Degradation of gluten in rye sourdough products by means of a proline-specific peptidase

The gluten content of rye sourdough during fermentation was monitored by a competitive ELISA based on the R5 antibody. Although a time-dependent decrease was found, the gluten content was not reduced below the threshold for gluten-free foods of 20 mg/kg, even after prolonged fermentation. Instead, Aspergillus niger prolyl endopeptidase (AN-PEP) extensively degraded gluten concentrations of up to 80,000 mg/kg in rye flour, rye sourdough, and sourdough starter under distinct temperatures and pH values. The enzyme did not lead to inactivation of the microorganisms in the sourdough starter. Gluten-free rye flour alone or in combination with sourdough starter was used to produce gluten-free bread, which was evaluated for its sensory properties. Whereas gluten-free sourdough bread had poor sensory attributes compared to a conventional rye bread used as reference, the replacement of sourdough by egg proteins yielded gluten-free bread comparable to the reference and with higher sensory quality than bread prepared from naturally gluten-free ingredients. Therefore, the feasibility of producing high-quality bread from originally gluten-containing cereals such as rye by means of treatment with AN-PEP has been shown. Rye products rendered gluten-free in this manner have the potential to increase the choice of high-quality gluten-free foods for celiac patients.