Thermal Chlorophyll Degradation Kinetics of Mint Leaves Puree

Thermal degradation kinetics of chlorophyll ‘a’, ‘b’ and total chlorophyll in mint leaves puree were investigated as function of pH (4.5–8.5) and processing temperature (80–145°C), respectively. Mint puree was processed at 80°to 100°C at pH 4.5, while that at pH 5.5 to 8.5 was processed at 105°to 145°C. Chlorophyll degradation followed the first order reaction kinetics. Good agreement was found between estimated and experimental chlorophyll retention in all cases (R² > 0.86; MRQE < 0.27). Activation energies ranged from 6.45 to 47.67 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 (ΔH^#) ranged from 3.14 to 44.66 kJ/mol, while entropy (ΔS^#) ranged from ?0.157 to ?0.266 kJ/(mol K). The overall free energy change was 105.76 kJ/mol. Results indicated that, the compensation effect did not exist for chlorophyll degradation in mint puree during thermal processing.     

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.     

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.     

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.     

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.     

热风干燥过程中榆叶叶黄素的降解动力学

目的：研究热风干燥过程中榆叶叶黄素的降解动力学。方法：采用高效液相色谱法测定榆叶中叶黄素的含量,对叶黄素降解过程进行反应动力学方程拟合,求解降解动力学参数。结果：新鲜榆叶中叶黄素含量较高,为（397.5±27.5）μg/g鲜质量（（1.414±0.105）mg/g干质量）。当风速为0.5 m/s,干燥温度为50、60、70 ℃时,榆叶中叶黄素的热降解符合一级反应动力学模型,半衰期分别为4.5、3.2、2.8 h;温度升高,降解反应速率增大;降解反应速率常数与干燥温度的关系符合Arrhenius公式,反应活化能为21.23 kJ/mol。结论：热风干燥榆叶时,采用较低的干燥温度有利于提高叶黄素保留率。     

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.     

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.     

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.     

香菜叶多酚氧化酶的分离纯化与部分酶学性质研究

新鲜香菜叶经匀浆、缓冲液提取、硫酸铵分级沉淀、DEAE-Sepharose离子交换层析、Superdex-200凝胶过滤层析,获得电泳纯的多酚氧化酶。该酶比活力达到5 622.95 U/mg,酶活回收率为3.90%,纯化倍数为126.08;全酶分子质量为111.10 kD,亚基分子质量为55.60 kD;最适温度为37 ℃,最适pH值为6.5;在25～45 ℃及pH 6.0～7.0范围内有较好的稳定性;在最适条件下测得其Km值为4.04×10－2 mol/L;甲醇、乙醇、异丙醇、氯仿及柠檬酸、抗坏血酸、Ca2＋、Hg2＋、Ba2＋对其有抑制作用,Co2＋、Pb2＋对其具有一定的激活作用。     

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。     

芥蓝叶制取叶绿素铜钠盐的工艺参数及其性质研究

用95％乙醇为溶剂提取芥蓝叶中的叶绿素,经过皂化、铜代、成盐等工序制成叶绿素铜钠盐,产品色泽鲜艳,性质稳定,质量达到国家GB3236-82标准。     

桑叶挂面的研制

介绍了桑叶的主要化学成分及作用 ,在此基础上 ,研究了桑叶方便面的生产工艺。     

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.     

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。     

竹叶保健饮料的加工制作

竹叶中含有黄酮类物质等有效成分,具有降血脂、降胆固醇、调节免疫的保健功能。本文叙述了用水煮法提竹叶中有效成分,并利用其制作几种保健饮料的加工工艺。     

黑龙江产芫荽籽精油成分及其清除DPPH自由基能力研究

用水蒸气蒸馏法提取黑龙江产芫荽籽,以0.50%的产率获得精油。用GC-MS联机对精油进行了成分分析,检测出31个成分,解析鉴定了占精油99.726%的29个成分。主要成分芳樟醇占总精油含量的73.614%。该精油对DPPH(1,1-Diphenyl-2-picrylhydrazyl)自由基的清除率为94%。水蒸气蒸馏后残渣的甲醇萃取物对DPPH的最大清除率为91%。     

苹果汁中维生素C热降解动力学研究

为了探索温度对苹果汁中维生素C降解的影响以及维生素C的降解动力学规律,采用可逆的一级反应模型,对加热温度30、40、50、60、70℃条件下苹果汁中还原型维生素C(AA)和氧化型维生素C(DHA)含量的变化及降解动力学进行了研究,结果表明:60℃的AA反应速率最大,DHA反应速率基本随着温度升高而增大;温度升高,可逆反应速率常数增大,其它降解途径速率常数变化不明显;AA无氧氧化速率与温度有一定关系,50℃的AA无氧氧化速率最大,70℃的AA无氧氧化速率最小;AA和DHA热降解反应活化能均低于一般化学反应活化能,说明苹果汁中维生素C热稳定性较差。维生素C的降解主要是有氧氧化反应,苹果汁中维生素C无氧降解速率比有氧降解速率慢;温度升高,苹果汁中维生素C有氧降解速度加快,无氧降解速度变化不明显。在苹果汁加工工艺中应尽量隔绝氧气,采用高温(70℃)短时热处理。对成品苹果汁应采用低温贮藏。