Caffeine isolation from coffee

Caffeine, the active substance responsible for the stimulant effect of the coffee plant s berry, is a methyl-xanthine, one of the family of stimulants present in more than 60 species of plants. The pure chemical forms white, bitter-tasting crystals, which were first isolated from coffee in 1820. Other family members are theophylline, found in tea leaves, and theobromine, found in the cacao pods that are ground to make chocolate. The most potent component in the coffee family by unit weight is theophylline, while theobromine, the weakest component by unit weight, stays in the body longer than does caffeine. 

Caffeine, the most popular natural stimulant, is found in a number of plants throughout the world. The drug was first isolated from coffee in 1821 and was named for that plant, but the effects of coffee and caffeine differ. In many ways coffee seems to be more powerful than refined caffeine or other caffeine-containing plants. 

Caffeine is an alkaloid isolated from coffee, tea or the dried leaves of Camellia sinensis (Iheaceae), or prepared synthetically. 

In connection with plant breeding programs, cell and tissue cultures of Coffea species have been studied extensively. We do not deal with this work here, however, and the reader is referred to Baumann and Frisch-knecht for a review (740,741). Although caffeine (46) can be easily isolated from coffee beans at low cost, a number of studies have been made on the production of caffeine in cell cultures of Coffea. The biotechnological aspects of the caffeine production by means of cell cultures has been reviewed by Prenosil et al. (109). 

The active ingredient that makes tea and coffee valuable to humans is caffeine. Caffeine is an alkaloid, a class of naturally occurring compounds containing nitrogen and having the properties of an organic amine base (alkaline, hence, alkaloid). Tea and coffee are not the only plant sources of caffeine. Others include kola nuts, mate leaves, guarana seeds, and, in small amount, cocoa beans. The pure alkaloid was first isolated from coffee in 1821 by the French chemist Pierre Jean Robiquet. 

Tea yields better-quality caffeine than that obtained from coffee. Caffeine from tea is relatively colorless, whereas the caffeine extracted from coffee is highly colored. About 25 mg of caffeine is isolated in either case. Sublimation removes much of the color from the tea and coffee samples. 

Table 29.1 Genes of iV-methyltransferases involved in caffeine biosynthesis isolated from coffee (Coffea arabica) plants...

Caffeine has been isolated from waste tea and from the decaffeiniza-tion of coffee by extraction at 70°C, using rotating countercurrent drums and an organic solvent, frequently trichloroethylene. The solvent is drained off, and the beans steamed to remove residual solvent. The extraction solvent is evaporated, and the caffeine is hot-water-extracted from the wax, decolorized with carbon, and recrystallized. 

Coffee and tea plants seem to contain a variety of N-methyltransferase enzymes that have varying substrate specificity (168, 169). For example, a caffeine synthase enzyme isolated from tea leaves catalyzes both the N-methylation of N-methylxanthine and theobromine (176). The substrate specificity of the methyltransferases can be changed by site-directed mutagenesis (177), and the crystal structure of two of the N-methyltransferases has been reported recently (178). 

Supercritical fluid extraction processes are particularly appropriate for the separation and isolation of biochemicals where thermal decomposition, chemical modification, and physiologically-active solvents are undesirable. Examples of these bioseparations include the extraction of oils from seeds using carbon dioxide (1), of nicotine from tobacco using carbon dioxide-water mixtures (2), and of caffeine from coffee beans again using carbon dioxide-water mixtures (3). 

The most common use of scC02 is in the extraction of caffeine from coffee or tea, nicotine from tobacco, and essential oils from plants. The isolation of products is simple, with the evaporation of the solvent with no residue. Another important application is in supercritical fluid chromatography (SFC). 

Carboxylic acids with an amino group on the ct-carbon are commonly called amino acids. Amino acids are linked together by amide bonds to form peptides and proteins (Section 23.7). Caffeine, another naturally occurring amide, is found in cocoa and coffee beans. Penicillin G, a compound with two amide bonds (one of which is in a i8-lactam ring), was first isolated from a mold in 1928 by Sir Alexander Fleming. 

