Digging through the weeds and finding gluten in ryegrass (sort of)

By Dr Sophia Escobar-Correas, Prof Michelle ColgraveAugust 16th, 2021

New research has found gluten-like proteins in ryegrass, which might – or might not – be a problem for people with gluten intolerance.

Sorghum, like millet and buckwheat, is a gluten-free crop that could include ryegrass and its gluten-like proteins. Credit: Jeremy Buckingham

Approximately 1 in 70 Australians are affected by coeliac disease. People with the condition undergo digestive problems when ingesting cereal grains that contain gluten – the three key ones being wheat, rye and barley.

Gluten describes a class of storage proteins rich in the amino acids proline and glutamine, which are resistant to gastrointestinal digestion. In most of us they have no adverse effects but in coeliac sufferers they trigger an immune reaction that leads to inflammation of the gut and a raft of uncomfortable and unpleasant symptoms.

The only solution for these patients is to commit to a strict gluten-free diet. However, about 30% of patients will still have symptoms despite the strict regimen.

Why does this happen? It could be that a close relative to gluten may be present in more foods than we thought. But we’ve found a way of detecting it in food products, giving our food safety systems and consumers a helping hand.

Ryegrass: one of the worst agricultural weeds in Australia

Lolium perenne: perennial ryegrass. Credit: Harry Rose from South West Rocks, Australia

Ryegrass is a type of grass that belongs to the same family as cereals as wheat, rye and barley. Although ryegrass and rye have similar names, they are very different. Rye refers to the cereal or small grain plant. People will be familiar with it by seeing rye bread in the grocery store. Ryegrass is a different species; perennial ryegrass is commonly used as a forage grass. Annual ryegrass is one of Australia’s most serious and costly weeds in cropping systems and is found in over 8 million hectares of grain and pulse crops, being particularly dominant in the southern and western grain growing regions where the vast majority of Australia’s food grain is grown.

Ryegrasses can grow in a field either as a herbicide resistant weed, in crop rotation or in neighbouring fields, presenting a challenge in terms of agricultural co-mingling, in other words generating cross-contamination during harvest.

The team at CSIRO and Edith Cowan University started by looking at perennial ryegrass and the possibility that grains from this grass could be a problem for gluten-free consumers. This fundamental research has revealed that ryegrass contains gluten-like proteins that share high-sequence similarity with traditional gluten proteins. The team has developed a method to test whether ryegrass is present as a contaminant in gluten-free crops and whether it persists in food products. The method can go beyond just detecting whether ryegrass is present, it can also differentiate ryegrass gluten from wheat, barley and rye gluten. This method could help food manufacturers assess incoming ingredients and outgoing products.

Is ryegrass in our food?

Dr Sophia Escobar-Correas in the lab

The team sourced a range of ryegrass varieties, which were converted into flour for testing. They extracted proteins and analysed them using a technology known as mass spectrometry to reveal the gluten-like suspects.

As to whether ryegrass is in our food, our research doesn’t yet answer this question, but we’re onto it. One of our next steps is to collect a series of gluten-free foods and test them for the presence of the suspect proteins.

The odds that ryegrass ends up in the food supply chain are fair. Research shows that despite the influence of routine weed control practices, seeds can persist from one season to the next and can be collected during crop harvest. However, grain that go into flours and foods labelled gluten-free typically go through more cleaning processes to remove contamination. A method that could determine if there is contamination from these seeds could help confirm the efficacy of these cleaning procedures.

Currently, food manufacturers test products for gluten using standardised tests such as enzyme-linked immunosorbent assays (or ELISA), an antibody-based technique. These tests were developed for testing gluten in wheat, barley and rye but not in other grains such as oats or ryegrass.

Our research will seek to verify if these kits still work for ryegrass to inform whether food manufacturers and analytical laboratories can continue to use them to pick this type of contamination.

We’re also aiming to unpack the clinical relevance of these proteins in ryegrass. We want to understand if these gluten-like proteins trigger a coeliac response and if they do, we’ll try to understand the prevalence of ryegrass in our food system. We’ll then be in a position to guide the development of new rapid tests for ryegrass, inform on-farm practices and educate consumers around the risk, if one does indeed exist.

But we won’t stop there. We’re also working on weeding out other potential culprits, including annual ryegrass. All to add to the suite of tools available to help ensure our food supply is as safe as possible.

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