Catechins of Green Tea - American Chemical Society

Chapter 9

Catechins of Green Tea

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 4, 2016 | http://pubs.acs.org Publication Date: October 1, 1992 | doi: 10.1021/bk-1992-0507.ch009

Antioxidant Activity T. L . Lunder N e s t l éResearch Centre, Nestec, Ltd., CH-1000 Lausanne 26, Switzerland

Green tea contains about 30% polyphenyls and the most important are the flavanols or tea catechins. Among these substances the Epigallocatechingallate (EGCG) which represents 50-60% of the total catechins seem to play an outstanding role in the antioxidant ac t i v i t y . Our preliminary analytical findings show that the antioxidant index (AI) could be related to the content of the EGCG. A Chinese legend places the introduction of tea drinking in the reign of the mythological emperor, Shen Nung, at about 2737 B.C., but the earliest credible mention is 350 A.D. when a tea handbook entitled Ch'a Ching was discovered. A favorite tale of the origin of tea concerns Daruma, a Budd hist priest who, having fallen asleep over his devotions, cut off his eyelids and upon awakening throws them on the ground where they take root and grow up as a bush whose leaves, when dried and infused in hot water, produce a beverage that would suppress sleep (1). The Dutch brought the first tea to Europe in approximately 1610. It reached Russia in 1618, Paris in 1648 and England and America in about 1650. Botany The tea plant was originally classified by linnaeus under the b i nomial system in 1753 as Thea sinensis, but the current name, ac cording to the international code of botanical nomenclature, is Camellia sinensis (family of Theaceae). There are many synonyms, including Thea Bohea, Thea viridis, Thea cantonensis, Thea assamica, Camellia Thea and others. Taxonomically speaking, two basic varieties of the tea plant are recognized: the northern (China) form, Camellia sinensis, and the southern (Assam) form, Camellia asamica. 0097-6156/92/0507-0114$06.00/0 © 1992 American Chemical Society

Huang et al.; Phenolic Compounds in Food and Their Effects on Health II ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

9. LUNDER

115

Catechins of Green Tea: Antioxidant Activity

The commercial tea b e l t of the world i s l a r g e l y confined to a ring of mountains around or near the Equator. The q u a l i t y of tea i s at i t s best at d i f f e r e n t seasons in the various tea countries. Generally speaking, there are three main classes of t e a : - unfermented or green tea - semi fermented or oolong tea - fermented or black tea


Chemistry Like a l l p l a n t - l e a f m a t e r i a l , the tea leaf contains the enzymes, biochemical intermediates and structural elements normally a s s o c i ated with plant growth and photosynthesis. In a d d i t i o n , i t contains substances that are known to be responsible f o r the unique properties of tea (2). A representative analysis of green and black tea i s given in Table I. Table I.

Approximate Analysis of Green and Black Tea (% w/w)

Component Proteins Fiber Pigments Caffeine Amino Acids Mineral S a l t s Carbohydrates Flavanols (catechins) Flavonol Glycosides Oxidized Polyphenols

Green Tea 15 30 5 4 4 5 7 17-30 3-4 0

Black Tea 15 30 5 4 4 5 7 5 2-3 25

Polyphenolic Substances. The polyphenols or tea tannins, as they are c a l l e d , constitute the major portion of fresh l e a f , green tea and black t e a . Their approximate amounts in fresh l e a f , green and black teas are in the range of 30 to 35%, 10-25% and 8 to 21%, respectivel y (3). The polyphenolic composition of tea i s shown in Table I I . The most important are the flavanols (catechins), which include (+)-Catechin, ( - ) - E p i c a t e c h i n , (+)-Gallocatechin, ( - ) - E p i g a l l o c a t e chin (-)-Epicatechingallate and ( - ) - E p i g a l l o c a t e c h i n g a l l a t e . F i g ures f o r the i n d i v i d u a l catechins are given i n Table I I I . Conversion of Green Tea to Black Tea. Catechins play the most s i g n i f i c a n t role i n the manufacture of black tea which i s the most widely consumed form of tea in Western countries. Black tea i s the r e s u l t of promoting the oxidation of fresh leaf catechins by atmospheric oxygen through c a t a l y s i s by tea polyphenoloxidase. Nutritional Value. The n u t r i t i o n a l s i g n i f i c a n c e of tea (green and black) seems to be confined to some vitamins and minerals. Vitamin C i s normally present in green tea leaves in excessively large amounts but, as a consequence of the drying process, t h i s vitamin i s almost


