The Use of Fractional Conversion Technique to Investigate the Effects of Testing Parameters on Texture Degradation Kinetics

ABSTRACT: To study the effects of testing parameters on texture degradation, texture loss of potatoes heated at 80 °C was measured using an Instron universal testing machine as well as a texture analyzer under 2 instrument crosshead speeds, 2 sample sizes, and either compression or shear modes of mechanical deformation. Using the fractional conversion as a texture index, the kinetics of texture degradation of potatoes fitted a single 1^st order reaction model, and the rate constant (or D value) was shown to be independent of the test used to determine the texture index. The average D value was 30 ± 1.2 min at 80 °C.     

Degradation Kinetics of Chlorophylls and Chlorophyllides

Thermal degradation of chlorophylls and chlorophyllides in spinach puree was studied from 100 to 145°C (2–25 min) for chlorophylls and from 80 to 115°C (2.5–39 min) for chlorophyllides. The derivatives formed were: pheophorbides, pyropheophorbides, pheophytins and pyropheophytins. Degradation kinetics of chlorophylls and chlorophyllides followed a first-order kinetic model. Reaction rate data showed that the a form of both chlorophylls and chlorophyllides degraded more rapidly than the b form. Chlorophyllides were less stable than chlorophylls. Activation energies ranged from 15.0 to 22.8 Kcal/mol. A kinetic compensation effect was observed for both chlorophylls and chlorophyllides with an isokinetic temperature of 160.8°C. The relative stability of these compounds suggests that methods to maximize chlorophyllides would not be effective for improving green color stability.     

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.     

蔬菜中有机磷农药残留降解方法的研究进展

目前有机磷农药是应用最为广泛的化学农药之一,蔬菜是其主要作用对象,有机磷农药带来的药残严重威胁人类的健康。对于有机磷药残的降解方法主要有物理降解、化学降解和生物降解,其中生物降解法是应用前景最为广泛的降解方法之一。     

果蔬中残留甲醛消解动态及其甲醛本底值的研究

采用五氟苯肼衍生液相色谱法分析果蔬中残留甲醛在不同条件下的消解动态,同时对部分果蔬中甲醛本底值进行测定。研究表明:果蔬中残留甲醛的消解速度与贮藏介质有关,在水中浸泡消解速度明显比在空气中自然消解速度快。在空气中甲醛自然消解的主要影响因素是空气温度和果蔬基质,温度越高,消解速度越快。在水中浸泡消解速度与水温、pH和果蔬基质有关,50℃水中的消解速度要高于25℃水中的消解速度;pH=9时消解速度要高于pH=7和pH=5条件下。甲醛本底含量检测发现32种果蔬中有31种存在一定的甲醛本底,其中鱼腥草中未检出甲醛本底,柑橘类中桔子和橙子的甲醛本底含量较高,可达0.79~2.52 mg/kg,其他果蔬中甲醛含量均处于0.08~0.61 mg/kg之间,这为果蔬中甲醛含量的检测提供了参考数据。     

Color and Texture Change Kinetics in Ripening Bananas

Kinetics of color and texture changes in ripening bananas were investigated as a function of storage temperature (10, 16, 22, 28 °C). Color was evaluated in terms of L, a and b values as well as the total color difference (ΔE) representing the residual deviations from the ripe stage. Puncture force (PF) was used to evaluate the texture properties of banana. The results indicated that the time dependence of L, ΔE and PF values followed a logistic model, while a and b values were well described by a simple zero-order and fraction conversion models, respectively. The Arrhenius equation adequately described the temperature dependence of the reaction rate constants for both color and texture parameters, from which the activation energies and rate constant at reference temperature 15 °C were obtained. There were significant linear correlations between color parameters (L, a, b, ΔE) and texture parameter (PF).     

O_3处理降解硫藏果蔬原料亚硫酸盐效果的研究

研究了臭氧处理对硫藏杏干、山楂及腌制姜3种果蔬原料中亚硫酸盐的降解效果及影响处理效果的因素。结果表明:经臭氧处理后的硫藏杏干、山楂、腌制姜,其SO2含量明显低于无处理,说明臭氧能有效降解亚硫酸盐;亚硫酸盐的降解率与臭氧通入时间、浸泡溶液pH等因素有关,表现为在一定范围内,随臭氧通入时间、pH的增加而提高;但是,在总浸泡时间和通入臭氧处理时间相同的条件下,浸泡期间内开始通入臭氧处理的时刻对样品最终SO2含量的影响不明显。     

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.     

