Aflatoxin analysis at the beginning of the twenty-first century

An ultrasensitive electrochemical aptasensor based on zeolitic imidazolate framework-67 loading gold nanoparticles and horseradish peroxidase for detection of aflatoxin B1

Aflatoxin B1 (AFB1) is one of the most toxic mycotoxins and poses a high risk to human health. Highly sensitive and rapid detection is one of the most effective preventive measures to avoid potential hazards. Herein, an electrochemical aptasensor based on DNA nanotetrahedron and zeolitic imidazolate framework-67 loading gold nanoparticles, horseradish peroxidase, and aptamers was designed for the ultrasensitive detection of AFB1. The high specific surface area and large pore volume of zeolitic imidazolate framework-67 can increase the loading capacity and further improve the detection sensitivity of electrochemical aptasensors. DNA nanotetrahedron can enhance the capture ability of AFB1 with steady immobilization. The developed aptasensor showed good analytical performance for AFB1 detection, with a detection limit of 3.9 pg mL-1 and a wide linear range of 0.01-100 ng mL-1. The aptasensor detected AFB1 in corn samples with recovery rates ranging from 94.19%-105.77% and has potential for use in food safety monitoring.

Raman hyperspectral imaging as a potential tool for rapid and nondestructive identification of aflatoxin contamination in corn kernels

The potential of Raman hyperspectral imaging with a 785 nm excitation line laser was examined for detection of aflatoxin contamination in corn kernels. Nine-hundred kernels were artificially inoculated in the laboratory, with 300 kernels each inoculated with AF13 (aflatoxigenic) fungus, AF36 (non-aflatoxigenic) fungus, and sterile distilled water (control). One-hundred kernels from each treatment were subsequently incubated for 3, 5, and 8 days. The mean spectra of single kernels were extracted from the endosperm side and the embryo area of the germ side, and local Raman peaks were identified based upon the calculated reference spectra of aflatoxin-negative and -positive categories separately. The principal component analysis-linear discriminant analysis models were established using different types of variable inputs including original full spectra, preprocessed full spectra, and identified local peaks over kernel endosperm-side, germ-side, and both sides. The results of the established discriminant models showed that the germ-side spectra performed better than the endosperm-side spectra. Based upon the 20 ppb-threshold, the best mean prediction accuracy of 82.6% was achieved for the aflatoxin-negative category using the original spectra in the combined form of both kernel sides, and the best mean prediction accuracy of 86.7% was obtained for the -positive category using the preprocessed germ-side spectra. Based upon the 100 ppb-threshold, the best mean prediction accuracies of 85.0% and 89.6% were achieved for the aflatoxin-negative and -positive categories separately, using the same type of variable inputs for the 20 ppb-threshold. In terms of overall prediction accuracy, the models established upon the original spectra in the combined form of both kernel sides achieved the best predictive performance, regardless of the threshold. The mean overall prediction accuracies of 81.8% and 84.5% were achieved with the 20 ppb- and 100 ppb-thresholds, respectively.

Nucleic Acid Aptamers for Pesticides, Toxins, and Biomarkers in Agriculture

Nucleic acid aptamers are short single-stranded DNA/RNA (ssDNA/RNA) oligonucleotides that can selectively bind to the targets. They are widely used in medicine, biosensing, and diagnostic assay. They have also been identified and extensively used for various targets in agriculture. In this review we summarize the progress of nucleic acid aptamers on pesticides (herbicides, insecticides, and fungicides), toxins, specific biomarkers of crops, and plant growth regulators in agricultural field in recent years. The basic process of aptamer selection, the already identified DNA/RNA aptamers and the aptasensors are discussed. We also discuss the future perspectives and the challenges for aptamer development in agriculture.

Estimating bulk optical properties of AFB1 contaminated edible oils in 300-900 nm by combining double integrating spheres technique with laser induced fluorescence spectroscopy

An optical detection platform based on laser induced spectroscopy and double integrating spheres techniques was developed to obtain absorption (μ_a), reduced scattering coefficients (μ'_s) and fluorescence intensity of oil. The validation experiment carried on liquid phantoms showed that the developed system could achieve high linearity, and the results of spectra analysis indicated that the fluorescence intensity has a significant negative correlation with both μ_a and μ'_s. A total of 1620 oils with six categories were detected. The reason for the difference of fluorescence and μ_a spectra was analyzed by comparing the measured chlorophyll, polyphenol and α-tocopherol contents. Linear discriminant analysis combined with principal component analysis based on fluorescence and μ_a spectra was employed, to calibrate the AFB₁ classification models. The discrimination results manifested that by integrating μ_a with fluorescence signal, the correct classification rate could be improved by more than 10%, and the false negative rate was greatly reduced.

Validation of a Simple and Reliable Method for the Determination of Aflatoxins in Soil and Food Matrices

Aflatoxins (AFs) are toxic fungal secondary metabolites that are commonly detected in food commodities. Currently, there is a lack of generic methods capable of determining AFs both at postharvest stages in agricultural products and preharvest stages, namely, the agricultural soil. Here, we present a simple and reliable method for quantitative analysis of AFs in soil and food matrices at environmentally relevant concentrations for the first time, using the same extraction procedure and chromatography, either by HPLC-FLD or LC-MS. AFs were extracted from matrices by ultrasonication using an acetonitrile/water mixture (84:16, v + v) without extensive and time-consuming cleanup procedures. Food extracts were defatted with n-hexane. Matrix effects in terms of signal suppression/enhancement (SSE) for HPLC-FLD were within ±20% for all matrices tested. For LC-MS, the SSE values were mostly within ±20% for soil matrices but outside ±20% for all food matrices. The sensitivity of the method allowed quantitative analysis even at trace levels with quantification limits (LOQs) between 0.04 and 0.23 μg kg^-1 for HPLC-FLD and 0.06-0.23 μg kg^-1 for LC-MS. The recoveries ranged from 64 to 92, 74 to 101, and 78 to 103% for fortification levels of 0.5, 5, and 20 μg kg^-1, respectively, with repeatability values of 2-18%. The validation results are in accordance with the quality criteria and limits for mycotoxins set by the European Commission, thus confirming a satisfactory performance of the analytical method. Although reliable analysis is possible with both instruments, the HPLC-FLD method may be more suitable for routine analysis because it does not require consideration of the matrix.

