Immunological Characterization of the Gluten Fractions and Their Hydrolysates from Wheat, Rye and Barley

Gluten proteins in wheat, rye and barley cause celiac disease, an autoimmune disorder of the small intestine, which affects approximately 1% of the world population. Gluten is comprised of prolamin and glutelin. Since avoidance of dietary gluten is the only option for celiac patients, a sensitive gluten detection and quantitation method is warranted. Most regulatory agencies have set a threshold of 20 ppm gluten in foods labeled gluten-free, based on the currently available ELISA methods. However, these methods may exhibit differences in gluten quantitation from different gluten-containing grains. In this study, prolamin and glutelin fractions were isolated from wheat, rye, barley, oats and corn. Intact and pepsin-trypsin (PT)-digested prolamin and glutelin fractions were used to assess their immunoreactivity and gluten recovery by three sandwich and two competitive ELISA kits. The Western blots revealed varied affinity of ELISA antibodies to gluten-containing grain proteins and no reactivity to oat and corn proteins. ELISA results showed considerable variation in gluten recoveries from both intact and PT-digested gluten fractions among different kits. Prolamin fractions showed higher gluten recovery compared to their respective glutelin fractions. Among prolamins, barley exhibited higher recovery compared to wheat and rye with most of the ELISA kits used. Hydrolysis resulted in reduced gluten recovery of most gluten fractions. These results suggest that the suitability of ELISA for accurate gluten quantitation is dependent upon various factors, such as grain source, antibody specificity, gluten proteins and the level of their hydrolysis in foods.