116

PHENOLIC COMPOUNDS IN FOOD AND THEIR EFFECTS ON HEALTH II

completely destroyed, or i t s amount l a r g e l y reduced (4). More i n teresting i s the F o l i c Acid whose amounts could represent, in caref u l l y dried green teas, up to 13% of the d a i l y requirements. Tea (black and green) has a r e l a t i v e l y important content of minerals and Table IV gives the quantities provided following an intake of f i v e cups per day.


Table I I .

Polyphenolic Composition of Tea (% w/w)

Unprocessed Tea (Green) Flavanols (Catechins) Flavonols + Flavonol Glycosides Phenolic Acids Fermented Tea (Black) Thearubigins Theaflavins Bisflavonols Phenolic Acids Unchanged Flavanols Flavonols + Flavonol Glycosides Table I I I .

15-20 1-2 2-4 4 1-3 2-3

Catechin Content of Green Tea Leaves

Catechin Epigallocatechin Gallocatechin Epicatechin Catechin Epigallocatechingallate Epicatechinqallate Table IV.

17-30 3-4 5

q/100q 2.35 0.37 0.63 0.35 10.55 2.75

Minerals Provided by Black and Green Tea

Minerals Sodium Potassium Magnesium Calcium Strontium Manganese Iron Copper Zinc Phosphorus

Average Intake from 5-6 Cups (Milliqrams) 6 982 18 4 0.06 1.8 0.02 0.2 2.4 10

Physiological Properties We must point out that tea i s the most popular beverage a f t e r water and that i t s excellent reputation i s j u s t i f i e d . I t s healthful ef-



9. LUNDER

Catechins of Green Tea: Antioxidant Activity

117

fects cannot be ascribed only to the presence of c a f f e i n e , but a great importance i s given to catechins ( f l a v a n o l s ) . Tea i s believed to e x h i b i t the following physiological properties (4-5): - stimulant - antidepressant - antiinflammatory - enhancement of Vitamin C a c t i v i t y - antihypertensive - antiatherosclerosis - hypocholesterolemic - protection against sunburn - antioxidant - retards tooth decay - protection against nitrosamines - protection against r a d i o a c t i v i t y Tea as an Antioxidant We focused our attention on the antioxidant properties of green tea extracts because the i n t e r e s t i n natural antioxidants i s growing (6-9). To determine the Antioxidant Index ( A I ) , tea leaves were not suitable and infusions were d i f f i c u l t to handle. To overcome t h i s drawback, a l l samples were i n the form of spray-dried aqueous ex tracts. The AI was carried out i n the Rancimat (iO) using a ternary mix e s p e c i a l l y developed f o r water-soluble substances. The Rancimat used to carry out these measures was the Metrohm Model 617 (Metrohm, SA, Switzerland). The composition of the ternary mix was the f o l l o w i n g : Topcithine (trademark f o r a l e c i t h i n ) 32% Vitamin Ε 3% Propylenglycol 58% Green Tea Extract 7% In the referenced ternary mix, Vitamin C replaced the tea ex t r a c t at the same l e v e l . The f a t used i n the Rancimat was the chicken f a t , Micana I I I , which i s a f a t devoid of Vitamin E. The AI i s given by Induction Time, i . e . , the time necessary to get the f a t rancid i n the presence of tea divided by the time required f o r the f a t alone to turn rancid. Results are expressed in graphic form and shown i n Figure 1. The codes appearing at the bottom of each bar are explained in Table V. Tea having the code MSCOP has the same composition as teas 4204/E and 3859/E2, which are mixtures of green and black tea i n r a t i o s from 4:1 to 3 : 1 . The MSCOP was extracted under pressure to get more s o l i d s , whereas the other two were ex tracted at atmospheric pressure ill). The mixture, Green:Black, gives a cold water-soluble powdered extract because catechins have the c a p a b i l i t y of breaking down the complex formed by caffeine with polyphenols. No chemicals or enzymes are therefore needed. Relationship between AI and EGCG Content. Catechins, and e s p e c i a l l y epigallocatechingallate (EGCG) which represent 50-60% of the whole catechin group, seem to be responsible f o r the antioxidant a c t i v i t y . We t r i e d to f i n d a r e l a t i o n s h i p between the main catechin, i . e . , the EGCG and the A I . The EGCG content of each sample was determined by


118



16

MSCOP

Figure 1.

