Development of rapid and simultaneous quantitative method for green tea catechins on the bioanalytical study using UPLC/ESI‐MS

A rapid and quantitative analytical method for the simultaneous determination of green tea catechins using ultra‐performance liquid chromatography/electrospray ionization–mass spectrometry was developed. Total analytical run time was 3.5 min for the detection of (?)‐epicatechin (EC), (?)‐epicatechin‐3‐O‐gallate (ECG), (?)‐epigallocatechin (EGC), (?)‐epigallocatechin‐3‐O‐gallate (EGCG) and myricetin as the internal standard (IS) in rat plasma. The calibration curves were linear over the range of 10–5000 ng/mL for all the catechins. The inter‐ and intra‐day precision (relative standard deviation) and accuracy (percentage deviation) of the method were both lower than 10%. The average extraction recoveries in plasma ranged from 68.5 to 86.5%, and the lower limits of quantification of EC, EGC, ECG and EGCG were 10 ng/mL with a signal‐to‐noise ratio of >10. The assay developed was successfully applied to a pharmacokinetic study of catechins following intravenous and intragastric administrations of green tea extract in rats. Plasma concentrations of four catechins were detected up to 5–24 h after administration, and the pharmacokinetic parameters of catechins were in agreement with previous studies. From these findings, taken together with the high productivity and precision, the developed method could be a reliable and reproducible tool for the evaluation of pharmacokinetic properties of catechins. Copyright © 2012 John Wiley & Sons, Ltd.     

Advanced separation methods of food anthocyanins,isoflavones and flavanols

In recent years, increasing knowledge of the positive health effects of food polyphenols has prompted the need to develop new separation techniques for their extraction, fractionation and analysis. This article provides an updated and exhaustive review of the application of counter-current chromatography, high performance liquid chromatography, capillary electrophoresis, and their hyphenation with mass spectrometry to the study of food polyphenols. Flavonoids constitute the largest class of polyphenols, widely spread in the plant kingdom and common in human diet which has been the most widely studied with respect to their antioxidant and biological activities. The main subgroups are anthocyanins, catechins, isoflavones, flavonols and flavones. They are reported to exhibit antioxidant, anti-carcinogenic, anti-inflammatory, anti-atherogenic, anti-thrombotic, and immune modulating functions, among others. Since red fruit anthocyanins, soy isoflavones and flavanols from grapes and teas are currently the most used phenolic compounds for producing new nutraceuticals and functional foods, this review is focused on these three flavonoid groups.     

Ionic liquids as stationary phase solvents for methylated cyclodextrins in gas chromatography

Summary Room temperature ionic liquids (RTIL) are molten salts with melting points well below room temperature. 1-butyl-3-methylimidazolium chloride is a typical example of such RTIL. It was used as a solvent to dissolve permethylated-β-cyclodextrin (BPM) and dimethylated-?cyclodextrin (BDM) to prepare stationary phases for capillary columns in gas chromatography for chiral separation. The RTIL containing columns were compared to commercial columns containing the same chiral selectors. A set of 64 chiral compounds separated by the commercial BPM column was tested on the RTIL BPM column. Only 21 were enantioresolved. Similarly, a set of 80 compounds separated by the commercial BDM column was passed on the RTIL BDM column with only 16 positive separations. It is proposed that the imidazolium ion pair could make an inclusion complex with the cyclodextrin cavity, blocking it for chiral recognition. All the chiral compounds recognized by the RTIL columns had their asymmetric carbon that was part of a ring structure. The retention factors of the derivatized solutes were lower on the RTIL columns than those obtained on the commercial equivalent column. The peak efficiencies obtained with the RTIL capillary were significantly higher than that obtained with the commercial column. These observations may contribute to the knowledge of the mechanism of cyclodextrin-based GC enantioselective separations.     

