Thermal Degradation Kinetics of Chlorophyll in Pureed Coriander Leaves

Coriander leaves are widely used in cooking throughout the world. Thermal degradation kinetics of chlorophyll a, b, and total chlorophyll in coriander leaf puree was investigated at varying levels of pH (4.5–8.5) and processing temperature (80–145°C). Coriander puree at pH 4.5 was processed at 80° to 100°C, whereas that at pH 5.5 to 8.5 was processed at 105° to 145°C. Chlorophyll degradation followed first-order reaction kinetics. Good agreement was found between estimated and experimental chlorophyll retention in all cases (R ² > 0.80). Activation energies ranged from 6.57 to 96.00 kJ/mol. Reaction rate and activation energy data indicated that chlorophylls were more stable at alkaline pH. Transition state theory was applied to estimate the enthalpy, entropy, and Gibbs free energy of activation. Enthalpy of activation (ΔH ^#) ranged from 3.46 to 91.99 kJ/mol, whereas entropy of activation (ΔS^#) ranged from −0.265 to −0.047 kJ/(mol K). The overall free energy change was 107.55 kJ/mol. Results indicated that, the compensation effect did not exist for chlorophyll degradation in coriander puree during thermal processing.     

Color Degradation Kinetics of Spinach, Mustard Leaves, and Mixed Puree

ABSTRACT: The kinetics of color degradation of spinach, mustard leaves, and mixed (mustard:spinach:fenugreek = 1:0.75:0.25) puree were investigated at temperatures between 75 and 115 °C. Color degradation was studied in respect to both visual green color (Hunter -a value) and total color [L × (-a) × b]. Degradation of color followed 1st-order reaction kinetics. Temperature dependence of the degradation rate constant obeyed the Arrhenius relationship with activation energies ranging between 19.71 and 41.64 kJ/mol. Higher activation energy value indicated greater temperature sensitivity of mustard leaves than spinach and mixed puree. Activation energies for visual green color were consistently higher than that for total color. Visual green color could therefore be used for on-line quality control of spinach, mustard leaves, and mixed puree during thermal processing.     

Thermal Degradation Kinetics of Carotenoids and Visual Color of Papaya Puree

The degradation kinetics of carotenoids and visual color of papaya puree were investigated at selected temperatures (70 to 105°C). The concept of fractional conversion was applied to determine the kinetic parameters. The degradation of papaya color was based on change of Hunter a and b values and it was found that combination of Hunter (a × b) value adequately represented thermal color change. Degradation of carotenoids and visual color followed first order reaction kinetics. Dependence of the rate constant followed the Arrhenius relationship. The process activation energies for carotenoids and visual color were 20.56 and 32.59 kJ/mol respectively. Higher activation energy value indicated greater temperature sensitivity of visual color as compared to carotenoids. The degradation of pigment and visual color varied linearly. Visual color could therefore be used for on‐line quality control of papaya puree.     

Degradation Kinetics of Chlorophyll in Peas as a Function of pH

The kinetics of chlorophyll degradation in pea puree were determined in a specially designed reactor with on‐line pH control capability. Without pH control, the pH of the pea puree decreased continuously with heating due to acid formation; the pH was maintained within ±0.1 of the desired value with on‐line pH control. Chlorophyll (both a and b) degradation followed the first‐order reaction model. The temperature dependence of the rate constant was adequately modeled by the Arrhenius equation. The activation energy was independent of pH and was 17.5 kcal/mol and 17 kcal/mol for chlorophyll a and chlorophyll b, respectively. The degradation rate constant decreased log‐linearly as the pH was increased. A mathematical model was developed to predict the chlorophyll concentrations as a function of time, temperature and pH.     

