AOAC ERP Gluten Assays - Dec 2018

Annex B

For this approach one needs to assume that the standard deviation of blank samples and samples with a low but measurable contamination is comparable. Using this approach the estimated LoDs for cereals, flour, and flakes were 1.7 mg/kg, 1.9 mg/kg, and 0.4 mg/kg, respectively (table 7). For confirmation, rice-based gluten-free foods were analyzed (table 8), since it is much easier to obtain rice-based foods completely free of gluten. Indeed, the rice-based foods showed gluten concentrations near to zero. Using the established LoD formula (mean + 3 x SD), an overall LoD of 2.3 mg/kg was estimated, matching the estimates for the oat-based foods.

Table 8. Estimation of LoD in rice-based gluten-free food matrices by extracting 6 replicates (arranged in two columns) and estimating the concentrations by extrapolation; for each matrix the mean concentration, standard deviation, and LoD = mean + 3-fold SD are given in mg/kg gluten.

Gluten-free matrix Food Cake Mix Food Cake Mix Food Cake Mix Pizza Crust Mix Pizza Crust Mix Pizza Crust Mix Rice Flour Blend Rice Flour Blend Rice Flour Blend

mg/kg

mg/kg

mean

SD

LoD

0.06 2.19 0.45 0.62 0.20 0.14 -0.25 0.08 0.11 0.20 1.51 0.53 0.45 0.22 -0.11

0.68 0.73 0.85 1.69 0.25 0.22 0.62 0.31 0.22 1.57 0.73 0.79 0.20 0.11 0.25

0.82

0.72

3.0

0.52

0.60

2.3

0.18

0.29

1.0

Bisquit Mix Bisquit Mix Bisquit Mix Brownie Mix Brownie Mix Brownie Mix

0.89

0.55

2.5

0.19

0.18

0.7

0.43

0.64

2.3

All results

4.1.7.2 Verification of Limit of Quantification (LoQ) As described in chapter 4.1.6.1, it was not possible to obtain true blank samples for flours, cereals and flakes. It was therefore decided to verify the LoQ by a spiking experiment at low level of 2 mg/kg gluten and/or 4 mg/kg gluten. The experiment was repeated in a second lot. As shown in table 9, mean values for blank samples were as expected from the LoD experiment. When spiking 2 mg/kg gluten to cereals, the mean recoveries (corrected for blank samples) were in the acceptable range between 67% and 83%. For the 4 mg/kg spike level, the results were more consistent at 84% which was also mirrored by CVs at or below 15%. Due to the lower gluten values for blank flours and flakes, only 4 mg/kg were spiked. The mean recoveries ranged from 64% up to 104%. CVs were also at or below 15%. This shows that quantification at the 5 mg/kg gluten level is possible with acceptable precision.

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RIDASCREEN ® Total Gluten In-house validation report 2018-10-21