26 years
Drink normal tea or green tea ? Which is better?and why?
Oct 6, 2014
Tea is one of the most ancient and popular beverages consumed around the world. Tea is made from the leaf of the plant Camellia sinensis. Shortly after harvesting, tea leaves begin to wilt and oxidize. The oxidation process is based on chemicals inside the leaves that get broken down by enzymes. The result is darkening of the leaves and the production of well-known tea aroma. This oxidation process can be stopped by heating, which inactivates the enzymes. The extent of oxidation and other aspects of processing determine a tea’s type. Black tea is produced when tea leaves are wilted, bruised, rolled, and fully oxidized. In contrast, green tea is made from unwilted leaves that are not oxidized. Oolong tea is made from wilted, bruised, and partially oxidized leaves, creating an intermediate kind of tea. White tea is made from young leaves or growth buds that have undergone minimal oxidation. Dry heat or steam can be used to block the oxidation process, and then the leaves are dried to prepare them for sale.
Tea is brewed from dried leaves and buds (either in tea bags or loose), prepared from dry instant tea mixes, or sold as ready-to-drink iced teas. So-called herbal teas are not really teas but infusions of boiled water with dried fruits, herbs, and/or flowers.
Tea is composed of polyphenols, alkaloids (caffeine, theophylline, and theobromine), amino acids, carbohydrates, proteins, chlorophyll, volatile organic compounds (chemicals that readily produce vapors and contribute to the odor of tea), fluoride, aluminum, minerals, and trace elements. The polyphenols are a large group of plant chemicals that includes the catechins, which are hypothesized to be behind the health benefits that have been long attributed to tea, especially green tea. The most active and abundant catechin in green tea is epigallocatechin-3-gallate (EGCG).
Unlike green tea, black tea possesses significantly lower concentrations of these catechins than green tea. The extended oxidation of black tea increases the concentrations of thearubigins and theaflavins, two types of complex polyphenols. Oolong tea contains a mixture of simple polyphenols, such as catechins, and complex polyphenols. White and green tea contain similar amounts of EGCG but different amounts of other polyphenols.
Although iced and ready-to-drink teas are growing more and more popular worldwide, they may not have the same polyphenol content as an equal volume of brewed tea. The polyphenol concentration of any particular tea beverage depends on:
- the type of tea
- the amount used
- the brew time, and
- the temperature.
The highest polyphenol concentration is found in brewed hot tea, less in instant preparations, and lower amounts in iced and ready-to-drink teas. As the percentage of tea solids (i.e., dried tea leaves and buds) decreases, this is accompanied with a parallel decrease in the polyphenol content. Ready-to-drink teas frequently have lower levels of tea solids and lower polyphenol contents because their base ingredient may not be brewed tea The addition of other liquids, such as fruit juice, will further dilute the tea solids. Decaffeination reduces the catechin content of teas.
The detoxifying potential of the antioxidants in all types of tea protects cells from free radicals, the damage that can lead to blood clot formation, atherosclerosis (fat plaques that clog the blood vessels), and cancer.
A good deal of scientific research has shown that drinking tea on a regular basis (two cups or more a day) imparts protective effects against heart disease and stroke, lowers total and LDL (often called "bad") cholesterol, and helps to have a faster recovery from heart attacks.
Some laboratory tests have also demonstrated that black and green tea may help boost metabolism to aid weight loss, block allergic response, slow the growth of tumors, protect bones, fight bad breath, improve skin, protect against Parkinson's disease, and even delay the onset of diabetes.
Tea as a food item is generally recognized as safe by the U.S. Food and Drug Administration.
As with other caffeinated beverages, such as coffee and colas, the caffeine contained in many tea products could potentially cause adverse effects, including tachycardia, palpitations, insomnia, restlessness, nervousness, tremors, headache, abdominal pain, nausea, vomiting, diarrhea, and diuresis. However, there is little evidence of health risks for adults consuming moderate amounts of caffeine (about 300 to 400 mg per day).
Black and green tea may inhibit iron bioavailability from the diet. This effect is especially important for individuals who suffer from iron-deficiency anemia. The interaction between tea and iron can be mitigated by consuming, at the same meal, foods that enhance iron absorption, such as those that contain vitamin C (e.g., lemons), and animal foods that are sources of heme iron (e.g., red meat). Consuming tea between meals has a less potent effect on interfering with iron absorption.
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