Celiac disease is a chronic autoimmune disorder in which the body reacts to gluten. Gluten is a protein found in grains such as wheat, rye, and barley. In people with celiac disease, the immune system attacks the lining of the small intestine after consuming gluten. This damages the intestinal villi, which severely impairs the absorption of nutrients.

Typical symptoms include diarrhea, abdominal pain, flatulence, weight loss, fatigue, and, in children, growth disorders.

Celiac disease is not an allergy, but an autoimmune disorder. The only effective treatment is a strict, lifelong gluten-free diet.

Celiac disease: Autoimmune disorder

When gluten is consumed, the immune system attacks the lining of the small intestine. This damages the intestinal villi, which can lead to nutrient deficiencies and chronic symptoms in the long term.

Food allergy: An overreaction of the immune system to certain proteins in foods, e.g., nuts or milk. Symptoms often occur very quickly and range from skin reactions to anaphylaxis.

Gluten is a protein mixture consisting of gliadin and glutenin found in wheat, rye, and barley.

Definition: Gluten consists of the storage proteins gliadin and glutenin.

Occurrence: Wheat, rye, barley, hybrid grains (e.g., kamut, triticale).

Function: Gives dough elasticity, provides the typical texture of bread and pastries.

Health:

• Celiac disease: gluten-related autoimmune disease
• Wheat allergy: reaction to other wheat proteins
• Non-celiac gluten sensitivity: symptoms without autoimmune reaction

Labeling: Food packaging must declare ingredients containing gluten (EU: LMIV Annex II, other countries have their own regulations)

Gluten is a collective term for certain proteins (gliadin and glutenin) found in some types of grain. The most important gluten-containing grains are:

• Wheat (all varieties including spelt, emmer, and einkorn)
• Rye
• Barley
• Kamut
• Triticale (a cross between wheat and rye)

These grains are often found in bread, pasta, baked goods, and many ready-made products. People with celiac disease, gluten sensitivity, or wheat allergy should avoid these grains or only consume them in gluten-free form.

Oats are naturally low in gluten, but can often be contaminated with gluten during processing and are only considered gluten-free if labeled as such.

Yes, the proteins differ in structure and effect.

• Wheat: Gliadins and glutenins
• Rye: Secalins
• Barley: Hordeins
• Oats: Avenins

The avenins in oats differ structurally from other gluten proteins. Pure, uncontaminated oats are tolerated by most people with celiac disease.

There are globally recognized limits for gluten in food, which are primarily intended to protect people with celiac disease.

Internationally, many countries follow the Codex Alimentarius (FAO/WHO). This stipulates that a food product is only considered gluten-free if it contains a maximum of 20 mg of gluten per kg food (20 ppm) (Codex Standard 118-1979). It is based on clinical studies that show that this amount is safe for most people with celiac disease.

This limit is also implemented in many countries, including the EU, USA (FDA), Canada, Australia, New Zealand, and numerous other countries.

For the analysis of gluten in food, different test systems are used, each with its own sensitivity and application range:

ELISA (enzyme immunoassay):

• most commonly used method in routine diagnostics
• detects specific allergenic proteins (the allergy‑triggering components)
• quantitative results
• R5-ELISA in combination with the Méndez-Cocktail is the reference method according to Codex (CODEX STAN 234-1999)

Rapid tests (lateral flow tests):

• primarily used on‑site for testing raw materials or production lines
• provide fast qualitative or quantitative results

PCR methods (DNA‑based tests):

• Distinction between gluten species
• detect DNA from gluten‑containing ingredients, even when the proteins have been altered by processing (SureFood® ALLERGEN 4plex Cereals)
• Multiplexing possible

Mass spectrometry (LC‑MS):

• highly specific
• can identify proteins and peptides even in heavily processed foods
• requires significant effort and cost
• demands extensive technical expertise
• involves complex sample preparation

-> used only rarely within allergen management

Yes, there is a recognized reference method.

The R5-Méndez method was defined as a Type I method for gluten determination in Codex Alimentarius Standard CXS 234-1999. The R5-Méndez method is a combination of an R5 antibody sandwich ELISA and the special Méndez cocktail for extracting gluten from heat-treated foods. A collaborative study published in 2003 using the R5-based RIDASCREEN^® Gliadin ELISA in combination with the Cocktail (patented) – the Méndez cocktail – formed the basis for the Codex Alimentarius Committee’s decision. The CODEX STAN cites the publication „Clin. Gastroenterol Hepatol. 2018 Jun;16(6):823-836“ which refers to the international collaborative study using R5 ELISA and the Cocktail (patented).

