| Abstract
| - The combined high pressure/thermal (HP/T) inactivation of tomato pectin methyl esterase (PME)and polygalacturonase (PG) was investigated as a possible alternative to thermal processingclassically used for enzyme inactivation. The temperature and pressure ranges tested were from 60°C to 105 °C, and from 0.1 to 800 MPa, respectively. PME, a heat-labile enzyme at ambient pressure,is dramatically stabilized against thermal denaturation at pressures above atmospheric and up to500−600 MPa. PG, however, is very resistant to thermal denaturation at 0.1 MPa, but quickly andeasily inactivated by combinations of moderate temperatures and pressures. Selective inactivationof either PME or PG was achieved by choosing proper combinations of P and T. The inactivationkinetics of these enzymes was measured and described mathematically over the investigated portionof the P/T plane. Whereas medium composition and salinity had little influence on the inactivationrates, PME was found less sensitive to both heat and pressure when pH was raised above itsphysiological value. PG, on the other hand, became more labile at higher pH values. The resultsare discussed in terms of isoenzymes and other physicochemical features of PME and PG. Keywords: tomato; Lycopersicon esculentum; pectin methylesterase; polygalacturonase; inactivation;kinetics; high pressure; temperature; stabilization; selective inactivation
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