INACTIVATION OF MALT PEPTIDASES DURING MASHING*

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Abstract
Malt contains at least eight different peptidases: three carboxypeptidases (pH optima 4·8, 5·2, 5·7), three aminopeptidases active on aminoacyl-β-naphthylamides (pH optima in hydrolysis of peptides at pH 5·8-6 5), and two (amino)peptidases acting on Leu-Tyr and Ala-Gly at higher pH (pH optima 8·6, 7·8). We have studied the progressive inactivation of these peptidases during mashing with a temperature programme from 45° to 70° C (pH 5·8 → 5·7). All peptidases were stable at 45° C. The five aminopeptidases were inactivated at different rates during a 30-min incubation at 55° C. The carboxypeptidases retained 70–100% of their activities at this temperature, and one of them had 40% residual activity after 60 min at 70° C. Liberation of amino acids continued at a considerable rate during the incubation at 70° C, probably catalysed by the heat-stable carboxypeptidase. Malt carboxypeptidases are therefore more heat-stable in mashing conditions than the aminopeptidases. This property, in combination with their high activities and suitable pH optima, makes them the most important enzymes in the production of free amino acids in mashing.