Chapter 3
Prophylactic Functions of Tea Polyphenols Yukihiko Hara
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Food Research Laboratories, Mitsui Norin Company Ltd., Fujieda 426, Japan
Since ancient times tea has been known to be effective in keeping "body and soul" in good condition. Among the soluble components of tea, the polyphenolic fraction constitutes the major part. With a view to linking the traditionally acclaimed health benefits of tea to these polyphenolic compounds we have fractionated and purified tea polyphenols and subjected them to a variety of experiments, not only in the laboratory, but also in animals and humans. As a result, tea polyphenols have proven to be multi-functionally effective in preventing rancidity and putrefaction of foods, infection of the alimentary canal, respiratory diseases, occurrence of cardiovascular disease and development of malignant tumors. In this review, methods of separating tea polyphenols from green tea or black tea and some of their functions revealed so far will be described in brief.
Method of Extracting Tea Polyphenols Catechins. The polyphenolic fraction is mostly composed of catechins, which are the major components of fresh tea leaves as well as the soluble matter in green tea. Crude catechin powder is obtainable by treating tea leaves with water and organic solvents, as shown in Figure 1. The total catechin content of this crude product is a little more than 90%. This crude catechin powder is then submitted to liquid chromatography to isolate five kinds of catechin compounds (1). The composition of the crude catechin powder is shown in Table I. Theaflavins. In the process of black tea manufacture, catechins are mostly oxidized to form pigments such as theaflavins or thearubigins (2). In the case of tropical black tea, these fractions exist in a ratio of 10-15% thearubigins, 1-2% theaflavins and 5-10% catechins on a dried tea basis. The amount of theaflavins is closely related to the commercial value of black tea. To separate theaflavins, black tea is extracted with water, then washed with solvents to remove impurities (3). The extraction process is shown in Figure 2 and
0097-6156/94/0547-0034$06.00/0 © 1994 American Chemical Society
Ho et al.; Food Phytochemicals for Cancer Prevention II ACS Symposium Series; American Chemical Society: Washington, DC, 1994.
HARA
Prophylactic Functions of Tea Polyphenols
Green tea, 5 kg JExtracted with water Water soluble green tea powder, 1 kg
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Dissolved In hot water Washed with chloroform Aqueous layer
Chloroform layer
Extracted with ethyl acetate Ethyl acetate Aqueous layer layer I Evaporated 1 Dissolved in water Concentrated
solution
J Freeze dried Crude catechin powder, 290 g Figure 1. Preparation of crude catechins from green tea.
Black tea, 50 g I Extracted with water X Spray dried Water soluble black tea powder, 10 g Dissolved in hot water Washed with chloroform Aqueous layer
Chloroform layer
Extracted with methyl isobutyl ketone methyl isobutyl ketone Aqueous layer layer I Evaporated 1 Dissolved in water Concentrated
solution
J Freeze dried Crude theaflavin powder, 300 mg Figure 2. Preparation of crude theaflavins from black tea.
Ho et al.; Food Phytochemicals for Cancer Prevention II ACS Symposium Series; American Chemical Society: Washington, DC, 1994.
36
FOOD PHYTOCHEMICALS II: TEAS, SPICES, AND HERBS
the composition of individual theaflavins is shown in Table II. Structural formulae of catechins and theaflavins are shown in Figure 3. Table I. Composition of crude catechins in green tea
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Catechins (+)-Gallocatechin (GC) (-)-Epigallocatechin (EGC) (-)-Epicatechin (EC) (-)-Epigallocatechin gallate (EGCg) (-)-Epicatechin gallate (ECg)
Absolute % 1.44 17.57 5.81 53.90 12 gl 91.23 t
Relative % 1.6 19.3 6.4 59.1 13.7 100.0
Table II. Composition of crude theaflavins in black tea Theaflavins Theaflavin (TF1) Theaflavin monogallate A (TF2A) Theaflavin monogallate B (TF2B) Theaflavin digallate (TF3)
Absolute % 13.35 18.92 18.64 33.46 84.37
Relative % 15.8 22.4 22.1 39.7 100.0
Antioxidative Action Edible oils. The antioxidative potency of crude catechin powder and individual catechins was tested in experiments on lard using Active Oxygen Method (AOM) (7). As shown in Figure 4, crude catechins reduced the formation of peroxides far more effectively than dl-a-tocopherol or B H A . In the same way, the antioxidative potency of each catechin was measured as shown in Figure 5. The antioxidative activity increased on a molarity basis in the order: EC
