Caffeine in coffee

Caffeine in coffee, tea, and soda is determined by a solid-phase microextraction using an uncoated silica fiber, followed by a GC analysis using a capillary SPB-5 column with an MS detector. Standard solutions are spiked with G3 caffeine as an internal standard. 

Zougagh, M., Valcarcel, M., and Rios, A., Automatic selective determination of caffeine in coffee and tea samples by using a supported liquid membrane-modified piezoelectric flow sensor with molecularly imprinted polymer. Trends Anal. Chem., 23, 399, 2004. 

Mazzafera, P, Wingsle, G., Olsson, O., Sandberg, G., S-adensoyl-L-methionine theobromine 1-N-methyltranferase, a enzyme catalyzing the synthesis of caffeine in coffee Phytochemistry 37 1577 1994... 

There are numerous methods in the literature for the determination of caffeine, theobromine, and theophylline in food matrices, including coffee, tea, and cocoa. Until recently, methods have emphasized the determination of the major methylxanthines in a commodity, for example, caffeine in coffee or theobromine in cocoa. Present methods range from being specific for one of the compounds in a single matrix to being an all-encompassing assay of major and minor methylxanthines in food products. 

GC has seen wide use in food analysis but has not seen a large following in the determination of the nonvolatile alkaloids in foods when compared to HPLC. The 13th edition of the AO AC Methods of Analysis22 lists a GC method for the determination of caffeine in coffee or tea using a thermionic KCI detector with a glass column 6 ft x 4 mm i.d. packed with 10% DC-200 on 80 to 100-mesh Gas Chrom Q. 

Levine, J., Determination of caffeine in coffee products, beverages and pharmaceuticals, JAOAC, 45,254,1962. 

Caffeine contained in tea beverage is absorbed at about the same rate as caffeine in coffee, cola drinks, or in pure water. Data to support this conclusion was obtained in a human feeding experiment.109 The theory that complexation of caffeine with the polyphenolic material in tea retards absorption110-111 is not borne out. 

Daly, J. W., Mechanism of action of caffeine, in Coffee, Caffeine, and Health, Garattini, S., Ed., Ravens Press, New York, 1993, chap. 4. 

Shanahan, M. P., and Hughes, R. N., Potentiation of performance-induced anxiety by caffeine in coffee. Psychological Reports 59, 83-86, 1986. 

The article Caffeine in coffee its removal why and how by K. Ramalakshmi and B. Raghavan in Critical Reviews in Food Science and Nutrition, 1999, 39, 441 provides an in-depth survey of the physicochemical factors underlying decaffeination of coffee with supercritical CO2. 

Experiment 48 Designing an Experiment for Determining Caffeine in Coffee and Tea... 

Many compounds that are present in plants are weak bases. Caffeine in coffee and piperidine in black pepper are two examples. A weak base, represented by B, reacts with water to form an equilibrium solution of ions. 

The home, workplace, and general environment each represent unique places of possible exposure to neuroactive agents (Table 15.5). The home contains a range of compounds that affect the nervous system caffeine in coffee and tea, alcohol, medicines, pesticides, cleaning agents, paints, and solvents to name just a few. Compounds such a lead or pesticides can be carried into the home on shoes or bare... 

Trugo, L. C., C. A. B. de Maria, and C. C. Werneck. Simultaneous determination of total chlorogenic acid and caffeine in coffee by high performance gel filtration chromatography. Food Chem 1991 42(1) 81-87. 

Nogueira, T., do Lago, C. L. (2007). Determination of caffeine in coffee products by dynamic complexation with 3,4-dimethoxycinnamate and separation by CZE. Electrophoresis, 28, 3570-3574. 

We have things that help us to remain alert. Caffeine in coffee and in tablet form prevents dozing and sleep, as do some prescription drugs. Unexpected stimuli, including noise and even pain, can help, and sometimes aerobic exercise. A useful distinction here is between staying awake and enhancing awareness. 

