Studies on the gluten-specific peptidase activity of germinated grains from different cereal species and cultivars

Abstract

Grains of common wheat, spelt, emmer, einkorn, rye, barley, oats, and maize (two cultivars each) were germinated for 7 days at 15 and 25 °C, respectively, lyophilized, and milled into flour and bran. The rate of storage protein (prolamins, glutelins) degradation in the bran was determined by an extraction/HPLC method and was used as an indication for gluten-specific peptidase activity. Species and cultivars with high storage protein degradation during germination were selected for further studies. The peptidase activity of the germinated grains was determined by using two gluten substrates namely gliadin (wheat prolamin fraction) and the celiac-toxic peptide PQPQLPYPQPQLPY. The activity assay implied extraction of bran with a sodium acetate buffer (0.2 mol/L, pH 4.0), incubation of the extract with both substrates, and quantitation of gliadin or peptide degradation by RP-HPLC. The assays were simple and generated reproducible values for the peptidase activity. In general, the activity was strongly affected by cereal species, cultivar, germination temperature, and pH value of the application. Some of the bran extracts were capable of degrading both gliadin and the celiac-toxic peptide extensively. Maximum degradation rates of gliadin and the celiac-toxic peptide were 67 and 100 %, respectively. Alternatively, germinated cereal grains were kiln-dried at 45 °C for 24 h instead of being lyophilized and were separated into kernels and roots/sprouts. When compared to the lyophilized bran, the combined kiln-dried material showed a more balanced peptidase activity toward both the gliadin and the peptide substrate.