Purification and thermostability of isoperoxidase from oranges

Soluble and ionically bound peroxidase were extracted from oranges (citrus sinenis (L.) Osbeck cultivar Large Valencia, Small Sweet and Navel. Cationic and anionic isoperoxidase were obtained by Rotofor and ion-exchange chromatography. The pI for the soluble isoenzymes (4.5 to 9.0) was measured using a surface electrode and the M-r (22 k to 44 k) was estimated by gel-filtration. The purified isoperoxidases (C-1 and C-2) were more heat stable than the peroxidase present in the crude extract. The inactivation of orange peroxidase activity in a mixture or individually in a purified state, was found to be non-linear with heating time. (C) 1998 Elsevier Science Ltd. All rights reserved.