Copper(II) complexes of methylated glycine derivatives: Effect of methyl substituent on their DNA binding and nucleolytic property

A set of copper(II) complexes of glycine and methylated glycine derivatives, Cu(aa)₂, consisting of C-dimethylglycine, l-alanine, N-dimethylglycine and sarcosine, was investigated for their DNA binding and nucleolytic properties by means of EPR and visible spectroscopy, and electrophoresis. They bind weakly to DNA with apparent binding constants in the range 1.8–2.9 × 10³ M⁻¹ with very similar orientation. No DNA cleavage is observed in the absence of exogenous agents. Copper(II) complexes of N-methylated derivatives bind to DNA more stereo-specifically and less strongly, and their oxidative DNA cleavage is less efficient than those of the corresponding C-methylated derivatives in the presence of hydrogen peroxide (H₂O₂) alone, or sodium ascorbate (NaHA) alone or tandem H₂O₂–NaHA. The oxidative DNA cleavage mechanism in the three systems involves a common copper(I) species. Neocuproine can inhibit DNA cleavage by these complexes.     

On-line pre-reduction of pentavalent arsenicals by thioglycolic acid for speciation analysis by selective hydride generation–cryotrapping–atomic absorption spectrometry

An improvement of current method of selective hydride generation based on pre-reduction for differentiation of tri- and pentavalent arsenicals is described, applied for the oxidation state specific speciation analysis of inorganic, mono-, di- and trimethylated arsenicals with minimum sample pretreatment using atomic absorption spectrometry with the multiatomizer. The preconcentration and separation of arsine, methylarsine, dimethylarsine and trimethylarsine are then carried out by means of cryotrapping. The presented study shows that 2% (m/v) L-cysteine hydrochloride monohydrate (L-cys) currently used for off-line pre-reduction of pentavalent arsenicals can be substituted with 1% (m/v) thioglycolic acid (TGA). Much faster pre-reduction of pentavalent arsenicals at 25 °C with equal sensitivities as in the case of L-cys has been achieved with TGA. A setup for on-line pre-reduction by TGA has been optimized, with the application of segmented flow analysis for suppression of axial dispersion in the pre-reduction coil. Standard calibrations measured with or without on-line pre-reduction indicate uniform and equal sensitivities for all As forms. The possibility of standardization by water standards of single species (e.g. iAs(III)) for quantification of all other As forms in urine is demonstrated in the recovery study. Limits of detection were 100 ng l^− 1 for iAs(III), 135 ng l^− 1 for iAs(V) and 30 to 50 ng l^− 1 for methylated arsenicals.     

高速逆流色谱结合制备液相色谱法分离制备葡萄籽中的多酚

采用高速逆流色谱结合制备液相色谱法从葡萄籽乙醇提取物中分离得到了8种多酚。高速逆流色谱以上相为固定相,下相为流动相,主机转速为900 r/min,流速为2 mL/min,分离温度为25℃,检测波长为280 nm,利用正向和反向洗脱相结合的模式,在正丁醇-乙酸乙酯-水（1∶14∶15,v/v/v）和正己烷-乙酸乙酯-水（1∶10∶10,v/v/v）溶剂系统下从葡萄籽提取物中分离得到了5种多酚。原花青素B₁、原花青素B₂、没食子酸、表儿茶素没食子酸酯和儿茶素的纯度分别为98.5%、97.2%、98.3%、98.9%和96.7%。利用制备液相色谱法对高速逆流色谱分离成分进一步分离纯化,获得了表儿茶素、表没食子儿茶素没食子酸酯和没食子儿茶素没食子酸酯,纯度分别99.2%、99.3%和99.2%。该方法单次制备量均达到毫克级,简便、快速、分离纯度高,适合于葡萄籽中多酚的分离制备。     

Studies on Binary Blends of Poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) and Natural Polyphenol Catechin: Specific Interactions and Thermal Properties

The existence of a specific intermolecular hydrogen‐bonding interaction between poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) [P(3HB‐co‐3HH)] and (+)‐catechin in their blends was demonstrated by Fourier‐transform infrared spectroscopy (FT‐IR). It was found that the experimentally estimated fraction of hydrogen‐bonded carbonyl groups was much lower than the theoretically predicted maximum fraction. Only one glass transition temperature (T_g) occurred in the blends with the compositions detected by differential scanning calorimetry (DSC), being further confirmed by the results of dynamic mechanical thermal analysis (DMTA). The decrease of the melting point (T_m) and the increase of the glass transition temperature of the blends observed by the DSC measurements also suggested the existence of a strong intermolecular interaction. It was interesting to note that, as a low‐molecular‐weight compound, catechin showed a glass transition, which arises from strong self‐association. As expected, the crystalline structure of P(3HB‐co‐3HH) in the blends showed no change, but the crystallinity of the copolymer component in the blends, calculated by wide‐angle X‐ray diffraction, decreased with the increase of catechin weight content. Investigated by tensile experiments, the maximum strength and modulus decreased sharply with the increase of catechin content; on the contrary, the elongation changed slowly.

The FT‐IR spectra in the wave‐number 1 680–1 780 cm^?1 region for blends of P(3HB‐co‐3HH)/catechin. A: HBH; B: HBHC10; C: HBHC20; D: HBHC30; E: HBHC40; F: HBHC50; and G: catechin.     

Comparison of the Effects of Conching Parameters on the Contents of Three Dominant Flavan3-ols,Rheological Properties and Sensory Quality in Chocolate Milk Mass Based on Liquor from Unroasted Cocoa Beans

The content of polyphenols in chocolate depends on many factors related to the properties of raw material and manufacturing parameters. The trend toward developing chocolates made from unroasted cocoa beans encourages research in this area. In addition, modern customers attach great importance to how the food they consume benefits their bodies. One such benefit that consumers value is the preservation of natural antioxidant compounds in food products (e.g., polyphenols). Therefore, in our study we attempted to determine the relationship between variable parameters at the conching stage (i.e., temperature and time of) and the content of dominant polyphenols (i.e.,catechins, epicatechins, and procyanidin B2) in chocolate milk mass (CMM) obtained from unroasted cocoa beans. Increasing the conching temperature from 50 to 60 °C decreased the content of three basic flavan-3-ols. The highest number of these compounds was determined when the process was carried out at 50 °C. However, the time that caused the least degradation of these compounds differed. For catechin, it was 2 h; for epicatechin it was 1 h; and for procyanidin it was 3 h. The influence of both the temperature and conching time on the rheological properties of chocolate milk mass was demonstrated. At 50 °C, the viscosity and the yield stress of the conched mass showed its highest value.     

半制备型液相色谱法分离纯化茶叶鲜叶中7种儿茶素类化合物

建立了从茶叶鲜叶中分离纯化7种儿茶素类化合物(没食子儿茶素(GC)、表没食子儿茶素(EGC)、儿茶素(C)、表没食子儿茶素没食子酸酯(EGCG)、表儿茶素(EC)、表没食子儿茶素3-O-(3-O-甲基)没食子酸酯(EGCG3"Me)和表儿茶素没食子酸酯(ECG))的半制备色谱法。铁观音鲜叶经甲醇超声浸提、浓缩、氯仿萃取后,向水相中加入碱式醋酸铅沉淀,得到茶多酚粗品。分别以甲醇-水、乙腈-水作为流动相,采用半制备色谱法纯化7种儿茶素类化合物,纯度均达到90%。此外,利用同样的方法分离纯化另外两种茶叶鲜叶中的7种儿茶素类化合物,得到相似的结果。该方法以溶剂提取、离子沉淀结合半制备色谱,适于简单、高效地同时分离制备多种儿茶素类化合物。     

(+)-Catechin Stereoisomer and Gallate Induce Oxidative Stress in Rat Aorta

The goal of the work was to study changes in the activity of the angiotensin-converting enzyme (ACE) and production of reactive oxygen species (ROS) in the aorta of rats after the intraperitoneal injection of stereoisomers of catechin and gallate. The activity of ACE in the aorta sections was determined by measuring the hydrolysis of hippuryl-l-histidyl-l-leucine. The production of ROS in the aorta sections was estimated from the oxidation of dichlorodihydrofluorescein. The time and dose dependences of the effect of catechin stereoisomers and gallate on ACE activity and ROS production in the aorta were studied. It was shown that (+)-catechin and gallate increased the ACE activity and ROS production, and (−)-catechin and (−)-epicatechin did not influence these parameters. The doses of (+)-catechin and gallate that increased the ACE activity to a half-maximal value (AD₅₀) were 0.04 and 0.03 µg/kg, respectively. Fucoidin, a blocker of leukocyte adhesion to the endothelium, reduced the ACE activity to the control level in the aortas of (+)-catechin-treated rats.