed icCLEIA for TeA detection with significantly improved sensitivity and satisfactory specificity is a promising alternative for environmental monitoring and food safety.

Secondary Metabolites of the Rice Blast Fungus Pyricularia oryzae: Biosynthesis and Biological Function

Plant pathogenic fungi produce a wide variety of secondary metabolites with unique and complex structures. However, most fungal secondary metabolism genes are poorly expressed under laboratory conditions. Moreover, the relationship between pathogenicity and secondary metabolites remains unclear. To activate silent gene clusters in fungi, successful approaches such as epigenetic control, promoter exchange, and heterologous expression have been reported. Pyricularia oryzae, a well-characterized plant pathogenic fungus, is the causal pathogen of rice blast disease. P. oryzae is also rich in secondary metabolism genes. However, biosynthetic genes for only four groups of secondary metabolites have been well characterized in this fungus. Biosynthetic genes for two of the four groups of secondary metabolites have been identified by activating secondary metabolism. This review focuses on the biosynthesis and roles of the four groups of secondary metabolites produced by P. oryzae. These secondary metabolites include melanin, a polyketide compound required for rice infection; pyriculols, phytotoxic polyketide compounds; nectriapyrones, antibacterial polyketide compounds produced mainly by symbiotic fungi including endophytes and plant pathogens; and tenuazonic acid, a well-known mycotoxin produced by various plant pathogenic fungi and biosynthesized by a unique NRPS-PKS enzyme.

Chemiluminescent Enzyme Immunoassay and Bioluminescent Enzyme Immunoassay for Tenuazonic Acid Mycotoxin by Exploitation of Nanobody and Nanobody-Nanoluciferase Fusion

The isolation of nanobodies (Nbs) from phage display libraries is an increasingly effective approach for the generation of new biorecognition elements, which can be used to develop immunoassays. In this study, highly specific Nbs against the Alternaria mycotoxin tenuazonic acid (TeA) were isolated from an immune nanobody phage display library using a stringent biopanning strategy. The obtained Nbs were characterized by classical enzyme-linked immunosorbent assay (ELISA), and the best one Nb-3F9 was fused with nanoluciferase to prepare an advanced bifunctional fusion named nanobody-nanoluciferase (Nb-Nluc). In order to improve the sensitivity and reduce the assay time, two different kinds of luminescent strategies including chemiluminescent enzyme immunoassay (CLEIA) and bioluminescent enzyme immunoassay (BLEIA) were established, respectively, on the basis of the single Nb and the fusion protein Nb-Nluc for TeA detection. The two-step CLEIA was developed on the basis of the same nanobody as ELISA, only with simple substrate replacement from 3,3',5,5'-tetramethylbenzidine (TMB) to luminol. In contrast with CLEIA, the novel BLEIA was conducted in one-step new strategy on the basis of Nb-Nluc and bioluminescent substrate coelenterazine-h (CTZ-h). Their half maximal inhibitory concentration (IC50) values were similar to 8.6 ng/mL for CLEIA and 9.3 ng/mL for BLEIA, which was a 6-fold improvement in sensitivity compared with that of ELISA (IC50 of 54.8 ng/mL). Both of the two assays provided satisfactory recoveries ranging from 80.1%-113.5% in real samples, which showed better selectivity for TeA analogues and other common mycotoxins. These results suggested that Nbs and Nb-Nluc could be used as useful reagents for immunodetection and that the developed CLEIA/BLEIA have great potential for TeA analysis.

Coordination of mycotoxins with lanthanides in luminescent complexes

The ability of several chelating mycotoxins to form coordination complexes with the lanthanide metals europium and terbium was explored. The mycotoxins examined included ochratoxin A, citrinin, cyclopiazonic acid (CPA), kojic acid, and tenuazonic acid (TeA). Of these compounds, TeA and CPA resulted in the greatest luminescence. Parameters influencing luminescence of TeA were investigated further. These included the type of lanthanide and its concentration, certain environmental factors, and the effect of competing metal cations. Of the two lanthanide metals, the terbium coordination complex (TeA-Tb³⁺) showed greater luminescence relative to the europium complex (TeA-Eu³⁺). The effects of solvent type, water content, and pH on the TeA-Tb³⁺ system suggested that optimal conditions for luminescence were in 90% methanol with 10% aqueous buffer at pH 3. In competitive assays, the luminescence of the TeA-Tb³⁺ complex decreased as the concentration of competing metal cations increased. Among the cations tested, Cu²⁺ was the best inhibitor followed by Al³⁺, Au³⁺, Fe³⁺, Co²⁺, Mn²⁺, Mg²⁺, and Ca²⁺. Two cations, Na⁺ and K⁺, showed no significant inhibition. This is the first report to describe the coordination of the metal-chelating mycotoxin TeA with lanthanides and the ability of TeA to serve as an "antenna" for the efficient transfer of energy to the lanthanide with resulting luminescence. Understanding the ability of mycotoxins such as TeA to chelate metals provides insight into how they exert their toxic effects.

