Effects of strontium gallate additions on sintering behavior of gadolinia-doped ceria

The densification behavior and grain growth of Ce_0.8Gd_0.2O_1.9 ceramics were investigated with the strontium gallate concentration ranging from 0 to 5 mol%. Both the sintered density and grain size were found to increase rapidly up to 0.5 mol% Sr₂Ga₂O₅, and then to decrease with further addition. Dense Ce_0.8Gd_0.2O_1.9 ceramics with 97% of the theoretical density could be obtained for 0.5 mol% Sr₂Ga₂O₅-added specimen sintered at 1250^∘C for 5 h, whereas pure Ce_0.8Gd_0.2O_1.9 ceramics needed to be sintered at 1550^∘C in order to obtain an equivalent theoretical density. The addition of Sr₂Ga₂O₅ was found to promote the sintering properties of Gd₂O₃-doped CeO₂.     

3,4,5-三羟基苯甲酸丙酯的合成

3，4，5-三羟基苯甲酸丙酯，俗名称没食子酸丙酯，本文以固体超强酸SO4^2-／TiO2为催化剂合成没食子酸丙酯，研究了催化剂在没食子酸与正丙醇反应中的催化活性，考察了焙烧温度对催化剂性能的影响以及酸醇物质的量比对酯收率的影响。实验结果表明：焙烧温度在500℃的条件下，制得的催化剂活性最高；没食子酸：正丙醇的物质的量比为1：15，1．8g固体超强酸SO4^2-／TiO2，在120℃下，反应时间2．5h。收率达96．3％。     

响应面法微波降解EGCG制备EGC研究

目的 为探究微波降解EGCG方法制备EGC的效果,以EGC得率最大化为目标,探究微波降解的最佳工艺参数,并建立反映各参数间关系的二次多元方程模型。方法 本研究采用EGCG溶液为原料,运用微波加热降解EGCG制备EGC,通过梯度设置EGCG浓度、微波时长、微波强度三个工艺参数,进行单因素实验、响应面分析及最佳工艺组合验证实验,优化确定EGCG微波降解制备EGC的最佳工艺参数。结果 综合单因素实验及响应面分析,得到的最佳微波降解参数为：EGCG浓度5mg/ml、微波时长3.5min、微波强度为400W,且利用响应面法建立了EGC得率(Y)与EGCG浓度(A)、微波时长(B)、微波强度(C)的二次多元方程模型：Y=59.52+8.38*A+5.38*B+3.53*C-4.04*AB+6.92*AC-9.19*BC-9.99A2⁺0.0786*B2^-15.36*C2^,模型中,EGC得率最高可达62.08%。对最佳微波降解工艺参数进行验证实验,EGC得率为63.40%,与模型预测值接近。结论 运用微波降解EGCG制备EGC具有操作简单,可行性高的优势,且EGC得率稳定性高。     

Low-temperature synthesis of nanocrystalline ZnGa2O4:Tb phosphors via the Pechini method

The synthesis of trivalent terbium doped ZnGa₂O₄ nanosized new phosphors by the Pechini method was reported. Well-crystallized ZnGa₂O₄:Tb³⁺ phosphors were obtained at low-temperature about 550 °C. The phosphors formed porous agglomerates which consist of spherical nanocrystallites with a uniform size at about 30 nm. The photoluminescence of the phosphors included both the luminescence of ZnGa₂O₄ host and characteristic emission of Tb³⁺, and the excitation spectra showed an energy transfer from the host lattice to the activator. The Tb³⁺ emission from the phosphors prepared by the Pechini process was more intensive than that of phosphors by solid-state reaction process.     

Exploring the Absorption Mechanisms of Imidazolium-Based Ionic Liquids to Epigallocatechin Gallate

Imidazolium-based ionic liquids are wildly used in natural product adsorption and purification. In this work, one typical polymeric ionic liquid (PIL) was synthesized by using L-proline as the anion, which exhibited excellent adsorption capacity toward tea polyphenol epigallocatechin gallate (EGCG). The adsorption conditions were optimized with the response surface method (RSM). Under the optimum conditions, the adsorption capacity of the PIL for EGCG can reach as high as 552 mg/g. Dynamics and isothermal research shows that the adsorption process of EGCG by the PIL particularly meets the quasi-second-order kinetic equation and monolayer adsorption mechanism. According to thermodynamic parameter analysis, the adsorption process is endothermic and spontaneous. The results of theoretical calculation by molecular docking also demonstrated the interaction mechanisms between EGCG and the ionic liquid. Considering the wide application of imidazolium-based ionic liquids in component adsorption and purification, the present study can not only be extended to other similar experimental mechanism validation, but also be representative for guiding the synthesis of PIL and optimization of adsorption conditions.     