Mycotoxins-Biomonitoring and Human Exposure

Mycotoxins are secondary metabolites produced by fungal species that commonly have a toxic effect on human and animal health. Different foodstuff can be contaminated and are considered the major source of human exposure to mycotoxins, but occupational and environmental exposure can also significantly contribute to this problem. This review aims to provide a short overview of the occurrence of toxigenic fungi and regulated mycotoxins in foods and workplaces, following the current literature and data presented in scientific papers. Biomonitoring of mycotoxins in plasma, serum, urine, and blood samples has become a common method for determining the exposure to different mycotoxins. Novel techniques are more and more precise and accurate and are aiming toward the simultaneous determination of multiple mycotoxins in one analysis. Application of liquid chromatography (LC) methodologies, coupled with tandem mass spectrometry (MS/MS) or high-resolution mass spectrometry (HRMS) has become a common and most reliable method for determining the exposure to mycotoxins. Numerous references confirm the importance of mycotoxin biomonitoring to assess the exposure for humans and animals. The objectives of this paper were to review the general approaches to biomonitoring of different mycotoxins and the occurrence of toxigenic fungi and their mycotoxins, using recent literature sources.

Low Temperature Greatly Enhancing Responses of Aptamer Electrochemical Sensor for Aflatoxin B1 Using Aptamer with Short Stem

Aflatoxin B1 (AFB1), one of the most toxic mycotoxins, poses great health risks. Rapid and sensitive detection of AFB1 is important for food safety, environment monitoring, and health risk assessment. We report here the development of a simple and reusable electrochemical aptasensor for rapid and sensitive detection of AFB1. Main improvements were achieved through engineering an aptamer containing a short stem-loop structure and enhancing the binding affinity at a lower temperature. The DNA aptamer with a methylene blue (MB) label at one end was immobilized on a gold electrode. Upon AFB1 binding, the aptamer folded into a stem-loop structure and brought MB close to the electrode surface, resulting in increases in electric current. The aptamer having a shorter stem (2-4 bp) underwent a larger conformation change upon target binding. The sensors built with the aptamer containing a 2 bp stem generated much higher signal-on responses to AFB1 at 4 °C than at room temperature (25 °C). The improvements resulted in a detection limit of 6 pM, enabling the determination of trace AFB1 in a complex sample matrix. This study demonstrates that low temperature greatly enhances the performance of aptamer electrochemical sensors. This aptasensor is simple to construct and readily regenerated by washing with deionized water for reuse. This aptasensor strategy could be applied to the development of an electrochemical aptasensor for other targets.

Development of Anti-Idiotypic Nanobody-Phage Based Immuno-Loop-Mediated Isothermal Amplification Assay for Aflatoxins in Peanuts

Aflatoxin contamination in agricultural products has posed serious health hazards and brought huge economic loss in the food and feed industries. Monitoring aflatoxins in various foods and feeds has become a crucial means to protect public health. This study aimed to report an immuno-loop-mediated isothermal amplification (iLAMP) assay by using an anti-idiotypic nanobody-phage for on-site and rapid detection of aflatoxin in real samples. The iLAMP method was developed on the basis of a competitive immunoassay and LAMP reaction performed in a simple water bath. This method can provide visualized test results: violet color represents positive samples while sky blue represents negative. The visual detection limits of iLAMP for aflatoxin B₁, B₂, G₁, and G₂ in peanut samples were 1.6, 1.6, 3.2, and 16 μg/kg, respectively. The developed assay was verified with high performance liquid chromatography (HPLC) for the analysis of aflatoxins in peanuts, which demonstrated that the iLAMP method can be applied to the detection of aflatoxin in real samples. The novel iLAMP assay eliminates the need for aflatoxin conjugates, the antibody labeling process, and special equipment, and offers an alternative to existing methods with advantages of time-saving, cost-effectiveness, and ease-of-use.

A Review: Sample Preparation and Chromatographic Technologies for Detection of Aflatoxins in Foods

As a class of mycotoxins with regulatory and public health significance, aflatoxins (e.g., aflatoxin B1, B2, G1 and G2) have attracted unparalleled attention from government, academia and industry due to their chronic and acute toxicity. Aflatoxins are secondary metabolites of various Aspergillus species, which are ubiquitous in the environment and can grow on a variety of crops whereby accumulation is impacted by climate influences. Consumption of foods and feeds contaminated by aflatoxins are hazardous to human and animal health, hence the detection and quantification of aflatoxins in foods and feeds is a priority from the viewpoint of food safety. Since the first purification and identification of aflatoxins from feeds in the 1960s, there have been continuous efforts to develop sensitive and rapid methods for the determination of aflatoxins. This review aims to provide a comprehensive overview on advances in aflatoxins analysis and highlights the importance of sample pretreatments, homogenization and various cleanup strategies used in the determination of aflatoxins. The use of liquid-liquid extraction (LLE), supercritical fluid extraction (SFE), solid phase extraction (SPE) and immunoaffinity column clean-up (IAC) and dilute and shoot for enhancing extraction efficiency and clean-up are discussed. Furthermore, the analytical techniques such as gas chromatography (GC), liquid chromatography (LC), mass spectrometry (MS), capillary electrophoresis (CE) and thin-layer chromatography (TLC) are compared in terms of identification, quantitation and throughput. Lastly, with the emergence of new techniques, the review culminates with prospects of promising technologies for aflatoxin analysis in the foreseeable future.

