Inactivation Kinetics Of Pectin Methylesterase Research Articles

The optimal time-temperature conditions for orange juice microwave−assisted pasteurization

In this work, the inactivation kinetics of pectin methylesterase (PME) and degradation kinetics of ascorbic acid (AA) of batch microwave-assisted pasteurized orange juice were studied, at time-temperature conditions from (70–90) °C between (0 and 180) s. The two-component first-order and the fractional kinetic models were adjusted for PME and AA data, respectively. The microwave treatment was effective for the inactivation of PME with minimal AA retention of 85%. The adjusted kinetics parameters at Tref = 90 °C, for PME were: D1, 90 °C = 0.18 s, D2, 90 °C = 32. 8 s, z1 = 10.6 °C, z2 = 11.8 °C, with α = 0.91. For AA were: k90 °C = 0.02 s−1 and z = 55.4 °C with AA∞/AA0 = 0.85. A time-temperature diagram created from the kinetics parameters indicates the best isothermal conditions for orange juice from 78 s at 82.5 °C to 18 s at 90 °C.

Inactivation of pectin Methylesterase and Lactobacillus Plantarum by ohmic heating in pomelo juice

AbstractThe use of ohmic heating (OH) to inactivate damaging elements in pomelo juice was evaluated. The work investigated the effect of frequencies (50–20 000 Hz) on pectin methylesterase (PME) and Lactobacillus plantarum (L. plantarum) in pomelo juice at 30 V cm−1 of electric field strength. The results show that frequency does not affect PME inactivation (P > 0.05) but affects bacterial reduction and has the most efficiency at 60 Hz, followed by 50 Hz, and in the frequency range at or higher than 500 Hz (P < 0.05). Additionally, the inactivation kinetics of PME and L. plantarum and the impact of nonthermal factors were given. The nonthermal element has contributed to the inactivation enhancement of L. plantarum and PME to reduce the necessary treatment temperature and time. The major spoilage bacteria and enzyme destruction in pomelo juice occurred faster under OH than under conventional heating (CH) suggesting that OH can be effectively used to pasteurise pomelo juice.

Effect of high pressure carbon dioxide on tomato juice: Inactivation kinetics of pectin methylesterase and polygalacturonase and determination of other quality parameters

Tomato juice, Lycopersicon esculentum cv. Canario, has been treated by high pressure carbon dioxide (HPCD) as non-thermal preservation treatment. The inactivation kinetics for pectinmethylesterase (PME) and polygalacturonase (PG) were determined at different pressures (8.5–20 MPa) and temperatures (35–55 °C). At the highest operating pressure and temperature essayed in this work, it was found that PME could be almost completely inactivated, whereas PG resulted to be more HPCD resistant at the working conditions. PME enzyme inactivation curves were properly described by a Weibull type model, while the fractional conversion model was the most appropriate for the PG with a sharp initial decrease in activity. On the contrary, high pressure processing (HPP) led to a nearly complete inactivation of PG while PME was very resistant at 600 MPa. It was also found that HPCD treatment led to a smaller particle size distribution of tomato juice.

Inactivation Kinetics of Pectin Methylesterase, Polyphenol Oxidase, and Peroxidase in Cloudy Apple Juice under Microwave and Conventional Heating to Evaluate Non-Thermal Microwave Effects

Continuous-flow microwave pasteurization provides important advantages over conventional heat exchangers such as fast volumetric heating, lower tube surface temperature, and possible non-thermal effects that enhance enzymatic and bacterial inactivation. Conventional and microwave-assisted inactivation of pectin methylesterase (PME), polyphenol oxidase (PPO), and peroxidase (POD) in cloudy apple juice were investigated to evaluate non-thermal effects. Experiments were conducted to provide uniform heating with accurate temperature acquisition and similar temperature profiles for conventional and microwave treatments. A two-fraction first-order kinetic model was successfully fitted to the data in a procedure that took into account the whole time-temperature profile instead of assuming isothermal conditions. Predicted inactivation curves for pasteurization at 70 and 80 °C of the cloudy apple juice showed that PME has the highest thermal resistance (residual activity of 30% after 250 s at 80 °C) and that there was no evidence of non-thermal microwave effects on the inactivation of these enzymes.

Thermal inactivation kinetics of pectin methylesterase and the impact of thermal treatment on the texture, electrical impedance characteristics and cell wall structure of Japanese radish (Raphanus sativus L.)

