Gluten-specific peptidase activity of barley as affected by germination and its impact on gluten degradation

Endogenous cereal peptidases have gained interest concerning the degradation of gluten in raw materials for the production of gluten-free beer. This study demonstrates that enzymes from barley malt are able to degrade celiac-active peptides PQPQLPYPQPQLPY (P1) and SQQQFPQPQQPFPQQP (P2). The gluten-specific peptidase activity can be significantly increased by systematic variation of the germination parameters moisture, temperature, and time. Statistical analysis using normalized, linear regression including non-linear terms showed different maxima between the substrates. Maximum peptidase activity for P1 (25.6 U/kg malt) was obtained at 48% water content, 18 °C germination temperature, and 6.6 d germination time and for P2 (8.3 U/kg) at 48%/12 °C/8d or 42%/18 °C/8d, respectively, with low correlations between the substrates (r = 0.54, α < 0.05). The degradation of hemoglobin (4567 U/kg; 45%/15 °C/4–8d), which has often been used for determination of hydrolytic activity, showed no correlation with the two peptide substrates. The degree of gluten degradation as affected by the germination time correlated significantly with both peptides (r = −0.78–0.86, α < 0.005) and to a lesser extend with hemoglobin (r = −0.67, α < 0.01). The results might help implementing gluten-specific peptidase activity of barley malt as quality parameter in the field of brewing.