In literature very little is published on the extraction of alkaloids on an industrial scale. The few papers available were published between 1950 and 1970 and concern the isolation of alkaloids from whole plants or plant parts 168,169). The extraction of catharanthine and vinblastine from C. roseus leaves on a pilot plant scale is described by Atta-ur-Rahman et al. (170). Svoboda developed a method for the extraction of ajmalicine, vinblastine, and vincristine which has been used by Eli Lilly Co. (169,171-173). Supercritical fluid extraction is a method which is used for the extraction of caffeine from coffee beans. This method also seems of interest for further studies of other alkaloids. 

Some examples of successful commercial selective extractions are the removal of caffeine from coffee or the solubilization of nicotine from tobacco both accomplished on moist matrices to aid in selectively solubilizing the alkaloid component. Selective extraction has been demonstrated for the segregation of essential oil from other lipid components in natural extracts derived from fruits and for the separation of aroma components in cocoa butter from the base oil. Other enrichment SEE schemes that have been reported include the fractionation of carotenoid from leaf protein concentrate [25], the fortification of sterols in seed oils [26], and the isolation of lecithin (phospholipid-containing fraction) from triglycerides [27]. 

In this experiment, caffeine is isolated from brewed tea or coffee using solid phase extraction (Technique 12, Section 12.14). It is offered as a Green Chemistry alternative to the procedure given in Experiment 13A in which methylene chloride is used for the extraction of caffeine from tea. 

We recommend a 6-mL column with 1000 mg of C18E sorbent (No. 8B-S001-JCH-S) for Experiment 13B. These columns are available from Phenomenex, 411 Madrid Avenue, Torrance, CA 90501-1430, phone (310) 212-0555. About 25 mg of caffeine can be isolated from one batch of tea or coffee solution. 

Solvent extraction is a valuable method for obtaining a desired substance from its natural source. A familiar example is the hot-water extraction of caffeine (19) and the various oils that constitute the flavors of freshly brewed coffee and tea from coffee beans and tea leaves. As contrasted to the liquid-liquid extractions described in Section 5.2, this process is an example of solid-liquid extraction. The theory underlying it is the same, however. Because most organic compounds we wish to isolate are insoluble in water, organic solvents such as diethyl ether, dichloromethane, ethanol, and acetone are used for extracting natural products, that is, compounds found in nature. 

During the period 1820-1827, three white crystalline substances called caffein or coffein, guar-anin, and thein were isolated from green coffee beans, guarana, and tea, respectively. These substances were shown in 1838-1840 to be identical. Later, caffeine was also discovered in mate prepared from Ilex paraguariensis and kola nuts. Since then, caffeine has been shown to be a natural constituent of more than 60 plant species. 

Coffea arabiaa. - An iV-methyltransferase was isolated from the green fruits of this species (coffee) which yields caffeine as the ultimate alkaloid The methyl group of S-adenosyl-L-methionine was transferred to several xanthines however, the main route to caffeine is considered to proceed from 7-methylxanthosine via 7-methylxanthine and theobromine. 

Stimulants. From coca leaves chewed by native laborers in South America to brewed teas and coffees used across the globe, stimulants have been used since antiquity. In these essentially naturally occurring forms, coca and caffeine were long known to provide a boost of energy, focus attention, and decrease appetite. However, compared to today s refined stimulants, the effects were relatively mild. There is no clear evidence that these substances were used to treat the ancient antecedents of psychiatric illness in past cultures. The isolation of cocaine in the mid-1700s and the synthesis of amphetamine in the late 1800s dramatically increased stimulant use (and abuse) in society. 

Caffeine (1,3,7-trimethylxanthine) is the well known stimulant present in tea and coffee. In mammals the end product of metabolic breakdown of nucleic acids is urea, but in birds and reptiles it is uric acid uric acid was one of the first heterocyclic compounds to be isolated as a pure substance, for it was obtained from gallstones by Scheele in 1776. 

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