nan Indrawati

Effects of combined pressure and temperature on enzymes related to quality of fruits and vegetables : From kinetic information to process engineering aspects

ABSTRACT Throughout the last decade, high pressure technology has been shown to offer great potential to the food processing and preservation industry in delivering safe and high quality products. Implementation of this new technology will be largely facilitated when a scientific basis to assess quantitatively the impact of high pressure processes on food safety and quality becomes available. Besides, quantitative data on the effects of pressure and temperature on safety and quality aspects of foods are indispensable for design and evaluation of optimal high pressure processes, i.e., processes resulting in maximal quality retention within the constraints of the required reduction of microbial load and enzyme activity. Indeed it has to be stressed that new technologies should deliver, apart from the promised quality improvement, an equivalent or preferably enhanced level of safety. The present paper will give an overview from a quantitative point of view of the combined effects of pressure and temperature on enzymes related to quality of fruits and vegetables. Complete kinetic characterization of the inactivation of the individual enzymes will be discussed, as well as the use of integrated kinetic information in process engineering.

Comparative study of the inactivation kinetics of pectinmethylesterase in tomato juice and purified form.

Pectinmethylesterase (PME) extracted from tomato fruit was purified by affinity chromatography. A single peak of PME activity was observed, presenting a molar mass of 33.6 kDa, an isoelectric point higher than 9.3, and an optimal temperature and pH for activity of 55 °C and 8.0, respectively. The processing stability of purified tomato PME in buffer solution was compared to PME stability in tomato juice. In both media, thermal inactivation of PME presented first‐order inactivation kinetics, PME in tomato juice being more heat‐labile than purified PME. Regarding high‐pressure treatment, tomato PME showed to be very pressure‐resistant, revealing an outspoken antagonistic effect of temperature and pressure. To avoid cloud loss in tomato juice, a time‐temperature treatment of 1 min at 76.5 °C was calculated in order to have a residual PME activity of 1 × 10−4U/mL.

Inactivation kinetics of polygalacturonase in tomato juice

a ¸ ´´ ˜ ´ Abstract The inactivation kinetics of polygalacturonase (PG) in tomato juice was studied during thermal and high-pressureythermal processing. In the temperature range of 55-70 8C the thermal inactivation of polygalacturonase in tomato juice followed a fractional conversion model, with a thermostable fraction of approximately 14%. Under conditions of combined high-pressurey thermal processing, 200-550 MPay5-50 8C, PG inactivation presented first order kinetics. A mathematical model to describe the inactivation rate constant as a function of pressure and temperature was formulated. Industrial relevance: Polygalacturonase is responsible for the decrease of viscosity in tomato-based products. However, little research on thermal and high pressure ythermal inactivation kinetics of tomato Polygalacturonase has been reported. This research clearly shows that it is possible to selectively inactivate PG by high pressureythermal processing without applying high temperatures. This leads to tomato-based products with improved functional properties while other quality attributes (color, flavor, nutritional value ) are maintained. 2002 Elsevier Science Ltd. All rights reserved.

Kinetics of Pressure Inactivation at Subzero and Elevated Temperature of Lipoxygenase in Crude Green Bean (Phaseolus vulgaris L.) Extract

Lipoxygenase (LOX) in crude green bean extract was irreversibly inactivated by pressure treatments combined with subzero or elevated temperature. LOX inactivation was described accurately assuming a first‐order reaction. In the entire pressure‐temperature domain studied (200 to 700 MPa and −10 to 60 °C), an increase in pressure at constant temperature enhanced the LOX inactivation rate, whereas at constant pressure, an increase in reaction rate was obtained by either increasing or decreasing temperature at 20 °C. At elevated pressure, LOX exhibited the greatest stability around 20 °C. Also the pressure dependence of the inactivation rate constants for LOX was the highest around 20 °C. On the basis of the estimated LOX inactivation rate constants, an iso‐rate contour diagram as a function of pressure and temperature was constructed, and an empirical mathematical model describing the combined pressure‐temperature dependence of the LOX inactivation rate constants was formulated.

The effect of pressure processing on food quality related enzymes: from kinetic information to process engineering

The present paper will give an overview of the combined effects of pressure and temperature on enzymes related to quality of fruits and vegetables, and this from a quantitative point of view. The enzymes considered include polyphenoloxidase (PPO) which is responsible for enzymatic browning, pectinmethylesterase (PME) which induces cloud loss and consistency changes and lipoxygenase (LOX) which is responsible for development of off-flavors, loss of essential fatty acids and color changes. Complete kinetic characterization of pressure-temperature inactivation of these enzymes will be discussed, as well as the use of integrated kinetic information in process engineering.

The Relevance of Kinetic Data in High Pressure Food Processing

High pressure is an emerging technology with high potential as a new unit operation in food preservation and processing. The most likely applications will be in combination processes, especially with moderate temperature elevation. However, there are a number of scientific, technological and industrial difficulties to be overcome in order to successfully apply HP/T processes to foods, both from a legislative point of view and from optimal quality and consumer acceptability requirements. To overcome these difficulties, a scientific kinetic basis for design, evaluation and optimization of HP/T processes is indispensable.

Pressure Stability of Lipoxygenase from Green Beans (Phaseolus vulgaris L.) at Subzero and Elevated Temperature

Green beans LOX could be irreversibly inactivated in the entire p/T area studied (up to 7 kbar and -10 to 63 °C). The inactivation followed a first order reaction and could be accelerated by a p increase at constant T. The inactivation kinetic parameters were described as D, z and zp values.

Modeling Kinetics of Pressure-Temperature Inactivation of Enzymes: A Case Study on Soybean Lipoxygenase

Complete kinetic characterization of thermal (60–70 °C) and pressure-temperature (0.1–650 MPa; 10–64 °C) inactivation of soybean LOX was accomplished. Seemingly, LOX exerted maximal pressure stability at temperatures slightly higher than room temperature. In a final stage, a mathematical model adequately describing pressure-temperature inactivation of soybean LOX was developed, using the Eyring equation as starting point.