title: Influence of beta-subunit on thermal and high-pressure process stability of tomato polygalacturonase.
abstract: Polygalacturonase (PG; E.C. 3.2.1.15) was extracted from tomato fruit and purified by cation-exchange chromatography. Two peaks containing PG activity were detected: the first denotes a thermolabile PG fraction (PG2) and the second a thermostable fraction (PG1). PG1 is a dimer of PG2 and a heat-stable protein called the beta-subunit. In contrast to its resistance to heat, PG is easily inactivated at elevated pressure. Although the thermal stability of purified tomato PG1 and PG2 is distinctly different, they show an identical pressure stability. To gain further insight into the thermal and pressure stability of both PG isoenzymes, the in vitro recombination of PG2 and beta-subunit was studied. After severe heat (up to 140 degrees C for 5 min) and pressure (up to 800 MPa for 15 min) treatments, the residual fractions containing the beta-subunit were able to convert PG2 into the heat-stable PG1, showing the extreme thermal and pressure stability of the beta-subunit. PG1 was detected in heat-treated tomato juice and, to a lesser extent, in tomato pieces. In contrast, as was the case for purified PG, no pressure-stable fraction was observed when tomato juice and pieces were treated under pressure. These data clearly show the differing behavior of the PG1-PG2-beta-subunit system under thermal and high-pressure treatments and offer the possibility of inactivating tomato PG using high pressure without the need for high temperatures.
authors.affiliation: Laboratory of Food Technology, Department of Food and Microbial Technology, Katholieke Universiteit Leuven, Kasteelpark Arenberg 22, B-3001 Leuven, Belgium.
authors.forename: Liesbet
authors.initials: L
authors.lastname: Peeters
authors.forename: Diana
authors.initials: D
authors.lastname: Fachin
authors.forename: Chantal
authors.initials: C
authors.lastname: Smout
authors.forename: Ann
authors.initials: A
authors.lastname: van Loey
authors.forename: Marc E
authors.initials: ME
authors.lastname: Hendrickx
mesh_terms: D004789:Enzyme Activation; D004795:Enzyme Stability; D005638:Fruit / Q000378:metabolism*; D007527:Isoenzymes / Q000032:analysis / Q000737:chemistry; D018551:Solanum lycopersicum / Q000201:enzymology*; D011096:Polygalacturonase / Q000032:analysis* / Q000737:chemistry* / Q000145:classification; D011312:Pressure; D021122:Protein Subunits / Q000032:analysis / Q000737:chemistry*; D013696:Temperature
chemical_list: D007527:Isoenzymes; D021122:Protein Subunits; D011096:Polygalacturonase