Detection of Aflatoxins in Different Matrices and Food-Chain Positions

Aflatoxins, produced mainly by filamentous fungi Aspergillus flavus and Aspergillus parasiticus, are one of the most carcinogenic compounds that have adverse health effects on both humans and animals consuming contaminated food and feed, respectively. Aflatoxin B1 (AFB1) and aflatoxin B2 (AFB2) as well as aflatoxin G1(AFG1) and aflatoxin G2 (AFG2) occur in the contaminated foods and feed. In the case of dairy ruminants, after the consumption of feed contaminated with aflatoxins, aflatoxin metabolites [aflatoxin M1 (AFM1) and aflatoxin M2 (AFM2)] may appear in milk. Because of the health risk and the official maximum limits of aflatoxins, there is a need for application of fast and accurate testing methods. At present, there are several analytical methods applied in practice for determination of aflatoxins. The aim of this review is to provide a guide that summarizes worldwide aflatoxin regulations and analytical methods for determination of aflatoxins in different food and feed matrices, that helps in the decision to choose the most appropriate method that meets the practical requirements of fast and sensitive control of their contamination. Analytical options are outlined from the simplest and fastest methods with the smallest instrument requirements, through separation methods, to the latest hyphenated techniques.

Facile dispersive solid-phase extraction based on humic acid for the determination of aflatoxins in various edible oils

Aflatoxins (AFs), as the secondary metabolites of the toxigenic fungi Aspergillus flavus and Aspergillus parasiticus, are well known to be extremely harmful to humans and animals because of their high toxicity, mutagenicity, carcinogenicity, and teratogenicity. Recurring and increasing studies on AF ingestion incidents indicate that AF contamination is a serious food safety issue worldwide. Currently, immunoaffinity chromatography (IAC) has become the most conventional sample clean-up method for determining AFs in foodstuffs. However, the IAC method may be limited to some laboratories because it requires the use of expensive disposable cartridges and the IA procedure is time-consuming. Herein, to achieve the cost-effective determination of AFs in edible oils, we developed a dispersive solid-phase extraction (DSPE) clean-up method based on humic acids (HAs), which is followed by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) analysis. HAs could be directly used as a DSPE sorbent after simple treatment without any chemical modification. In the HA-DSPE, AFs could remain on the HA sorbent by both hydrophobic and hydrophilic interactions, whereas the oil matrix was retained on HA via only hydrophobic interactions. The oil matrix could be sufficiently washed off by n-hexane, whereas the AFs could still be retained on HA; thus, the selective extraction of AFs and clean-up of oil matrices were achieved. Under the optimal conditions of HA-DSPE, satisfactory recoveries ranging from 81.3% to 106.2% for four AFs (B1, B2, G1, and G2) were achieved in various oil matrices i.e. blended oil, mixed olive oil, tea oil, sunflower seed oil, rapeseed oil, sesame oil, soybean oil, rice oil, corn oil, and peanut oil. Minor matrix effects ranging from 89.3% to 112.9% were obtained for the four AFs, which were acceptable. Moreover, the LODs of AFs between 0.063 and 0.102 μg kg-1 completely meet the regulatory levels fixed by the Food and Drug Administration (FDA), the European Union (EU), China, or other countries. The proposed methodology was further validated using a naturally contaminated peanut oil, and the results indicated that the accuracy of the HA-DSPE could match the accuracy of the referenced IAC. In addition, HA-DSPE can be used to directly treat diluted edible oil without liquid-liquid extraction and HA is cheap and can be easily obtained from the market worldwide; these advantages make the proposed methodology simple, low-cost, and accessible for the determination of AFs in edible oils.

A Sensitive, Point-of-Care Detection of Small Molecules Based on a Portable Barometer: Aflatoxins In Agricultural Products

Sensitive and point-of-care detection of small toxic molecules plays a key role in food safety. Aflatoxin, a typical small toxic molecule, can cause serious healthcare and economic issues, thereby promoting the development of sensitive and point-of-care detection. Although ELISA is one of the official detection methods, it cannot fill the gap between sensitivity and point-of-care application because it requires a large-scale microplate reader. To employ portable readers in food safety, Pt-catalysis has attracted increasing attention due to its portability and reliability. In this study, we developed a sensitive point-of-care aflatoxin detection (POCAD) method via a portable handheld barometer. We synthesized and characterized Au@PtNPs and Au@PtNPs conjugated with a second antibody (Au@PtNPs-IgG). A competitive immunoassay was established based on the homemade monoclonal antibody against aflatoxins. Au@PtNPs-IgG was used to catalyze the production of O₂ from H₂O₂ in a sealed vessel. The pressure of O₂ was then recorded by a handheld barometer. The aflatoxin concentration was inversely proportional to the pressure recorded via the barometer reading. After optimization, a limit of detection of 0.03 ng/mL and a linear range from 0.09 to 16.0 ng/mL were achieved. Recovery was recorded as 83.1%–112.0% along with satisfactory results regarding inner- and inter-assay precision (relative standard deviation, RSD < 6.4%). Little cross-reaction was observed. Additionally, the POCAD was validated by high-performance liquid chromatography (HPLC) by using peanut and corn samples. The portable POCAD exhibits strong potential for applications in the on-site detection of small toxic molecules to ensure food safety.

Human Biomonitoring of Mycotoxins in Blood, Plasma and Serum in Recent Years: A Review

This manuscript reviews the state-of-the-art regarding human biological monitoring (HBM) of mycotoxins in plasma serum and blood samples. After a comprehensive and systematic literature review, with a focus on the last five years, several aspects were analyzed and summarized: a) the biomarkers analyzed and their encountered levels, b) the analytical methodologies developed and c) the relationship between biomarker levels and some illnesses. In the literature reviewed, aflatoxin B1-lysine (AFB1-lys) and ochratoxin A (OTA) in plasma and serum were the most widely studied mycotoxin biomarkers for HBM. Regarding analytical methodologies, a clear increase in the development of methods for the simultaneous determination of multiple mycotoxins has been observed. For this purpose, the use of liquid chromatography (LC) methodologies, especially when coupled with tandem mass spectrometry (MS/MS) or high resolution mass spectrometry (HRMS), has grown. A high percentage of the samples analyzed for OTA or aflatoxin B1 (mostly as AFB1-lys) in the reviewed papers were positive, demonstrating human exposure to mycotoxins. This review confirms the importance of mycotoxin human biomonitoring and highlights the important challenges that should be faced, such as the inclusion of other mycotoxins in HBM programs, the need to increase knowledge of mycotoxin metabolism and toxicokinetics, and the need for reference materials and new methodologies for treating samples. In addition, guidelines are required for analytical method validation, as well as equations to establish the relationship between human fluid levels and mycotoxin intake.

