Isao Kouno

Chemistry of Secondary Polyphenols Produced during Processing of Tea and Selected Foods

This review will discuss recent progress in the chemistry of secondary polyphenols produced during food processing. The production mechanism of the secondary polyphenols in black tea, whisky, cinnamon, and persimmon fruits will be introduced. In the process of black tea production, tea leaf catechins are enzymatically oxidized to yield a complex mixture of oxidation products, including theaflavins and thearubigins. Despite the importance of the beverage, most of the chemical constituents have not yet been confirmed due to the complexity of the mixture. However, the reaction mechanisms at the initial stages of catechin oxidation are explained by simple quinone–phenol coupling reactions. In vitro model experiments indicated the presence of interesting regio- and stereoselective reactions. Recent results on the reaction mechanisms will be introduced. During the aging of whisky in oak wood barrels, ellagitannins originating from oak wood are oxidized and react with ethanol to give characteristic secondary ellagitannins. The major part of the cinnamon procyanidins is polymerized by copolymerization with cinnamaldehyde. In addition, anthocyanidin structural units are generated in the polymer molecules by oxidation which accounts for the reddish coloration of the cinnamon extract. This reaction is related to the insolubilization of proanthocyanidins in persimmon fruits by condensation with acetaldehyde. In addition to oxidation, the reaction of polyphenols with aldehydes may be important in food processing.

Phyllaemblic acid, a novel highly oxygenated norbisabolane from the roots of Phyllanthus emblica

Phyllaemblic acid, a novel highly oxygenated norbisabolane was isolated from the roots of Phyllanthus emblica, and its structure was fully characterized by spectroscopic and chemical means. The absolute stereochemistry was determined by applying modified Moshers method to an opportune degradation product

Synthesis and antioxidant activity of novel amphipathic derivatives of tea polyphenol

Hydrophobic derivatives of a tea polyphenol have been synthesized. 6, 8-Bis(octylthiomethyl)-epigallocatechin 3-O-gallate, 6, 8-bis(octylthiomethyl)-4 beta-(2-hydroxyethylthio)epigallocatechin 3-O-gallate and epigallocatechin 3-O-[4-O-(N-octadecylcarbamoyl)gallate] showed strong inhibition activity against lipid peroxidation of liposome caused by both lipid-soluble and water-soluble radical generators.

Neolignans and a phenylpropanoid glucoside from Illicium difengpi

Abstract Six new constituents comprising three 2-phenyldihydrobenzofuranpropanol-type neolignans, two 1-phenyl-2-phenoxypropane-1,3-diols, and 4- O -(2-hydrox

Distribution of ellagic acid derivatives and a diarylheptanoid in wood of Platycarya strobilacea

Abstract 4- O -Xylosides of ellagic acid, 3′- O -methylellagic acid and 3,3′-di- O -methylellagic acid have been isolated from the sapwood of Platycarya strobilacea ; these compounds were absent in the heartwood. A new diphenylether-type diarylheptanoid, named platycarynol, was also isolated from the heartwood, together with ellagic acid, 3′- O -methylellagic acid and two known terpenoids.

A new catechin oxidation product and polymeric polyphenols of post-fermented tea.

A new epicatechin oxidation product with a 3,6-dihydro-6-oxo-2H-pyran-2-carboxylic acid moiety was isolated from a commercially available post-fermented tea that is produced by microbial fermentation of green tea. The structure of this product was determined by spectroscopic methods. A production mechanism that includes the oxygenative cleavage of the catechol B-ring of (-)-epicatechin is proposed. In addition, polymeric polyphenols were separated from the post-fermented tea and partially characterised by (13)C NMR spectroscopy and gel-permeation chromatography. The polymers appear to be primarily composed of epigalloacetechin-3-O-gallate and the molecular weight (Mn) of the acetylated form was estimated to be ∼3500.

Oxidation and epimerization of epigallocatechin in banana fruits.

To examine the metabolism of proanthocyanidins in banana fruit, (-)-epigallocatechin was treated with the homogenate of the fruit flesh to yield (-)-gallocatechin and an oxidation product, 1-(3,4,5-trihydroxyphenyl)-3-(2,4,6-trihydroxyphenyl)-2-hydroxy-1-propan one. The latter product is a stable form of a key intermediate in the oxidative metabolism of flavan-3-ols, and is also related to the biogenesis of A-type proanthocyanidins. In addition, treatment of the reaction mixture with o-phenylenediamine afforded monomeric and dimeric phenazine derivatives generated by condensation with the o-quinone form of the oxidation product.

New anisatin-like sesquitepene lactones from pericarps of illicium majus

Abstract Two new sesquiterpene lactones, isolated from the pericarps of Illicium majus together with anisatin, have been assigned structures with an anisatin skeleton on the basis of detailed spectroscopic analysis and established by an X-ray diffraction method.

Structures of two new oxidation products of green tea polyphenols generated by model tea fermentation

Abstract To clarify the oxidation mechanism of green tea catechins during tea fermentation, pure catechins were oxidized with a catechin-free homogenate of tea leaf. Oxidation of a mixture of (−)-epicatechin and (−)-epigallocatechin yielded a new metabolite, named dehydrotheaflavin, produced by the oxidation of a benzotropolone moiety of the black tea pigment theaflavin. Similar oxidation of a mixture of (−)-epicatechin and (−)-epigallocatechin 3- O -gallate afforded a new dimer of (−)-epigallocatechin 3- O -gallate, which was generated by the oxidation and cycloaddition of two pyrogallol rings. Structures were determined by spectroscopic method, and the oxidation mechanisms for the formation of the products were proposed.

Triterpenoids and glycosides from Geum japonicum

Abstract Two new glucosides and two known ester glucosides have been isolated from Geum japonicum . The two new glucosides were isolated by formation of their acetates and were identified as glucosides of 2-isopropyl-5-methylhydroquinone by chemical and spectral studies. The two known ester glucosides were identified as niga-ichigoside F1 and suavissimoside F1 by direct comparison with authentic samples. 2α,19α-Dihydroxyursolic acid and the known glycoside, gein, were also isolated from the same plant, in addition to a mixture of 2α-hydroxyursolic acid and 2α-hydroxyoleanolic acid.