The thermal inactivation characteristics of pectin methylesterase (PME) from Japanese radish were described by the fractional conversion model at temperatures between 50 and 70 °C. The calculated values of the inactivation rate constant k exhibited an Arrhenius-type temperature dependence. The estimated value of the apparent activation energy Ea (190.29 kJ mol−1) was lower and the z-value (9.64 K) was higher than that of other agricultural products. The results suggest that PME from Japanese radish tissues is more thermally stable than PME from other agricultural products. The impact of changes in cell membrane function and cell wall structure on texture during thermal treatment was also examined. Changes in texture were observed to occur in two phases. In the first phase, the elastic properties decreased because of a decrease in cellular turgor caused by the loss of cell membrane function, as determined by electrical impedance analysis. In the second phase, observed at temperatures above 70 °C, the breaking force (firmness) of the tissues decreased due to the β-elimination-driven degradation of pectins present in the middle lamella of the tissues.

Effect of moderate electric fields on inactivation kinetics of pectin methylesterase in tomatoes: The roles of electric field strength and temperature

The objective of this study was to investigate the effect of Moderate Electric Fields (MEF) on pectin methylesterase (PME) activity in tomatoes. Inactivation kinetics parameters of MEF and conventional thermal treatments were determined for samples of identical prior source and pretreatment history, subjected to nearly identical linearly increasing temperature histories. The presence of electric field (60 Hz, sine wave) resulted in activation of PME at 70 (±1) °C, and accelerated inactivation at higher temperatures. This effect increased with field strength. The results may be interpreted in light of molecular motion calculations for PME, which suggest that enzyme molecules subjected to an oscillating electric field experience electrophoretic motion, and behave as if at a slightly higher temperature than that of the bulk, resulting in an activating effect at lower temperatures, but an inactivation effect at higher temperatures.

New insights into heat induced structural changes of pectin methylesterase on fluorescence spectroscopy and molecular modeling basis

Heat-induced structural changes of Aspergillus oryzae pectin methylesterase (PME) were studied by means of fluorescence spectroscopy and molecular modeling, whereas the functional enzyme stability was monitored by inactivation studies. The fluorescence spectroscopy experiments were performed at two pH value (4.5 and 7.0). At both pH values, the phase diagrams were linear, indicating the presence of two molecular species induced by thermal treatment. A red shift of 7nm was observed at neutral pH by increasing temperature up to 60°C, followed by a blue shift of 4nm at 70°C, suggesting significant conformational rearrangements. The quenching experiments using acrylamide and iodide demonstrate a more flexible conformation of enzyme with increasing temperature, especially at neutral pH. The experimental results were complemented with atomic level observations on PME model behavior after performing molecular dynamics simulations at different temperatures. The inactivation kinetics of PME in buffer solutions was fitted using a first-order kinetics model, resulting in activation energy of 241.4±7.51kJmol−1.

Combined osmodehydration and high pressure processing on the enzyme stability and antioxidant capacity of a grapefruit jam

A combined osmodehydration process and high pressure treatment (OD–HHP) was developed for grapefruit jam preservation. The inactivation kinetics of pectin methylesterase (PME) and peroxidase (POD) in the osmodehydrated (OD) jam treated by combined thermal (45–75°C) and high pressure (550–700MPa) processes were fitted using special cases of first-order kinetics, the fractional conversion and biphasic models and the Weibull distribution function. No complete inactivation was achieved by any combination of temperature and pressure, and 27–40% and 51–70% of PME and POD, respectively, were pressure-stable fractions. Two PME fractions with different pressure stabilities were observed and kinetic models successfully explained that behavior. POD was found to be very baroresistant and only the labile fraction could be inactivated. The extent of enzyme inactivation was lower in the OD jam in comparison with other food matrices showing a protective effect against the high pressure treatment. The antioxidant capacity was not affected by any treatment. The proposed high pressure preservation processing was able to improve the enzymatic stability of jam obtained by osmotic dehydration without affecting the bioactive content.

