The thermostability of purified isoperoxidases from Brassica oleracea VAR gemmifera

The thermostabilities of four previously purified isoperoxidases from Brussels sprouts (Brassica oleracea VAR. gemmifera.)have been determined. The heating time periods selected (10 s - 0.5 min intervals) are comparable to those used during commercial blanching. Non-linear regression (NLR) equation fitting, using common goodness of fit criteria (low chi-squared value, high regression coefficient and low residuals) points to a mechanism of peroxidase heat inactivation involving two consecutive reactions during the initial periods of heating. In the consecutive model, native peroxidase (Eo) is converted into a partially active from (E(1)) and then into the inactivated enzyme (E(2)) during short periods of heating. The order of calculated decimal reduction times for the two anionic (A1 and A2) and two cationic (C1 and C2) Brussels sprouts isoperoxidases was A1 greater than or equal to C1 > A2 > C2. Calculated concentration changes for E(0), E(1) and E(2) during heat inactivation were quite different for the four isoperoxidase preparations and indicated the generation of more stable forms of partially denatured peroxidases. The anionic isoenzymes showed greater regeneration of enzymatic activity after heat treatment and this could have been due to their greater ability to regain previously liberated haem. (C) 1999 Elseiver Science Ltd.. All rights reserved.