Thermal destruction kinetics of Bacillus licheniformis spores in carrot juice extract as influenced by pH,type of acidifying agent and heating method

The combined effects of different heating methods (conventional (CH) vs. Ohmic (OH)), types of acidifying agent (citric vs malic acid) and pH levels (pH 4.5, 5.5 and 6.2) were investigated to study their influence on destruction kinetics of spores of Bacillus licheniformis. The ultimate aim to generate relevant kinetic data on an indicator microbial spore is useful for assessing the efficacy of thermal processes for acid or acidified low acid foods. Kinetic parameters were evaluated according to the first-order kinetic model. Temperature and pH showed a highly significant (p < 0.01) effect on the spore destruction kinetics. Ohmic heating showed marginally better rate of bacterial destruction than conventional heating. The overall range of D and z values were 1.1–11.2 min and 12.6–17 °C, respectively, depending up on the pH and temperature levels, method of heating as well as the type of acidulate used. The shortest D_97°C = 1.1 min was obtained at pH of 4.5 when citric acid was used as an acidifying agent in OH. No significant difference (p > 0.05) was observed with respect to D and z values between the two types of acidifying agents.     

Seasonality of the Thermal Kinetics of Color Changes in Whole Spinach (Spinacia Oleracea) Leaves Under Pasteurization Conditions

Color changes in whole spinach (Spinacia oleracea) leaves at pasteurization temperatures (65 to 90°C) indicate that the parameter of “greenness” (-a_t/b_t) increased during a short initial period of heating, followed by a loss that was more pronounced at higher temperatures. Seasonality was evident in kinetic models for color changes possibly due to seasonal difference in chemical composition influencing color degradation kinetics. The mechanism for loss of greenness at lower temperatures was attributed to enzymatic activity while cell collapse, cell compaction, and oxidative changes were probably more important at higher temperatures. Lower temperatures resulted in a higher retention of green color of spinach leaves during the thermal pasteurization process and the kinetic models presented in this work could be used for optimizing pasteurization processes.     

Degradation Kinetics of Anthocyanin in Blueberry Juice during Thermal Treatment

ABSTRACT: The kinetics of anthocyanin degradation in blueberry juice during thermal treatment at 40, 50, 60, 70, and 80 °C were investigated in the present study. Anthocyanin degradation was analyzed up to the level of 50% retention using a pH differential method. The degradation of anthocyanin at each temperature level followed a first-order kinetic model, and the values of half-life time (t_1/2) at temperatures of 40, 50, 60, 70, and 80 °C were found to be 180.5, 42.3, 25.3, 8.6, and 5.1 h, respectively. The activation energy value of the degradation of the 8.9 ° Brix blueberry juice during heating was 80.4 kJ·mol⁻¹. The thermodynamic functions of activation (ΔG, ΔH, and ΔS) have been determined as central to understanding blueberry degradation.     

差示扫描量热法对DHA、EPA甘油酯的热氧化动力学研究

利用差示扫描量热法(DSC)对DHA和EPA甘油酯的热氧化动力学进行了研究。通过对DSC曲线的分析表明:DHA和EPA甘油酯的酰基甘油组成较复杂,而脂肪酸种类较少。用Ozawa法和Kissinger法计算DHA和EPA甘油酯的热氧化反应动力学参数,两种计算方法得到的动力学参数具有一致性。     

Kinetics of Vitamin A Degradation in Beef Liver Puree on Heat Processing

The effects of heating on Vitamin A (measured as trans-retinol) in beef liver puree were investigated. The liver puree was heated in capillary tubes at five temperatures in the range 103-127°C, the typical canning temperature range for meat products. It was found that in this system and over the temperature range studied, the observed rate of degradation followed first order kinetics. The activation energy for the temperature dependence of the rate constant was 112 ± 9 kJ/mole.     

Kinetics of Chlorophyll Degradation to Pyropheophytin in Vegetables

Pyropheophytins a and b were determined as predominant chlorophyll derivatives in heat processed spinach. Chlorophylls a, b, pheophytins a, b and pyropheophytins a, b were quantitated in fresh, blanched and heat processed spinach at 116, 121 and 126°C. First order degradation rate constants were determined to calculate activation energies of 25.2 and 22.5 Kcal/mole for chlorophylls a and b and 20.7 and 15.7 Kcal/mole for pheophytins a and b, respectively. Based on the results, the suggested mechanism for the decomposition of chlorophyll during heat processing of vegetables is: Chlorophyll Pheophytin Pyropheophytin. Pyropheophytins a and b were major chlorophyll degradation products found in all commercially canned vegetable products surveyed.     

