Sampling dried figs for aflatoxin – Part 1: variability associated with sampling, sample preparation, and analysis

Abstract

The variability associated with the aflatoxin test procedure used to estimate aflatoxins in bulk shipments of dried figs was investigated. Sixteen 10 kg laboratory samples were taken from each of twenty commercial bulk lots of dried figs suspected of aflatoxin contamination. Two 55 g test portions were taken from each comminuted laboratory sample using water-slurry comminution methods. Finally, two aliquots from the test portion/solvent blend were analysed for both aflatoxin B1 and total aflatoxins. The total variance associated with testing dried figs for aflatoxins was measured and partitioned into sampling, sample preparation and analytical variance components (total variance is equal to the sum of the sampling variance, sample preparation variance, and analytical variance). Each variance component increased as aflatoxin concentration increased. Using regression analysis, mathematical expressions were developed to model the relationship between aflatoxin concentration and the total, sampling, sample preparation and analytical variances when testing dried figs for aflatoxins. The regression equations were modified to estimate the variances for any sample size, test portion size, and number of analyses for a specific lot aflatoxin concentration. When using the above aflatoxin test procedure to sample a fig lot at 10 μg/kg total aflatoxins, the sampling, sample preparation, analytical, and total variances were 47.20, 0.29, 0.13, and 47.62, respectively. The sampling, sample preparation, and analytical steps accounted for 99.1, 0.6, and 0.3% of the total variance, respectively. For the aflatoxin test procedure used in this study, the sampling step is the largest source of variability.

Improved Sample Selection and Preparation Methods for Sampling Plans Used to Facilitate Rapid and Reliable Estimation of Aflatoxin in Chicken Feed

“…As reported in the literature, aflatoxin contamination is characterized by heterogeneous spatial distribution and nugget effect [ 37 , 60 ]. Wet milling is more efficient than dry milling in producing a more homogenous sample [ 35 , 39 , 43 , 61 ]. Indeed, water slurring was recently incorporated as a sample homogenizing procedure for aflatoxin analysis in maize [ 42 ] and dried figs [ 35 ].…”

“…Aflatoxin detection methods include immunoassays [ 16 , 32 ], fluorimetry [ 18 ] and chromatographic methods [ 14 , 32 , 33 , 34 ] such as LC-MS/MS for multi-mycotoxin analysis [ 15 , 19 ]. While these methods have different performance, the largest uncertainty associated with the measurement of aflatoxin content is due to lack of homogeneity of the contaminant in food and feed leading to variability [ 4 , 35 ]. It is indeed not easy to get a representative sample [ 11 , 36 , 37 ] that accurately estimates true aflatoxin content in a bulk consignment, as observed by Matumba et al [ 38 ].…”

“…Aflatoxin analysis in food and feed is a three-step process: selection of the sample of a given size, sample preparation and quantification [ 4 , 40 ]. Development of chemical analysis often focuses on the last step, yet the sample selection step is the largest source of variability, followed by sample preparation, while quantification is the smallest contributor [ 35 , 37 , 39 , 41 ]. High variability necessitates increase in replicates to achieve required accuracy, thereby increasing the sample analysis turnaround time.…”

“…There is need for test procedures with improved accuracy and precision for estimation of true aflatoxin exposure to ensure feed safety [ 36 ]. Recent data on aflatoxin contamination in figs [ 35 ] and maize [ 42 ] show that optimization of upstream procedures can considerably reduce the measurement uncertainty. In this study, sample selection, reduction and extraction steps were designed and validated to ensure representativeness of collected samples as well as appropriateness of the procedures and sampling tools used for estimation of aflatoxin residues in chicken feed.…”

“…In this study, sample selection, reduction and extraction steps were designed and validated to ensure representativeness of collected samples as well as appropriateness of the procedures and sampling tools used for estimation of aflatoxin residues in chicken feed. We first optimized sample selection procedures, and then incorporated a wet milling (water slurring) step in the feed sample preparation procedure, a critical modification that enhances sample homogenization more effectively than dry milling and a lesson learned from food analysis [ 35 , 39 , 41 , 42 , 43 ]. This reduces inter-assay variability and need for measurement replications thus decreasing sample analysis turnaround time.…”