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。     

Kinetic Parameters for Thermal Degradation of Green Asparagus Texture by Unsteady-state Method

An unsteady-state method was developed for estimating texture degradation during heating-cooling of green asparagus spears. The method used a mathematical model of heat transmission for time-temperature history estimation, and a nonlinear regression of texture measurements of asparagus spears to estimate kinetic parameters. The specific heat, conductivity and convective coefficient of green asparagus were determined experimentally and used in the mathematical model for temperature estimation. Values obtained were Ea = 76.19±0.13 kJ/mol and k_1158°C= 0.00528±0.00005 s^-1. Good agreement was found between predicted and observed texture values. The method was compared with the classical steady-state method. The mathematical model and kinetic parameters estimated could be used to design and evaluate thermal processes for green asparagus.     

桑葚花色苷的分离纯化及其热降解动力学研究

通过AB-8大孔树脂、乙酸乙酯萃取和Toyopearl TSK HW-40S凝胶柱层析对桑葚汁中的花色苷进行分离纯化,得到两个单一的化合物组分。经HPLC-MS鉴定这两种花色苷分别为矢车菊素-3-芸香糖苷和矢车菊素-3-葡萄糖苷。在此基础上,研究了不同纯度花色苷的降解动力学,结果表明:桑葚花色苷粗提物中所含的黄酮类化合物对花色苷的热降解有较强的保护作用,含黄酮的花色苷体系对p H值的变化更为敏感。在p H 3.5时,矢车菊素-3-芸香糖苷和矢车菊素-3-葡萄糖苷的热稳定性基本相同;在p H 4.0时,矢车菊素-3-芸香糖苷的热稳定性略好于矢车菊素-3-葡萄糖苷。     

不同温度、pH、光照条件下毛蕊花苷的降解动力学

为了研究毛蕊花苷的稳定性,本文采用高效液相色谱法研究毛蕊花苷在不同温度(37、50、60、80、100 ℃)、不同pH(2、6、7、8)、光照/避光条件下的降解动力学。结果表明,毛蕊花苷在不同温度、pH和光照/避光条件下的降解反应均属于一级反应。对毛蕊花苷半衰期的计算结果表明,高温(60 ℃以上)、近中性环境(pH6~8)、光照均不利于毛蕊花苷的保存;毛蕊花苷在中低温(37、50 ℃)、低pH(2)及避光条件下更稳定,半衰期明显延长。本文分析了影响毛蕊花苷稳定性的主要因素,可为毛蕊花苷提取、纯化和活性分析等相关研究提供重要的参考。

     

蓝莓花色苷降解动力学及稳定性

以蓝莓花色苷为原料,采用pH示差法测定了不同pH值、温度、光照强度、氧化剂和还原剂对花色苷稳定 性的影响。结果表明：不同pH值下花色苷热降解符合一级动力学方程,强酸性条件下蓝莓花色苷的热稳定性强于 弱酸和中性;花色苷的热稳定性差,随着温度升高,花色苷的降解速率k明显增大,降解半衰期和递减时间D值明 显减小,pH 6.0时活化能最小,为44.77 kJ/mol,pH 1.0时活化能最大,为83.73 kJ/mol,热降解反应为吸热非自发反 应;光照和H2O2会加快蓝莓花色苷的降解,花色苷在光照和H2O2处理条件下降解均符合一级动力学方程,在光照条 件下的降解速率为0.014 8 d－1,半衰期为47 d,花色苷降解速率随着H2O2体积分数的升高明显增加;此外,质量分 数0.20% Na2SO3对花色苷的降解起到抑制作用,而质量分数0.05%、0.10%、0.15% Na2SO3会促进花色苷降解反应。     

超声对花色苷稳定性的影响及其降解动力学

为研究超声对花色苷稳定性影响规律及其降解动力学,采用单因素试验在超声提取模拟体系中研究4 种因 素（功率密度、温度、溶剂、pH值）对5 种常见花色苷稳定性的影响规律,采用试错法分析花色苷超声降解动力 学,并结合液相色谱-质谱联用技术分析超声处理后的降解产物。结果表明：随着温度的升高,花色苷在超声处理 下的降解率下降;5 种花色苷在体积分数70%乙醇溶液中降解最少;pH 1～5范围内,花色苷降解率呈先增加后减 少趋势。飞燕草素-3-葡萄糖苷的超声降解符合一级动力学模型,矢车菊素-3-葡萄糖苷、天竺葵素-3-葡萄糖苷、锦 葵素-3-葡萄糖苷、芍药素-3-葡萄糖苷的超声降解符合零级动力学模型。在天竺葵素-3-葡萄糖苷、锦葵素-3-葡萄糖 苷、芍药素-3-葡萄糖苷、矢车菊素-3-葡萄糖苷的降解产物中都检测到8-β-D-吡喃葡萄糖基-2,4-二羟基-6-氧代环己 基-2,4-二烯基乙酸,同时也检测到山柰酚、槲皮素、丁香酸、阿魏酸、2,6-二甲氧基苯酚等。     

