Current Trends in Mycotoxin Detection with Various Types of Biosensors

One of the most important tasks in food safety is to properly manage the investigation of mycotoxin contamination in agricultural products and foods made from them, as well as to prevent its occurrence. Monitoring requires a wide range of analytical methods, from expensive analytical procedures with high-tech instrumentation to significantly cheaper biosensor developments or even single-use assays suitable for on-site monitoring. This review provides a summary of the development directions over approximately a decade and a half, grouped according to the biologically sensitive components used. We provide an overview of the use of antibodies, molecularly imprinted polymers, and aptamers, as well as the diversity of biosensors and their applications within the food industry. We also mention the possibility of determining multiple toxins side by side, which would significantly reduce the time required for the analyses.

Interference of mycotoxin binders with ELISA, HPLC and LC-MS/MS analysis of aflatoxins in maize and maize gluten

The aim of this study was to investigate the impact of mycotoxin binders on the determination of aflatoxins in maize and maize gluten using various analytical methods, including ELISA, HPLC and LC-MS/MS. Three types of commercially available mycotoxin binders, yeast cell wall, mineral, and a mixture of mineral and bacterium, were investigated at inclusion levels of 0.1%, 0.2% and 0.4%. The binders were added to maize and maize gluten contaminated with aflatoxins at concentrations between 6.9 and 26.7 μg kg^-1. The samples were analysed and the values were compared with corresponding controls (samples without binders) using ANOVA. The yeast cell wall binder had no significant effect (p=0.05) on the concentration of aflatoxins measured in either maize or maize gluten at any of the three inclusion levels, regardless of which analytical method was used. The mineral binder and the mixed mineral and bacterium binder had no significant effect (p=0.05) on the measured aflatoxin concentrations in either maize or maize gluten at any of the three inclusion levels when analysis was conducted using LC-MS/MS. Inclusion of these binders resulted in significant lower (p<0.01) detection of aflatoxins in both maize and maize gluten when analysis was conducted using ELISA; the effect was dose-dependent. They also resulted in significant lower detection of aflatoxins in maize extracted by methanol/water (70/30 v/v) (p<0.0001) and in maize gluten extracted by acetonitrile/water (80/20 v/v) (p<0.05) when analysis was conducted using HPLC. However, neither the mineral binder nor the mixed mineral and bacterium binder had significant effects (p=0.05) on aflatoxin concentrations measured in maize using HPLC, when extracted by acetonitrile/water (80/20 v/v). The study demonstrated that mycotoxin binders could result in underestimation of the levels of aflatoxin contamination, depending on the nature of the binder, the extraction solvent used in the analytical method, and the composition of tested sample.

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%.

Determining mycotoxins in baby foods and animal feeds using stable isotope dilution and liquid chromatography tandem mass spectrometry

We developed a stable isotope dilution assay with liquid chromatography tandem mass spectrometry (LC-MS/MS) to determine multiple mycotoxins in baby foods and animal feeds. Samples were fortified with [(13)C]-uniformly labeled mycotoxins as internal standards ([(13)C]-IS) and prepared by solvent extraction (50% acetonitrile in water) and filtration, followed by LC-MS/MS analysis. Mycotoxins in each sample were quantitated with the corresponding [(13)C]-IS. In general, recoveries of aflatoxins (2-100 ng/g), deoxynivalenol, fumonisins (50-2000 ng/g), ochratoxin A (20-1000 ng/kg), T-2 toxin, and zearalenone (40-2000 ng/g) in tested matrices (grain/rice/oatmeal-based formula, animal feed, dry cat/dog food) ranged from 70 to 120% with relative standard deviations (RSDs) <20%. The method provides sufficient selectivity, sensitivity, accuracy, and reproducibility to screen for aflatoxins at ng/g concentrations and deoxynivalenol and fumonisins at low μg/g concentrations in baby foods and animal feeds, without using conventional standard addition or matrix-matched calibration standards to correct for matrix effects.