An electrochemical immunosensor based on a combined amplification strategy with the GO–CS/CeO2–CS nanocomposite for the detection of aflatoxin M1

Herein, a sensitive electrochemical immunosensor modified with graphene oxide–chitosan (GO–CS) and cerium oxide–chitosan (CeO₂–CS) using screen-printed electrodes (SPEs) was developed for the determination of aflatoxin M₁(AFM₁) in milk.

Adverse Effects, Transformation and Channeling of Aflatoxins Into Food Raw Materials in Livestock

Aflatoxins are wide-spread harmful carcinogenic secondary metabolites produced by Aspergillus species, which cause serious feed and food contaminations and affect farm animals deleteriously with acute or chronic manifestations of mycotoxicoses. On farm, both pre-harvest and post-harvest strategies are applied to minimize the risk of aflatoxin contaminations in feeds. The great economic losses attributable to mycotoxin contaminations have initiated a plethora of research projects to develop new, effective technologies to prevent the highly toxic effects of these secondary metabolites on domestic animals and also to block the carry-over of these mycotoxins to humans through the food chain. Among other areas, this review summarizes the latest findings on the effects of silage production technologies and silage microbiota on aflatoxins, and it also discusses the current applications of probiotic organisms and microbial products in feeding technologies. After ingesting contaminated foodstuffs, aflatoxins are metabolized and biotransformed differently in various animals depending on their inherent and acquired physiological properties. These mycotoxins may cause primary aflatoxicoses with versatile, species-specific adverse effects, which are also dependent on the susceptibility of individual animals within a species, and will be a function of the dose and duration of aflatoxin exposures. The transfer of these undesired compounds from contaminated feed into food of animal origin and the aflatoxin residues present in foods become an additional risk to human health, leading to secondary aflatoxicoses. Considering the biological transformation of aflatoxins in livestock, this review summarizes (i) the metabolism of aflatoxins in different animal species, (ii) the deleterious effects of the mycotoxins and their derivatives on the animals, and (iii) the major risks to animal health in terms of the symptoms and consequences of acute or chronic aflatoxicoses, animal welfare and productivity. Furthermore, we traced the transformation and channeling of Aspergillus-derived mycotoxins into food raw materials, particularly in the case of aflatoxin contaminated milk, which represents the major route of human exposure among animal-derived foods. The early and reliable detection of aflatoxins in feed, forage and primary commodities is an increasingly important issue and, therefore, the newly developed, easy-to-use qualitative and quantitative aflatoxin analytical methods are also summarized in the review.

The overall and variations of Aflatoxin M1 contamination of milk in Iran: A systematic review and meta-analysis study

Major databases were searched until January 2019 and 77 eligible studies were included in the meta-analysis to estimate the overall mean of AFM1 in milk in Iran. The mean of AFM1 levels was obtained 55.97 ng/kg (95% CI: 50.09-61.84). However, the pooled estimated mean of AFM1 levels in milk were 94.58 (95% CI: 70.24-118.92), 59.19 (95% CI: 51.84-66.54) and 35.23 ng/kg (95% CI: 31.53-38.92), considering 4, 55 and 18 TLC, ELISA and HPLC-based studies (including 354, 9224 and 2606 samples), respectively. Also, there is a wide variation of AFM1 levels among different geographical regions which were the highest in northern (88.77 ng/kg). The AFM1 contamination of milk taken from the areas with humid climate was higher than the arid climate. AFM1 Levels were the highest in winter (48.70 ng/Kg). The level of AFM1 in pasteurized, raw, and UHT milk were 49.76, 55.08 and 94.81 ng/kg, respectively.

A signal-on electrochemical aptasensor for rapid detection of aflatoxin B1 based on competition with complementary DNA

Aflatoxin B1 (AFB1) is the most toxic mycotoxin, causing harmful effects on human and animal health, and the rapid and sensitive detection of AFB1 is highly demanded. We developed a simple electrochemical aptasensor achieving rapid detection of aflatoxin B1 (AFB1). A short anti-AFB1 aptamer having a methylene blue (MB) redox tag at the 3'-end was immobilized on the surface of a gold electrode. In the absence of AFB1, a complementary DNA (cDNA) strand hybridized with the MB-labeled aptamer, causing MB apart from the electrode surface and low current of MB. In the presence of AFB1, AFB1 competed with the cDNA in the binding to the MB-labeled aptamer, and the aptamer-AFB1 binding caused formation of a hairpin structure, making the MB close to the electrode surface and current of MB increase. Under optimized conditions, we achieved detection of AFB1 over dynamic concentration range of 2 nM-4 μM by using this signal-on electrochemical aptasensor. This method only required a simple 5-min incubation of sample solution prior to rapid electrochemical sensing, more rapid than other electrochemical aptasensors. The sensor could be well regenerated and reused. This sensor allowed to detect AFB1 spiked in 20-fold diluted beer and 50-fold diluted white wine, respectively. It shows potential for detection of AFB1 in wide applications.

A competitive thrombin-linked aptamer assay for small molecule: aflatoxin B1

We described a competitive thrombin-linked aptamer assay for small molecule, using aflatoxin B₁ (AFB₁) as a model, taking advantage of aptamer affinity binding and enzymatic activity of thrombin. We designed a dual functional DNA probe that contained the aptamer sequence for thrombin and the aptamer sequence for AFB₁. Thrombin was labeled on the DNA probe by affinity binding between thrombin and anti-thrombin aptamer. This thrombin-labeled DNA probe was attached on AFB₁-bovine serum albumin conjugate (BSA-AFB₁) coated on a microplate through the affinity interaction between AFB₁ and anti-AFB₁ aptamer. The thrombin attached on the microplate catalyzed the cleavage of peptide substrate into detectable product, generating signal for detection. In the presence of AFB₁, free AFB₁ competed with BSA-AFB₁ in the binding to the limited amount of DNA probe, leading to signal decrease. Detection of AFB₁ was achieved by measuring the signal change. Under optimized conditions, AFB₁ was successfully detected in the range from 0.5 nM to 1 μM when fluorogenic peptide substrate of thrombin and fluorescence analysis were applied. The use of chromogenic peptide substrate in the assay allowed the detection of AFB₁ ranging from 0.5 to 125 nM by simple absorbance analysis. The thrombin-linked aptamer assay showed good selectivity towards AFB₁, and enabled the detection of AFB₁ spiked in diluted beer and corn flour. This TLAA strategy extends the analytical application of thrombin and aptamers in detection of small molecules. Graphical abstract.

