Visual examination key to meeting safety standards for bakers, says gluten-free certifying agent

By Douglas Yu

- Last updated on GMT

One GCG per kilogram of grains is the highest level of gluten contamination for gluten-free consumers.  Pic: ©GettyImages/Shaiith
One GCG per kilogram of grains is the highest level of gluten contamination for gluten-free consumers. Pic: ©GettyImages/Shaiith

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The Gluten Intolerance Group (GIG), a certifying agent in the US gluten-free market, said visual examination is pivotal in determining the safety of whole grains, beans, seeds, pulses and legumes.

In its latest study published in a special section of the Journal of AOAC International​ focusing on food allergens and gluten, GIG said obtaining representative test samples for antibody-based testing (traditional way for testing gluten) is challenging when analyzing whole grains for gluten.

“When whole grains are ground into flour for testing… gluten tends to exist as aggregates within the starch background, making single-sample testing inaccurate and complicating the ability to arrive at an accurate average from multiple samples,”​ wrote the study's authors.

However, intact grains offer an opportunity for gluten detection because “contaminating gluten-containing grains (GCGs) are visible and identifiable to the trained eye or properly calibrated equipment.”

The GIG researchers said one GCG per kilogram of grains would be the highest level of gluten contamination that would be acceptable to consumers.

“In order to reduce the risk of a consumer purchasing a grain product with one or more GCGs/kg to under 1%, GIG recommends a threshold of 0.25 GCG/kg for visual examination," ​they added.

Sampling plan

The initial step in analyzing grains for the presence of GCGs is “to develop a strict definition of a lot/batch​.

“For example, if a grain processor uses visual examination for GCGs to accept or reject shipments from their growers, the processor may consider each complete shipment from a grower as one batch," ​said the authors.

“The lot/batch is not defined by grain weight, but processors must balance the time and personal investment in visual examination versus the financial cost of rejecting large amounts of product.”

Once the lot size has been defined… take 20 samples from the lot while it is in motion and it can be sampled across the complete width and depth of the grain stream; take samples at uniformly distributed time points from the beginning to the end of the lot.

"Clean each sample to remove fine materials and large contaminants such as rocks and stems.”

Finally, the processor needs to reduce each sample to 500g before visually examining, recording the total number and calculating the GCGs per kilogram.

GIG’s visual examination study was conducted at Grain Millers’ and Cream Hill Estates’ oat facilities, and the results showed that GCGs in both plants were below the threshold of 0.25 GCG/kg.

The group added that, even though its study sets a threshold for GCGs per kilogram, gluten contamination could also occur in the form of very small fragments or dust.

“The use of a combination of visual examination and antibody-based testing is necessary to determine the safety of these commodities for gluten-free consumers,”​ they concluded.


Journal of AOAC International; Vol 101 NO. 1 2018; DOI: 10.5740

“The use of visual examination for determining the presence of gluten-containing grains in gluten-free oats and other grains, seeds, beans, pulses, and legumes”

Authors: Laura K. Allred, Cynthia Kupper and Channon Quinn

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