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

Abstract

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.

Fusarium Mycotoxins in Maize Field Soils: Method Validation and Implications for Sampling Strategy

“…As suggested by the authors, the following weighing factors were tested: 1/x 0.5 , 1/x, 1/x 2 , 1/y 0.5 , 1/y and 1/y 2 with x as the nominal concentration and y as the peak area. The matrix effect was assessed as the signal suppression enhancement ratio (SSE) and calculated as the deviation of matrix-matched calibration slopes from the solvent calibration slope, expressed in percent [29]. Additionally, the signals of NIV and DON were related to the respective internal standard signal.…”

“…While ZEN does not seem to be extractable by this method without modification, the method proposed in this study successfully validated two additional mycotoxins NIV and 15-AcDON. Furthermore, a recent study by Albert et al [29], with a very similar acetonitrile:water approach, proved that this method is also suitable for analysis of aflatoxins in soil. This may be of particular interest, since climate change may cause a spread of Aspergillus to European regions where Fusarium is currently predominant [60,61].…”

“…These parameters can be highly variable even at small field scales [27,28], leading to the necessity of the matrix effect assessment of individual samples. Therefore, extraction and exact quantification of mycotoxins in soils is challenging [29]. The usefulness of isotopically-labeled internal standards has been reported on in several studies [20,30,31].…”

Kinetics of microbial and photochemical degradation of aflatoxin B1 in a sandy loam and clay soil

“…organic carbon content, pH, soil texture, microbial biomass and activity (Table 1 ). The soil organic carbon and clay mineral contents, as reflected in soil texture (clay content), are of particular interest as these soil fractions represent sorption sites for AFs 23 , 25 , 38 as well as may attenuate the UV light 39 . Basal respiration (BR) and glucose-induced respiration (substrate induced respiration, SIR) of the soil were determined using the MicroResp setup 40 according to Schirmel et al 41 .…”

“…Aflatoxins, namely AFB1, AFB2, AFG1 and AFG2, in the soil samples were extracted with MeCN:H2O (84 : 16, v + v) and analyzed via high performance liquid chromatography with fluorescence detection (HPLC-FLD), according to Albert et al 38 . AFB2a was analyzed using the same method with excitation and emission wavelength of the fluorescence detector set to 365 and 455 nm.…”