Yoshinori Takino

Studies on the Mechanism of the Oxidation of Tea Leaf Catechins:Part III. Formation of a Reddish Orange Pigment and its Spectral Relationship to Some Benzotropolone Derivatives

A study is made on the oxidation of a mixture containing epigallocatechin and epicatechin with tea oxidase as well as a oxidizing reagent, in order to understand the formation of red pigments in tea manufacture. As the reaction proceeds a remarkable colored substance is formed, which can be obtained in reddish orange needles (from water) and is supposed to be a troponoid compound having a 3′,4′-dihydroxybenzotropolone nucleus as suggested by a tentative structural formula III from a consideration of its spectral characteristics.

Studies on the Flavonoids in Tea Leaves

Yellow needle crystals, C21H20O13•H2O have been isolated from tea leaves. The crystals yield myricetin (hexaacetate, m.p. 211~212°C), glucose and galactose on hydrolysis. As analytical data indicate the molecular ratio of myricetin to the sugars to be 1:1 and the only bonding position of the sugars to be position 3 of the aglycone, the crystals are concluded to consist of two kinds of glycosides, namely myricetin-3-glucoside and myricetin-3-galactoside.

Studies on the Oxidation of Myricetin Glycosides by Tea

products, was obtained in the largest quantity, the elucidation of its construction was tried first of all. Yield: 2.5g from 30g of myricitrin. Yellow needles (recrystallized from water), m.p. 215•Ž (decomp.). Anal. Found: C, 54.38; H, 4.34. Calcd. for C42H38O24, assuming G3 to be a dimer of myricitrin: C, 54.43; H, 4.10%. Hydrolysis with 5% sulfuric acid yielded the aglycone in yellow needles (water), m.p. 246•Ž (decomp.).

Studies on the Mechanism of Oxidation of Catechins Part V

紅茶からエステル型テアフラビンP2およびP3を結晶状に単離し,一方カテキン類の組合せ酸化によってそれら合成して同定した.また,これらの色素の加水分解を行なって没食子酸の結合数を確認した. P2はECとEGgから形成されるtheaflavin monogallate, P3はECgとEGgから形成されるtheaflavin digallateである.

Studies on the Mechanism of the Oxidation of Tea Leaf Catechins: Part IV. Formation of Categallin and Pyrogallin, New Compounds of Benzotropolone Nature Derived from Epigallocatechin

Oxidations of epigallocatechin in the presence of catechol or pyrogallol with tea oxidase as well as with an oxidizing reagent and the isolation of the oxidation products, categallin (II) and pyrogallin (III), in crystalline form are described. Their absorption spectra are compared with those of pigment P(I) obtained by the oxidation of epigallocatechin and epicatechin, and their structural relationships are discussed.

Studies on the Mechanism of the Oxidation of Tea Leaf Catechins:Part II Formation of Diethyl 4, 4', 5, 5', 6, 6'-Hexahydroxydiphenate by the Enzymic Oxidation of Ethyl Gallate

In order to understand the mechanism of the enzymic oxidation of epigallocatechin, ethyl gallate was taken up as a model substrate on account of its close structural similarity to the w-trihydroxyphenyl group, which indeed is supposed to be attacked by oxidase, when epigallocatechin is oxidized enzymically. By the action of tea or apple oxidase at pH 5.5, it gave a characteristic polyphenolic substance, which was obtained in prisms, C18H18O10·2H2O, and proved to be diethyl 4,4′,5,5′,6,6′-hexahydroxydiphenate, as the product was converted into ellagic acid by hydrolysis of ester linkage and then lactone formation.

Studies on the Flavonoids in Tea Leaves:Part VI. On the Myricetin-glycoside

Yellow needle crystals, C21H20O13•H2O have been isolated from tea leaves. The crystals yield myricetin (hexaacetate, m.p. 211~212°C), glucose and galactose on hydrolysis. As analytical data indicate the molecular ratio of myricetin to the sugars to be 1:1 and the only bonding position of the sugars to be position 3 of the aglycone, the crystals are concluded to consist of two kinds of glycosides, namely myricetin-3-glucoside and myricetin-3-galactoside.

Studies on the Oxidation of Vitamin C in the Process of Green Tea Manufacture

1. 緑茶製造工程中に於ける還元型ビタミンC含有量の變化を檢する目的を以て標準機械製茶法,直火熱風火爐を用いた機械製茶法,標準冬茶製造法及び手蒸法にて蒸熱時間を異にした場合に就き試驗した。その場合測定法は藤田氏のインドフェノール法によつた。 2. 手蒸法にては蒸熱時間を25秒(若蒸), 45秒(適蒸), 60秒(過蒸)の3種に分ち,一番茶,二番茶及び三番茶に就き試驗し,乾燥工程を終えた荒茶中の還元型ビタミンC含有量は蒸熱直後の約60～75%に減少することを認めた。殊にその減少の大部分(約75%)が粗揉工程中に行われ,而もその工程の初期に著しいことが判明した。尚蒸熱時間の差異のみに基く還元型ビタミンCの變化に著しい差異が認められない。 3. 機械蒸による標準機械製茶法及び直火熱風火爐による機会製茶法に於ては上記工程中に於ける減少が極めて著しく,又標準冬茶製造法に於ては減少が甚だ少い特長を有する。 終りに本研究を行うに當り終始御指導を賜つた山本亮博士に深甚の感謝を捧げ,試料の摘採並びに実驗に協力された下田美智子たちに深謝する。本實驗の費用の一部は文部省科學研究費に仰いだ事を附記して謝意を表する。