Caffeine in tea

Caffeine in tea and coffee is determined by CZE using nicotine as an internal standard. The buffer solution is 50 mM sodium borate adjusted to pH 8.5 with H3PO4. A UV detector set to 214 nm is used to record the electropherograms. 

NAIK J P and NAGALAKSHMi s (1997) Determination of caffeine in tea products by an unproved high-performance liquid chromatography method , JAgric Food Chem, 45, 3973-5. 

WORTH c c, wiESSLER M and SCHMITZ o J (2000) Analysis of catechins and caffeine in tea extracts by micellar electrokinetic chromatography . Electrophoresis, 21 (17), 3634-... 

FERNANDEZ P L, MARTIN M J, GONZALEZ A G, PABLOS F (2000) HPLC determination of catechins and caffeine in tea. Differentiation of green, black and instant teas, Analyst, 125,421-5. 

Several studies have investigated the biosynthesis of caffeine in tea. The results of a study by Suzuki and Takahashi27 30 suggest a pathway for caffeine biosynthesis in tea from 7-methylxanthine to theobromine and then to caffeine. Additionally they suggest that theophylline is synthesized from 1-methylxanthine. Another study by Ogutuga and Northcote31 proposes a pathway through 7-methylxanthosine to theobromine followed by caffeine. 

Suzuki, T. and Takahashi, E., Further investigation of the biosynthesis of caffeine in tea plants, Biochemistry, 160,81,1976a. 

Fujimori, N., Suzuki, T., and Ashihara, H., Seasonal variations in biosynthetic capacity for the synthesis of caffeine in tea leave, Phytochemistry, 30,2245,1991... 

By weight, tea leaves have double the caffeine as coffee beans 25 however, the caffeine content is greatly diluted during preparation. Caffeine in tea has been reported to range from 2.7 to 4.1% in selected varieties of tea,7 comparable with an estimate of 4% caffeine content in tea.26 While tea is the most commonly consumed caffeinated beverage, the caffeine content is only one third to one half that of coffee, contributing less to overall caffeine exposure than coffee. 

THE CONTENTS OF INDIVIDUAL CATECHINS. GALLIC ACID AND CAFFEINE IN TEAS. 

Caffeine in tea and coffee inhibits the phosphodiesterase that degrades cAMP. The resultant increase in cAMP levels, therefore, mimics the action of mediators such as the catecholamines that modulate adenylate cyclase. Caffeine and the related theophylline (both purine alkaloids, see Box 11.12) are thus effective stimulants of the CNS. 

S Kuhr, UH Engelhardt. Determination of flavanols, theogallin, gallic acid and caffeine in tea using HPLC. ZLebensm Unters Forsch 192 526-529, 1991. 

This neurotransmitter has diverse functions throughout the brain that are also related to our sleep—wake cycles. We know a lot about it because of the ready availability of a very safe, highly effective adenosine receptor antagonist that is served hot or cold, with or without cream, throughout the world—caffeinated coffee Caffeine is also commonly found with theophylline (a molecule that is very similar to caffeine) in tea. Indeed, although caffeine is found in at least 63 plant species, 54% of the world s... 

The robusta strain of coffee plant cultivated in Indonesia and Africa contains about 2.2% caffeine, while the arabica variety, grown in Central and South America, contains half that concentration. The caffeine in tea was purified in 1827, and was initially given its own name of theine, as chemists of the day thought it different from the caffeine in coffee. 

Methylxanthine is the major purine constituent of human urine (3.1 g in 10001) (1898ZPC(24)364). 3- and 7-Methylpurines are also minor constituents of urine, especially following large doses of caffeine or other methylated xanthines. 1,3-Dimethylxanthine (theophylline) occurs with caffeine in tea leaves and is a powerful diuretic and has been used clinically for this purpose (generally as an adduct with salts of organic acids) and also in the treatment of asthma. 1,7-Dimethylxanthine (paraxanthine) is also an efficient diuretic and, in addition, possesses antithyroid properties (45JCS751). The main purine constituent... 

Wu, J. C., Xie, W., and Pawliszyn, J. 2000. Automated in-tube solid-phase microextraction coupled with HPLC-ES-MS for the determination of catechins and caffeine in tea. Analyst 125 2216-22. 

Lin YS, Tsai Y J, Tsay JS, Lin JK. Factors affecting the levels of tea polyphenols and caffeine in tea leaves. J Agric Food Chem 2003 51 1864-1873. 

Caffeine (in tea, coffee, cola, etc.) may interfere with dipyrida-mole-thallium-201 scintigraphy tests. Similarly, theophylline can also reduce some of the effects of dipyridamole. 

The doeumentation is somewhat sparse and there is a need for more study over the range of benzodiazepines and related drugs, but the overall pie-ture is that these interactions are established. The extent to which these xanthines aetually reduce the anxiolytic effects of the benzodiazepines remains uncertain (it needs assessment) but be alert for redueed benzodiazepine effects if both are used. Caffeine in tea or eoffee appears to reduee the sedative effeets of triazolam and zopielone. This would appear to be a disadvantage at night, but may possibly be useful the next morning. 

Konishi, S., M. Ozasa, and E. Takahashi Metabolic conversion of N-methyl carbon of Y-glutamylmethylamide to caffeine in tea plants. Plant Cell Physiol. 13, 365 (1972). 

Caffeine in tea accounts for its mildly stimulating properties, while the tannins contribute pungency, slight astringency, and color to tea. An essential oil contributes the flavor. The amount of caffeine in a cup of tea depends upon the steeping time. 

Caffeine levels vary in developing coffee fruits from 0.2% to 2% (w/w) in the pericarp, and remain above 1% (w/w) in seeds. Caffeine is also detectable in leaves and cotyledons but absent in roots and older shoots. Young leaves also contain theobromine albeit at lower levels than caffeine. In tea, most of the caffeine is localized to the leaves, with small amounts... 

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