基于高倍富集放大反应的双点电位滴定法测定谷物中氟含量

【目的】饮食中氟可影响人体健康与安全,简捷准确检测饮食中氟含量就显得十分重要。【方法】以现有GB/T 5009. 18-2003的氟离子电极电位滴定法为基础,以高倍富集放大反应为获得高灵敏度的突破点,以双点电位滴定法为确保方法准确的手段,探寻出灵敏准确测定谷物中微量氟的新方法。以方法的检测限(LOD)、加标回收率和相对标准偏差(RSD)等为衡量指标,通过单因素试验法对影响富集反应的富集剂种类、用量、温度、时间、反应体系酸度(pH)、搅拌速率和洗涤次数等因素考察后,针对富集反应主要影响因素富集剂用量、反应温度、反应时间和反应体系酸度(pH)等用L₉(3^₄)正交试验优化获得最适宜的测定条件。【结果】所得最适宜条件为：含Ca^₂₊复合富集剂用量为(m_氟/m_复合剂) = 1:1×10^₅,反应时间200min,反应温度22℃,反应体系酸度pH 5.5,搅拌速率200~300 r/min,沉淀物洗涤4次。该法的LOD_F = 5.3×10^_-3 μg/g,且c_F在1.0×10^_-6 mol/L ~ 1.0×10^_-1 mol/L内呈良好定量函数关系：E = 38.657 lgc - 174.44 (R2 = 0.996)。加标回收率为91.5 %~100.3 %,测定结果较稳定(RSD≤2.7%)。实样氟含量测定值符合GB 2762-2005氟限量要求。【结论】本法集合了富集反应的高倍放大的效果和双点电位滴定法的高精准的特点,测定选择性高,速度快,灵敏度较高,是种实用可靠的微量氟的定量分析方法。且有易于实现自动化和智能化快捷在线检测的潜能。     

油莎豆热风干燥特性及数学模型研究

以新鲜油莎豆为原料,研究风温和风速对油莎豆热风干燥特性的影响,计算干燥过程中有效扩散系数与活化能,并选取8种干燥动力学模型进行拟合分析。实验结果表明：热风温度越高,干燥速率越快,干燥时间越短;风速对干燥速率影响较小。本试验干燥过程主要发生在降速阶段,油莎豆有效水分扩散系数2.2856×10^-10～7.8112×10^-10,平均活化能为35.31kJ/mol,Two-term模型可以很好的反映油莎豆热风干燥过程,实验值与预测值吻合度较高,拟合效果良好。     

聚缬氨酸修饰电极法测定食品中2, 6-二叔丁基对甲苯酚的方法研究

目的 建立一种快速、灵敏地测定食品中2, 6-二叔丁基对甲苯酚的新方法。方法 通过探讨聚缬氨酸修饰电极的制备条件,确定了采用循环伏安法制备聚缬氨酸修饰电极的最优聚合条件,研究了2,6-二叔丁基对甲苯酚在此电极上的电化学行为。试验从测定pH、电位、扫描速率等方面进一步探讨了测定2,6-二叔丁基对甲苯酚最佳条件。在最优条件下找出了氧化峰电流与浓度的线性关系,作为工作曲线,进一步对食品中的2,6-二叔丁基对甲苯酚进行了测定。结果 在pH=4.0的磷酸盐缓冲溶液中,2,6-二叔丁基对甲苯酚的氧化峰电流与其浓度在4.0×10_^-7～4.0×10_^-5mol/L范围内呈线性关系,线性方程：ipa=1.27×10-7+0.23c(mol/L),相关系数为0.9962,检出限4.0×10_^-8mol/L。结论 方法简单、快速、灵敏,已运用在食品中2, 6-二叔丁基对甲苯酚的检测,获得了满意的结果。此研究建立了测定食品中2,6-二叔丁基对甲苯酚的新方法。     

