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REVIEW ARTICLE
Year : 2011  |  Volume : 1  |  Issue : 2  |  Page : 110-115

Chemistry and pharmacology of caffeine in different types of tea leaves


Pharmacy Department, Oman Medical College, Muscat, Oman

Date of Submission06-Dec-2010
Date of Acceptance08-Mar-2011
Date of Web Publication23-Aug-2011

Correspondence Address:
A R Mullaicharam
Oman Medical College, Pharmacy Department, Muscat
Oman
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2231-0738.84198

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   Abstract 

"Shai" is the Arabic noun for the English word tea. This substance is widely consumed by the Asian continent initially and later spread out to the rest of the world. The Arabs have another drink which is as popular known "Kahwa" which is coffee in English. The two ways of serving tea in coffee shops and restaurants is either by tea bags which is then dipped in the boiling water for its content to diffuse throughout the water content, or by brewing the loose leafs and serving it. This review article focused on chemistry and pharmacology and various methods of preparation of caffeine in different types of tea leaves.

Keywords: Analysis of caffeine, pharmacology of caffeine


How to cite this article:
Amaresh N, Mullaicharam A R, El-Khider MA. Chemistry and pharmacology of caffeine in different types of tea leaves. Int J Nutr Pharmacol Neurol Dis 2011;1:110-5

How to cite this URL:
Amaresh N, Mullaicharam A R, El-Khider MA. Chemistry and pharmacology of caffeine in different types of tea leaves. Int J Nutr Pharmacol Neurol Dis [serial online] 2011 [cited 2019 Mar 18];1:110-5. Available from: http://www.ijnpnd.com/text.asp?2011/1/2/110/84198


   Introduction Top


The story of tea begun according to legend of the early emperor named Shen Nung who was a skilful ruler, imaginative scientist, and patron of the arts, 5 000 years ago in ancient china. For him, with his prophetic law to be compulsory among other things, he assured that all drinking water should be boiled as a hygienic precaution. The emperor visited a distant region in his realm on a summer day when he and his court stopped to rest. In harmony with his prophetic law, his servant started to boil water that would be for the emperor's court to drink. Dried leaves were all over the place; when some of it fell into the water, a brown color started to infuse into the boiling water. [1] The emperor being a scientist was so interested to what the liquid had become, he started to drink some of it and he was very refreshed. And that was the legend of how tea was originated, which many historians believe to be closely related to the discovery of tea where the real actual story has already been lost in the books of history. [2]

Discovery of caffeine in tea

The history of caffeine that is present in tea was initially discovered in 1827 and was first named theine. After a while, theine was also found in some other plants that were related to tea plants. Sooner or later, evidences show that theine that was found in tea was similarly the same with caffeine that is found in coffee, so the term theine was never used again. [3]

Different types of tea

  • Black Tea contains caffeine in nature and can be decaffeinated to remove most of the caffeine content. Examples of this are English breakfast, Chai Spice, and Earl Grey.
  • Ooolong tea contains caffeine in nature, and the content is normally less than black tea has to offer and it can be decaffeinated to remove most of the caffeine content. Examples of this are China Oolong, Formosa Oolong Bay Jong, and Ti Kuan Yin.
  • Green tea contains caffeine in nature, and it is normally lesser than the content that is present in oolong tea and it can be decaffeinated to remove most of the caffeine content. Examples of this are Premium Green, Kangra Green Gunpowder, and Darjeeling Green.
  • White tea contains caffeine in nature and it is normally less than the content that is present in green tea and it can be decaffeinated to remove most of the caffeine content. Examples of this are Mutan White, Flowery Pekoe White, and White Pearls.
  • Decaffeinated tea is the result of caffeine removing from the black, oolong, green, or white tea. Examples of this are Decaf Earl Grey, Decaf Chai Spice, and Decaf Sencha Green.
  • Herbal "tea" is a natural tea that is caffeine free. An example of this is Chamomile, Peppermint, Lemon, and Blossom. [4] [Table 1]
Table 1: Caffeine content in vorious type tea

Click here to view


Production of tea

The initial phase for this process is manually harvesting the tea leaves from the branches which will yield a high-quality product since each leave is individually picked by the worker which excludes harvesting leaves that do not meet the standard required quality.

