Coffee bitter taste

C8H10N4O2. An alkaloid occurring in tea, coffee and guarana, from which it may be prepared by extraction, It is also manufactured by the methylation of theobromine and by the condensation of cyanoacetic acid with urea. Crystallizes with H2O or anhydrous from organic solvents. M.p. (anhydrous) 235"C, sublimes at 176 C. Odourless, and with a very bitter taste. Caffeine acts as a stimulant and diuretic, and is a constituent of cola drinks, tea and coffee. 

Alkaloids are compounds that contain nitrogen in a heterocyclic ring and are commonly found in about 15-20% of all vascular plants. Alkaloids are subclassified on the basis of the chemical type of their nitrogen-containing ring. They are formed as secondary metabolites from amino acids and usually present a bitter taste accompanied by toxicity that should help to repel insects and herbivores. Alkaloids are found in seeds, leaves, and roots of plants such as coffee beans, guarana seeds, cocoa beans, mate tea leaves, peppermint leaves, coca leaves, and many other plant sources. The most common alkaloids are caffeine, theophylline, nicotine, codeine, and indole... 

The roasting of foods such as malt or coffee can result in bitter-tasting compounds however, until recently little was known about the chemistry of any compounds formed in the MaiUard reaction that could be responsible for such tastes. Frank et al. [33] identified a new class of compound, l-oxo-2,3-dihydro-lH-indolizinium-6-oxalates, from reaction mixtures containing xylose, rham-nose and alanine (Fig. 12.1). A number of such compounds have been reported and they appear to have low taste thresholds (below 1x10" mmol/L). 

Fruit juices can be deacidified with a weak base anion-exchange resin. Removal of compounds which cause a bitter taste is a more popular application (26,27). It is accomplished with resins that have no ion-exchange fimctionality. In essence, they are similar to the copolymer intermediates used by resin manufacturers in the production of macroporous cation and anion exchangers. These products are called polymeric adsorbents. They are excellent for removal of limonin [1180-71-8] and naringin [1023647-2], the principal compounds responsible for bitterness in orange, lemon, and grapefruit juices. The adsorbents are regenerated with steam or alcohol. Decaffeination of coffee (qv) and tea (qv) is practiced with the same polymeric adsorbents (28). 

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. 

The bitter taste in foods is not always disliked by people. There are unexpectedly many cases in which a bitter taste has a positive effect of adding richness to food such as beer, coffee, and green tea. In these cases, if the bitter taste is eliminated or replaced by other compounds, the intrinsic value of the food might be completely lost. Therefore, the bitter taste is essential for these foods. On the contrary, however, methods to eliminate the unpleasant bitterness of cheese and grapefruit have also been investigated. These efforts also contribute to the progress in research on the bitter taste.118... 

Despite the supposed universality of bitter taste rejection, many commonly consumed foods and beverages such as fruits, tea, coffee, chocolate, and alcohol have bitterness as a major sensory attribute which, in the overall taste profile of a food, is often appreciated by the consumers. Some alkaloids are certainly responsible for the bitter taste of known food the taste threshold is available only for atropine (0.1 mM), cocaine (0.5 mM), and morphine (0.5 mM) (Table 3.1). 

No. Coffee has a bitter taste of its own which would probably cover the taste of the strychnine. ... 

Caffeine is a bitter-tasting compound found in coffee, tea, cola beverages, and chocolate. Caffeine is a mild stimulant, usually imparting a feeling of alertness after consumption. It also increases heart rate, dilates airways, and stimulates the secretion of stomach acid. Caffeine is an alkaloid, a naturally occurring amine derived from a plant source. In Chapter 25 we learn about the properties and reactions of amines. 

Caffeine gives coffee its bitter taste and some people a feeling of restlessness. 

Properties—Caramel is found in commerce as a concentrated solution or in solid masses or in powder as coffee essence. The solid forms an amorphous, reddish brown, brittle mass which is porous aud highly deliquescent. It is completely soluble in water and partly soluble in alcohol. It has a bitter taste due to the presence of assamar, and is not fermented by yeast. Its melting-point is about 135° C. It reduces the salts of the heavy metals and is precipitated from aqueous solutions by baryta and by neutral lead acetate, as well as by paraldehyde in alcoholic solution. 

It is described as having a warm, but nauseating, sweet-herbaceous odor with mildly tobacco-like notes and moderate tenacity, but in extreme dilution it displays a sweet-herbaceous, quite pleasant odor (Arctander, 1967). According to Winter et al. (1977c), it imparts an astringent and bitter taste to a neutral soluble coffee beverage at a concentration of 40 ppm. 