基于温度控制的猕猴桃片微波真空干燥特性研究

目的：研究温度控制下猕猴桃片微波真空干燥特性,并确定其最佳数学干燥模型。方法：以猕猴桃片为原料,利用自制的温度自适应微波真空干燥机干燥猕猴桃片,研究不同控制温度、真空度和微波功率密度对其干燥特性和水分有效扩散系数的影响,利用SPSS 19.0软件将试验数据与6个常用的薄层干燥模型进行非线性拟合,以确定系数R²,均方根误差R_MSE及卡方χ²作为评价指标,筛选出最佳干燥模型。结果：温度控制条件下的猕猴桃片的微波真空干燥为降速干燥过程,无明显恒速阶段。在试验范围内,控制温度与真空度对猕猴桃片的干燥特性影响显著,控制温度越高、真空度越大,物料的干燥速率越大;根据费克第二定律计算出猕猴桃于温度控制下微波真空干燥过程中的水分有效扩散系数,且随着控制温度与真空度的增大而增大,其最大值为6.814 97×10^-6 m²/s,平均活化能为70.77 kJ/mol。所选用的6个模型中,Two-term exponential模型具有最大的确定系数R²（0.999 9）,最低的R_MSE（0.002 02）和最小的χ²（0.000 30）,是猕猴桃片温度控制下微波真空干燥的最佳模型。结论：控制温度、真空度对猕猴桃片微波真空干燥特性、干燥速率和水分有效扩散系数具有显著影响。在试验范围内,Two-term exponential模型的拟合度最高,可有效描述猕猴桃片温度自适应下微波真空干燥过程中的水分随时间的变化规律。     

芒果切片热风干燥特性及模型

目的：为对芒果热风干燥过程进行预测与控制。方法：以新鲜金煌芒为试验材料,研究热风温度（60,65,70 ℃）和芒果切片厚度（0.8,1.0,1.2 cm）对芒果热风干燥曲线、干燥特性曲线、水分有效扩散系数等的影响,并选取常用的适用于果蔬的6种干燥模型进行拟合、分析及验证,选出最适合芒果热风干燥的模型。结果：随温度的升高,切片厚度的减小,加快了芒果片的干燥速率,所需的干燥时间越短。水分有效扩散系数随温度和厚度的增大而增大,为1.401 39×10^-10～3.655 46×10^-10 m²/s。Logarithmic模型的R²最大、X²和RMSE最小,分别为0.998 87,0.000 124 779,0.001 37。结论：Logarithmic模型预测值与试验值验证基本吻合,可以较好反映芒果片在干燥过程中水分含量的变化规律。     

红小豆种皮色素提取及膜分离工艺研究

以水为溶剂对红小豆种皮中的红色素进行浸提,采用压力驱动的膜技术（微滤、纳滤等）优化红小豆种皮色素分离工艺。结果表明,红小豆种皮色素的最佳提取工艺为料液比（m_{红小豆种皮}∶V_水）1∶30 （g/mL）、浸提温度90 ℃、浸提时间90 min,此时浸提液的色价为7.53;优化的膜分离工艺为微滤（0.22 μm）和纳滤膜（NF245）相结合,微滤压力0.075 MPa,膜通量12.47 L/（m²·h）,色素透过率为87.16%;纳滤操作的最佳压力为0.3 MPa,稳定通量为16.06 L/（m²·h）,截留液中色素质量浓度提高至810.19 mg/L,总酚、糖和蛋白质浓度进一步降低。纯化后的红豆皮花色苷冻干粉中花色苷含量为（145.80±0.17） mg/g,色价为58.08±0.09,为纯化前的2.41倍。     

青叶苎麻叶多酚超声辅助提取工艺优化及抗氧化活性研究

优化了青叶苎麻叶多酚的提取工艺参数,并以没食子酸为对照评价了青叶苎麻叶多酚的抗氧化活性。结果表明:优化出的多酚提取工艺参数分别为料液比(m_苎麻∶V_乙醇) 1∶33 (g/mL)、乙醇体积分数40%、提取温度42 ℃,在此条件下青叶苎麻多酚提取量为47.97 mg/g。青叶苎麻叶多酚清除DPPH自由基和ABTS⁺自由基的IC₅₀值分别为(0.15±0.00),(2.28±0.03) μg/mL,氧自由基吸收能力为(42.41±0.01) g Trolox/g多酚,均明显优于没食子酸,具有良好的抗氧化效果。     

表面增强拉曼光谱法快速检测茶叶中百草枯与敌百虫农药残留

目的 对茶叶中的百草枯与敌百虫进行定性与定量检测,满足茶叶生产中对这两种农药残留的快速、便携、准确的检测需求。方法 采用表面增强拉曼光谱(surface enhanced Raman spectroscopy SERS)技术对不同浓度的百草枯和敌百虫农药标准溶液进行光谱采集和峰位归属,再对不同茶类茶汤中的梯度农药残留进行检测,建立峰强与农药残留浓度的线性关系。结果 发现在不同茶类中,以茶叶中百草枯在843 cm_^-1处的拉曼特征峰作为识别峰所建立回归模型预测的百草枯在绿茶、红茶、黑茶茶汤中的最低可检测浓度为1×10_^-7 moL/L,在乌龙茶茶汤中的最低可检测浓度为1×10_^-6 moL/L,灵敏度均满足国家规定的茶叶中百草枯最大农药残留限量(0.2 mg/kg);敌百虫的检测中,茶汤中咖啡碱的SERS峰强受敌百虫浓度影响,随敌百虫浓度的增加而减小且呈现显著负线性相关,因此可用茶叶中咖啡碱的拉曼特征峰作为敌百虫浓度的间接识别的依据,所建立的回归模型显示敌百虫在绿茶、红茶、乌龙茶茶汤中的最低可检测浓度为1×10_^-7 moL/L;在黑茶茶汤中的最低可检测浓度为1×10_^-6 moL/L,均可达到国家茶叶最大残留限量(2 mg/kg)。结论 使用SERS技术可实现不同茶类茶汤中的百草枯与敌百虫农药残留的简单、快速、准确分析。     

大叶千斤拔黄酮类成分提取及抗氧化活性研究

通过单因素试验及响应面试验优化大叶千斤拔总黄酮的乙醇回流提取工艺条件,并对提取物的抗氧化活性进行评价。结果表明：优化后的提取工艺条件为提取时间52 min,料液比（m_{大叶千斤拔}∶V_乙醇）1∶6 （g/mL）,乙醇体积分数70%,提取温度60 ℃,该条件下提取物的总黄酮含量为75.47 μg/mg;提取物对ABTS⁺自由基、DPPH自由基清除能力的IC₅₀分别为0.044 9,0.212 3 mg/mL,总抗氧化能力及对Cu²⁺和Fe³⁺还原能力的IC₅₀分别为0.389 6,0.221 9,0.731 7 mg/mL。说明建立的最佳提取工艺可有效获取大叶千斤拔总黄酮成分;大叶千斤拔黄酮类物质具有较强的体外抗氧化活性。     

柠檬明串珠菌KM20中D-乳酸脱氢酶的特性

目的：分析柠檬明串珠菌中D-乳酸脱氢酶（D-LDH）的酶学特性。方法：对柠檬明串珠菌KM20中D-乳酸脱氢酶基因进行克隆表达并构建表达质粒,转化至Escherichia coli BL21（DE3）中实现过表达。结果：经Ni-NTA柱亲和层析纯化后,D-LDH-1与D-LDH-2编码的蛋白分子质量分别为40.0,38.5 kDa;比活力分别为2.18,153.10 U/mg;在丙酮酸还原中两种酶的最适pH值与最适温度均为8.0与40 ℃;而乳酸氧化时D-LDH-2的最适pH值与最适温度分别为12.0与30 ℃。D-LDH-1与D-LDH-2对草酰乙酸、苯丙酮酸和2-酮戊二酸具有较强的催化能力,且Ca²⁺、Cu²⁺和Na⁺对其酶活性均具有促进作用,Zn²⁺与SDS对酶活性有极高的抑制作用。此外,两种酶对丙酮酸的K_m值分别为2.98,6.11 mmol/L,对丙酮酸的K_cat/K_m分别为6.04×10²,2.28×10⁴ L/（mol·s）,LDH-2对D-乳酸的K_cat/K_m为65.0 L/（mol·s）。结论：D-LDH-1与D-LDH-2为柠檬酸明串珠菌中催化D-乳酸合成的关键酶。     