The next phase involves processing the harvested leaves; this is carried out through CTC which is a term that stands for "Crush, tear, curl" and it is the method of choice when handling lower quality type of leaves. CTC is carried out through big machines by applying force to squeeze out most of the leaf saps, and finally they are drained out of water. [5]

This method of extracting tea has the disadvantage of not being efficient to provide high-quality tea. However, it is quite effective when quantity not quality is the goal of production since it is a mechanized process that allows larger amounts to be produced in a shorter period of time with least consumption of human resources.

The other method of processing is known as the orthodox method which is more complex when compared with the CTC method. This type of processing differs depending on the type of tea processed but mainly it consists of a combination of withering, rolling, oxidation, and heating. [6]

Withering

The leaves are spread out for them to become a limp which will further on make the rolling process much easier to accomplish. By spreading the leaves out in a shaded area, the chances of the leaves to crumble during the following processes are decreased to a significant extent.

Rolling

This process is machinery based which aids in combining all the constituents to form a mix that will facilitate the process of oxidation. In certain circumstances, it could be accomplished manually with extensive labor effort, but these efforts are saved only when producing tea products of very high quality.

Oxidation

The leaves are left to oxidize, starting from the rolling phase until a specified period of time based on the type of tea species used. Depending on the desired product quality, the manufacturer could decide the extent of the flavor and the strength of the product by manipulating the period of oxidation, since longer oxidation would result in a less flavorful product; however, it will be more pungent.

Heating

This phase marks the end of the oxidation process and prepares the final product for storage. [7]

Important points during tea storage

Environmental factors are the factors which play a role in affecting the taste of tea leading to a stale tea with diminished taste. Therefore, controlling these factors would result in better taste and satisfaction of the consumer. The most suitable tea container is airtight as well as opaque to avoid degradation from both air and light. Another important point is to assure that the area of storage is cool with least humidity; also, the surrounding elements should be odorless for the tea not to pick them up. It is important to keep in mind that storing in a cold environment should also be avoided since it would entirely ruin the tea due to condensation. [8]

Decaffeinating tea products

The industry developed techniques to reduce the caffeine content in the tea products to provide consumers with different caffeine content suitable for each individual needs. The term "decaf" could be misunderstood for a tea product from which caffeine is purely isolated; however, that is not always the case since decaf usually means taking just a certain concentration of caffeine out of the product.

The following are the methods used to obtain decaffeinated tea:

Ethyl acetate method

Indirect application of this method involves wetting the leaf either with steam or with water. Next is the application of ethyl acetate that interacts with the moistened leaf and binding which bind with the caffeine. Finally, the leaf is rinsed again to clear all the ethyl acetate residues. Direct method is different from the indirect method since it is carried out directly through the dry leaf. [9]

CO 2 method

This method is carried out only indirectly through the use of pressurized CO 2 that is applied on the moistened tea leafs in a sealed chamber which develops a reaction leading to the formation of a solvent which is responsible for both binding and extracting the caffeine from the leafs.

Both methods if followed accurately could give a final product which is 99.6% caffeine free. [10]

Methylene chloride method

Methylene chloride has the ability to extract caffeine by forming a bond. This method is carried in the same way as the ethyl acetate method directly and indirectly. [11]

Tea constituents


Tea is composed of many compounds aside from caffeine that give the different effects that arise from its ingestion. These components might have various effects based on the individuals' consumption and the quality of the tea. The following are some of the tea components with a brief explanation:

Tannins

One of the chemical constituents of tea is tannin. This compound is the reason behind the dry and puckery feeling following the intake of tea. These compounds posses the property of protein-precipitating which causes the formation of a stable, coherent membrane due to the deposition of protein on the epithelial layer whenever applied on the mucus membrane. This effect would lead to the formation of a protective layer along the GI tract which would cut down the absorption of harmful toxins along the permeable membrane. This property explains the use of tea as a remedy for the self-treatment of diarrhea. [12]

Catechins

A fresh tea leaf is constituted of 25% of this compound. This compound proved to have beneficial effect on different health concerns, ranging from serious health risks such as the prevention of stroke, heart failure, diabetes, and cancer. Other less significant benefit found was having the ability to enhance the reduction of weight when accompanied with exercise. [13],[ 14]

Theophylline

This component is highly significant in the medical industry; thus, it is synthetically manufactured. This compound is the active ingredient in medicines used for the treatment of respiratory disorders such as chronic obstructive pulmonary disease (COPD) and asthma. [15],[ 16]

Vitamin B complex

This is a combination of eight water-soluble vitamins numbered from 1 to 8. These are essential to support body functions of normal growth, maintenance of body tissues, and coenzymes supporting the normal functioning of enzymes to provide energy-producing reactions. Therefore, inadequate intake of Vitamin B Complex would affect various body systems such as the digestive, nervous system, skin, and blood. [17]

Caffeine content in tea

Most of the tea products are extracted from the leaves of Camellia sinensis. All the tea products extracted from this tree contain certain caffeine content. There are other types of tea products that are caffeine free such as Yerba mate.

