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الموضوع: Caffeine

  1. #1
    عضو ذهبي الصورة الرمزية تسنيم
    تاريخ التسجيل
    Jul 2011
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    افتراضي Caffeine


    • Caffeine


      Caffeine is a bitter, white crystalline xanthinealkaloid that is a psychoactivestimulant. caffeine was isolated from coffee in 1820 by a German chemist, Friedlieb Ferdinand Runge, and in 1821 by French chemists working independently; namely, by Robiquet and by Pelletier and Caventou. It was Pelletier, noting that the drug had been isolated from coffee (French: café), who coined the word "cafeine", which became the English word "caffeine".
      Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants. It is most commonly consumed by humans in infusions extracted from the bean of the coffee plant and the leaves of the tea bush, as well as from various foods and drinks containing products derived from the kola nut. Other sources include yerba maté, guarana berries, and the yaupon holly.
      In humans, caffeine acts as a central nervous system (CNS) stimulant, temporarily warding off drowsiness and restoring alertness. caffeine is the world's most widely consumed psychoactive substance,[7] but, unlike many other psychoactive substances, is legal and unregulated in nearly all jurisdictions.[clarification needed] Beverages containing caffeine, such as coffee, tea, soft drinks, and energy drinks, enjoy great popularity; in North America, 90% of adults consume caffeine daily. The U.S. Food and Drug Administration (FDA) lists caffeine as a "multiple purpose generally recognized as safe food substance".]Caffeine has diuretic properties when administered in sufficient doses to subjects who do not have a tolerance for it. Regular users, however, develop a strong tolerance to this effect, and studies have generally failed to support the common notion that ordinary consumption of caffeinated beverages contributes significantly to dehydration.


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  2. #2
    عضو ذهبي الصورة الرمزية تسنيم
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    Jul 2011
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    افتراضي رد: Caffeine

    Occurrence


    Roasted coffee beans, a common source of caffeine


    Caffeine is found in many plant species, where it acts as a natural pesticide, with high caffeine levels being observed in seedlings still developing foliage, but are lacking mechanical protection;Caffeine paralyzes and kills certain insects feeding upon the plant. High caffeine levels have also been found in the surrounding soil of coffee bean seedlings. Therefore, caffeine is understood to have a natural function as both a natural pesticide and an inhibitor of seed germination of other nearby coffee seedlings, thus giving it a better chance of survival.
    Common sources of caffeine are coffee, tea, and (to a lesser extent) chocolate derived from cocoa beans.Less commonly used sources of caffeine include the yerba maté and guarana plants,[unreliable source?] which are sometimes used in the preparation of teas and energy drinks. Two of caffeine's alternative names, mateine and guaranine, are derived from the names of these plants. Some yerba mate enthusiasts assert that mateine is a stereoisomer of caffeine, which would make it a different substance altogether.[unreliable source?]This is not true because caffeine is an achiral molecule,and therefore has no enantiomers; nor does it have other stereoisomers. The disparity in experience and effects between the various natural caffeine sources could be because plant sources of caffeine also contain widely varying mixtures of other xanthinealkaloids, including the cardiac stimulants theophylline and theobromine, and other substances such as polyphenols that can form insoluble complexes with caffeine.
    One of the world's primary sources of caffeine is the coffee "bean" (which is the seed of the coffee plant), from which coffee is brewed. Caffeine content in coffee varies widely depending on the type of coffee bean and the method of preparation used; even beans within a given bush can show variations in concentration. In general, one serving of coffee ranges from 80–100 milligrams, for a single shot (30 milliliters) of arabica-variety espresso, to approximately 100–125 milligrams for a cup (120 milliliters) of drip coffee. In general, dark-roast coffee has very slightly less caffeine than lighter roasts because the roasting process reduces a small amount of the bean's caffeine content. Arabica coffee normally contains significantly (+/-50%) less caffeine than the robusta variety. Coffee also contains trace amounts of theophylline, but no theobromine.
    Tea is another common source of caffeine. Although tea contains more caffeine than coffee (by dry weight), a typical serving contains much less, as tea is normally brewed much weaker. Besides strength of the brew, growing conditions, processing techniques and other variables also affect caffeine content. Certain types of tea may contain somewhat more caffeine than other teas. Tea contains small amounts of theobromine and slightly higher levels of theophylline than coffee. Preparation and many other factors have a significant impact on tea, and color is a very poor indicator of caffeine content.[unreliable source?] Teas like the pale Japanese green tea, gyokuro, for example, contain far more caffeine than much darker teas like lapsang souchong, which has very little

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  3. #3
    عضو ذهبي الصورة الرمزية تسنيم
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    افتراضي رد: Caffeine


    What is Caffeine: Molecule Structure






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  4. #4
    عضو ذهبي الصورة الرمزية تسنيم
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    افتراضي رد: Caffeine

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  5. #5
    عضو مميز الصورة الرمزية قمر بلحاج
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    Jul 2012
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    افتراضي رد: Caffeine

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