Tea leaves contain more caffeine than the coffee bean, but because a relatively smaller quantity of leaves is used in preparing tea, this beverage contains slightly less caffeine than does coffee. In green tea there is a considerable quantity of a volatile oil that also passes into the infusion, and the flavor of black tea also arises from volatile substances (theon). Both black and green tea contain about 7% tannic acid, but this is extracted only slowly. The bitter taste in tea that has been prepared too long is due to the tannic acid. 

Caffetannic Acid, ChHibOt, caffetannin, is an example of a tannin derived from protocatechuic acid. It occurs in coffee berries. When fused with potassium hydroxide, it yields protocatechuic acid and acetic acid, and when heated alone it gives pyrocatechol. It is not affected by a solution of gelatin. It does, however, form an insoluble compound with a protein present in milk. It is for this reason that the bitter taste of tea,... 

Davis, R. G., 1978, Increased bitter taste detection thresholds in Yucatan inhabitants related to coffee as a dietary source of niacin, Chem. Senses Flav., 3 423. 

Even though coffee itself is acidic overall, it oontains some naturally occurring bases (such as caffeine) that give it a bitter taste. 

As we saw in Chapter 5, an acid is a compoimd characterized by its sour taste, its ability to dissolve some metals, and its tendency to form ions in solution. A base is a compound characterized by its bitter taste, its slippery feel, and its tendency to form OH ions in solution. Some common acids and bases are listed in Table 7.3. Acids and bases are also foxmd in many everyday substances. Foods such as lemons, limes, and vinegar contain acids. Soap, coffee, and milk of magnesia all contain bases. 

The interaction between the molecules in coffee that taste bitter and the taste receptors on the tongue is caused by intermolecular forces—attractive forces that exist between molecules. Living organisms depend on intermolecular forces not only for taste but also for many other physiological processes. For example, in Chapter 19, we will see how intermolecular forces help determine the shapes of protein molecules—the workhorse molecules in living organisms. Later in this chapter—in the Chemistry and Health box in Section 12.6—we learn how intermolecular forces are central to DNA, the inheritable molecules that serve as blueprints for life. 

Bases are less common in foods than acids because of their bitter taste. A Sour Patch Kid coated with a base would never sell. Our aversion to the taste of bases is probably an adaptation to protect us against alkaloids, organic bases foimd in plants (see the Chemistry and Health box in Section 14.9). Alkaloids are often poisonous—the active component of hemlock, for example, is the alkaloid coniine—and their bitter taste warns us against eating tirem. Nonetheless, some foods, such as coffee, contain small amounts of base (caffeine is a base). Many people enjoy the bitterness, but only after acquiring the taste over time. 

Like acids, bases can be identified by their properties. When washing your hands with soap, you experience one of the properties of bases, their slippery feel. Soap is basic and, like all bases, feels slippery on the skin. If you have ever tasted soap, you know another property of bases, their bitter taste. The bitter taste of coffee, milk of magnesia, and some medicines is due to their base content. 

The bitter taste of coffee is due partly to the presence of caffeine, a base. 

Some of our most important medicinal drugs have originated from plants. Lewis and Clark took Peruvian bark, or cinchona bark, with them as a medicine on their 1804 expedition from the eastern United States to the Pacific Coast and back. The bitter essence of cinchona bark is quinine, an amine drug that has been used to combat malaria. Quinine is responsible for the bitter taste of tonic water, a carbonated beverage (Figure 16.4). Some other amines that come from plants are caffeine (from coffee, a stimulant), atropine (from the deadly nightshade, used to dilate the pupil of the eye for eye exams), and codeine (from the opium poppy, used as a painkiller). 

Caffeine and the quinic acid lactones listed in Table 21.13 are the bitter substances in the coffee drink. Accordingly, these lactones are almost exclusively responsible for the bitter note of a decaffeinated coffee drink (Table 21.13). Although the concentrations of the lactones III-VII, IX and X in the drink are lower than their threshold concentrations (cf. Table 21.13), they still additively contribute to the bitter taste (cf. 5.1.2 additive effect). 

Frank, O., Zehentbauer, G., Hofmann, T. Bioresponse-guided decomposition of roast coffee beverage and identification of key bitter taste compounds. Eur. Food Res. Technol. 222,492 (2006)... 

A bitter taste is desirable for some foods, where it is a typical taste. Examples include grapefruits, chicory leaves, cocoa, coffee, beer and tonic drinks. However, sometimes a bitter taste is considered undesirable (ofif-flavour) and the affected foods can have an unacceptable taste and can be even inedible (such as oranges, carrots... 

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