Different tea products and their caffeine content. [18]

Caffeine chemistry

[Figure 1] shows chemical structure of caffeine. Caffeine's chemical name is 3,7-dihydro-1, 3, 7-trimethyl-1H-purine-2,6-dione. It is also known as theine, methyl theobromine, and 1, 3, 7-trimethylxanthine. Its molecular formula is C 8 H 10 N 4 O 2 H 2 O and it consists of bicyclic molecules derived from the purine ring system. [19]
Figure 1: Chemical structure of caffeine

Click here to view


In its pure form, caffeine is a fleecy white solid or long silky crystal. It is odorless, but has a distinctive bitter taste. When heated, caffeine loses water at 176΀F (80΀C), sublimes at 352.4΀F (178΀C), and/or melts at 458.2΀F (236.8΀C). It is only slightly soluble in water and alcohol, but dissolves readily in chloroform. Water solutions of caffeine are essentially neutral (pH = 6.9).

Caffeine is a member of the alkaloid family, a group of compounds obtained from plants whose molecules consist of nitrogen-containing rings. In general, alkaloids tend to have identifiable physiological effects on the human body, although these effects vary greatly from compound to compound. [20]

Caffeine pharmacokinetics

Absorption and distribution


When caffeine is administered independently, it shows is rapid absorption when taken orally in a period of approximately 45 minutes to an hour to an extent which reaches up to 99%. However, it is absorbed to a lesser extent when administered as Tea or Coffee. [21]

The caffeine molecule is of a lipophilic nature which explains its easy passage through the biological membranes throughout the gastrointestinal (GI) tract. It has low binding property to proteins which increases the amount of caffeine freely circulating in the blood as well as their passage into the blood cells. In infants as well as in newborns, the concentration of caffeine in plasma and the cerebrospinal fluid is comparable. When caffeine is taken heavily by pregnant women, studies have showed that premature infants have high levels of caffeine due to the fact that the placenta does not act as a barrier for the transfer of caffeine from the mother to the fetus. [22]

Half-life

A single cup of tea would approximately provide a dose of 0.4 to 2.5 mg/kg of caffeine. Peak plasma concentration is reached in 15 to 120 minutes after oral intake. The half-life of caffeine lasts for 4.5 hours in both young and elderly when taking a dose of 10 mg/kg. However, neonates have an increased half-life because of the decreased activity of cytochrome P-450. [23]

Clearance

Caffeine clearance is the lowest during the first period of life at the age of 1 month (31 ml/kg/h) and reaches its peak in infants of 5- to 6-month-old (331 ml/kg/h), and declines in adults to a mid value (155 ml/kg/h). [24]

In adult smokers, the half-life of caffeine drops to value from 30 to 50% less than the clearance of nonsmoking males. On the other hand, oral contraceptives would double the caffeine clearance when taken by the females. [25]

Metabolism

Caffeine is metabolized in the liver to form a number of metabolites such as dimethylxanthine, monomethylxanthine, dimethylallantoin, and uric acid. All these reactions are carried out in the liver microsomes. [26]

These metabolic pathways are saturable since the elimination half-life of caffeine is dose dependent. A caffeine concentration of 1.1 mg/kg would give a plaam1 level of 0.5 to 1.5 mg/l.

Pharmacology

One theory states that caffeine's therapeutic actions arise from its action on cyclic nucleotide phosphodiesterases, particularly by inhibiting it. Yet, this theory lacks solid evidence which could lead to contradiction of its accuracy since caffeine concentrations that are below the threshold to inhibit phosphodiesterase do cause an increase in the blood pressure.