Evaluation of the effect of mycotoxin binders in animal feed on the analytical performance of standardised methods for the determination of mycotoxins in feed

Recently, the use of substances that can suppress or reduce absorption, promote the excretion of mycotoxins or modify their mode of action in feed, so-called mycotoxin binders, has been officially allowed in the European Union as technological feed additives. The influence of the addition of mycotoxin binders to animal feed on the analytical performance of the official methods for the determination of mycotoxins was studied and the results are presented. Where possible standardised methods for analysis were applied. Samples of 20 commercial mycotoxin binders were collected from various companies. The following mycotoxins were included in the study: aflatoxin B₁, deoxynivalenol, zearalenone, ochratoxin A, fumonisins B₁ and B₂, T-2 and HT-2 toxins. A binder (or binders combined in a group) was mixed with feed material containing the mycotoxin, and the feed material was analysed. For data evaluation, the mean values were compared by Student's t-test (an independent two-sample t-test with unequal sample sizes and equal variance). The repeatability standard deviation of each method was used as an estimate of method variability. No significant differences (p = 0.05) in mycotoxin levels between binder-free material and the material containing different binders were found. Further, the possible effects of binder addition in combination with processing (pelletising) on the amount of aflatoxin B₁ determined in feed were studied. Three commercial mycotoxin binders containing hydrated sodium calcium aluminosilicate (HSCAS) as the main component were used in these experiments. Feed samples with and without mycotoxin binders were pelletised with and without steam treatment. After pelletising, materials were analysed for AFB₁. Only the combination pelletising and a mixture of binders added at a total level of 1.2% had a significant effect (41% reduction) on the amount of AFB₁ determined.

Field control of Fusarium ear rot, Ostrinia nubilalis (Hübner), and fumonisins in maize kernels

BACKGROUND

A 6 year study was conducted to evaluate the possible support of pesticides in mitigating mycotoxin contamination in maize grown in northern Italy. Different pesticides to control Ostrinia nubilalis (Hübner) (ECB), Fusarium verticillioides (Sacc.) Nirenb. and Aspergillus flavus Link were considered to check their efficacy and the best schedule to reduce fumonisin and aflatoxin contamination.

RESULTS

Fumonisin B1 (FB1) contamination at harvest has been reduced by ECB control, while the addition of ingredients targeted to F. verticillioides gave a limited advantage, mainly with low FB1 contamination; nevertheless, fusaria control is relevant in high-risk conditions, when FB1 is likely to exceed the legal limit. The combination of fungal and pest control in a single spray at silk browning stage (BBCH 67) is the best way of application. These results are robust because they were obtained in a 6 year trial, with relevant differences in meteorological conditions, ECB and fungal presence and mycotoxin contamination.

CONCLUSION

Insecticides have been shown to give advantages in their application, while the low FB1 contamination in the final years of the study did not lead to conclusive data on the advantage of adding a fungicide. Chemicals applied did not modify A. flavus incidence or aflatoxin contamination (only detected in trace amounts).

Growth and aflatoxin production of an Italian strain of Aspergillus flavus: influence of ecological factors and nutritional substrates

The aim of this study was to define quantitative relationships between temperature and water activity (aw), fungal growth and aflatoxin B1 (AFB1) production. A strain of Aspergillus flavus isolated from maize in north Italy, and previously tested and found positive for AFB1 production, was used for these experiments. The optimum temperature for AFB1 production was at 25 °C, slightly lower with respect to results obtained in other countries. 0.83 aw was the limit for growth of this strain of A. flavus after 60 days incubation at the optimum temperature. The solutes used to modify aw, glycerol and NaCl, influenced both growth and secondary metabolite production. Media modified with glycerol resulted in more AFB1 production when compared to the non-ionic solute NaCl added media. Maize based media, prepared with flour obtained from kernels at different ripening stages, only slightly influenced growth rates of A. flavus. The quantitative relationship obtained between fungal growth and AFB1 production in diverse temperature and aw levels were used to develop a valid predictive model for A. flavus presence and AFB1 production in the field.

Effect of the inclusion of adsorbents on aflatoxin B1 quantification in animal feedstuffs