The effect of ascorbic acid,citric acid and low pH on the extraction of green tea: How to get most out of it

Green tea seems to have a positive impact on health due to the therein-found flavanols. The amounts of these substances depend on tea preparation. In this paper, the influence of steeping time (3–7 min) and temperature (70–100 °C) on the content of the main flavanols in green tea (epicatechin EC, epicatechin gallate ECg, epigallocatechin EGC, and epigallocatechin gallate EGCg) is presented. Furthermore, additives (phosphate buffers, ascorbic acid in different amounts, and citric acid) are used to investigate the influence of pH, antioxidative, and chelating agents, simulating the addition of lemon juice or pure vitamin C.     

市售茶饮料中茶多酚、咖啡因以及茶氨酸的含量分析

测定了茶饮料中的茶多酚(Tea Polyphenols,TP)、游离氨基酸总量、表没食子儿茶素没食子酸酯(Epigallocatechi Gallate,EGCG)、咖啡因(Caffeine,CAF)和茶氨酸(L-Theanine,TA)的含量.结果表明:目前市售茶饮料的品质与品牌无关,乌龙茶TP、EGCG和CAF含量最高,乌龙茶和花茶中TP含量完全符合国家标准,绿茶合格率为85.0%,而红茶合格率仅为50.0%.除了两个绿茶饮料样本低于国家标准外,其它样本中的CAF含量全部符合国家标准.     

表没食子儿茶素没食子酸酯的提取分离工艺研究

采用无水乙醇对茶叶进行浸提,用乙酸乙酯和蒸馏水分别对浸提液进行萃取后浓缩包含表没食子儿茶素没食子酸酯[epigallocatechin gallate,（-）-EGCG]在内的黄酮类物质。利用聚酰胺装填的层析柱对茶叶中的（-）-EGCG进行分离,并对分离产品结果进行分析。本实验以活性炭为脱色剂,考察了活性炭的用量、脱色时间、脱色次数、脱色后溶液pH、乙酸乙酯与水的配比以及洗脱荆中乙醇浓度等条件对实验结果产生的影响。在各项条件最优的情况下,每10g绿茶可以提取出纯度大于98％的（-）-EGCG单体0．39g。     

Antioxidative activities and the chemical constituents of two Chinese teas,Camellia kucha and C. ptilophylla

Two kinds of green tea were prepared with the young shoots of Camellia kucha and C. ptilophylla, and antioxidative activities of the chemical constituents were determined. Levels of alkaloids, catechins, total polyphenols, flavonoids and amino acids were determined by high‐performance liquid chromatography and UV‐Vis spectrophotometer. Antioxidative activity was evaluated by applying 2,2‐diphenyl‐1‐picrylhydrazyl radical assay and ferric reducing antioxidant power assay. Our results showed that theobromine was the only alkaloid in C. ptilophylla, while there was theacrine in C. kucha, which was coexisting with the caffeine. We confirmed the high content of (?)‐gallocatechin gallate in C. ptilophylla was not the epimerisation of (?)‐epigallocatechin gallate during the heating procedure. These wild teas had higher content of tea polyphenols, water extracts, amion acids and stronger antioxidative activity compared with the longjing tea. They could be used for the development of noncaffeine beverages and new types of tea.     

Interaction of β‐casein with (−)‐epigallocatechin‐3‐gallate assayed by fluorescence quenching: effect of thermal processing temperature

The interactions between the flavan‐3‐ol (?)‐epigallocatechin‐3‐gallate (EGCG) and bovine β‐casein in phosphate‐buffered saline (PBS) of pH 6.5 subjected to thermal processing at various temperatures (25–100 °C) were investigated using fluorescence quenching. The results indicated that different temperatures had different effects on the structural changes and EGCG‐binding ability of β‐casein. At temperatures below 60 °C, the β‐casein–EGCG interaction changed little (P > 0.05) with increasing temperature. At temperatures above 80 °C, native assemblies of β‐casein in solution dissociated into individual β‐casein molecules and unfolded, as demonstrated by a red shift of the maximum fluorescence emission wavelength (λ_max) of up to 8.8 nm. The highest quenching constant (K_q) and the number of binding sites (n) were 0.92 (±0.01) × 10¹³ m ^?1 s^?1 and 0.73 (±0.02) (100 °C), respectively. These results provide insight into the potential of interactions between β‐casein–EGCG that may modulate bioactivity or bioavailability to be altered during thermal process.