Puri®cation, Characterization, Thermal, and High-Pressure Inactivation of Pectin Methylesterase from Bananas (cv Cavendish) B. Ly Nguyen, A. Van Loey, D. Fachin, I. Verlent, I. M. Hendrickx Laboratory of Food Technology, Department of Food and Microbial Technology, Faculty of Agricultural and Applied Biological Sciences, Katholieke Universiteit Leuven, Kasteelpark Arenberg 22, B-3001 Heverlee (Leuven), Belgium; telephone: +32-16-321585; fax: +32-16-321960; e-mail: marc.hendrickx@agr.kuleuven.ac.be Received 27 September 2001; accepted 2 January 2002 DOI: 10.1002/bit.10249 Abstract: Pectin methylesterase (PME) was extracted from bananas (cv Cavendish) and puri®ed by af®nity chromatography on a CNBr±Sepharose±PME inhibitor (PMEI) column. A single protein and PME activity peak was obtained. For banana PME, a biochemical charac- terization in terms of molar mass (MM), pI, and kinetic parameters was performed. In a second step, the ther- mal and high-pressure stability of the enzyme was studied. Isothermal inactivation of puri®ed banana PME could be described by a ®rst-order kinetic model in a temperature range of 65° to 72.5°C, whereas its isobaric± isothermal inactivation followed a fractional-conversion model. Banana PME was found to be more thermally stable compared with PMEs extracted from orange, tomato, and apple. ã 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 78: 683±691, 2002. Keywords: bananas; pectin methylesterase (PME); puri®cation; thermal inactivation; high-pressure inactivation INTRODUCTION The enzyme pectin methylesterase (pectinesterase, PME, PE, EC 3.1.1.11), which has been found in plants as well as in pathogenic fungi and bacteria, catalyzes the hy- drolysis of the methylester groups from pectin and leads to the formation of a calcium pectate gel (Alonso et al., 1995a, 1997; Ben-Shalom et al., 1985; Powell et al., 1982; Walkinshaw and Arnott, 1981). Consequently, its activation causes cloud loss in juices and nectars (Krop and Pilnik, 1974a, 1974b; Laratta et al., 1995; Romb- outs et al., 1992; Rothschild and Karsenty, 1974), en- hances the texture of fruit and vegetable products (Alonso et al., 1995a, 1997; Alvarez et al., 1999; Fuchigami et al., 1995; Reeve, 1972), eectively in- creases the extraction yield of juices by conventional methods (Anastasakis et al., 1987), or promotes water removal from the tissues upon drying (Manabe, 1982). The studies on PME of dierent sources, therefore, have been of great interest. In plants, PME is bound to the cell wall by electro- static interaction, and high-ionic-strength solutions are required to solubilize the enzyme (Giovane et al., 1994). PME has been extracted and/or puri®ed from dierent sources, including tomatoes (Delincee and Radola, 1970; Gae et al., 1994; Giovane et al., 1994; Markovic and Jornvall, 1986; Nakagawa et al., 1970; Pressey and Avants, 1972; Tucker et al., 1982; Warrilow et al., 1994; Warrilow and Jones, 1995), oranges (Baron et al., 1991; Cameron and Grohmann, 1996; Evans and Machale, 1978; Hou et al., 1997; Korner et al., 1980; Manabe, 1973; Rillo et al., 1992; Versteeg et al., 1978; Wicker et al., 1988), apples (Al-Delaimy and Ali, 1969; Castaldo et al., 1989; DeneÂs et al., 2000; King, 1990, 1991; Lee and Wiley, 1970; Macdonald and Evans, 1996; Miyairi et al., 1975), and grapefruits (Cameron and Grohmann, 1995; Robertson, 1976; Seymour et al., 1991). Bio- chemical properties, thermal stability, and food appli- cation of PME from those sources have also been reported by the aforementioned investigators. PME from bananas (Musa acuminata) was investi- gated many years ago. Hultin and coworkers (1965, 1966) described three forms of pectin methylesterase in bananas. De Swardt and Maxie (1967) con®rmed an apparent increase in pectin methylesterase in ripening bananas. Markovic et al. (1975) and Brady (1976) pu- ri®ed banana PME from dierent varieties. However, no further data with regard to puri®ed banana PME have been reported. Conventional thermal processing has a deteriorative eect on texture, ¯avor, and nutritional attributes. High-pressure processing at mild temperatures, in con- trast to high-temperature treatment, is speci®c insofar as Correspondence to: I. M. Hendrickx Contract grant sponsors: Research Council of KU Leuven; Fund for Scienti®c Research, Flanders; Flemish Government±IWT ã 2002 Wiley Periodicals, Inc.