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I. VERLENT, C. Smout, T. Duvetter, A. Van Loey, and M. Hendrickx. Laboratory of Food Technology, Dept. of Food and Microbial Technology, Katholieke Univ. Leuven, Kasteelpark Arenberg 22, Leuven, 3001, Belgium The presence of both active endogenous pectinmethylesterase (PME) and polygalacturonase (PG) in tomato-based products will result in short deesterified pectin chains and as a consequence in an undesirable decrease in viscosity. However, at suitable high-pressure/temperature (HHP/T) conditions PME may remain active while PG is inactivated, resulting in a preserved viscosity as pectin chains may crosslink. The objective is to study the enzymatic reaction catalyzed by tomato PG in presence of polygalacturonic acid (PGA) and pectin, partly deesterified by tomato PME, during HHP/T-treatments. Extracted tomato PG and PME were isolated using cation-exchange chromatography. Apple pectin was deesterified (35% DM) by tomato PME (t-pectin). Isothermal experiments were performed in a water bath with temperature control, whilst a laboratory scale, multivessel high-pressure equipment was used to perform isothermal-isobaric experiments (25 to 80° C, 0.1MPa-500MPa). After treatment, the amount of reducing groups formed was determined spectrophotometrically. At atmospheric pressure and at pH 4.4 (pH of tomato-based products), the optimal temperature for initial tomato PG activity in presence of PGA and t-pectin is situated around 55 to 60° C and 50° C respectively. For both substrates, the optimal temperature for initial tomato PG activity during processing shifted to lower values at elevated pressure as compared to atmospheric pressure and with increasing pressure, a decreasing enzyme activity was observed which was more pronounced at higher temperatures. Although PG activity exhibits the same trend when using both PGA and t-pectin, the catalytic activity of tomato PG during HHP/T-treatments is always significantly lower on t-pectin as compared to PGA as substrate. Yet, action of tomato PG on pectin deesterified by tomato PME can still lead to drastic losses in viscosity of tomato-based products. Based on this study, suitable high-pressure conditions can be chosen to keep tomato PG activity as low as possible in order to preserve the viscosity of tomato-based products.
Session 34, Nonthermal Processing: General I
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |