Katsunori Kohata

Analysis of tea components by high-performance liquid chromatography and high-performance capillary electrophoresis.

Tea is one of the most popular beverages in the world. The number of reports on the analysis of tea components, especially for catechins, has recently been increasing. We review the recent reports on the analysis of tea components using the analytical methods of high-performance liquid chromatography and high-performance capillary electrophoresis.

Rapid determination of caffeine in tea leaves.

For the purpose of efficient screening of low-caffeine tea shoots, a method for the rapid determination of caffeine was developed using high-performance liquid chromatography. Polyvinylpolypyrrolidone was packed in a pre-column and used to remove polyphenols from tea extracts on-line. The concentrations of caffeine extracted from powdered tea leaves at 50 degrees C during 1 day could be analyzed in 2-5 min intervals. The pre-column and the analytical column could be used for the analysis of more than 2000 samples.

Techniques for Universal Evaluation of Astringency of Green Tea Infusion by the Use of a Taste Sensor System

A practical method for universal evaluation of the astringency of green tea infusion by a taste sensor system was established. The use of EGCg aqueous solution as a standard enabled analysis with high accuracy and reproducibility. The sensor output was converted into taste-intensity on the basis of Weber’s and Weber-Fechner laws, which was named the “EIT ast ” value (“EIT” and “ast” are abbreviations for “Estimated Intensity of Taste” and “astringency” respectively). It was clarified that green tea infusion is to be classified into eight grades on the EIT ast scale. Furthermore, the high correlation of the EIT ast value with the human gustatory sense and the high stability of the taste sensor were proved.

Reduction of catechin astringency by the complexation of gallate-type catechins with pectin

The reductive effect of pectin on tea catechin astringency was investigated by using a taste sensor system and 1H-NMR spectroscopy. The sensor analysis revealed that the astringency of gallate-type catechins (EGCg and ECg) was reduced by the addition of pectin, whereas that of non-gallate-type catechins (EGC and EC) hardly changed. Changes in the 1H-NMR chemical shifts of the catechins and pectin in mixed solutions showed that the gallate-type catechins formed complexes with pectin more closely than the non-gallate-type catechins. These results demonstrate that complexation between the gallate-type catechins and pectin is a factor for reducing catechin astringency.

Binding Energy of Tea Catechin/Caffeine Complexes in Water Evaluated by Titration Experiments with 1H-NMR

Evaluating the binding energy of a catechin/caffeine complex in water is important in order to elucidate the ability for molecular recognition of tea catechins. The results of this study revealed that the stoichiometric ratio of the complexation between tea chatechins (EGCg, ECg, EGC, and EC) and caffeine was 1:1 at least up to a concentration of 5.0 mM. The free energy (−ΔG) values for binding in water at 301 K were evaluated to be 2.7, 2.6, 2.2, and 2.0 kcal/mol for EGCg, ECg, EGC, and EC, respectively, by the titration method with 1H-NMR. An investigation of the 1H-NMR chemical shift change and NOESY spectra in the catechin/caffeine solutions showed the participation of the A-rings of the catechins in complexation, as well as that of the galloyl groups or B-rings.

Identification of pinitol as a main sugar constituent and changes in its content during flower bud development in carnation (Dianthus caryophyllus L.)

Summary An unknown sugar-like compound other than glucose, fructose, sucrose and myo -inositol was detected in the ethanol extract of carnation ( Dianthus caryophyllus L.) leaves and isolated using high performance liquid chromatography. The isolated compound was identified as D -(+)- chiro -inositol monomethylether (pinitol) by 1 H-NMR and 1 C-NMR spectra. Pinitol was the most abundant sugar in the leaf and also was present in stem, petal and the remaining part of flower in large amounts in 4 cultivars tested. In petals, the pinitol content remained constant during flower bud development on a fresh weight basis, but the organ pinitol content increased markedly. The pinitol content was also high in the other parts of the flower. These findings suggest that pinitol, a major sugar constituent, contributes to the bud growth and subsequent petal opening in the carnation together with other metabolic sugars, such as glucose and sucrose.

Identification of Methyl β-Glucopyranoside and Xylose as Soluble Sugar Constituents in Roses (Rosa hybrida L.)

Two unidentified sugars were isolated from rose petals using HPLC. The isolated compounds were identified as methyl β-glucopyranoside and xylose using (1)H-NMR, (13)C-NMR, and GC-MS. Methyl β-glucopyranoside and xylose were distributed in three cultivars tested relatively in large amounts. These results indicate that methyl β-glucopyranoside and xylose occur universally as soluble sugar constituents in roses.

Identification of L-Bornesitol and Changes in Its Content during Flower Bud Development in Sweet Pea (Lathyrus odoratus L.)

An unidentified carbohydrate was isolated from sweet pea (Lathyrus odoratus L. cv. Diana) petals using HPLC. The isolated compound was identified as L-1-O-methyl-myo-inositol, called L-bornesitol, using (1)H-NMR, (13)C-NMR, and CI-MS. L-Bornesitol was distributed in all organs at high concentrations. L-Bornesitol concentration of petals gradually decreased during flower bud development, but the L-bornesitol content increased by about 5 times.

Indirect spectrophotometric determination of trace cyanide with cationic porphyrins.

Three highly sensitive methods for the determination of cyanide have been developed, based on the fact that the complexation of silver ions with three cationic porphyrins, 5,10,15,20-tetrakis-(1-methyl-2-pyridinio)porphine [T(2-MPy)P], 5,10,15,20-tetrakis(1-methyl-3-pyridinio)porphine [T(3-MPy)P] and 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphine [T(4-MPy)P], in alkaline media is inhibited by cyanide and the decrease in absorbance of the silver(II) complex is proportional to the cyanide concentration. Sensitivities of the procedures developed are 0.133, 0.126 and 0.234 ng/cm(2), respectively for an absorbance of 0.001. Cadmium(II), copper(II), mercury(II), zinc(II), iodide and sulfide interfere with the cyanide determination. One of the proposed methods was applied to the determination of cyanide in waste-water samples, with satisfactory results.

SOLVENT EXTRACTION OF INDIUM WITH l-(4-ALKYLPHENYL)-3-HYDROXY-2-METHYL-4-PYRIDONES

ABSTRACT 1-(4-Alkylphenyl)-3-hydroxy-2-methyl-4-pyridones (AHMP or HL) having 1 to 12 carbon atoms in their alkyl chains were synthesized and used for the extraction of indium(III) from aqueous solutions into 1,2-dichloroethane. The extracted species were InL3 for all AHMP. The partition coefficients, KD of AHMP and the distribution constants, KDC of indium(III)-AHMP complexes increased with an increase in the carbon number in the alkyl chain. The increments of log KD and log KDC were 0.52 and 1.67 per a carbon atom, respectively. The proton dissociation constants of AHMP and the extraction constants and the formation constants of their indium(III) complexes were also determined.