Gluten Contamination in Foodstuff Labeled as “Gluten-free” in the United States: A Pilot Study

Introduction: Gluten is the main storage protein in grains and consists of gliadin and glutelin occurring in the same ratio.   Persons suffering from intolerances including celiac disease (CD) must avoid foods containing gluten or products containing wheat, barley, and rye.  Accordingly, gluten detection is of high interest for food safety of celiac patients.

Purpose: This study was designed to determine concentrations of gluten in foods labeled as ‘gluten-free’ available in United States. 

Methods: Seventy-eight samples labeled as ‘gluten-free’ were collected and analyzed using a gliadin competitive enzyme-linked immunosorbent assay (ELISA).  The calculation of gluten is based on the assumption of the same ratio between gliadin and glutenin.

Results: Forty-eight of the 78 (61.5%) samples contained less than the limit of quantification (LOQ) of 10 mg/kg for gluten. Fourteen of the 78 (17.9%) labeled as ‘gluten-free’ samples contained less gluten than the guidelines established by the Codex guide line for gluten-free labeling (20 mg/kg). Sixteen samples (20.5%) did contain gluten levels ≥ 20 mg/kg, with gluten levels ranging from 20.3 mg/kg to 60.3 mg/kg; in particular, 5 out of 8 breakfast cereal samples showed gluten contents higher than 20 mg/kg.

Significance: These results are alarming as gluten sensitivity is known to vary among CD patients.