Further applications of a spectrophotometric method are described for the determination of polyphenolic oxidation products in black tea liquors for the assessment of quality in tea. In addition to calculating theaflavin and thearubigin contents from optical density measurements at 380 mu, values for total colour and brightness have been calculated from optical density measurements at 460 mu. Confirmation has been obtained that theaflavin content is an extremely important factor in determining quality in black tea, and in determining ‘brightness’ in tea infusions. Thearubigins contribute to colour and strength. The effects of seasonal variations and of methods of manufacture on the composition of tea have been examined. Changes in composition during storage of tea under adverse conditions of temperature and moisture content have been related to losses of quality. The effects of the composition of the water used on the composition and colour of tea infusions are also indicated.

Methods are described for the fractionation of the complex mixture of phenolic substances and their oxidation products occurring in manufactured tea. Products of oxidation detected include two fractions, S I and S II, responsible for the greater part of the colour intensity of a tea infusion, and nine unidentified substances, A, B, C, D, P, Q, X, Y and Z. S I and S II have been obtained almost free from other contaminants. They have acidic properties, and mean molecular weights of the order 600. They are probably mixtures of dimers, each dimer consisting of two oxidized flavanol units. X and Y have no acidic properties and are also distinguished from S I and S II by several characteristic colour reactions. P may be an anthocyanidin.

No abstract

The brown acidic pigments and the yellow neutral pigments of black tea are provisionally named thearubigins and theaflavins respectively. These and other substances characteristic of black tea are formed during the fermentation process, mainly as the result of the enzymic oxidation of (—)‐epigallocatechin and (—)‐epigallocatechin gallate. It is probable that the theaflavins are intermediates in thearubigin formation.

Many of the substances occurring in freshly plucked tea shoots are listed and the chemical changes taking place during withering and fermentation are discussed. In fermentation (-)-epigallocatechin and its gallate are the only polyphenols to undergo appreciable chemical change. A scheme for the oxidation of these substances is developed which suggests that substances A, B and C are bisflavanols, and that theaflavin and the;;-flavin gallate are derivatives of purpurogallin. Thearubigins are probably formed as a result of coupled oxidation of theaflavins. Structures are also suggested for the minor components P, Q, R and Z. I t is probable that theaflavins and thearubigins account for the colour and strength of tea liquors, and that theaflavins also contribute towards quality and briskness.