Kinetics of Protein Extraction in Reverse Micelle

Sodium bis (2-ethylhexyl) sulfosuccinate (AOT)-sodium dodecyl sulfate (SDS)/isooctane-octanol reverse micelle extraction was tested an efficient and effective approach to separate peanut protein from full-fat peanut powder. Here, important kinetic factors including pH, ion strength, and temperature were studied during reverse micelle backward extraction. The extraction conditions were obtained by response surface experiments as follows: pH 7.5, ion concentration 1.1 mol/L at temperature 35°C. Under these optimum extraction conditions, the extraction rate of protein reached 79.03%. A model on the kinetic partitioning of peanut protein was also developed. The backward extraction in this reverse micelle system was controlled by interfacial resistance instead of diffusion resistance in reverse micelle and aqueous phase with the total mass transfer rate of 0.8×10^?5 m³·s^?1. A two-film theory may be the mechanism for flat interface. Results of mass transfer process are helpful for creating an reverse micelle extraction process, and used for purification of peanut proteins, promoting the development of food industry.     

Kinetics of Color Change of Grape Juice Generated using Linearly Increasing Temperature

Kinetics of the color change of grape juice was studied using linearly increasing temperature for heating Noble grape juice in a stainless steel reactor. The juice was heated from 60^o to 95^oC in 9 hr. Kinetic parameters for the color change were determined using Hunter L, a, b-values, chroma values, and Total Color Difference (TCD) values. The reaction of the color change of grape juice measured by L- and a-values, and Chroma value followed first order kinetics with activation energies of 114.75, 131.80, and 121.21 kJ/mol and frequency factors of 1.30 × 10¹², 8.95 × 10¹⁴ and 1.93 × 10¹³ sec^?1, respectively. However, the reaction measured by TCD followed zero order kinetics with the activation energy and the frequency factor of 92.81 kJ/mol and 4.80 × 10¹⁰ mol/l/sec, respectively.     

Green ultrasound and microwave extraction of carotenoids from passion fruit peel using vegetable oils as a solvent: Optimization,comparison, kinetics,and thermodynamic studies

The aim of this study was to examine the effect of green processes like ultrasonication assisted extraction (UAE) and microwave assisted extraction (MAE) using olive oil (OO) and sunflower oil (SO) as solvents on the extractability of carotenoids from passion fruit peel (PEP) that is discarded as waste. Using optimized conditions of UAE, 91.4% (OO) and 86.7% (SO) of the carotenoids present were extracted while MAE extracted 86.9% in OO. Comparison of energy density revealed that UAE is more efficient than MAE. UAE treated OO was acceptable for different quality parameters and the oil was enriched with carotenoids by more than three times and phenolic content by fifteen times. The extraction kinetics and thermodynamic studies for carotenoids extracted from PEP using UAE and CE (conventional extraction) processes with OO as solvent were performed at different combinations of extraction time and temperature. The extraction rate constant (k_s) for UAE and CE was in the range of 0.0022–0.0048 100 g/μg carotenoids min and 4.02 × 10⁻⁵ − 6.85 × 10⁻⁵ 100 g d.w./μg carotenoids min, respectively. The effective diffusion coefficient of UAE and CE for the extraction of carotenoids varied between 2.3740 ×10⁻¹³ and 2.8260 ×10⁻¹³ m²/s and 0.997×10⁻¹⁴and 2.336 ×10⁻¹⁴ m²/s, respectively and corresponding mass transfer rate ranged from 1.625 ×10⁻⁷ – 1.8731 ×10⁻⁷ m/s and 0.0728 ×10⁻⁸ – 0.1714 ×10⁻⁸ m/s. The kinetics information mainly rate constant, effective diffusivity and mass transfer coefficient obtained from the green extraction process using ultrasonication would allow the prediction of operation conditions for industrial implementation.     