Thermophysical Properties of Papaya Puree

The effects of soluble solids content and temperature on thermal properties of papaya puree were studied. Density and specific heat were measured using a pycnometer and differential scanning calorimeter, respectively, while thermal conductivity was measured using a line heat source probe. Thermal diffusivity was then calculated from the experimental results of the specific heat, thermal conductivity, and density. Thermal properties of papaya puree were experimentally determined within a soluble solids content range of 10 to 25 °Brix and temperature between 40 and 80°C. The density, specific heat, thermal conductivity, and thermal diffusivity of papaya puree were found to be in the ranges of 1014.6 to 1098.9 kg/m³, 3.652 to 4.092 kJ/kg °C, 0.452 to 0.685 W/m °C, and 1.127?×?10^?7 to 1.650?×?10^?7 m²/s, respectively. Moreover, the empirical models for each property as a function of soluble solids content and temperature were obtained.     

Thermal Degradation Kinetics of Prickly-Pear-Fruit Red Pigment

The color stability of betacyanine from prickly pear was determined in the fruit juice at temperatures up to 90 °C. The degradation rates were dependent on pigment concentration, being slower for higher concentrations. The lack of a significant oxygen effect or inhibitory action of ascorbic acid did not support autooxidation as the exclusive chemical process responsible for decolorization.     

Kinetics of Thermal Inactivation of Peroxidase and Color Degradation of African Cowpea (Vigna unguiculata) Leaves

Cowpea leaves form an important part of the diet for many Kenyans, and they are normally consumed after a lengthy cooking process leading to the inactivation of peroxidase (POD) that could be used as an indicator for the potential shelf life of the vegetables. However, color degradation can simultaneously occur, leading to poor consumer acceptance of the product. The kinetics of POD in situ thermal (for thermal treatments in the range of 75 to 100 °C/120 min) inactivation showed a biphasic first‐order model, with Arrhenius temperature dependence of the rate constant. The kinetic parameters using a reference temperature (T_ref) of 80 °C were determined for both the heat‐labile phase (k_ref = 11.52 ± 0.95 × 10^?2 min^?1 and E_a of 109.67 ± 6.20 kJ/mol) and the heat‐stable isoenzyme fraction (k_ref = 0.29 ± 0.07 × 10^?2 min^?1 and E_a of 256.93 ± 15.27 kJ/mol). Color degradation (L*, a*, and b* value) during thermal treatment was investigated, in particular as the “a*” value (the value of green color). Thermal degradation (thermal treatments between 55 and 80 °C per 90 min) of the green color of the leaves followed a fractional conversion model and the temperature dependence of the inactivation rate constant can be described using the Arrhenius law. The kinetic parameters using a reference temperature (T_refC = 70 °C) were determined as k_refC = 13.53 ± 0.01 × 10^?2 min^?1 and E_aC = 88.78 ± 3.21 kJ/mol. The results indicate that severe inactivation of POD (as an indicator for improved shelf life of the cooked vegetables) is accompanied by severe color degradation and that conventional cooking methods (typically 10 min/100 °C) lead to a high residual POD activity suggesting a limited shelf life of the cooked vegetables.     

Kinetics of chemical marker formation in whey protein gels for studying microwave sterilization

The kinetics of 4-hydroxy-5-methy-3(2H)-furanone (M-2) formation in a model food system (20% whey protein gel) was determined for studying cumulative time–temperature effects in high-temperature-short-time processes. M-2 was formed from -ribose and amines through non-enzymatic browning reactions and enolization under low acid conditions (pH > 5). The order of the reaction for M-2 formation was determined by non-linear regression analysis and further confirmed by graphical method. M-2 formation followed a first-order kinetics and the rate constant temperature dependence was described using an Arrhenius relationship. The reaction rates and activation energy were determined using two-step, multi-linear and non-linear regression analyses. This study also demonstrated the use of M-2 formation in determining the cumulative heating effect in a model food system subjected to 915 MHz microwave heating.     