Inactivation kinetics of pectin methylesterase and cloud retention in sonicated orange juice

The effect of sonication on pectin methylesterase (PME) activity and cloud stability of orange juice was studied. Ultrasonic acoustic energy density (AED) levels of 0.42, 0.47, 0.61, 0.79 and 1.05 W/mL and treatment times of 0 (Control), 2, 4, 6, 8 and 10 min were investigated. The highest PME inactivation level observed was 62% for sonication at the highest AED level and treatment time. A fraction conversion model adequately described the PME inactivation compared to first order or polynomial models. A significant change in particle size distribution was observed in sonicated samples due to cavitational effects. These results indicate that the cloud stability of sonicated orange juice depends not only on PME inactivation but also on particle size reduction. Power ultrasound is a non thermal pasteurisation method that has been identified to meet the US FDA requirement for a 5 log reduction in E. coli pertinent to fruit juices. Apart from microbial inactivation, cloud stability is a critical orange juice quality parameter influencing product shelf life and consumer acceptance. This work demonstrates that sonication at low AED levels and temperatures can be employed to achieve the desired cloud stability.

Inactivation kinetics of pectin methylesterase in orange juice as a function of pH and temperature/time process conditions

AbstractPasteurisation of orange juice (OJ) is necessary to prevent spoilage due to microorganisms and enzymes, mainly pectin methylesterase (PME). PME has a higher thermal resistance than the bacteria and yeasts existing in OJ and therefore its inactivation is used as a parameter to define the time/temperature combination of the thermal process. The enzyme has isoforms with different activities and thermal resistances. A three‐parameter model can be used to describe the kinetics of PME inactivation, where the more and less thermally resistant fractions are represented. In this study the thermal inactivation kinetics was evaluated at six pH values (3.6, 3.7, 3.8, 3.9, 4.0 and 4.1), three minimal temperatures (82.5, 85.0 and 87.5 °C) and at least six holding times for each condition. It was found that the thermolabile PME fraction (a) was influenced by pH and processing temperature. A slower reaction rate constant (k1) was found for juices with pH values of 3.8 and 3.9 at the studied temperatures. The highest inactivation levels were obtained in juices with pH values of 3.6 and 3.7. Copyright © 2006 Society of Chemical Industry

Inactivation kinetics of pectin methylesterase of greek Navel orange juice as a function of high hydrostatic pressure and temperature process conditions

The inactivation kinetics of endogenous pectin methylesterase (PME) in freshly squeezed orange juice under high hydrostatic pressure (100–800 MPa) combined with moderate temperature (30–60 °C) was investigated. Atmospheric pressure conditions in a temperature range of 50–80 °C were also tested. PME inactivation followed first order kinetics with a residual PME activity (5–20%) at all pressure–temperature combinations used. The values of activation energy and activation volume were estimated as 109 kJ mol −1 and −19.76 ml mol −1 at a reference pressure of 600 MPa and reference temperature of 50 °C respectively. Pressure and temperature were found to act synergistically, except in the high temperature–low pressure region where an antagonistic effect was found. The PME inactivation rate constant was expressed as a function of the temperature and pressure process conditions used. This function incorporates the observed exponential dependence of activation energy on the pressure conditions, as well as the linear dependence of activation volume on process temperature.

Thermal vs. Microwave Inactivation Kinetics of Pectin Methylesterase in Orange Juice Under Batch Mode Heating Conditions

Thermal and microwave inactivation kinetics of pectin methylesterase (PME) in single-strength orange juice were evaluated under batch mode heating conditions. For thermal inactivation, aliquots of orange juice sealed in glass ampoules were subjected to conventional heat treatments in a well agitated water-bath for various times at selected temperatures (60, 70, 80, 85 and 90 °C). For microwave inactivation, different amounts of orange juice in a glass beaker (100 mL capacity) were heated in a microwave oven for preselected time intervals to yield the desired final temperatures (50, 55, 60 and 65 °C). Heating times under both modes were corrected to accommodate only their effective portions for kinetic data handling. Based on residual PME activities and first order rate of inactivation kinetics, kinetic parameters were evaluated. Results indicated the enzyme inactivation data to be characterized by the following: microwave: D 60= 7·37 s (z = 13·4 °C); thermal: D 60= 154 s (z = 17·6 °C). Thus, the PME inactivation in orange juice was significantly faster in the microwave heating mode than in conventional thermal heating mode indicating some contributory nonthermal effects under the microwave heating conditions. Thermal inactivation also indicated the presence of two fractions, one more heat sensitive than the other, while only one fraction was apparent with microwave heating. Inactivation kinetics were also dependent on pH and soluble solids content of orange juice. PME was more sensitive to thermal inactivation at lower pH and higher soluble solids concentration.