Production of gluten-free beer by peptidase treatment

Celiac disease patients adhering to a gluten-free diet are allowed to drink only beer surrogates, which differ from barley-based beers in terms of aroma and taste. An enzyme-active malt extract produced from special barley malt with high gluten-specific peptidase activity was applied in the brewing process to obtain gluten-free beer in line with the German beer regulations. A commercially available, highly active prolyl endopeptidase from Aspergillus niger (AN-PEP) was also used. Results showed that both AN-PEP and the enzyme-active malt extract were able to degrade celiac-active peptides in a beer matrix. AN-PEP was more stable than malt enzymes under conditions of variable temperature and ethanol content. Analysis by a competitive R5 ELISA indicated that the resulting beers were gluten-free. Aroma and taste were significantly better compared to a commercial gluten-free millet beer. Additionally, the gluten-free beers and the gluten-containing reference beer had comparable quality attributes, except for the foam stability of the extract-treated beer. Identification of hordein peptides in the beers by LC-MS2 analysis after chymotryptic digestion partly conflicted with the ELISA results and highlighted the difficulties of gluten quantitation in a beer matrix as well as the need for an independent and reliable method to detect partially hydrolyzed gluten in fermented beverages.