Aflatoxin-specific monoclonal antibody selection for immunoaffinity column development

Antibodies are the basic components of immunoanalytical systems used for detection of a wide range of analytes. Although there are some ground rules for antibody selection, analyte- and assay-specific criteria are the ones that determine the ultimate success of the immunoassays. In this study, we introduced an effective antibody selection procedure for the development of immunoaffinity columns for aflatoxins. The designed scheme puts emphasis on solvent- and matrix-related characterization steps and was used to comparatively evaluate eight monoclonal antibodies. The selected antibody was tolerant to 40% methanol, 20% acetonitrile, 30% acetone and 40% ethanol and did not interact with corn, red pepper or hazelnut extracts. Immunoaffinity columns developed with the selected antibody were validated by 15 independent aflatoxin analysis laboratories.

Prevalent Mycotoxins in Animal Feed: Occurrence and Analytical Methods

Today, we have been witnessing a steady tendency in the increase of global demand for maize, wheat, soybeans, and their products due to the steady growth and strengthening of the livestock industry. Thus, animal feed safety has gradually become more important, with mycotoxins representing one of the most significant hazards. Mycotoxins comprise different classes of secondary metabolites of molds. With regard to animal feed, aflatoxins, fumonisins, ochratoxins, trichothecenes, and zearalenone are the more prevalent ones. In this review, several constraints posed by these contaminants at economical and commercial levels will be discussed, along with the legislation established in the European Union to restrict mycotoxins levels in animal feed. In addition, the occurrence of legislated mycotoxins in raw materials and their by-products for the feeds of interest, as well as in the feeds, will be reviewed. Finally, an overview of the different sample pretreatment and detection techniques reported for mycotoxin analysis will be presented, the main weaknesses of current methods will be highlighted.

Use of Visible-Near-Infrared (Vis-NIR) Spectroscopy to Detect Aflatoxin B1 on Peanut Kernels

Current methods for detecting aflatoxin contamination of agricultural and food commodities are generally based on wet chemical analyses, which are time-consuming, destructive to test samples, and require skilled personnel to perform, making them impossible for large-scale nondestructive screening and on-site detection. In this study, we utilized visible-near-infrared (Vis-NIR) spectroscopy over the spectral range of 400-2500 nm to detect contamination of commercial, shelled peanut kernels (runner type) with the predominant aflatoxin B₁ (AFB₁). The artificially contaminated samples were prepared by dropping known amounts of aflatoxin standard dissolved in 50:50 (v/v) methanol/water onto peanut kernel surface to achieve different contamination levels. The partial least squares discriminant analysis (PLS-DA) models established using the full spectra over different ranges achieved good prediction results. The best overall accuracy of 88.57% and 92.86% were obtained using the full spectra when taking 20 and 100 parts per billion (ppb), respectively, as the classification threshold. The random frog (RF) algorithm was used to find the optimal characteristic wavelengths for identifying the surface AFB₁-contamination of peanut kernels. Using the optimal spectral variables determined by the RF algorithm, the simplified RF-PLS-DA classification models were established. The better RF-PLS-DA models attained the overall accuracies of 90.00% and 94.29% with the 20 ppb and 100 ppb thresholds, respectively, which were improved compared to using the full spectral variables. Compared to using the full spectral variables, the employed spectral variables of the simplified RF-PLS-DA models were decreased by at least 94.82%. The present study demonstrated that the Vis-NIR spectroscopic technique combined with appropriate chemometric methods could be useful in identifying AFB₁ contamination of peanut kernels.

GO-amplified fluorescence polarization assay for high-sensitivity detection of aflatoxin B1 with low dosage aptamer probe

Aflatoxin B₁ (AFB₁) is the most toxic mycotoxin of the aflatoxins (AFs) and shows carcinogenic, teratogenic and mutagenic effects in humans and animals. AFB₁ is widely seen in cereal products such as rice and wheat. This research proposed a low-cost, high-sensitivity fluorescence polarization (FP) assay for detection of AFB₁ using aptamer biosensors based on graphene oxide (GO). The aptamers labelled with fluorescein amidite (FAM) were adsorbed on the surface of GO through π-π stacking and electrostatic interaction, thus forming aptamer/GO macromolecular complexes. Under these conditions, the local rotation of fluorophores was limited and the system had a high FP value. When there was AFB₁ in the system, aptamers were dissociated from the GO surface and combined with AFB₁ owing to their specificity to form aptamer/AFB₁ complexes. As a result, large changes were observed in the molecular weights of aptamers before, and after, the combination, therefore leading to the apparent changes in FP value. The results showed that when only 10 nM of aptamer was used, the changes in FP and the AFB₁ concentration had a favourable linear relationship within 0.05 to 5 nM of AFB₁, and the lowest detection limit (LOD) was 0.05 nM. In addition, the recoveries of rice sample extract ranged from 89.2% to 112%. The method is simple, highly sensitive, cost-efficient and shows potential application prospects.

Biological Activity of the Carrier as a Factor in Immunogen Design for Haptens

Immunoanalytical methods are frequently employed in the detection of hazardous small molecular weight compounds. However, antibody development for these molecules is a challenge, because they are haptens and cannot induce a humoral immune response in experimental animals. Immunogenic forms of haptens are usually prepared by conjugating them to a protein carrier which serves as an immune stimulator. However, the carrier is usually considered merely as a bulk mass, and its biological activity is ignored. Here, we induced an endocytic receptor, transferrin receptor, by selecting its ligand as a carrier protein to enhance antibody production. We conjugated aflatoxin, a potent carcinogenic food contaminant, to transferrin and evaluated its potential to stimulate antibody production with respect to ovalbumin conjugates. Transferrin conjugates induced aflatoxin-specific immune responses in the second immunization, while ovalbumin conjugates reached similar antibody titers after 5 injections. Monoclonal antibodies were successfully developed with mice immunized with either of the conjugates.

