THERMAL AND HIGH-PRESSURE STABILITY OF PURIFIED PECTIN METHYLESTERASE FROM PLUMS (PRUNUS DOMESTICA) CLÁUDIA S. NUNES 1 , SÓNIA M. CASTRO 1 , JORGE A. SARAIVA 1 , MANUEL A. COIMBRA 1 , MARC E. HENDRICKX 2 and ANN M. VAN LOEY 2,3 1 Departmento de Química Universidade de Aveiro Campus Universitário de Santiago 3810-193 Aveiro, Portugal 2 Laboratory of Food Technology Faculty of Applied Bioscience and Engineering Katholieke Universiteit Leuven Kasteelpark Arenberg 22 B-3001 Heverlee (Leuven), Belgium Received for publication February 18, 2005 Accepted for publication July 5, 2005 ABSTRACT Pectin methylesterase (PME) from greengage plums (Prunus domestica) has been extracted and purified using affinity chromatography. Only one band on sodium dodecyl sulfate–polyacrylamide gel electrophoresis was obtained, with an estimated molecular weight of 31 kDa. On isoelectric focusing elec- trophoresis, two bands with neutral isoelectric points (6.8 and 7.0) were detected. The optimal pH and temperature for plum PME activity were 7.5 and 65C, respectively. A study of purified plum PME thermostability was per- formed at pH 7.5 and 4.0, indicating a higher thermostability at pH 7.5 than at pH 4.0. A biphasic inactivation behavior was observed for thermal treat- ments (54–70C), whereas its pressure inactivation could be described by a first-order kinetic model in a pressure range of 650–800 MPa at 25C. Purified plum PME was found to be relatively stable to thermal and pressure (600 MPa) treatments, compared to PME from other fruits. INTRODUCTION Greengage plum (Prunus domestica) or “Rainha Cláudia Verde” is a Portuguese regional variety. This type of plum can be consumed as fresh fruit, 3 Corresponding author. TEL: +3216321567; FAX: +3216321960; EMAIL: ann.vanloey@agr. kuleuven.ac.be Journal of Food Biochemistry 30 (2006) 138–154. All Rights Reserved. © 2006, The Author(s) Journal compilation © 2006, Blackwell Publishing 138