4204/E Tea eamplee

439Θ/Ε3

254

Antioxidant index (AI) of d i f f e r e n t types of t e a .

16

9 α

I

I

5

I

I

7

I

I

9

I

J L

11

1

1

1

13

% EP1GALLOCATECHNGALLATE

Figure 2. Relationship between Antioxidant index (AI) and Epigallocatechingallate (EGCG) content i n t e a .


1—

«

9. LUNDER

Catechu of Green Tea: Antioxidant Activity

119

HPLC (12) and we found that there was a good c o r r e l a t i o n between the AI and the EGCG content. Table V gives the values f o r both the AI and EGCG f o r several experimental tea e x t r a c t s , and Figure 2 shows that an increase in EGCG content i s accompanied by an increase in the AI.


Table V. Relationship between Antioxidant index (AI) and Epigallocatechingallate (EGCG) content of d i f f e r e n t types of tea Epigallocatechingallate Antioxidant Sample (% EGCG) Index (AI) Green Teas 7.68 ΑΤΟ 11.4 254 14.7 16.8 4398/E3 11.0 12.5 4394/E3 13.0 15.0 4398/E4 17.0 14.0 Green-Black Tea Mixtures 4204/E 8.50 12.0 3859/E2 12.0 8.20 MSCOP 10.0 5.10 ΑΤ0 = Japanese Green Tea 254, 4394, 4398 = Experimental Green Tea 4204, 3859 = Mixtures of Green and Black Teas MSCOP = Mixture of Green and Black Tea Extracted Under Pressure Conclusion Green tea e x t r a c t s , as well as extracts containing d e f i n i t e mix tures of green and black tea (these extracts have the properties to be cold-water s o l u b l e ) , e x h i b i t i n t e r e s t i n g antioxidant properties which seem to correlate well with the EGCG content. This substance would be e s p e c i a l l y useful in evaluating the antioxidant properties of tea infusions because the Rancimat t e s t cannot be carried out on samples in l i q u i d form. Acknowledgement. We are f u l l y indebted to Ms. E. P r i o r for having carried out the tests on the Rancimat. Literature Cited 1. 2. 3. 4. 5. 6.

Graham, H. In Encyclopedia of Chemical Technology, 3rd Ed; John Wiley & Sons: New York, 1978, Vol.22; pp 628-44. Sanderson, G. W. Recent Adv. Phytochem. 1972, 5, 247-315. Das, D. N.; Ghosh, J. J.; Bhattacharyya, K. C.; Guha, B. C. Indian J. Appl. Chem. 1965, 28(1), 15-40. Stagg, G. V . ; Millin, D. J. J. Sci. Fd. Agric, 1975, 26, 1439-59. Graham, Η. N. In The Methylxanthine Beverages and Foods: Chemistry, Consumption and Health Effects; A. R. Liss: New York, 1984, 29-74. Hara, Y. New Food Ind. 1990, 32(2), 33-8.


120

7. 8. 9. 10. 11.


Herrmann, K. Fette, Seifen u. Anstrichmit. 1973, 75(18), 499-504. Bokuchava, Μ. Α.; Skobeleva, Ν. I. CRC in Food &Nutrition, 1979, 12(4), 303-70. Loeliger, J. Swiss Patent 0 326 829, 1989 Lunder, T. L., Swiss Patent 0 201 000, 1986 Hoefler, A. C.; Coggon, P. J. Chromatog. 1976, 129, 460-63. June 15, 1992


RECEIVED


Catechins of Green Tea - American Chemical Society

Recommend Documents