Direct fluorescence anisotropy approach for aflatoxin B1 detection and affinity binding study by using single tetramethylrhodamine labeled aptamer

The discovery of aptamers for aflatoxin B1 (AFB1), one of toxic carcinogens, has allowed to develop aptamer-based sensors and assays for aflatoxin. In this work, we reported a direct fluorescence anisotropy (FA) assay for investigation of aptamer-AFB1 binding and detection of AFB1 with the aptamer having single tetramethylrhodamine (TMR) label on a specific site. From a series of labeling sites of a 50-mer aptamer, we screened out the aptamer with TMR labeling at the 26th T, capable of generating good and large FA-decreasing response to AFB1. By using the T26-labeled 50-mer aptamer probe in FA analysis, we determined the affinity and selectivity of aptamer, and identified the crucial region of aptamer and optimum experimental conditions for strong binding. The aptamer could be further truncated to as short as 26 nucleotides in length, and this shorter aptamer possessed a simple stem-loop secondary structure and retained good binding affinity. Nucleotides in the loop region of the aptamer were conserved and important for affinity recognition. We achieved FA detection of AFB1 with a detection limit about 2 nM by using the TMR-labeled aptamer probe. The cross reactivity of aflatoxin B1, aflatoxin B2, aflatoxin M1, aflatoxin M2, aflatoxin G1, and aflatoxin G2 with aptamer were estimated to be 100%, 61%, 23%, 21%, 6.3%, 6.5%, respectively. The aptamer probe presented good selectivity over other mycotoxins and showed potential in complex sample analysis. This study of affinity binding between aptamer and aflatoxins will be helpful for developing other aptamer-based assays and sensors for aflatoxins.

Development of aptamer fluorescent switch assay for aflatoxin B1 by using fluorescein-labeled aptamer and black hole quencher 1-labeled complementary DNA

Aflatoxin B1 (AFB1) is one of the most toxic mycotoxins and draws great concern in health and food safety. A DNA aptamer against AFB1 having a stem-loop structure shows high binding affinity to AFB1 and promise in assay development for AFB1 detection. Based on the structure-switching property of the aptamer, we report an aptamer fluorescence assay for AFB1 detection. Aptamer with fluorescein (FAM) label at 5' end was used as affinity ligand, while its short complementary DNA (cDNA) with BHQ1 (black hole quencher 1) label at 3' end was used as a quencher. In the absence of AFB1, FAM-labeled aptamer hybridized with BHQ1-labeled cDNA, forming a duplex of cDNA and aptamer, resulting in fluorescence quenching of FAM. When AFB1 bound with aptamer, the BHQ1-labeled cDNA was displaced from aptamer, causing fluorescence restoration of FAM. We tested a series of FAM-labeled aptamers and BHQ1-labeled cDNAs with different lengths. The lengths of the aptamer stem and the cDNA, Mg²⁺ in binding buffer, and temperature had significant influence on the performance of the assay. Under optimized conditions, we achieved sensitive detection of AFB1 by using a 29-mer FAM-labeled aptamer and a 14-mer BHQ1-labeled cDNA, and the detection limit of AFB1 reached 0.2 nM. The maximum fluorescence recovery rate of FAM-labeled aptamer caused by AFB1 was about 69-fold. This method enabled the detection of AFB1 in complex sample matrix, e.g., diluted wine samples and maize flour samples. This aptamer-based fluorescent assay for AFB1 determination shows potential for broad applications. Graphical abstract ᅟ.

Novel quartz crystal microbalance immunodetection of aflatoxin B1 coupling cargo-encapsulated liposome with indicator-triggered displacement assay

A simple and sensitive quartz crystal microbalance (QCM) immunosensing platform was designed for the high-efficient detection of aflatoxin B₁ (AFB₁) in foodstuff. Initially, phenoxy-derived dextran molecule was immobilized on the surface of QCM gold substrate by using thiolated β-cyclodextrin based on the supramolecular host-guest chemistry between phenoxy group and cyclodextrin. Then, AFB₁-bovine serum albumin (AFB₁-BSA)-conjugated concanavalin A (Con A) was assembled onto the QCM probe through the dextran-Con A interaction. Glucose-loaded nanoliposome, labeled with monocolonal anti-AFB₁ antibody, was used for the amplification of QCM signal. Upon target AFB₁ introduction, the analyte competed with the immobilized AFB₁-BSA on the probe for the labeled anti-AFB₁ antibody on the nanoliposome. Based on specific antigen-antibody reaction, the amount of the conjugated nanoliposomes on the QCM probe gradually decreased with the increment of target AFB₁ in the sample. Upon injection of Triton X-100 in the detection cell, the carried nanoliposome was lysed to release the encapsulated glucose molecules. Thanks to the stronger affinity of Con A toward glucose than that of dextran, AFB₁-BSA-labeled Con A was displaced from the QCM probe, resulting in the change of the local frequency. Under the optimum conditions, the shift of the functionalized QCM immunosensing interface in the frequency shift was proportional to the concentration of target AFB₁ within a dynamic range from 1.0 ng kg^-1 to 10 μg kg^-1 at a low detection limit of 0.83 ng kg^-1. In addition, the acceptable assayed results on precision, reproducibility, specificity and method accuracy for the analysis of real samples were also acquired. Importantly, our strategy can provide a signal-on competitive immunoassay for the detection of small molecules, e.g., mycotoxins and biotoxins, thereby representing a versatile sensing schemes by controlling the corresponding antibody or hapten in the analysis of food safety.