Caffeine taken at higher levels would decrease the uptake as well as the storage of calcium within the sarcoplasmic reticulum which would increase the level of free calcium in the striated muscles. At the concentration of 0.2 mmol or more, caffeine would cause relaxation in the smooth muscle with the presence of norepinephrine and angiotensin which are potent activators of contraction.

At adenosine receptors, it acts as an antagonist through the competitive inhibition mechanism when given in quantities within the therapeutic range. This explains the reason behind observing the same effects of caffeine by removing adenosine from the body and decreasing it to a certain extent.

Other effects of caffeine are potentiation of inhibitors of prostaglandin synthesis and the possibility that methylxanthines reduce the uptake and/or metabolism of catecholamines in non-neuronal tissues. [27]

Mechanism of action

Almost all of the experienced effects of caffeine are mediated via adenosine receptors through its competitive inhibitory action discussed earlier in the pharmacology. Adenosine is responsible for the sleepy feeling and the yawning that we experience.

By competing with adenosine for the same receptors, caffeine is able to counteract the effects of adenosine produced by our body when given in concentrations that enables it to occupy most of the available receptors. For this idea to be easily understood, it could be explained as if the receptor is adenosine's chair in the office and caffeine occupies it, inhibiting adenosine from performing its work. [28]

Caffeine and health

The past decade has been passed with extensive research on caffeine regarding some fibrocystic disease, behavior on children, reproductive function, cardiovascular disease, behavior in children, birth defects and cancer has no significant health hazard from normal caffeine consumption.

Most of the researches that was made about the health hazards that caffeine can inflict to human health, especially with studies on teratology, reproduction behaviors, carcinogenicity, and cardiovascular disease has no traces that certain use of caffeine on beverages would lead to health injuries. People who always take tea and coffee have no worries about their intake of caffeine since there is no serious concern about it as long as there is moderate diet and alcohol consumption, according to researches done over the decades. [29]

Pros of caffeine

Caffeine has advantages that are of certain significance; however, it is still controversial whether it out weights its advantages or weight more than its disadvantages to the consumers. Caffeine has the ability to increase the person's ability to work, enhance the respiratory process, and enhance the ability to perform intellectual tasks. It increases the person's reaction time by stimulating the central nervous system, giving the feeling of alertness.

In the medical field, caffeine is used by doctors to help newborns with respiratory difficulties to help in dilating the bronchioles and facilitating the airways for the oxygen intake. Caffeine also has the property of acting as a pain killer to relieve headache, especially when it is taken in combination with another non-steroidal anti-inflammatory drugs (NSAID) such as ibuprofen. [30]

Six studies have specifically concluded that adults who drink coffee at a regular basis are 80% less likely to develop Parkinson's. Another study showed that consuming an amount of two cups a day would give a drop in the risk of developing liver cirrhosis and colon cancer. [31]

Caffeine has benefits for the athletes as well since it increases the muscle strength, endurance, and ability to fight fatigue in the short term. It also contributes to breaking down fat and fatty acids, which is why caffeine is one of the components of diet pills. [32]

Cons of caffeine

Most popular side effect of consuming high concentration of caffeine is caffeinism. This syndrome is composed of anxiety, restlessness, and sleep disorders. Chronic caffeine intake of low doses leads to depression and aggravation of Premenstrual Syndrome in Women.

Other side effects of caffeine intake are diarrhea, copious urination, and facial blushing. Panic attacks occur after high consumption of caffeine since caffeine acts by triggering the fight or flight feedback in our body, but after staying for longer periods of time, it just changes to panic attacks and feeling of bad things could happen at any time. Also, it causes physical and emotional fatigue since it does not allow the body to realize when to simply rest when it is exhausted.

Another issue is the addictions to caffeine. Once an individual gets used to consuming a certain amount of caffeine daily, the body starts to crave for it whenever it is unavailable, which would lead to the feeling of irritability and is the reason for experiencing the withdrawal symptoms. [33]

Acidity of tea

The flavor and color of the tea are due to the organic compounds mentioned earlier and based on how much of each compound is present, the taste and color of the tea would vary. The method of production mentioned earlier contributes to the flavor and color of the tea solution. The acidity of the tea could be easily determined through the use of pH papers. Tannins which are the phenolic compounds are the contributors for the extent to which a tea solution is acidic; the more the tea has tannins, the more acidic it would be.

 
   References Top

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    Figures

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[Pubmed] | [DOI]



 

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