Most alkaloids exist in nature not in their free-base form but rather as the salt of naturally occurring acids known as tannins, a group of phenol-based organic acids that have complex structures. The alkaloid salts of these acids are usually much more soluble in hot water than in cold water. The caffeine in coffee and tea exists in the form of the tannin salt, which is why coffee and tea are more effectively brewed in hot water. As Figure 12.19 relates, tannins are also responsible for the stains caused by these beverages. 

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. 

Finally, purines such as caffeine (including dietary caffeine in coffee, tea, colas, and chocolate) and synthetic derivatives, such as theophylline, can interfere with the vascular actions of dipyridamole, These agents act to inhibit the adenosine A2A receptor, which serves to further emphasize the role of adenosine in the pharmacologic actions of dipyridamole (41-43), It has also been shown that this effect on A2A receptors is restricted to the vessel wall the direct anti-aggregatory actions of dipyridamole are not blocked by purines and may, if anything, be enhanced by the indirect effect of purines to upregulate A2A receptors (44,45). 

MAZZAFERA, P., WINGSLE, G., OLSSON, O., SANDBERG, G S-Adenosyl-L-methionine theobromine 1-jV-methyltransferase, an enzyme catalyzing the synthesis of caffeine in coffee. Phytochemistry, 1994,37,1577-1584. 

Such biochemical peculiarities include those of secondary metabolites such as alkaloids the composition of alkaloids makes them efficient - often chelating ligands. Although concentrations of such alkaloids usually are small (e.g. 1.5-6% of caffeine in coffee beans), there is a considerable (both mass and stoichiometric) excess with respect to metal ions. Accordingly, alkaloids can be expected to influence both metal partitioning and E (L) ff (because values for N-heterocycles are rather high) of leaves, fruits etc. considerably. Indeed, for Taraxacum officinale (dandelion) leaves. 

Fig. 7.9. Influence of moisture content on the efficiency of the SFE with CO,. (A) Kinetic curves for the extraction of pyrene from sewage sludge ( 2% moisture, 45% moisture). (B) Extraction efficiency for caffeine in coffee with variable moisture content. (Reproduced with permission of the American Chemical Society and Elsevier, respectively.)...

Additive stimulant effects of caffeine Caffeine is present in many products that contain ephedra alkaloids, and those who take these products might also be consuming considerable quantities of caffeine in coffee, tea, and soft drinks. Caffeine can enhance the undesirable effects of ephedrine on the heart, blood supply system, and brain function. 

Caffeine in coffee, tea, and soft drinks may help reduce drowsiness. 

A great number of methods have been developed for the determination of caffeine in coffee,... 

Quantitative det. of caffeine in beverages using CE Caffeine in coffee, tea, cola cocoa samples Drinks made according to instructions, diluted, filtered... 

Let us proceed to some of the technical facets of the decaffeination process. Figure 10.1 is a graph of the solubility of neat caffeine in ctu-bon dioxide (Krukonis, 1981a). The solubility of caffeine is about 0.2 wt% at 60°C and 300 bar. The caffeine content of most coffees is about 1 wt%. If, during the extraction process, the caffeine in coffee dissolves to the solubility limit during extraction at, say, 60°C and 300 bar, the amount of carbon dioxide required to decaffeinate coffee is easily calculated. It is 5.0 pounds per pound of coffee. 

Casal S., Oliveira M.B. and Ferreira M.A. (2000b) HPLC/diode-array applied to the thermal degradation of trigonelline, nicotinic acid and caffeine in coffee. Food Chem. 68 (4), 481-5. 

Nakabayashi T. and Masano M. (1986b) A simple method for the simultaneous determination of trigonelline and caffeine in coffee. Nippon Shokuhin Kogyo Gakkaishi (J. Jpn. Soc. Food Sci. Technol) 33( 10), 729-33 (Chem. Abstr. 106, 49727). 

---