The sandwich ELISA is part of the reference method. An ELISA is used when allergens in food need to be detected quantitatively. ELISA detects proteins and provides accurate concentration values. It is ideal for laboratory analyses, quality assurance, and traceability of raw materials or finished products. Heavily processed foods can make protein detection more difficult.

For example, gluten proteins in food products can be quantitatively determined using RIDASCREEN^® Gliadin (reference method) or RIDASCREEN®EASY Gluten.

An LFD (lateral flow device / rapid test) is used when quick results are required. For example, it can be applied directly during incoming goods inspection of raw materials, for hygiene monitoring of production lines, for testing rinse water, or for on‑site product checks. LFDs are easy to use and provide qualitative or quantitative results within minutes.

With the qualitative RIDA^®QUICK Gliadin, surfaces can be wiped directly with the strip, for example. The RIDA®QUICK Gluten quant. enables quantitative evaluation.

• RIDASCREEN® Gliadin (Art. No. R7001): Codex type I method (reference method) and best validated method; applicability for food in general
• RIDASCREEN®EASY Gluten (Art. No. RAE7071): Easiest extraction and most rapid ELISA method (30 min incubation time)
• RIDA®QUICK Gluten quant. (Art. No. RAL7073): Quantitative LFD – most rapid and most simple immunological method (no lab equipment needed)
• RIDASCREEN® Total Gluten (Art. No. R7041): Specialty ELISA method for oats
• RIDASCREEN® Gliadin competitive (Art. No. R7021): Specialty ELISA method (competitive) for fermented and hydrolyzed food
• RIDA®QUICK Gliadin (Art. No. R7003/R7004/R7005): Simple qualitative LFD, which can be directly used for swabbing (no lab equipment needed)
• Surefood® ALLERGEN 4plex Cereals (Art. No. S7006): Differentiation between cereal species, including wheat, barley, and rye.
• SureFood® ALLERGEN Gluten qPCR (Art. No. S3606):Detection of gluten containing cereals without differentiation

Food products consist of many different components such as fats, carbohydrates, and proteins, as well as vitamins and trace elements. Since each food has a different composition, this so‑called matrix can influence the analysis of gluten. Such matrix effects may be unspecific (e.g., interferences) or specific (e.g., cross‑reactions with the test system).
In addition, processing steps can alter the structure of proteins that are detected in immunological tests (e.g. fermentation, as in beer production, can break down proteins).

In principle, any food can be tested for gluten, but it must first be evaluated to ensure it is suitable for the specific test system before being used in routine analysis. It is particularly important that the sample is homogeneous, meaning well mixed, to achieve reliable results.

In principle, gluten can also be detected in hydrolyzed and fermented foods. However, it must be taken into account that proteins may be partially or completely broken-down during hydrolysis or fermentation. Immunological tests can only recognize these altered structures under certain conditions.

In sandwich ELISAs (antibody-antigen-antibody), only larger protein fragments containing at least two epitopes can be detected. If proteins are broken-down into many small fragments, they can only be detected using competitive test systems, where a single epitope is sufficient for recognition.

The RIDASCREEN^® Gliadin competitive is available for the analysis of hydrolyzed or fermented foods. It also detects small peptides, such as those produced in hydrolyzed/fermented foods.

So-called incurred samples are food samples in which the gluten is intentionally incorporated into the product before processing. Unlike spiked samples, where the gluten is added only to the finished end product, the gluten in incurred samples pass through the entire manufacturing process of a food.

This approach realistically simulates natural contamination during production. Because proteins undergo structural changes during processing steps such as mixing, heating, baking, roasting, or fermentation, these changes affect how well they can be detected by a test method. For this reason, incurred samples are considered realistic and representative test materials.

Official bodies such as the AOAC also recognize the importance of incurred samples and updated their guidelines for validating immunological test systems for food allergens accordingly in 2023.

The RIDA^®QUICK Gluten quant. and RIDASCREEN®EASY Gluten test systems have been validated according to the latest AOAC guidelines using incurred samples. As part of an extensive matrix extension, RIDASCREEN^® Gliadin was also tested with incurred samples and, based on this, received the unique AOAC-Official Methof of Analysis^TM claim “in foods” from the AOAC.