Special Edition: Lab Technology
Vicam lateral flow evaluated to determine aflatoxins in maize
The validation study for the AFLA-V AQUA provided information on the method precision profile, cut off values and false suspect and false negative rates.
The aim was to evaluate the analytical performances of a commercial lateral flow device (LFD) to determine aflatoxins in maize after water-based extraction, according to Commission Regulation (EU) No. 519/2014.
Validation study results
Total precision for contaminated samples varied from 14%-29%. Cut off values calculated considering 2 μg kg−1 or 4 μg kg−1 as the screening target concentration (STC) were 1.24 and 2.18 μg kg−1, respectively, whereas the false suspect rate for blanks was 42% and 8%, respectively.
False negative rate for samples containing the target analytes above the screening target concentrations was <1% in all statistical evaluation.
This is in compliance with the maximum 5% set in Commission Decision 657/2002/EC and Regulation 519/2014/EU.
Analysis of naturally contaminated maize samples performed by using a LFD and the AOAC official method revealed a good correlation (parameters of the linear regression: r = 0.97, slope = 0.96) between results.
A satisfactory agreement between reference values and test results was found in the analysis of reference materials.
In the US, an action level of 20 μg kg−1 of aflatoxins has been set by the US Food and Drug Administration.
In the European Union maximum permitted levels are 2 μg kg−1 Aflatoxin B1 and 4 μg kg−1 total aflatoxins.
Outside the lab with screening tests
Screening tests can play an important role in safety monitoring of food and feed chains, allowing rapid decision making and interventions and affecting the final product price.
The use of LFDs with water-based extraction protocols eliminates the use of hazardous solvents and makes them more practical for assays to be performed outside the lab.
In the study, each sample set included 25 samples belonging to three maize batches with different origins.
Negative samples contained Aflatoxin B1 at levels lower than 0.5 μg kg−1 (i.e. the LOQ of the LC-MS/MS method), whereas two positive sample sets were prepared containing Aflatoxin B1 at about 2 and 4 μg kg−1, respectively.
For the blank samples, a high relative standard deviation of the test response was seen but an acceptable rate of false positive results for these samples was obtained.
Contribution of the matrix-to-matrix variation was not surprising considering the extract was applied to the LFD without dilution.
“However the overall precision <30% indicated an acceptable robustness of the method, also taking into consideration the low target levels of AFB1 considered for validation.”
Performances at the STC of 2 μg kg−1, in spite of having an adequate cut off value, found the screening method had a high rate of false suspect results (42%) for the blanks.
“A high false positive rate may affect the economic benefit of the test, because false suspect results require the application of confirmatory methods to samples that are actually compliant with legal or target levels.
“The lateral flow test being less expensive and organic solvent free, and requiring less time and skills, the overall balance of the pros (costs and time) and cons (42% false positive) could be still positive.”
Source: Analytical Methods, 2018, 10, 123-130
“Validation of a lateral flow immunoassay for the rapid determination of aflatoxins in maize by solvent free extraction”
Authors: Veronica M. T. Lattanzio, Natascia Guarducci, Stephen Powers, Biancamaria Ciasca, Michelangelo Pascale and Christoph von Holst