**1. Introduction**

Brewed tea has been the most widely consumed beverage throughout history. Attractively, this is attributed to its present taste, aromatic odor and healthful effects to the human body. Tea (*Camellia sinensis*) is used for the production of green tea, oolong tea and black tea, depending on the fermentation process. Without fermentation, green tea can be made from fresh tea shoots at a high temperature, thereby inactivating the oxidizing enzymes such as polyphenol oxidase (PPO) and leaving the intact polyphenols. Many ingredients persisting in green tea products are flavonols, flavanols, chlorogenic acid, coumarylquinic acid, theogallin (3-galloylquinic acid), vitamin P (flavonoids), alkaloids, caffeine, theophylline, theobromine, theanine, volatile compounds, fluoride, minerals (e.g. aluminium and magnesium), trace elements and other unidentified compounds. During fermentation, these polyphenolic compounds undergo PPO-catalyzed oxidative polymerization giving rise to the formation of theaflavins and thearubigins which are the major antioxidants in black tea [1]. Besides being a world-wide, well-known beverage, green tea has many benefits for health, including antioxidative, free radical scavenging, iron-chelating, anti-hyperglycemic and anti-diabetic, weight-lowering, anti-aging, neuro-protective and rescue, thrombosis-inhibitory, antiinflammatory, exercise-endurating, hepatoprotective, hepatic phase II enzyme activityinducing, cardioprotective, neoangioprotective, anti-mutagenic, anti-carcinogenic and cancerpreventive, anti-microbial, as well as immunomodulatory activities. Tea products generally provide refreshment and diuretic benefits, as well as contributing to feelings of alertness; however; green tea extraordinarily exhibits such biological and pharmacological properties depending on several specific active phytochemical constituents; particularly catechins. Nowadays, crude extracts, purified catechin fractions and synthetic catechin derivatives of green tea are applicable in alternative and complementary medicines for the prevention, treatment and co-treatment of many diseases and disorders.

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#### **2. Sources and compositions of green tea** complementary medicines for the prevention, treatment and co-treatment of many diseases and disorders.

Tea has traditionally been cultivated across four continents in the manufacturing of a refresh‐ ing drink. The tea products that are available are directly related to the process used at the origin, and can be classified as black tea, green tea, yellow tea, red tea, green pressed tea, as well as instant tea and tea dyes [1]. Green tea is manufactured by using conventional and modified methods. One of these methods involves a 2-3-day process of to drying fresh tea leaves and then rolling the dry leaves with a commercial machine. Alternatively, another method involves the very rapid process of baking the tea leaves in a house-hold microwave oven (800 watt, 3 minutes) at a working temperature of 115 º C. This process will shock the persisting PPO enzyme and result in higher catechins content [2]. A typical green tea beverage is normally prepared at a proportion of 1 g dry weight of tea leaves in 100 ml of hot water in a 3-minute brew (an approximate temperature of 80 º C). This brew usually contains 250 – 350 mg tea solids, 30 – 42% catechins (74 mg) and 3–6% caffeine [3]. HPLC analysis shows the green tea extract (GTE) is comprised of at least six major catechins, including (-)-epicatechin (EC), (-)-epicatechin 3-gallate (ECG), (-)-epigallocatechin (EGC), (-)-epigallocatechin 3-gallate (EGCG), (+)-catechin (C) and (-)-gallocatechin (GC), of which EGCG is the major isomer followed by ECG, EGC and EC (Figure 1) [4]. Gallic acid (GA) is derivatized to one of the hydroxyl groups of the catechins, which has been directly attributed to the biological activities of the catechin species. **2. Sources and compositions of green tea**  Tea has traditionally been cultivated across four continents in the manufacturing of a refreshing drink. The tea products that are available are directly related to the process used at the origin, and can be classified as black tea, green tea, yellow tea, red tea, green pressed tea, as well as instant tea and tea dyes [1]. Green tea is manufactured by using conventional and modified methods. One of these methods involves a 2 - 3-day process of to drying fresh tea leaves and then rolling the dry leaves with a commercial machine. Alternatively, another method involves the very rapid process of baking the tea leaves in a house-hold microwave oven (800 watt, 3 minutes) at a working temperature of 115 C. This process will shock the persisting PPO enzyme and result in higher catechins content [2]. A typical green tea beverage is normally prepared at a proportion of 1 g dry weight of tea leaves in 100 ml of hot water in a 3-minute brew (an approximate temperature of 80 C). This brew usually contains 250 – 350 mg tea solids, 30 – 42% catechins (74 mg) and 3–6% caffeine [3]. HPLC analysis shows the green tea extract (GTE) is comprised of at least six major catechins, including (-)-epicatechin (EC), (-)-epicatechin 3-gallate (ECG), (-)-epigallocatechin (EGC), (-) epigallocatechin 3-gallate (EGCG), (+)-catechin (C) and (-)-gallocatechin (GC), of which EGCG is the major isomer followed by ECG, EGC and EC (**Figure 1**) [4]. Gallic acid (GA) is derivatized to one of the hydroxyl groups of the catechins, which has been directly