龙葵果花色苷降解动力学

通过研究4种龙葵果花色苷提取物在不同pH值和温度下的降解动力学过程,得出其降解规律。结果显示,龙葵果花色苷的降解符合一级反应动力学模型。相同pH下随着温度的升高,龙葵果花色苷的降解速率常数呈现指数型增长趋势,半衰期呈现指数型下降趋势。60℃和70℃时随着pH的增大,粗提物、一级精制物的降解速率常数呈现对数型增长趋势,而组分1和组分2的降解速率常数则呈现指数型增长趋势,4种提取物的半衰期均呈现指数型下降的趋势。而80℃和90℃时,4种花色苷提取物的降解速率常数和半衰期并未呈现规律性的变化。4种龙葵果花色苷提取物均在60℃、pH 1.0时降解最慢,稳定性最好,其中粗提物的稳定性最强。     

Predictive Models for Microbial Inactivation and Texture Degradation in Surimi Seafood During Thermal Processing

Models for Staphylococcus aureus inactivation and texture degradation during thermal processing of surimi seafood were developed based on the modified thermal‐death‐time (TDT) concept. Validation studies showed good fit between experimental and predicted values. The models allow input of processing parameters, resulting in a surface response that determines microbial inactivation and texture degradation. D‐values for microbial inactivation were determined between 55 and 95 °C. The z‐value, however, was not linear. Therefore, a polynomial equation was used to calculate D‐values at intermediate temperatures. Texture degradation between 55 and 95 °C followed a power function. Therefore, power “n” was used as the degradation rate for modeling purposes. Polynomial equation was used to calculate “n” at intermediate temperatures.     

白菜中二硫代磷酸酯类有机磷农药降解动力学研究

培养8 叶期无菌白菜幼苗,添加5 种二硫代磷酸酯类有机磷农药（马拉硫磷、乐果、甲拌磷、乙拌磷及特丁硫磷）,用气相色谱及液相色谱-质谱联用法检测二硫代磷酸酯类农药及O,O-二甲基二硫代磷酸酯残留量。结果表明：二硫代磷酸酯类农药的含量在实验过程中呈减少的趋势,农药在样本培养过程被逐渐降解,10 d内降解水平为13.4%～65.0%,无菌苗添加药物组降解速率明显低于正常培养添加药物对照组。使用一级反应动力学模型对农药代谢动力学进行评价,无菌条件下马拉硫磷降解速率最快,降解速率常数为0.034 67,降解半衰期为19.9 d,特丁硫磷降解速率常数最小,降解速率常数为0.007 17,降解半衰期为96.7 d,乐果、甲拌磷及乙拌磷相对稳定,但降解动力学差别较大。     

Degradation Kinetics of Myosin Heavy Chain of Pacific Whiting Surimi

Pacific whiting surimi paste was ohmically heated to investigate degradation of myosin heavy chain (MHC) caused by endogenous proteinase over a range of 40–85°C and 0.5–35 min. Degradation was best described with an apparent reaction order of 1.4. Changes of degradation rate increased with temperature and reached a maximum at 57°C. Then, rate of MHC degradation decreased with higher temperature and reached a minimum at 75°C. E_a values of activation and inactivation zone were 142.3 and 83.1 kJ/mol, respectively. Generally, failure shear stress and shear strain increased linearly with MHC content. Proteolytic degradation of actin exhibited the same trend as that of MHC but at a slower rate. The synergistic effect of actin in the gelation of whiting surimi was predominant at ≥75°C.     

Nitrogen-to-Protein Conversion Factors for Common Vegetables in Japan

Twenty (JAPANESE) vegetables in Japan were analyzed for total nitrogen, amino acid nitrogen, amide nitrogen, and nonprotein nitrogen and then calculated nitrogen-to-protein conversion factors were calculated. The average conversion factor based on quantitative amino acid composition data was 6.00. However, the use of this factor for estimating protein content led to a considerable difference from estimates based on amino acid residue concentrations, due to the presence of high levels of nonprotein nitrogen. The distribution of protein nitrogen to total nitrogen averaged 73%. Adjusted conversion factors, defined as the proportion of amino acid nitrogen to total nitrogen, averaged 4.39. Protein contents estimated with this factor agreed well with contents determined by amino acid residues.     

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。