Aflatoxins in peanut oil: food safety concerns

Aflatoxins are widely recognised as important natural contaminants of a wide range of foods, including maize and peanuts (groundnuts), which form part of the staple diet in many countries of the developing world, especially in Africa. There is a frequent misconception based on solubility considerations and developed market surveys that aflatoxins do not occur in peanut oil. Thus, the use of peanut oil in human food is frequently overlooked as a source of aflatoxin exposure, yet artisanal oil extraction from contaminated peanuts in local facilities in the developing world results in carryover of these mycotoxins into the oil. Consequently, these peanut oils can have high contamination levels. This review highlights food safety concerns and addresses inter alia the analytical adaptations required to determine the polar aflatoxins in peanut oil. The determination of aflatoxins in peanut oil was first achieved by thin-layer chromatography, which was later mostly superseded by high-performance liquid chromatography (HPLC) with fluorescence detection, or later, by mass spectrometric detection. More recently, a specially modified HPLC method with immunoaffinity column clean-up and fluorescence detection has achieved official method status at AOAC International. In addition, the review deals with toxicology, occurrence and detoxification of contaminated oil. Although various methods have been reported for detoxification of peanut oil, the toxicity of degradation products, the removal of beneficial constituents and the effect on its organoleptic properties need to be considered. This review is intended to draw attention to this often overlooked area of food safety.

Achievements and Prospects in Electrochemical-Based Biosensing Platforms for Aflatoxin M₁ Detection in Milk and Dairy Products

Aflatoxins, which are mainly produced by Aspergillus flavus and parasiticus growing on plants and products stored under inappropriate conditions, represent the most studied group of mycotoxins. Contamination of human and animal milk with aflatoxin M₁, the hydroxylated metabolite of aflatoxin B₁, is an important health risk factor due to its carcinogenicity and mutagenicity. Due to the low concentration of this aflatoxin in milk and milk products, the analytical methods used for its quantification have to be highly sensitive, specific and simple. This paper presents an overview of the analytical methods, especially of the electrochemical immunosensors and aptasensors, used for determination of aflatoxin M₁.

Competitive horseradish peroxidase-linked aptamer assay for sensitive detection of Aflatoxin B1

Aflatoxin B1 (AFB1) is one of highly toxic mycotoxins and a known human carcinogen. The frequent contamination of AFB1 in food products and large health risk of AFB1 have raised global concerns. Sensitive detection of AFB1 is of vital importance and highly demanded. Herein, we reported a competitive horseradish peroxidase (HRP)-linked aptamer assay for AFB1, combining the advantages of aptamer for affinity binding and enzyme label for signal amplification. In this assay, free AFB1 in solution competed with a covalent conjugate of bovine serum albumin-AFB1 (BSA-AFB1) coated on the wells of microplate in binding to the HRP-labeled aptamer probe. HRP attached on BSA-AFB1 in the wells catalyzed the conversion of substrates into products, allowing the final detection of AFB1 through measurement of the generated products. When TMB (3,3',5,5'-tetramethylbenzidine dihydrochloride) was used as substrate, absorbance analysis of the product of enzyme reaction enabled the detection of AFB1 at 0.2nM. We further lowered the detection limit of AFB1 to 0.01nM through chemiluminescence analysis by using chemiluminescence substrate of HRP. This assay enabled the detection of AFB1 in complex sample matrix, such as diluted white wine and maize flour. This assay provides a simple, sensitive and rapid method for AFB1 determination.

Occurrence of aflatoxin M1 in milk samples from Italy analysed by online-SPE UHPLC-MS/MS

The occurrence of aflatoxin M1 in 69 milk samples collected in a south region of Italy in 2016 was evaluated. The samples were analysed using an automated method based on online SPE coupled with UHPLC tandem mass spectrometry. After a salt induced liquid-liquid extraction with acetonitrile to remove protein from milk, the extract was diluted with water and analysed using an automated online SPE MS/MS method. Among the analysed samples no one had AFM1 higher than the legally allowable limits whereas 71.4% of the other analysed samples were above the LOD of the method. The highest contamination level of AFM1 was found in pasteurised milk (44.39 ng kg^-1). The results show the worrying and widespread of AFM1 contamination, highlighting the necessity of monitoring studies in order to evaluate the reduction of the maximum legal limit.

Simple determination of aflatoxins in rice by ultra-high performance liquid chromatography coupled to chemical post-column derivatization and fluorescence detection

A fast and simple analytical method was developed and characterized for the determination of aflatoxins (B₁, B₂, G₁ and G₂) in rice. The procedure is based on a simple solid-liquid extraction without further clean-up, and analysis by ultra-high performance liquid chromatography coupled with fluorescence detection. Fluorescence emission of aflatoxins B₁ and G₁ was enhanced by post-column chemical derivatization using pyridinium bromide perbromide. The analytical method was satisfactorily characterized in white and brown rice. Under optimum conditions, external calibration in solvent could be used for quantification purposes and limits of quantification were below the maximum contents established by the European Union regulation for these contaminants/commodity group combination (0.07-0.14 µg/kg for white rice and 0.20-0.28 µg/kg for brown rice). Recovery studies carried out at three different concentration levels (0.5, 2 and 5 µg/kg) showed values in the range of 84.5-105.3%, and RSDs ≤ 5%.

High-performance liquid chromatography ultraviolet-photodiode array detection method for aflatoxin B1 in cattle feed supplements

AIM

The objective of the current study is to determine the concentration of aflatoxin B1 using high-performance liquid chromatography (HPLC) with a photodiode array (PDA) detector.

MATERIALS AND METHODS

Aflatoxin B₁ certified reference grade from Trilogy Analytical Laboratory dissolved acetonitrile (ACN) at 10 µg/mL was using standard assessment. HPLC instruments such as ultraviolet-PDA detector used a Shimadzu LC-6AD pump with DGU-20A5 degasser, communication module-20A, and PDA detector SPD-M20A with FRC-10A fraction collector. The HPLC was set isocratic method at 354 nm with a reverse-phase ODS C18 column (LiChrospher^® 100 RP-18; diameter, 5 µm) under a 20°C controlled column chamber. Rheodyne^® sample loops were performed in 20 µL capacities. The mobile phase was performed at fraction 63:26:11 H₂O: methanol:ACN at pH 6.8. A total of 1 kg of feed contained 10% bread crumbs and 30% concentrated, 40% forage, and 20% soybean dregs were using commercials samples. Samples were extracted by ACN and separated with solid phase extraction ODS 1 mL than elution with mobile phase to collect at drying samples performed. The samples were ready to use after added 1 mL mobile phase than injected into the system of HPLC.