Microwave and ultrasound assisted extraction of phytocompounds from black jamun pulp: Kinetic and thermodynamics characteristics

The present study focuses on the extraction of phenolic compounds, anthocyanin and antioxidants from black jamun pulp by microwave and ultrasound assisted extraction process. The microwave-assisted extraction was carried out for 240 s at microwave power level of 100–400 W. The yield of total anthocyanin and total phenolic content in the microwave assisted extraction process at 400 W power level after an extraction period of 240 s was 8.197 mg of C3G g⁻¹ and 37.671 40.632 mg GAE g⁻¹, respectively. The ultrasound assisted extraction was performed at temperatures of 40, 50, 60, and 70 °C for 150 min. In the ultrasound assisted extraction at a sonication temperature of 70 °C, the yield of anthocyanin was 8.525 mg of C3G g⁻¹, while the yield of the phenolic compound was 47.331 mg GAE g⁻¹. The pseudo-second order model was found to be the most suitable model to represent the extraction kinetics of anthocyanin, phenolic compounds, and antioxidant activity of black jamun pulp. The effective diffusion coefficient for ultrasound assisted extraction of phenolic components, anthocyanin, and antioxidant activity in the temperature range of 40-70 °C was 5.704× 10⁻¹²–10.515 10⁻¹², 2.485× 10⁻¹² -8.507× 10⁻¹², and 2.061× 10⁻¹²–11.977 × 10⁻¹² m².s⁻¹ respectively. The negative Gibbs free energy change values for extraction of phenolic compounds and anthocyanin specified that the reaction was feasible and spontaneous. Thermodynamic parameters such as positive enthalpy change and positive entropy change indicated that the ultrasound assisted extraction process was endothermic and irreversible in nature.     

Experimental characterization and modelling of drying of pear slices

The effect of temperature on the drying kinetics of pear slices was investigated. The drying process was carried out at temperatures of 55, 65, and 75°C. Drying time decreased considerably with increased air temperature. Seven mathematical models available in the literature were tested with the drying patterns. The Wang and Singh, and Midilli et al. models were given the best results in describing drying of pear slices. Effective moisture diffusivity increased with increasing air temperature, and varied from 0.85 to 2.18×10^?10 m²/s over the temperature range investigated, with activation energy equal to 44.78 kJ/mol.     

Modeling Effective Moisture Diffusivity of Orange Slice (Thompson Cv.)

The present study was conducted to compute effective moisture diffusivity and activation energy of orange slices during convection drying. The thin-layer drying experiments were carried out at five air temperatures of 40, 50, 60, 70, and 80^ºC, three air velocities of 0.5, 1.0, and 2.0 m/s and three orange slice thicknesses of 2, 4, and 6 mm. Results indicated that drying took place in the falling rate period. Moisture transfer from orange slices was described by applying the Fick's diffusion model. The effective diffusivity values were increased from 6.27 × 10^?10 to 3.50 × 10^?9 m²/s for the temperature range used in this study. An Arrhenius relation with an activation energy value of 16.47 to 40.90 kJ/mol and the diffusivity constant value of 7.74 × 10^?7 to 3.93 × 10^?3 m²/s were obtained. It was found that with increasing the temperature and air velocity the effective diffusivity increases while slice thickness showed no considerable changes on the effective diffusivity.     

