Tei Yamanishi

Studies on the Flavor of Green Tea: Part IV. Dimethyl Sulfide and its Precursor

With an assumption that the laver-like odor of green tea is due to dimethyl sulfide, an attempt to isolate dimethyl sulfide from commercial green tea was made, and the identification of dimethyl sulfide was successful by making the co-ordinated compound with mercuric chloride, 2 (CH3) 2S·3HgCl2. In addition, the presence of methylmethionine sulfonium salt in tea extract as a precursor of dimethyl sulfide was examined.

Studies on the Flavor of Green Tea:Part IX. Identification and Composition of Intermediate and High Boiling Constituents in Green Tea Flavor

By continuing flavor analysis of green tea from a previous paper, further twenty seven compounds were newly identified. These compounds are limonene, α-cubebene, α-copaene, caryophyllene, α-humulene, α- and γ-muurolene, β-sesquiphellandrene, δ-cadinene, calamenene, cubenol, α-cadinol, α-terpineol, n-heptanol, n-nonanol, furfurylalcohol, n-nonanal, N-ethylformylpyrrole, pyrrylmethylketone, 6-methyl-trans-3,5-heptadien-2-one, 2′,2″-dihydro-α-ionone, 6,10,14-trimethyl-2-pentadecanone, cis-3-hexenylcaproate, cis-3-hexenylbenzoate, α-terpinylacetate, coumarin and diphenylamine.Relative quantities of known compounds in intermediate- and high-boiling fraction were determined.

Progress of Tea Aroma Chemistry

Over 60% (w/w), of the components of essential oils from tea were identified before 1960 by classical chemical methods. With the advent of GC and GC-MS, many new compounds were identified, compounds important in contributing to characteristic tea aromas even though present in small concentrations. Now 99.9% (w/w) of the components of essential oils from tea have been determined. With the identification of components and with further improvements in analytical methods, differences in different types of teas and detailed changes in the processing of teas were elucidated. Advanced analytical methods have also made possible the study of stereochemistry of tea aroma compounds. Some of the important optical isomers, such as the structures of linalool, linalool oxides and methyl jasmonate are discussed. Enzymatic studies showed that the main aroma components precursors of black tea are present as glycosides, some of which were separated and identified by the use of HPLC, NMR and FABMS. Synthetic glycosides are used as substrate of glycosidase prepared from fresh tea leaves and primeverosides are hydrolyzable by this enzyme system.

Flavor of Black Tea:Part V Comparison of Aroma of Various Types of Black Tea

In comparing the aroma concentrates from various types of black tea by the use of gas chromatography (GLC), differences of aroma pattern were recognized among these black tea of Ceylon, India, Peru, Formosa and Japan.One of the typical differences, by which the variety would be characterized, appeared in the proportion of linalool (include its oxides) to geraniol and phenylethanol. Furthermore the ratio of the total area of peaks before and after linalool seemed to have some relation with the variety of black tea.Also, top note of black tea aroma was compared by head space vapor analyses.

Flavor Components in Vietnamese Green Tea and Lotus Tea

The aroma concentrates from Vietnamese green tea and lotus tea were prepared and analyzed. Characterization of the components were carried out using coupled gas chromatography and mass spectrometry and infrared spectrometry, besides gas chromatographic retention data.Anethole and 1,4-dimethoxybenzene have been identified for the first time as the flavor constituents in green tea. Linalool, two linalooloxides (cis and trans, five membered), 3,7-dimethyl-1,5,7-octatriene-3-ol, 2,5 (or 2,6)-dimethylpyrazine and 1-ethyl-2-formylpyrrole were the predominant components in Vietnamese green tea.1,4-Dimethoxybenzene has been identified as the main component in lotus tea. The compound was also isolated from both dried and fresh lotus pollen.

Studies on the Flavor of Green Tea: Part VI. Neutral Fraction of the Essential Oil of Tea-leaves

The neutral fraction of the essential oil from freshly plucked tea-leaves was submitted to gas chromatography and the eluted components condensed in the capillary traps. The components were identified by the retention times, the odor as well as by infrared spectra, elementary analyses and preparation of derivatives. Among fourty two components, three isomers of linalooloxide and cis-jasmone were newly identified and the presence of acetates of trans- and cis-3-hexen-l-ol was presumed.

Studies on the Flavor of Green Tea: Part II. Changes in Components of Essential Oil of Tea-leaves

In order to investigate how the flavor of fresh tea-leaves turn into that of green tea, six essential oils were obtained from chopped fresh tea-leaves, whole tea-leaves, and their residues after steaming, green tea and black tea by steam-distillation. They are then compared with each other in regard to their flavor, amount of I2-absorption, βγ-hexenol content and ultraviolet spectrum. It is concluded that the change mentioned above is produced partly by fleeing of βγ-hexenol and partly by some chemical change concerning βγ-hexenol.

Flavor of Black Tea:Part VI. Intermediate and High Boiling Components of the Neutral Fraction

Intermediate and high boiling neutral compounds in the aroma concentrate from black tea were isolated by fractional distillation, silica-gel column chromatography and gas chromatography.Identification of the compounds was verified by the agreement of IR and mass spectra as well as gas chromatographic data with those of authentic compounds.Eleven compounds; α-muurolene, δ-cadinene, furfuryl alcohol, methyl phenyl carbinol, cadinenol, geranial, pyrrole-2-aldehyde, benzyl formate, phenylethyl formate, cis-3-hexenyl benzoate and indole, were newly identified as constituents of black tea aroma and ten known components; α-terpineol, 3, 7-dimethyl-l, 5, 7-octatrien-3-ol, trans, trans-2, 4-decadienal, 2-phenyl-2-butenal, α- and β-ionone, cis-jasmone, theaspirone, lactone of 2-hydroxy-2, 6, 6-trimethylcyclohexylidene-l-acetic acid and phenylacetonitrile were confirmed. The geometric structure of theaspirone in tea aroma was determined as the cis-form.

Studies on the Flavor of Green Tea:Part VII. Flavor Components of Manufactured Green Tea

The essential oil from manufactured green tea was separated into carboxylic, phenolic, carbonyl and alcoholic fractions and analysed by gas chromatography.Seventeen alchols, two carbonyls, seven acids and two phenolic compounds were identified on the basis of their relative retention times and aroma of effluents by comparing with authentic compounds.The quantities of these compounds were also determined by gas chromatography.Four alcohols (present in rather high amounts), two caronyls, three esters and two phenols have remained unidentified.

Flavor of Black Tea: Part II. Alcohols and Carbonyl Compounds

The neutral fraction of the essential oils from three kinds of black tea (same samples as described in the previous paper,1) i.e., Assam, Shan and Benihomare) was separated into carbonyl and carbonyl-free fractions and analysed by gas chromatography. On the basis of relative retentions and aroma of effluents with the references of the chromatographic data obtained by the previous works,2–4) the major alcohols were found to be cis-2-pentenol, n-hexanol, cis-3-hexen-1-ol, three isomers of linalooloxide, linalool, nerol, geraniol, benzylalcohol, and phenylethylalcohol. In the carbonyl fraction, phenylacetaldehyde was newly identified, and besides it, the presence of iso- and n-butyr-, iso- and n-valer- aldehyde, methylethylketone, trans-2-hexenal, benzaldehyde were recognized. There were no differences in the components among three kinds of black tea, but the relative quantity of each component in the essential oil was different among three varieties.