Recent Developments in the Analysis of Mycotoxins
Sampling, Sample Preparation and Sample Extraction and Clean-up for the Analysis of Mycotoxins
Introduction
This and the following chapter highlight key developments in methods for the analysis of mycotoxins which occurred, primarily, during 2019.
A previous review has addressed the development of analysis methods from 2017 to 2019 (Tittlemier et al. 2019), and general and advanced methods for the detection and measurement of aflatoxins and their metabolites have been recently reviewed (Mahfuz et al. 2018).
Part 1 describes recent developments in:
- • Sampling and Sample Preparation
- • Sample Extraction and Clean-up
The analysis of specific mycotoxins is considered under the headings described above.
Sampling and Sample Preparation
The importance of employing effective sampling and sample preparation procedures at the beginning of the analytical sequence has previously been comprehensively discussed (Turner et al. 2015). Briefly, it is essential that the method employed for the collection of the aggregate sample, from the
Email: This email address is being protected from spam bots, you need Javascript enabled to view it batch of food or feed under evaluation, accommodates the heterogeneous distribution of mycotoxins (especially the aflatoxins) such that the sample is truly representative of the original batch. Similarly, it is equally important that the aggregate sample is comminuted and sub-divided in a manner which maintains the representative nature of the aggregate sample; and, that the final laboratory sample is representative of the sub-sample. These criteria are best met by employing a sub-sampling mill to comminute and sub-divide the aggregate sample, and by converting the resultant sub-sample into a homogeneous aqueous slurry. Typically, lOOg representative laboratory samples are then withdrawn from the slurry, prior to their analysis.
In recent developments, a cost effective sampling and analysis method for mycotoxins in cereals has been described (Focker et al. 2019), together with sample preparation and analytical considerations for the US aflatoxin sampling program for shelled groundnuts (Davis et al. 2018). A method for the precise quantitation of aflatoxin, involving the preparation of maize meal slurries has also been described (Kumphanda et al. 2019).
The study performed by Focker et al. (2019) attempted to find the most cost- effective sampling and analysis plan for the determination of deoxynivalenol (DON) in a wheat batch and aflatoxins in a maize batch. Considering the cost of the plan as a major constraint, an optimization model was constructed which maximized the number of correct decisions for accepting or rejecting a batch of cereals. The 'decision variables' were: the number of incremental samples collected from the batch; the number of sample aliquots analysed; the choice of the analytical method (i.e. liquid chromatography combined with mass-spectrometry (LC-MS/MS), enzyme linked-immunosorbent assay (ELISA), or lateral flow devices (LFD). For DON in w'heat, the difference between the optimal plaits using the three different analytical methods was minimal. However, for aflatoxins in maize, the cost effectiveness of the plan using LC-MS/MS or ELISA were comparable, whereas the plan considering onsite detection with LFDs was least cost effective.
Davis et al. (2018) concluded that sample preparation was a greater source of variation than analytical testing, when determining the aflatoxin content of batches of groundnuts. They recommended that sample preparation should be performed using a vertical cutter mill, which converts a 22 kg aggregate sample into a homogeneous paste. A 1100 g subsample of the latter was prepared by combining randomly collected aliquots of paste before converting the subsample to an aqueous slurry, from which 122.8 g portions (equivalent to 50 g groundnut) were taken for analysis.
Although the authors recognised that disagreement exists within the US groundnut industry regarding the relative performance of a widely used subsampling mill and a vertical cutter mill, they observed that a subsampling mill provides significantly less comminution compared to a properly sized vertical cutter mill. Consequently, they argue, the aflatoxin distributions among subsamples produced from a subsampling mill remain more positively skewed than subsample distributions derived from a vertical cutter mill, which are more normally distributed around the sample mean.
However, it was also noted that there is a significant difference between the cost of a sub-sampling mill and an appropriate vertical cutter mill, which are priced at around $5,000 and $40,000, respectively.
The iieed to maintain the representative nature of the samples, from the original batch to the laboratory sample is especially important when considering so-called 'point-of-need' screening tests (Soares et al. 2018). Here, the volumes of the sample solutions subjected to analysis can be of the order of iianolitres. Needless to say, ensuring that such a small sample volume accurately represents the mycotoxin coiicentration of, for example, a 20 tonne batch of groundnuts is a very significant challenge! However, it should be remembered that if the represeiitative nature of the samples is not maintained throughout the analytical sequence, then the final analysis result will be meaningless.