 **Pharmacology and Nutritional Intervention in the Treatment of Disease** 

constituents; particularly catechins. Nowadays, crude extracts, purified catechin fractions and synthetic catechin derivatives of green tea are applicable in alternative and

> 1.8 mg EGCG, and 0.8 mg ECG) for Yule (India) black tea; 7.5 mg total catechins (<0.5 mg EGC, 4.0 mg EC, 2.6 mg EGCG, and 1.0 mg ECG) for PG tips (UK) black tea;5.15 mg total catechins (16.3 mg EGC, 4.7 mg EC, 26.3 mg EGCG, and 4.4 mg ECG) for Chinese green tea; 84.9 mg total catechins (28.7 mg EGC, 9.4 mg EC, 40.8 mg EGCG, and 5.9 mg ECG) for Japanese green tea; and 21.1 mg total catechins (7.7 mg EGC, 1.7 mg EC, 11.5 mg EGCG, and 0.5 mg ECG) for Chinese oolong tea [5]. EGCG has so far received the most attention because it represents approximately 59% catechin content, EGC at approximately 19%, ECG at approximately 13.6%, and EC at approximately 6.4% of the total catechin content [6]. Green tea also contains other phenolic acids, such as chlorogenic acid and caffeic acid, as well as other flavonols, such as

> Green tea catechins have proven to be quite stable in water that is room temperature; however,

leaves are unusually rich in polyphenolic catechins that may constitute up to 30% of the dry leaf weight [9]. As a result of the immediate inactivation of PPO enzyme, the compositions of catechins in green tea are very similar to those of the fresh tea leaves. Various quinines, which are subsequently produced by the enzymatic oxidations, undergo condensation reactions to produce *bis*-flavanols, theaflavins, epitheaflavic acids and thearubigens. These compounds

In our Thai green tea, EGCG was found to be the most abundant catechin (at about 60% of the total catechin content), followed by EGG, ECG, and EC, respectively and the assay yield of the total green tea catechin content was found to be 26-29 g/100 g dry tea leaves (Table 1) [2]. In comparison, Taiwan green tea (1 g dry weight) contained 93.3 mg total catechin content,

**Amounts EGCG EGC ECG EC Total catechins** mg/g dry weight 169.4±7.2 60.1±6.2 19.3±2.6 16.3±5.6 279.8±15.2 % (*w*/*w*) 60.6±2.2 21.5±1.4 6.9±1.0 5.9±2.1 100

In general, an antioxidant refers to any substance capable of preventing the oxidation catalyzed by reactive oxygen species (ROS)/reactive nitrogen species (RNS). Thus, an antioxidant that protects against iron toxicity is a substance that can: i) chelate iron and prevent the reaction with oxygen or peroxides; ii) chelate iron and maintain it in a redox state that makes iron unable to reduce molecular oxygen; iii) trap already formed radicals, which is a putative action of any substance that can scavenge free radicals in biological systems, regardless of whether they have originated from iron-dependent reactions or not. Not only can natural products chelate

impart the characteristic taste and color properties of black and oolong tea [10].

followed by 43.2 mg EGCG, 33.6 mg ECG, 0.7 mg C, 3.3 mg EC and 2.7 mg ECG [11].