Effect of blanching on the diffusion of glucose from potatoes

Glucose losses from potato slabs into the water during blanching at 60, 70, 80 and 90 °C were studied after 10, 20, 30, 40, 50 and 60 min. In general, an increase of temperature during the considered times produced a higher glucose loss. The apparent diffusion coefficients (D) for glucose losses from potatoes were calculated under the blanching conditions. The D-values were found to be in the range of 3 × 10^?10 to 8 × 10^?10 m² · s^?1 and could be related to temperature by an Arrhenius equation, having an activation energy of 29.1 kJ/mol. The results will allow the prediction of mean glucose concentration in potato tissues, and hence the overall losses incurred, after a given blanch treatment in this time and temperature range.     

Modeling sulfur dioxide uptake in dent corn during steeping

A mathematical model is employed to describe sulfur dioxide (SO₂) diffusion and reaction during steeping of dent corn. Experiments are performed to measure change of SO₂ content of grain during process. A computer-aided nonlinear optimization technique is used to estimate the effective diffusion coefficients and rate constants in the temperature range 25–55 °C. The effective diffusion coefficient for SO₂ varied between 2.27×10⁻¹¹ and 6.24×10⁻¹¹ m²/s and had an Arrhenius activation energy of 24.3 kJ/mol. The reaction rate of SO₂ in dent corn followed first-order kinetics, with rate constants in the range of 0.80×10⁻⁶–5.38×10⁻⁶ s⁻¹ and activation energy of 49.16 kJ/mol.     

Mass Transfer Coefficients for the Drying of Pumpkin (Cucurbita moschata) and Dried Product Quality

The aim of this work was to determine the mass transfer properties of pumpkin (Cucurbita moschata) exposed to air drying. The drying temperatures tested ranged between 30°C and 70°C, and the kinetic behavior was studied in this temperature band. The samples were analyzed in terms of moisture content, acidity, proteins, lipids, and crude fiber, both in the fresh state and after drying. From the chemical analyses made, it was possible to conclude that drying induces some reductions in acidity, lipids, fibers, and proteins. As to the influence of the drying temperature on the process, it was observed that a temperature rise from 30°C to 70°C led to a 70% saving in drying time. The results obtained by fitting the experimental data to the kinetic models tested allowed concluding that the best model for the present case is Henderson–Pabis, and the worst is Vega–Lemus. Furthermore, in this work, it was possible to determine the values of the diffusion coefficient at an infinite temperature, D _e⁰, and activation energy for moisture diffusion, E _d, which were, respectively, 0.0039 m²/s and 32.26 kJ/mol. Similarly, the values of the Arrhenius constant and the activation energy for convective mass transfer, respectively, h _m⁰ and E _c, were also calculated, the first being 3.798 × 10⁸ m/s and the latter 86.25 kJ/mol. These results indicate that the activation energy for convective mass transfer is higher than that for mass diffusion.     

Drying kinetics of grape seeds

Drying of grape seeds representing waste products from white wine processing (Riesling), red wine processing (Cab Franc), and juice processing (Concord) was studied at 40, 50, and 60 °C and constant air velocity of 1.5 m/s. Equilibrium moisture content had a significant effect on the normalized drying curve and was determined for each grape seed at each drying temperature. Effective moisture diffusivity ranged between 1.57 and 3.96 × 10⁻¹⁰ m²/s for Riesling seeds, 2.93–5.91 × 10⁻¹⁰ m²/s for Concord seeds, and 3.89–8.03 × 10⁻¹⁰ m²/s for Cab Franc seeds. The temperature dependence of the effective diffusivity followed an Arrhenius relationship, and the activation energies were 40.14 kJ/mol for Riesling seeds, 30.45 kJ/mol for Concord seeds, and 31.47 kJ/mol for Cab Franc seeds. Three thin-layer models were used to predict the drying curves: Page model, Lewis model, and the Henderson–Pabis model. All three models were found to produce accurate predictions compared to the mass average moisture loss for each grape seed variety (percent error less than 10%), and the Lewis model was shown to be an excellent model for predicting all three grape seed varieties (percent error less than 5%).