Regulatory Mechanism of Mycotoxin Tenuazonic Acid Production in Pyricularia oryzae

Tenuazonic acid (TeA) is a mycotoxin produced by the rice blast fungus Pyricularia oryzae and some plant pathogenic fungi. We previously demonstrated that TeA is biosynthesized in P. oryzae by TeA synthetase 1 (TAS1) and that its production is induced by osmo-sensory MAPK-encoding gene (OSM1) deletion or the addition of 1% DMSO to cultures; however, the regulatory mechanisms of TeA production were unknown. Here, we identify a Zn(II)₂-Cys₆-type transcription factor in the upstream region of TAS1, which is encoded by TAS2 and regulates TeA production. We also find PoLAE1, which is a homologue of LaeA, a regulator of fungal secondary metabolism. Analysis of PoLAE1 deletion and overexpression strains indicate that PoLAE1 drives TeA production. We also demonstrate that two TeA-inducing signals, 1% DMSO addition and OSM1 deletion, were transmitted through PoLAE1. Our results indicate that TeA production is regulated by two specific regulators, TAS2 and PoLAE1, in P. oryzae.

AlternariaMycotoxins in Food and Feed: An Overview

Alternariais one of the major mycotoxigenic fungal genera with more than 70 reported metabolites.Alternariamycotoxins showed notably toxicity, such as mutagenicity, carcinogenicity, induction of DNA strand break, sphingolipid metabolism disruption, or inhibition of enzymes activity and photophosphorylation. This review reports on the toxicity, stability, metabolism, current analytical methods, and prevalence ofAlternariamycotoxins in food and feed through the most recent published research. Half of the publications were focused on fruits, vegetables, and derived products—mainly tomato and apples—while cereals and cereal by-products represented 38%. The most studied compounds were alternariol, alternariol methyl ether, tentoxin, and tenuazonic acid, but altenuene, altertoxins (I, II, and III), and macrosporin have been gaining importance in recent years. Solid-liquid extraction (50%) with acetonitrile or ethyl acetate was the most common extraction methodology, followed by QuEChERS and dilution-direct injection (both 14%). High- and ultraperformance liquid chromatography coupled with tandem mass spectrometry was the predominant determination technique (80%). The highest levels of alternariol and alternariol methyl ether were found in lentils, oilseeds, tomatoes, carrots, juices, wines, and cereals. Tenuazonic acid highest levels were detected in cereals followed by beer, while alternariol, alternariol methyl ether, tenuazonic acid, and tentoxin were found in legumes, nuts, and oilseeds.

Detection and Quantitative Analysis of the Non-cytotoxic allo-Tenuazonic Acid in Tomato Products by Stable Isotope Dilution HPLC-MS/MS

Tenuazonic acid (1) is a mycotoxin produced mainly by fungi of the genus Alternaria. It occurs in a variety of agricultural products. allo-Tenuazonic acid (2) is an isomer of 1 that is not chromatographically separated from 1 in most analytical methods. Therefore, both isomers are quantitated as a sum parameter. In this study a QuEChERS (quick, easy, cheap, effective, rugged and safe) based stable isotope dilution HPLC-MS/MS method including the chromatographic separation of both isomers was developed and applied to 20 tomato products from the German market. All products showed contamination with both toxins. 1 was found in a range from 5.3 ± 0.1 to 550 ± 15 μg/kg (average = 120 μg/kg) and 2 in a range from 1.5 ± 0.4- to 270 ± 0.8 μg/kg (average = 58 μg/kg). 2 represents 7.0-44% of the sum of both isomers (average = 29%). This is the first reported occurrence of 2 in food samples. To evaluate and compare the cytotoxicities of 1 and 2, both compounds were isolated from a synthetic racemic mixture. 1 showed moderate cytotoxic effects on HT-29 cells starting at 100 μM, whereas 2 exhibited no activity. 2 was not produced in liquid cultures of Alternaria alternata in yeast extract sucrose (YES) medium, but could be detected in small amounts in tomato puree inoculated with the fungus.

Biosynthesis of the mycotoxin tenuazonic acid by a fungal NRPS-PKS hybrid enzyme

Tenuazonic acid (TeA) is a well-known mycotoxin produced by various plant pathogenic fungi. However, its biosynthetic gene has been unknown to date. Here we identify the TeA biosynthetic gene from Magnaporthe oryzae by finding two TeA-inducing conditions of a low-producing strain. We demonstrate that TeA is synthesized from isoleucine and acetoacetyl-coenzyme A by TeA synthetase 1 (TAS1). TAS1 is a unique non-ribosomal peptide synthetase and polyketide synthase (NRPS–PKS) hybrid enzyme that begins with an NRPS module. In contrast to other NRPS/PKS hybrid enzymes, the PKS portion of TAS1 has only a ketosynthase (KS) domain and this domain is indispensable for TAS1 activity. Phylogenetic analysis classifies this KS domain as an independent clade close to type I PKS KS domain. We demonstrate that the TAS1 KS domain conducts the final cyclization step for TeA release. These results indicate that TAS1 is a unique type of NRPS–PKS hybrid enzyme.

