Isolation and partial characterization of thermostable isoperoxidases frompotato (Solanum tuberosum L.) tuber sprouts

Peroxidases (POD; EC 1.11.1.7) can cross-link cell wall polymers and may ha ve an impact on the final textural quality of potato tubers. Because heat t reatments are important during processing, the thermal properties of isoPOD s from soluble and ionically and covalently bound fractions were studied fr om both potato tubers and sprouts. For both tissues, the ionically bound fr action was the most thermostable; similar to 20% of POD activity remained a fter a heat treatment of 10 min at 90 degrees C (for sprouts). The temperat ure profile of the ionically bound sprout fraction appeared to be nonlinear and suggested the presence of a very thermostable POD, which still showed activity after a heat treatment at 100 degrees C. Visualization by using is oelectric focusing confirmed the occurrence of a thermostable isoPOD with a n IEP of 9.5, which displayed regeneration of activity after heat inactivat ion. This cationic POD was further purified by chromatography techniques, a nd by SDS-PAGE its molecular mass was estimated at 38 kDa.