The Effect of Grind and Extraction Size on Aflatoxin Result Variability
Collin L. Maune, Carrie K. Maune, Bruce R. Malone, Ronald Niemeijer, Jenny B. Buhr
Trilogy Analytical Laboratory, 870 Vossbrink Drive, Washington, MO 63090 USA
Aflatoxin contamination in the 2012 US corn crop was widespread.
This resulted in an increase of the overall amount of Aflatoxin testing performed on corn and corn products.
Sample preparation of products being tested for Aflatoxin is a critical part of the total analytical process.
It is well documented that sampling contributes a large portion of the total overall analytical variability.
Differences in sample grind size as well as the amount of sample extracted can also contribute to the overall analytical variability.
An evaluation was conducted to compare the exraction of corn naturally contaminated with Aflatoxin utilizing different sample grinds and different sample extraction weights.
The naturally contaminated corn was ground to various mesh sizes, homogenized and various sample sizes were extracted.
The extractions were performed using acetonitrile/water (84/16).
The extracts were then analyzed by HPLC using a modification of AOAC method 994.08.
Data presented shows the effect grind size and sample extraction size has on result variability of aflatoxin.
Ten pounds of whole corn known to be naturally contaminated with aflatoxin was selected for this evaluation and ground to four different mesh size and sampled as described below.
Four different sizes (25.0 g, 10.0 g, 5.0 g and 1.0 g) were weighed in replicates of ten from each of these samples.
1. The entire ten pound sample was ground through a burr mill with settings to ensure approximately 50% passed through a 10 mesh sieve. After grinding 100 grams were sieved to determine exact mesh size composition of the sample. The remaining sample was then mixed to homogenize.
2. The remaining sample from above was ground through a burr mill so that approximately 50% passed through a 20 mesh sieve. After grinding, 100 grams were sieved as above to determine exact mesh size composition of the sample. The remaining sample was then mixed to homogenize.
3. The remaining sample from above was ground through a burr mill with settings to ensure approximately 95% passed through a 20 mesh sieve. After grinding, 100 grams were sieved as above to determine exact mesh size composition of the sample. The remaining sample was then mixed to homogenize
4. The remaining sample from above was ground through a Retsch Mill fitted with a 30 mesh screen so that 100% passed through a 30 mesh sieve. After grinding, 100 grams were sieved as above to determine exact mesh size composition of the sample. The remaining sample was then mixed to homogenize.
All samples were then extracted with Acetonitrile/water (84/16) and analyzed for aflatoxin with AOAC method 994.08 using a KOBRA cell for post column bromination.
Historically, much emphasis has been placed on the effect sampling has on aflatoxin testing and the large amount of variability contributed by sampling procedures. This poster demonstrates the importance of sample preparation in aflatoxin analyses and the variability that can also be incurred with different sample preparation parameters.
- This evaluation demonstrates the finer a sample is ground the result variability decreases, however appropriable sample mesh size for extraction must be maintained or variability increases.
- Larger sample size improved variability, however 10 mesh and 20 mesh (50%) did not produce results with less than a 46% cv at any sample extraction size.
- This evaluation also indicates that a one gram sample size, regardless of grind size should never be utilized.
- While five grams is not the preferred sample extraction weight, the variability at thirty mesh and twenty mesh (95%) appears to be consistent with a CV of 13.58% to 14.44%. If a 5.0 gram sample size is utilized, the sample must be finely ground in order to provide reasonable results.
- This research confirms that a twenty-five gram sample at either a twenty mesh (95%) or a thirty mesh (100%) or a ten gram sample at thirty mesh (100%) all have less than a 10% cv. One of these three testing parameters should be utilized for aflatoxin testing.
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