Tenuazonic acid is a mycotoxin produced by various plant pathogenic fungi but its biosynthetic gene is unknown to date. Here, the authors identify the tenuazonic acid biosynthetic gene encoding a protein with a unique KS domain that conducts cyclization step for tenuazonic acid release in Magnaporthe oryzae.

Structure and tautomerism of tenuazonic acid--a synergetic computational and spectroscopic approach

All reasonable tautomers and rotamers of tenuazonic acid, which is considered to be of the highest toxicity amongst the Alternaria mycotoxins, were investigated by DFT calculations at different levels of theory in gas phase and in solution to obtain optimized geometries for further examinations. Calculated NMR spectra of tautomeric structures are being presented and compared to experimental data to finally achieve a synergetic computational and spectroscopic approach for structure elucidation of 3-acetyltetramic acids, affording the predominant tautomer of tenuazonic acid in aqueous solution. Furthermore we were able to simulate the less hindered rotation of the exocyclic acetyl group, which occurs after dissociation of tenuazonic acid in protic solvents.

Development of analytical methods for the determination of tenuazonic acid analogues in food commodities

Analogues of the Alternaria mycotoxin tenuazonic acid (TA, biosynthesized by the fungus from the amino acid isoleucine) derived from valine (ValTA), leucine (LeuTA), alanine (AlaTA) and phenylalanine (PheTA) were synthesized and characterized by mass spectrometry (MS) and (1)H nuclear magnetic resonance (NMR) spectroscopy. Concentrations of stock solutions were determined by quantitative (1)H NMR (qHNMR). Two analytical methods based on high performance liquid chromatography (HPLC) and MS detection were developed, one with derivatization with 2,4-dinitrophenylhydrazine (DNPH) and one without derivatization. Limits of detection (LODs) were between 1-3 μg/kg (with derivatization) and 50-80 μg/kg (without derivatization). Respective limits of quantitation (LOQs) were about three times higher. Beside TA, the analogues LeuTA (about 4% of TA content) and ValTA (about 10% of TA content) were found in highly contaminated sorghum infant cereals and sorghum grains. Other analogues were not detected. Quantification of LeuTA and ValTA was performed using [(13)C6,(15)N]-TA as internal standard and matrix matched calibration. Recovery was between 95±11% and 102±10% for both compounds. Precision (relative standard deviation of triplicate sorghum cereal analyses three times during 3 weeks) was 7% for TA (912±60 μg/kg), 17% for LeuTA (43±8 μg/kg) and 19% for ValTA (118±22 μg/kg). These results indicate that several TA-like compounds, which are not yet characterized in aspects of their toxic properties, were detected in sorghum based infant food highly contaminated with TA, already.

Developments in mycotoxin analysis: an update for 2011-2012

This review highlights developments in mycotoxin analysis and sampling over a period between mid-2011 and mid- 2012. It covers the major mycotoxins aflatoxins, Alternaria toxins, ergot alkaloids, fumonisins, ochratoxin, patulin, trichothecenes, and zearalenone. A section on mycotoxins in botanicals and spices is also included. Methods for mycotoxin determination continue to be developed using a wide range of analytical systems ranging from rapid immunochemical-based methods to the latest advances in mass spectrometry. This review follows the format of previous reviews in this series (i.e. sections on individual mycotoxins), but due to the rapid spread and developments in the field of multimycotoxin methods by liquid chromatography-tandem mass spectrometry, a separate section has been devoted to advances in this area of research.

Antibody generation and immunoassay development in diverse formats for pyrimethanil specific and sensitive analysis

Immunochemical techniques are complementary tools to modern analytical requirements. These methods rely on the production of immunoreagents with adequate binding properties. In the present study, a rationally designed and functionalized derivative of pyrimethanil--a modern anilinopyrimidine fungicide--was synthesized in order to generate for the first time high-affinity and selective antibodies to this xenobiotic. A single coupling procedure--based on hapten activation using N,N'-disuccinimidyl carbonate and purification of the active ester--was followed to prepare both immunizing and assay conjugates. Polyclonal antibodies were produced and characterized by enzyme-linked immunosorbent assay (ELISA) in four alternative formats: one indirect and three direct competitive procedures. The selected immunoassay displayed a limit of detection of 0.024 μg L(-1), far lower than the official maximum residue limits and close to the sensitivity of regular instrumental assays. This ELISA was shown to be robust to buffer changes and tolerant to the presence of little amounts of methanol, ethanol and acetonitrile. Finally, the developed assay was applied to the analysis of pyrimethanil in carrot juice samples, and a limit of quantification of 0.040 mg L(-1) was determined.