There is scientific evidence to support the introduction of moderate amounts of pure oats in the gluten-free diet of individuals suffering from celiac disease (Pulido et al. 2009
). Pure oats are recommended because it is believed, and has been shown to some extent, that the commercial oat supply is contaminated with other grains. In order to determine the extent of this contamination we analysed a large selection of packaged oat products that are readily available in the Canadian retail market. shows the gluten levels determined for the oat composites tested in this study using the RIDASCREEN® R-7001 sandwich ELISA (R5-ELISA). Of the 133 samples analysed only nine (6.8%) were found to contain levels of gluten below the 20 mg kg−1
limit proposed by the Codex Alimentarius Commission for naturally gluten-free foods (Catassi and Fasano 2008
). Three of these samples had undetectable amounts of gluten, while the remaining samples were between 5 and 20 mg kg−1
. The remaining samples (n = 124, 93.2%) showed contamination levels above this limit and ranged from approximately 21 to 3800 mg kg−1
. Previous studies that have measured the gluten content in oats had a limited number of samples from the Canadian market, but showed similar contamination levels to this study. For example, one study found eight of 12 samples of oats purchased in Canada (67%) were contaminated (Gélinas et al. 2008
) while another found that seven of ten samples purchased in Canada (70%) were contaminated with gluten at levels higher than 20 mg kg−1
(Hernando et al. 2008
Figure 1. Survey results of the average gluten levels in a sampling of pre-packaged oats sold in Canadian retail stores using a commercial ELISA kit. The insert is an expanded region of the lower-level samples along with a line representing the 20 mg kg−1 (more ...)
Another aspect of this study that is of interest is the variance within different lots of commercial oats sold in Canada. Is it possible to find a brand of oats that is consistently low in gluten? As mentioned above there were three samples of oats that showed undetectable levels of gluten using the R5-ELISA. Two of these samples were different lots from the one company and the last sample was part of a set of six different lots of rolled oats from a different company. The former two lots of oats from one company tested negative for gluten while the six lots from the other company ranged from zero to 133 mg kg−1 of oats. This was not an isolated example and all oat types showed variance within the different lots sold in Canada. The variability between different types of oats available on the Canadian market was also investigated by determining the average gluten level for the different types of oats (). Analysis of variance (ANOVA) for the different oat samples confirms there is no significant difference between the oat types (ρ = 0.06). Interestingly, analysis of the data obtained for regular and organic oats shows that there is a significant difference (ρ < 0.0001) between organic oats (mean = 240 mg kg−1, n = 31) and regular oats (mean = 616 mg kg−1, n = 102), but this crop is still significantly contaminated with gluten.
Gluten content as a function of type of oat product.
In order to determine the type of grain that has contaminated the oat samples a selection of oat types purchased were analysed again using an ELISA method that is insensitive to barley hordeins. The R5-ELISA responds to a peptide sequence that is present in gliadin and then reports the amount of gluten by referencing to a gliadin material based on multiple wheat cultivars (Van Eckert et al. 2006
). This assay also responds to barley and rye because the same peptide sequence is present in hordeins and secalins; however, the gluten assay that responds to the ω-gliadin fraction of wheat has a low cross-reactivity (5%) towards barley hordeins. A high response from the R5-ELISA and a low response from the ω-ELISA is an estimate of the type of gluten contamination (Gélinas et al. 2008
). For example, the level of gluten for sample 63 () using the R5-ELISA was determined to be 216 mg kg−1
while the level for the same sample using the ω-gliadin ELISA was only 10 mg kg−1
. The response from the ω-ELISA is approximately 5% of the R5-ELISA and suggests that barley is the source of the gluten contamination for this sample. In another example, sample 36 reported 59 mg kg−1
using the R5-ELISA and 16 mg kg−1
using the ω-ELISA, suggesting the gluten contamination is likely a mixture of wheat and barley or possibly differences in the ω-gliadin content of sample. The data in indicate that the majority of samples (13 of 14) in the subset that tested positive for gluten were contaminated at some level with barley. Although individuals with gluten sensitivities also react to the hordeins in barley, the actual level of gluten in the sample, measured by the R5-ELISA, can be overestimated due to the differences between barley and wheat, the latter of which has been used to calibrate the method (Kanerva et al. 2006
). Canadian regulations do not require allergen labelling of grains like oats that are destined for further processing and allow the presence of a certain percentage of foreign components, which may include gluten-containing cereals (Canadian Grain Regulations 2008
). Packagers of oats can voluntary provide precautionary statements to warn allergic or intolerant consumers about the potential risk of cross-contamination. The results of this study have shown that precautionary labelling practices of commercial oats vary greatly (). For example, the oat products tested either had no precautionary statement pertaining to wheat or gluten (n = 65) or presented various statements ranging from, ‘may contain traces of wheat’ (n = 43) to less clear statements such as ‘good manufacturing practices have been used to segregate ingredients in a facility that also processes peanuts, tree nuts, milk, eggs, wheat, sulfites and soy ingredients’ (n = 11). The latter statement is confusing and contains some uncertainty for many individuals with food allergies (Verrill and Choiniere 2009
) and may be a reason why precautionary statements are increasingly being ignored by allergic consumers (Sheth et al. 2010
). A concern to no precautionary statement, or an ambiguous one, is a precautionary statement that provides an incomplete list of allergens potentially present through unavoidable cross-contamination. For example, some of the oat samples contained statements indicating the potential presence of other allergens including peanut, tree nuts, sesame and soy, but not for wheat or gluten. Given the increased knowledge of potential cross-contamination a consumer will likely know that these products will still be contaminated with gluten. The only sample that was gluten free in both lots that were tested actually had a wheat-free claim on the package and represents a pure oat product. In regard to oat varieties in Canada it would be suggested that all warnings should be adhered to and avoidance of all commercial oat varieties other than pure oats be followed. Although there were some varieties of prepackaged oats that were low in gluten the vast majority would not be safe for the allergenic or intolerant consumers.
Results for the determination of gluten source for a subset of samples using two different ELISA kits.
Number of occurrences for different precautionary statements.