Thermal Inactivation Kinetics of Peroxidase in Coriander Leaves

Design of efficient blanching treatments requires knowledge of critical factors such as enzyme inactivation kinetic parameters and relative proportions of heat-labile and heat-resistant fractions, which is unique in each vegetable. Thermal inactivation curves for peroxidase in coriander leaves were determined in the temperature range of 70 to 100 °C and in steam. The isothermal data were statistically treated using both linear and nonlinear regression. Applicability of various enzyme inactivation models available in the literature was critically evaluated. The two-fraction first-order model was found to be the best model to describe the peroxidase inactivation kinetics in coriander leaves (R ² > 0.97). Kinetic parameters were determined for heat-labile and heat-resistant isoenzyme fractions. The temperature dependence of the rate parameters in the present study did not follow the Arrhenius relationship.     

Kinetics of thermal inactivation of tomato lipoxygenase

The kinetics of thermal inactivation of tomato lipoxygenase were studied. Tomato dices and a non-purified enzymatic extract were treated at different time–temperature combinations in the range of 0–150 min and 80–98 °C and the thermodynamic (activation energy) and kinetic (D_T and z) parameters for lipoxygenase inactivation were calculated. The kinetic behaviour of lipoxygenase from the tomato samples indicated the presence of two different isoenzymes having different thermal stabilities. Furthermore, the results showed that the isoenzymes were more heat-resistant than expected on the basis of literature reports and that the determined D_T and z values for lipoxygenase were orders-of-magnitude larger than those for microrganisms. This suggested that high temperature-short time treatments cannot be sufficient to achieve complete inactivation of tomato lipoxygenase.     

热降解动力学研究方法在阻燃皮革上的应用

简单介绍了几种热降解动力学的研究方法及其优缺点，综述了热降解动力学在纺织、塑料等领域的应用情况及其在皮革领域的发展现状，并对热降解动力学研究方法在阻燃皮革研究上的应用前景进行了展望。     

Thermal Kinetics of Color Change, Rheology, and Storage Characteristics of Garlic Puree/Paste

ABSTRACT Kinetics of color change of garlic puree at selected temperatures and rheological behavior and effects of packaging materials and storage temperatures on color of garlic paste were investigated. Results indicated that color change during thermal processing of garlic puree followed first-order reaction kinetics with an activation energy of 13.78 kJ/mol. Garlic paste behaved as a pseudoplastic material and flow activation energy at 100 rpm equaled 13.30 kJ/mol. Both temperature and duration of storage had effect (P≤ 0.05) on total color of garlic paste. Degreening of garlic paste was observed during storage at 25°C and complete degreening occurred at about 48 to 52 d. Storage of garlic paste at 5°C enhanced greening.     

A Fraction Conversion Kinetic Model for Thermal Degradation of Color in Red Chilli Puree and Paste

The kinetics of degradation of color was evaluated using a fraction conversion model during thermal treatment of red chilli puree at 60, 70, 80 and 90°C (up to 20 min) and storage of red chilli paste at 5, 25 and 37°C (up to 6 mo). Red chilli puree was subjected to heat treatment at different temperatures in a well-stirred water bath. Test samples were removed from the bath at selected time intervals (0-20 min after come-up), cooled immediately and analysed for color using a Hunterlab colorimeter. Chilli paste was prepared by a standard formulation by adding common salt (8%) and the required volume of citric acid to bring the pH to 4.0. The paste was thermally processed at 85°C for 15 min, filled into glass bottles and stored at selected temperatures for 6 mo. Red chilli color was expressed as a tristimulus combination value (L·a·b) as well as the total color difference (ΔE). The fraction conversion model adequately described the kinetic changes in both color values during thermal treatment of puree and storage of puree. The process activation energies were 24.2 and 24.8 kJ/mol, respectively, for ΔE and L·a·b during the thermal treatment, and during the storage the respective values were 24.1 and 25.0 18;kJ/mol. Up to the end of the 6-mo storage, the paste was microbiologically stable with no major changes in other physico-chemical characteristics.