RESULTS

We found that the retention time of aflatoxin B₁ was approximately 10.858 min. Linearity of 0.01-0.08 µg/mL aflatoxin B₁ dissolved in mobile phase was obtained at R²=0.9. These results demonstrate that these methods can be used to analyze aflatoxin B₁ and gain 89-99% recovery. The limit of detection of this assay was obtained at 3.5 × 10^-6 µg/mL.

CONCLUSION

This method was easy to apply and suitable to analyzing at small concentrations of aflatoxin B₁ in formulated product of feed cattle.

Large-Scale Membrane- and Lignin-Modified Adsorbent-Assisted Extraction and Preconcentration of Triazine Analogs and Aflatoxins

The large-scale simultaneous extraction and concentration of aqueous solutions of triazine analogs, and aflatoxins, through a hydrocarbon-based membrane (e.g., polyethylene, polyethylene/polypropylene copolymer) under ambient temperature and atmospheric pressure is reported. The subsequent adsorption of analyte in the extraction chamber over the lignin-modified silica gel facilitates the process by reducing the operating time. The maximum adsorption capacity values for triazine analogs and aflatoxins are mainly adsorption mechanism-dependent and were calculated to be 0.432 and 0.297 mg/10 mg, respectively. The permeation, and therefore the percentage of analyte extracted, ranges from 1% to almost 100%, and varies among the solvents examined. It is considered to be vapor pressure- and chemical polarity-dependent, and is thus highly affected by the nature and thickness of the membrane, the discrepancy in the solubility values of the analyte between the two liquid phases, and the amount of adsorbent used in the process. A dependence on the size of the analyte was observed in the adsorption capacity measurement, but not in the extraction process. The theoretical interaction simulation and FTIR data show that the planar aflatoxin molecule releases much more energy when facing toward the membrane molecule when approaching it, and the mechanism leading to the adsorption.

Low-cost humic acid-bonded silica as an effective solid-phase extraction sorbent for convenient determination of aflatoxins in edible oils

Aflatoxins (AFs) are highly toxic, mutagenic, carcinogenic, and teratogenic secondary metabolites produced by the toxigenic fungi Aspergillus flavus and Aspergillus parasiticus. AFs tend to contaminate a wide range of foods which is a serious and recurring food safety problem worldwide. Currently, immunoaffinity chromatography (IAC) has become the most conventional sample clean-up method for determining AFs in foodstuffs. However, IAC method is limited in the large-scale food analysis because it requires the use of expensive disposable cartridges and the IA procedure is time-consuming. Herein, to achieve the cost-effective determination of AFs in edible oils, we developed a promising solid-phase extraction (SPE) method based on commercially available humic acid-bonded silica (HAS) sorbent, followed by high performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS) analysis. In HAS-SPE, AFs can be captured by the HAS sorbent with both hydrophobic and hydrophilic interactions, whereas the oil matrix was captured only with the hydrophobic interactions. The oil matrix can be sufficiently washed off with isopropanol, while the AFs were still retained on the SPE packing, thus achieving selective extraction of AFs and clean-up of oil matrices. Under the optimal conditions of HAS-SPE, satisfactory recoveries ranging from 82% to 106% for four AFs (B₁, B₂, G₁, and G₂) were achieved in various oil matrices, containing blended oil, tea oil, rapeseed oil, peanut oil, sunflower seed oil, corn oil, blended olive oil, rice oil, soybean oil, and sesame oil. Only minor matrix effects ranging from 99% to 105% for four AFs were observed. Moreover, the LODs of AFs between 0.012 and 0.035 μg/kg completely meet the regulatory levels fixed by the EU, China or other countries. The methodology was further validated for assaying the naturally contaminated peanut oils, and consistent results between the HAS-SPE and the referenced IAC were obtained. In addition, HAS-SPE can directly treat diluted oil sample without liquid-liquid extraction and is automatable, thus making it simple and convenient for the large-scale determination of AFs in edible oils. Using this method, we successfully detected four AFs in the naturally contaminated peanut oils, which is, to the best of our knowledge, the first report about the determination of AFs in edible oils using HA-based SPE.

Development of Methods for Determination of Aflatoxins

Aflatoxins can cause damage to the health of humans and animals. Several institutions around the world have established regulations to limit the levels of aflatoxins in food, and numerous analytical methods have been extensively developed for aflatoxin determination. This review covers the currently used analytical methods for the determination of aflatoxins in different food matrices, which includes sampling and sample preparation, sample pretreatment methods including extraction methods and purification methods of aflatoxin extracts, separation and determination methods. Validation for analysis of aflatoxins and safety considerations and precautions when doing the experiments are also discussed.

Monoclonal IgA Antibodies for Aflatoxin Immunoassays

Antibody based techniques are widely used for the detection of aflatoxins which are potent toxins with a high rate of occurrence in many crops. We developed a murine monoclonal antibody of immunoglobulin A (IgA) isotype with a strong binding affinity to aflatoxin B1 (AFB1), aflatoxin B2 (AFB2), aflatoxin G1 (AFG1), aflatoxin G2 (AFG2) and aflatoxin M1 (AFM1). The antibody was effectively used in immunoaffinity column (IAC) and ELISA kit development. The performance of the IACs was compatible with AOAC performance standards for affinity columns (Test Method: AOAC 991.31). The total binding capacity of the IACs containing our antibody was 111 ng, 70 ng, 114 ng and 73 ng for AFB1, AFB2, and AFG1 andAFG2, respectively. Furthermore, the recovery rates of 5 ng of each AF derivative loaded to the IACs were determined as 104.9%, 82.4%, 85.5% and 70.7% for AFB1, AFB2, AFG1 and AFG2, respectively. As for the ELISA kit developed using non-oriented, purified IgA antibody, we observed a detection range of 2–50 µg/L with 40 min total test time. The monoclonal antibody developed in this research is hitherto the first presentation of quadruple antigen binding IgA monoclonal antibodies in mycotoxin analysis and also the first study of their utilization in ELISA and IACs. IgA antibodies are valuable alternatives for immunoassay development, in terms of both sensitivity and ease of preparation, since they do not require any orientation effort.