**Table 1.** HPLC analysis of catechin compositions in six green tea extract solutions (2 g%, *w*/*v*).

C for 7 hours and epimerized to

Green Tea: Just a Drink or Nutraceutical http://dx.doi.org/10.5772/57519 365

C for 20 minutes [8]. Fresh tea

kaempferol, myricetin and quercetin [7].

**3. Nutritional value of green tea**

they can be destroyed at a rate of 20% under brewing at 98 º

other derivatives (e.g. EGCG → GCG) under autoclaving at 120 <sup>º</sup>

**Figure 1.** Chemical structures of catechins in green tea (Redrawn from [4])

attributed to the biological activities of the catechin species.

2 Moreover, tea products have different amounts and compositions of catechins, which is possibly due to biodiversity, different processing methods, different planting areas and different varieties of tea strains. For instance, Khokhar and colleagues reported that 1 g dry weight of tea product contained 48.4 mg total catechins (9.1 mg EGC, 7.9 mg EC, 22.9 mg EGCG, and 8.5 mg ECG) for Ceylon (NL) black tea; 5.6 mg total catechins (<0.5 mg EGC, 3.1 mg EC, 1.8 mg EGCG, and 0.8 mg ECG) for Yule (India) black tea; 7.5 mg total catechins (<0.5 mg EGC, 4.0 mg EC, 2.6 mg EGCG, and 1.0 mg ECG) for PG tips (UK) black tea;5.15 mg total catechins (16.3 mg EGC, 4.7 mg EC, 26.3 mg EGCG, and 4.4 mg ECG) for Chinese green tea; 84.9 mg total catechins (28.7 mg EGC, 9.4 mg EC, 40.8 mg EGCG, and 5.9 mg ECG) for Japanese green tea; and 21.1 mg total catechins (7.7 mg EGC, 1.7 mg EC, 11.5 mg EGCG, and 0.5 mg ECG) for Chinese oolong tea [5]. EGCG has so far received the most attention because it represents approximately 59% catechin content, EGC at approximately 19%, ECG at approximately 13.6%, and EC at approximately 6.4% of the total catechin content [6]. Green tea also contains other phenolic acids, such as chlorogenic acid and caffeic acid, as well as other flavonols, such as kaempferol, myricetin and quercetin [7].

Green tea catechins have proven to be quite stable in water that is room temperature; however, they can be destroyed at a rate of 20% under brewing at 98 º C for 7 hours and epimerized to other derivatives (e.g. EGCG → GCG) under autoclaving at 120 <sup>º</sup> C for 20 minutes [8]. Fresh tea leaves are unusually rich in polyphenolic catechins that may constitute up to 30% of the dry leaf weight [9]. As a result of the immediate inactivation of PPO enzyme, the compositions of catechins in green tea are very similar to those of the fresh tea leaves. Various quinines, which are subsequently produced by the enzymatic oxidations, undergo condensation reactions to produce *bis*-flavanols, theaflavins, epitheaflavic acids and thearubigens. These compounds impart the characteristic taste and color properties of black and oolong tea [10].

In our Thai green tea, EGCG was found to be the most abundant catechin (at about 60% of the total catechin content), followed by EGG, ECG, and EC, respectively and the assay yield of the total green tea catechin content was found to be 26-29 g/100 g dry tea leaves (Table 1) [2]. In comparison, Taiwan green tea (1 g dry weight) contained 93.3 mg total catechin content, followed by 43.2 mg EGCG, 33.6 mg ECG, 0.7 mg C, 3.3 mg EC and 2.7 mg ECG [11].


**Table 1.** HPLC analysis of catechin compositions in six green tea extract solutions (2 g%, *w*/*v*).