The extraction efficiency of aflatoxin B1 (AFB1) in cattle feed containing nine adsorbents (ADSs) was investigated using two organic/aqueous solvents composed of methanol/water (80/20 v/v; MeOH) and acetone/water (85/15 v/v; AC). Samples were obtained including a highly AFB1-contaminated (HC) and a low-level AFB(1)-contaminated (LC) feedstuff (15.33 and 7.57 microg kg(-1), respectively), nine ADSs (four clay minerals; one yeast cell wall-based product; one activated carbon and three commercial ADS products) at two different levels of inclusion (10 and 20 g kg(-1)). After solvent extraction and immunoaffinity column clean-up, all samples were analysed for AFB1 by high-performance liquid chromatography (HPLC) with fluorescence detection. For each contamination level (HC and LC), the data obtained were analysed using a factorial arrangement in a completely randomized design. Means were compared with the correspondent controls using the Dunnett's test. No statistical difference was found in AFB1 levels of feedstuffs not containing ADSs when extracted with AC or MeOH, even if numerically higher values were obtained with AC. A dose-dependent effect (p < 0.01) of ADSs inclusion was observed on AFB1 recoveries that were lower when the higher ADS level (20 g kg(-1)) was included in the HC and LC feedstuffs. Higher AFB(1) recoveries were obtained using AC compared with MeOH, both in HC (75.0% versus 12.0%, respectively) and in LC (84.0% versus 22.8%, respectively) ADSs containing feedstuffs. However, when the activated carbon and the sodium bentonite were included in feeds, lower AFB1 concentrations with respect to control values (p < 0.001 and <0.05, respectively) were obtained also using AC. The data obtained in this study indicate that routine use of the MeOH solvent for AFB1 analysis of unknown feedstuffs, can produce misleading results if they contain an ADS.

Aflatoxin B1 contamination in maize related to the aridity index in North Italy

The aim of this study was to develop a prototype simple predictive system for aflatoxin B1 contamination in maize based on meteorological data. A database was developed with meteorological data and aflatoxin B1 contamination level of maize samples collected over a five-year period. All data were georeferenced. An aridity index was computed to summarise meteorological conditions and was used to estimate the probability of aflatoxin B1 contamination running a logistic regression. Relevant differences were found between years both for meteorology and aflatoxin B1 contamination. North Italy is not arid and conditions for Aspergillus flavus development and aflatoxin B1 contamination of maize do not commonly occur. Nevertheless, arid areas were found in some years, and favourable conditions for aflatoxin B1 production were confirmed by maize kernels surveys. The aridity index is a good indicator to summarise meteorological conditions being significantly correlated to maize kernels contamination at harvest. The logistic regression gave acceptable warning on aflatoxin B1 contamination in maize with 64% correct predictions and 23% overestimates. Underestimates were 13%, but only half of these were contaminated with aflatoxin B1 above 5 µg/kg, the European legislative limit for maize to be subjected to sorting or other physical treatment before human consumption or to be used as an ingredient in foodstuffs as well as for complete feedingstuffs for dairy animals. First indications with this simple predictive system are available before mid-July with conclusive information in early September, which is a good time to plan maize management pre- and post-harvest.

Assessment of the multi-mycotoxin-binding efficacy of a carbon/aluminosilicate-based product in an in vitro gastrointestinal model

A laboratory model, set to simulate the in vivo conditions of the porcine gastrointestinal tract, was used to study the small intestinal absorption of several mycotoxins and the effectiveness of Standard Q/FIS (a carbon/aluminosilicate-based product) in reducing mycotoxin absorption when added to multitoxin-contaminated diets. Mycotoxins were quickly absorbed in the proximal part of the small intestine at levels of 105 and 89% for fumonisins B1 and B2, respectively, 87% for ochratoxin A, 74% for deoxynivalenol, 44% for aflatoxin B1, and 25% for zearalenone. Addition of Standard Q/FIS to the diet (up to 2%, w/w) significantly reduced mycotoxin absorption, in a dose-dependent manner, up to 88% for aflatoxin B1, 44% for zearalenone, and 29% for the fumonisins and ochratoxin. Standard Q/FIS was ineffective in reducing deoxynivalenol uptake. These findings suggest that Standard Q/FIS can be used as a multitoxin adsorbent material to prevent the individual and combined adverse effects of mycotoxins in animals.

