Tea: A Nature’s Blessing turned Toxin

Tea is not only a hot drink, but it has gained a status of cosmopolitan hot drink, so much so that it becomes a facilitator of conversation among the people. After water, it is the most widely consumed drink in the world [1]. 
Tea is a processed product of leaves and leaf buds of a species of evergreen shrub or small tree of Camellia sinensis ver sinensis, or ver assamica [2]. It is consumed in different forms, namely, oolong, green, black and Ilex tea depending on post-harvest treatment and chemical components.

Chemistry of Tea
However, here the author is only concerned with the health issues related to consumption of tea on the basis of complex chemical correlations with human physiology. Indeed, the chemistry of tea has to see in at two different stages, the chemical composition of leaves & the same in processed tea.  However, the conversion of chemicals during processing is a function of temperature, total dissolved solids, pH, etc.

Chemical composition of tea includes Polyphenols, Pigments, Amino acids, carbohydrate, and methyl-xanthine, etc. Approximately 30K polyphenols have been reported so far, which are synthesized from amino acids in the presence of light.

The major flavanols in tea are: catechin (C), epicatechin (EC), epicatechin gallate (ECG), gallocatechin (GC), epigallocatechin (EGC), and epigallocatechin gallate (EGCG). EGCG is the most active of these catechins and is often the subject of studies regarding tea antioxidants. Tea flavanols are sometimes collectively referred to as catechins [3].

Amino acids give tea it's brothiness or umami taste. Tea leaves contain many amino acids, the most abundant of which is theanine. In the tea field, sunlight converts amino acids to polyphenols, and as such; shade-grown tea contains more amino acids than tea grown in direct sunlight. Some tea bushes are even deliberately shaded for several weeks before harvest to enhance the tea’s amino acid content. L-Theanine is responsible for promoting alpha brain wave activity which promotes relaxation. L-Theanine in concert with caffeine can induce a state of “mindful alertness” in the tea drinker. In steeped tea, amino acids make up 6% of the extract solids [4].

How Colour of Tea comes 

On the bush, tea leaves contain thousands of chemical compounds when they are processed, these compounds break down, form complexes and form new compounds. When we steep tea leaves, our senses are tingled by the thousands of volatile compounds (collectively known as the “aroma complex”) from the tea liquor and the thousands of non-volatile compounds and the complexes between them, not all of which are water soluble, and the ones that are water soluble are soluble at a function of the properties of the water used for steeping like temperature, total dissolved solids, pH, etc.

Graph showing the composition of various components in tea

The volatile substances in tea leaves are largely responsible for a tea’s flavor and aroma. The flavor and aroma of each tea depends on a wide variety of combinations of these compounds, hence the name aroma complex. Compounds such as linalool and linalool oxide are responsible for sweetness; geraniol and phenylacetaldehyde are responsible for floral aromas; nerolidol, benzaldehyde, methyl salicylate and phenyl ethanol are responsible for fruity flavors; and trans-2-hexenal, n-hexanal, cis-3-hexanol, and b-ionone are responsible for a tea’s fresh flavor6. When studying tea’s aroma complex, it is sometimes broken into two parts:

• primary aroma (from fresh tea leaves) and
• secondary aroma (products of manufacture).

Regardless, more and more research is being done on tea volatiles and how our olfaction the system works in general, so we may expect some clarity on this issue in the coming years.

Benefits of Tea

The list of supposed benefits from drinking tea is seemingly endless.  Recent research, for instance, suggests drinking tea may help everything from bad breath to Parkinson's disease.  Some studies indicate it may even save lives.  Here are some recent claims:[5, 6, 7, 8].  Being rich in natural antioxidants, tea is reported to be used in the management of colon, esophageal, and lung cancers, as well as urinary stone [9].

• ·      Prevention of arthritis in older women
• ·      Cancer prevention [10; 11]
• ·      Immunity to flu [12]
• ·      Reduced cholesterol levels
• ·      Reduced risk of heart disease
• ·      Reduced blood pressure
• ·      Protection against Parkinson's disease
• ·      Protection against Huntington's disease
• ·      Prevention of cavities and gum disease [13]
• ·      Protection against bad breath [14]
• ·      Prevention of type-2 diabetes
• ·      Defense against HIV

Milk Tea: How Good or How Bad?

Usually, in our society, people take milk tea, which also contains traces of casine protein. Thus, in the due process of digestion, HCl is secreted in the stomach in order to kill pathogens, the quaternary structure of protein & activate pepsinogen. Now, the question is the fate of surplus HCl & pepsin? Because in tea very less amount of milk and accordingly quite less amount of casine is found in tea which is not able to combat the number of acids secreted. This surplus acid ultimately damages the stomach wall.

Flavor of Tea 

The mechanism of acid secretion and damage of stomach wall by it can be explained as follows.  Amino acids and polypeptides interact with antral gastrin cells to cause gastrin release [15, 16] and directly with oxyntic cells in the body and fundus regions of the stomach to stimulate acid secretion [17]. Milk can trigger acid production and the worst thing is that milk has a rebound effect, which triggers acid secretion and makes you deal with heartburn. Caffeine is another stimulating agent for acid production [18]. In an experiment conducted by Yusuf et. al. [19] to assess the impact of de-sialylation of mucus by a variety of damaging agents (0.1 M HCl, 2 mg ml⁻¹ pepsin and 2 M NaCl) and concluded that gastric acidity alone is not inherently damaging and that resistance of gastric mucosa to destructive agents may be dependent on the integrity of the sialic acids.

Conclusively, tea is a great gift of nature which should use accordingly. if you have to take only milk tea, take after some heavy snacks.