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T. DUVETTER1, B. Ly Nguyen, I. Verlent, C. Smout, A. Van Loey, and M. Hendrickx. (1) Laboratory of Food Technology, Dept. of Food and Microbial Technology, Katholieke Univ. Leuven, Kasteelpark Arenberg 22, Heverlee, 3001, Belgium The degree and pattern of methyl-esterification of pectin determine several quality properties of fruit and vegetable products. Pectinmethylesterase (PME) catalyses the de-esterification of pectin and may be added during processing to modify the pectin structure and alter product properties. The objective of this work was to study the effect of temperature and pressure on the rate and the mode of pectin de-esterification by Aspergillus PME and on the enzyme stability. PME activity was studied by incubating the enzyme with pectin at different pressure-temperature-conditions. The reaction rate was calculated from the amount of product formed versus time. By characterizing the pectin degradation products the mode of de-esterification was analyzed. PME stability was studied by subjecting the enzyme without substrate to different temperature-pressure-treatments. The changes in protein configuration were analyzed with FT-IR-spectroscopy. Residual enzyme activity was measured titrimetrically and kinetic inactivation parameters were estimated. Aspergillus PME was observed to de-esterify pectin following a multiple-chain, multiple-attack mechanism. The mode of action was not modified by increasing temperature or pressure. The rate of pectin de-esterification was highly depending on pressure and temperature. Highest activity was measured at 300MPa and 50° C. PME was inactivated by temperature (46 to 56° C) following a first order model. No loss of activity was noticed for pressure-treatments up to 700MPa, even not when combined with elevated temperatures. These observations were confirmed by FT-IR-studies showing a disturbance of the secondary and tertiary structure during thermal treatment, but no structural changes during pressurizing. When PME is applied to modify the pectin structure and improve the quality of fruit and vegetable products, the reaction rate can be highly influenced by choosing the optimal pressure and temperature conditions, while the mode of action will not be changed. PME is stable at high pressures and can be inactivated by a thermal treatment at atmospheric pressure.
Session 34, Nonthermal Processing: General I
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |