Aflatoxins, detection

As regards the aflatoxin detection, UV spectrophotometry has been definitively abandoned, because of the lack of selectivity and the very poor analytical response, resulting in a very high detection limit. Since aflatoxins show fluorescence under UV light, spectrofluorimetric detection has been adopted in the last years. 

Plastic microdevices for high-throughput screening with MS detection were also prepared for detection of aflatoxins and barbiturates. These devices incorporated concentration techniques interfaced with electrospray ionization MS (ESI-MS) through capillaries [2], The microfluidic device for aflatoxin detection employed an affinity dialysis technique, in which a poly (vinylidene fluoride) (PVDF) membrane was incorporated in the microchip between two channels. Small molecules were dialyzed from the aflatoxin/antibody complexes, which were then analyzed by MS. A similar device was used for concentrating barbiturate/antibody complexes using an affinity ultrafiltration technique. A barbiturate solution was mixed with antibodies and then flowed into the device, where uncomplexed barbiturates were removed by filtration. The antibody complex was then dissociated and electrokinetically mobilized for MS analysis. In each case, the affinity preconcentration improved the sensitivity by at least one to two orders of magnitude over previously reported detection limits. 

Several research groups have reported antibodies for aflatoxins and other mycotoxins (27). Commercial kits for aflatoxin detection in various substrates have been announced. The introduction of such kits will permit on-site detection of aflatoxins to be confirmed immediately rather than having to wait for analytical results from a remote laboratory following detection of fluorescing materials in a commodity. Since aflatoxins and other microbial toxins have a number of structural variations, the antibodies used in their analysis must be carefully selected to assure that the proper compounds are being detected and accurately measured. 

Source Adapted from Manetta, A. C. 2011. Aflatoxins Their measure and analysis. In Aflatoxins—Detection, Measurement and Control, ed. Dr Irineo Torres-Pacheco, InTech Publisher, http //www.intechopen.com/books/aflatoxins-detection-measurement-and-control/aflatoxins-their-measureand-analysis. With permission. 

Strains of AFP were evaluated with respect to their ability to produce aflatoxins. Fourteen strains (51.7%) were aflatoxigenic, and the principle aflatoxins detected were and B, except for two isolates of barley that produced aflatoxin B, B, and G. Barley samples were imported, and this suggests the possible presence of aflatoxins in the Venezuelan imported-food market. 

Post-column in-line photochemical derivatization permits fluorescence detection of the common aflatoxins Bl, B2, Gl, and G2 (60). Chromatographic evidence indicates that photolysis causes the hydration of the nonfluorescent Bl and Gl components to B2a and G2a components, respectively. Analysis of naturally contaminated com samples show no interfering peaks and permits the deterrnination of 1 and 0.25 ppb for Bl and B2, respectively. 

There have been compared the methods of mycotoxin control in food products with aflatoxin as an example, using both HPLC method with fluorescent detecting on the apparatus Thermo FL 3000 with a column BDS Hypersil C 2.1x150, as well as a chromatodensitometry method on the apparatus CAM AG TLS Scanner 3. 

Sophisticated and veiy sensitive methods have been developed in the food industry for detecting many other microbial toxins. For example, aflatoxin deteetion in seedstuffs and their oils is performed by solvent extraction, adsorption onto columns containing selective antibodies for them, and detected by exposure to ultraviolet light. 

In a clinical trial performed in China, the administration of 300 mg/day of copper chlorophyllin to humans who had detectable levels of serum aflatoxin due to unavoidable food contamination resnlted in a 50% reduction of median urinary levels of aflatoxin-DNA adducts. If health benefits from consuming natural chlorophylls were confirmed, it wonld be easy to add green leafy vegetables to a daily diet to obtain the benefit. Since leafy vegetables contain usually up to 200 mg chloro-phylls/100 g fresh weight, the intake of approximately 1 to 2 cups of raw spinach/day... 

No aflatoxin B1 was detected in a large number of green coffee samples. In order to evaluate aflatoxin B1 in coffee, green coffee beans were artificially contaminated. The aflatoxin B1 in these artificially contaminated green coffee beans was mostly decomposed by roasting and was further decomposed during coffee brew preparation.207... 

A protocol approved by the FDA to determine the safety of low gossypol cottonseed kernels for human consumption was the basis for the second study by Reber (7 ). To prepare raw cottonseed flour, raw kernels were ground to meet Ro-tap sieve specifications of lab chow. To prepare roasted cottonseed flour, raw kernels were dry roasted at not less than 121°C for not less than 5 min. To prepare cooked cottonseed flour, raw kernels were cooked in steam until batch temperature had been at or above 121°C for 5 min. All cottonseed kernels were ground in the manner described above. The kernels contained not more than 0.037% (370 ppm) of free gossypol. They were free of Salmonella and did not contain detectable amounts of aflatoxin. The proximate analyses of the cottonseed flours are shown in Table I. 

The stages in commodity handling at which aflatoxin and other mycotoxins can be detected and their amounts modified are shown in Figure 9.4. Aspergillus spp. thrive in hot, humid, subtropical and tropical climates. When environmental conditions favor aflatoxin production, accumulation is rapid, both in the field and in storage. 

Most manufacturing processes do not detoxify aflatoxin and therefore if the aflatoxins are not detected, products will be marketed. One of the processes used for reducing aflatoxin levels is nixtamalization (alkaline cooking), which is used during the making of corn tortillas, tortilla chips, and corn chips, and gives a 51 to 78% reduction in aflatoxin levels (Torres et al., 2001). 

Did this FDA position make any scientific sense It implied that if aflatoxin could be detected by reliable analysis, it was too risky to be consumed by humans, but that if the aflatoxin happened to be present below the minimum detectable concentration it was acceptable. (Analytical chemists can never declare that a chemical is not present. The best that can be done is to show that it is not present above some level - 20 ppb in the case of aflatoxins, and other, widely varying, levels in the case of other chemicals in the environment.) To be fair to the FDA, perhaps the word acceptable should be withdrawn the agency s position was not so much that all concentrations of aflatoxin up to 20 ppb were acceptable, but that nothing much could be done about them, because the chemists could not determine whether they were truly present in a given lot of food until the concentration exceeded 20 ppb. 

As in aflatoxin producers, also producers of Fusarium toxins have been detected by PCR assay which were based on primers hybridizing to genes... 

Geisen, R. (1996). Multiplex polymerase chain reaction for the detection of potential aflatoxin and sterigmatocystin producing fungi. Syst. Appl. Microbiol. 19, 388-392. 

Scherm, B., Palomba, M., Serra, D., Marcello, A., and Megheli, Q. (2005). Detection of transcripts of the aflatoxin genes aflD, aflO, and aflP by reverse transcription-polymerase chain reaction allows differentiation of alfatoxin-producing and non-producing isolates of Aspergillus flavus and Aspergillus parasiticus. Int. J. Food Microbiol. 98, 201-210. 

Groopman, J. D. and Sabbioni, G. "Detection of aflatoxin and its metabolites in human biological fluids" In Mycotoxins, Cancer and Health, Bray, G. A. and Ryran, D. H., Eds. Pennington Center Nutrition Series Louisiana State University Press Baton Rouge, LA, 1991, VoL 7, pp. 18-31. 

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