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QUIZ Final Report (G03030)

Project Code: G03030;
Publication:

La Mura, M., Allnutt, T.R., Greenland, A., Mackay, I. & Lee, D. (2010) Application of quiz for GM quantification in food. Food Chemistry, published online doi: 10.1016/j.foodchem.2010.10.002

01/08/2011

QUIZ is an alternative method for GMO quantification. The test DNA sample is diluted to a point at which aliquots from it may or may not contain the molecule of interest. The starting number of the molecule can be calculated from the frequency of negatives using binomial probability. The technique can independently determine, within a given sample, the absolute numbers of a GMO-specific marker and a reference marker, and the relative values of the two provide an estimation of GMO content.

Project G03025 demonstrated proof of principle of QUIZ by measuring the RoundUp Ready™ soya content of a set of DNA admixture samples and assessed its accuracy by comparing the results obtained using 384 wells for each of the two targets, with the industry standard – real-time PCR (RT-PCR) performed by a commercial tester (idNA, Norwich).

The follow-on project, G03030, explores QUIZ further and seeks to assess some of its limitations.
Modelling and computer simulations demonstrate the performance of QUIZ and the accuracy of GMO values obtained can be quantified: the precision is determined by sample size and the positive/negative ratio of each marker.
The GMO contents of two sets of samples, one containing RoundUp Ready™ soya and the other MON810 maize, extracted from certified reference materials (CRMs), were measured by QUIZ using 96-well format PCR and by RT-PCR. Repeated measurements generated by both partners of the project (NIAB and CSL) allow an assessment of inter- and intra-laboratory variations as well as a comparison with the industry standard.
A trend of overestimation of the MON810 and underestimation of the RoundUp ReadyTM soya contents can be attributable to difference in amplicon lengths of the GMO and reference markers amplified by PCR.
Empirical determination of the DNA content of ‘unknown’ samples is a pre-requisite for QUIZ and can be performed by limiting template PCR created by serial dilutions of the sample. Multiple sampling at each dilution produces ‘mini-QUIZ’ data that can be used to estimate percent GMO in addition to DNA concentration. This may be all that is required to show, within acceptable confidence limits, whether samples exceed statutory labeling thresholds.
For ease of GMO quantification, software has been developed for QUIZ estimation that corrects for the well known bias in estimation of most probable number in small samples.

Food testing results suggest more work is required to reduce variability in data to make the method operationally routine. However, estimates of GM content were obtained for processed foods containing MON810 and/or RoundUp ReadyTM soya and that these values were as good results obtained from RT-PCR.

Final Report

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