Studies on Aspergillus section Flavi isolated from maize in northern Italy

In 2003, for the first time in Italy, significant problems arose with colonization and contamination of maize destined for animal feed with Aspergillus section Flavi and aflatoxins (AFs). This resulted in milk and derived products being contaminated with AFM(1) at levels above the legislative limit. There was little knowledge and experience of this problem in Italy. The objectives of this research were thus to study the populations of Aspergillus section Flavi in six northern Italian regions and obtain information on the relative role of the key species, ability to produce sclerotia, production of the main toxic secondary metabolites, aflatoxins and cyclopiazonic acid, and tolerance of key environmental parameters. A total of 70 strains were isolated and they included the toxigenic species A. flavus and A. parasiticus. A. flavus was dominant in the populations studied, representing 93% of the strains. Seventy percent of strains of Aspergillus section Flavi produced AFs, with 50% of strains also producing cyclopiazonic acid. Sixty-two percent of A. flavus strains and 80% of A. parasiticus were able to produce sclerotia at 30 degrees C. Using 5/2 agar, only 1 strain developed S sclerotia and 19 L sclerotia. With regard to ecological studies, growth of Aspergillus section Flavi was optimal at between 25 and 30 degrees C, while AFB(1) production was optimal at 25 degrees C. Regarding water availability (water activity, a(w)), 0.99 a(w) was optimal for both growth and AFs production, while the only aflatoxin produced in the driest condition tested (0.83 a(w)) was AFB(1). This information will be very useful in identifying regions at risk in northern Italy by linking climatic regional information to levels of fungal contamination present and potential for aflatoxin production in maize destined for animal feed. This would be beneficial as part of a prevention strategy for minimising AFs in this product.

Determination of aflatoxin B1 in tiger nut-based soft drinks

An analytical method for the determination of aflatoxin B1 in a tiger nut-based soft drinks named 'horchata' is described. The method is based on an immunoaffinity clean-up, followed by HPLC separation and fluorescence detection after electrochemical post-column derivatization. The detection limit (S/N = 3) and the quantification limit (S/N = 10) were 0.02 and 0.06 microg kg(-1), respectively. The mean recovery at a level of 2 microg l(-1) was 88% (n = 6) and the coefficient of variation was 9%. The method was applied to conduct a small market survey for a beverage named 'horchata' that is frequently consumed by parts of the population in Southern Europe. Twenty-two samples from Spanish and Belgian supermarkets were analysed. As a result, only one sample was found to contain aflatoxin B1 at the limit of quantitation of the method.

Development of immunosensor based on OWLS technique for determining Aflatoxin B1 and Ochratoxin A

Mycotoxins are toxic secondary metabolites produced by a number of different fungi, and can be present in a wide range of food and feed commodities including cereal grains, oil seeds, dried fruits, apple juice, wine and meat products from animals fed contaminated meal. Many mycotoxins are highly resistant, and survive food processing, and therefore enter the food chain and provide a threat to human health. The optical waveguide lightmode spectroscopy (OWLS) technique has been applied to the detection of Aflatoxin and Ochratoxin in both competitive and in direct immunoassays. After immobilizing the antibody or antigen conjugate for the direct or indirect measurement, respectively, the sensor chip was used in flow-injection analyser (FIA) system. When using non-competitive method, sensor responses were obtained first only at analyte concentrations of 5-10 ng ml(-1). In both cases, the responses were very unstable. For competitive sensor investigation with the sensitized chip first the optimal dilution rate of monoclonal antibodies was determined, for the measurement of Ochratoxin A and Aflatoxin B1 the monoclonal antibody stock solution was diluted to 1 microg ml(-1) and to a 1:400 dilution, respectively. During the competitive measurement standard solutions were mixed with monoclonal antibodies at the appropriate concentration, the mixture was incubated for 1 min and injected into the OWLS system. The sensitive detection range of the competitive detection method was between 0.5 and 10 ng ml(-1) in both cases. After the establishment of the indirect method, barley and wheat flour samples were measured, and the results were in good correlation by those measured by enzyme linked immuno-sorbent assay (ELISA). Regression coefficient between the two methods for Ochratoxin and Aflatoxin was determined as 0.96 and 0.89, respectively.

High-performance liquid chromatography with post-column derivatisation and fluorescence detection for sensitive determination of aflatoxin M1 in milk and cheese

A new HPLC method with fluorescence detection using pyridinium hydrobromide perbromide as a post-column derivatising agent has been developed to determine aflatoxin M1 in milk and cheese. The detection limits were 1 ng/kg for milk and 5 ng/kg for cheese. The calibration curve was linear from 0.001 to 0.1 ng injected. The method includes a preliminary C18-SPE clean-up and the average recoveries of Aflatoxin M1 from milk and cheese, spiked at levels of 25-75 ng/kg and 100-300 ng/kg, respectively, were 90 and 76%; the precision (RSDr) ranged from 1.7 to 2.6% for milk and from 3.5 to 6.5% for cheese. The method is rapid, easily automatable and therefore useful for accurate and precise screening of aflatoxin M1 in milk and cheese.