*2.2.1 Caffeine*

*Mineral Deficiencies - Electrolyte Disturbances, Genes, Diet and Disease Interface*

org/vocab.asp) [28].

acids especially the quinic acid moiety.

in Robusta coffee hybrids and in commercial clones.

low body, sweet fruits, floral and dry wine taste [37].

Taste is normally perceived as the feeling in the mouth after sipping the beverage whereas aftertaste is perceived as the lingering remnant sensation experienced at the back of the throat after swallowing but often changes over time [24]. In a balanced cup, a complementary synergistic combination of flavor, aftertaste, mouth feel and bitter/sweet aspect ratio occurs when the four attributes are in equal intensities [24]. Soft, pleasing and delicate taste derived from acidity and sweet coffee is obtained from fruit acids, high sugars levels and chlorogenic acids (http://www.ico.

There are four major reactions that determine to a great extent of the aroma of roasted beans. Firstly is the Maillard reaction that occurs between nitrogen containing substances such as amino acids, proteins, trigonelline and serotonine with carbohydrates such as sugars. Degradation of individual amino acids, particularly sulphur amino acids, hydroxy-amino acids and praline is the second reaction. Thirdly, sucrose degrades to aliphatic acids compounds and caramel- like substances that contribute to flavour either as volatile aroma compounds, or nonvolatile taste compounds [29–31]. The fourth reaction is the degradation of phenolic

Roast bean fat has been shown to be positively significantly correlated with aroma, body, acidity, flavor, aromatic intensity and quality, overall judgment and preference [18, 19, 23, 32, 33]. Higher bean yields produced under favourable environmental conditions have reduced acidity. Caffeine content has been found to be negatively, significantly correlated with cup quality attributes although, [34, 35] reported positive correlation coefficients between preference and acidity and aroma

Specialty coffee markets demand distinctive cup attributes such as homogeneity, regularity and reliability. Organoleptic cup attributes have to be stable, for the roaster and the consumer [17]. Evaluation of organoleptic cup attributes and other quality parameters using various scientific methods reveal varietal differences and similarities in genetic traits. Genotypic as well as environmental effects influence cup quality that is determined further by the way cherries and beans are picked, shipped and roasted [36]. Varying cup differences that result from genotypic differences contribute greatly to market value, as is the case for Central America consumers who prefer traditional cultivars (Bourbon, Caturra, Catuai, Pacamara) to newer cultivars derived from the 'Hybrid of Timor' hybridization. In Uganda, where *C. canephora* has evolved over years and traditionally cultivated as a culture, farmers and buyers have been less inclined to consume products of Arabusta hybrids selected on quality and other desirable agronomic traits even when they have resistance to the coffee wilt disease. Genotypes show different cup qualities under different environments. For instance, Blue Mountain genotype, has superior liquor quality when grown under Latin American farmer conditions than when grown by East African farmers [17]. Coffee from Africa tend to have high acidity,

Coffee from Asian countries such as India, Java, Sumatra, Sulawesi and Papua New Guinea is perceived to have low acidity, high body and smoothness, earthy and spice flavor characteristics [38] whereas Latin America countries such as Brazil, Columbia, Costa Rica, Guatemala, Nicaragua, Mexico, El Salvador, Peru, Panama and Honduras produce coffee with medium acidity and body, intense aroma but has

The interaction of caffeine, oil, sucrose, chlorogenic acids, and trigonelline is what determines the final cup quality of coffee [39]. Organoleptic factors such as

**52**

a full spectrum of tastes.

**2.2 Biochemical compounds of coffee**

Caffeine (1, 3, 7-trimethyl xanthine), is the main alkaloid found in its natural form in leaves, seeds or fruits in 63 different plant species [40]. This chemical occurs in natural form in leaves, seeds, or fruits of 63 different plant species [40]. The biological role of caffeine in plants has not been clear, although it has been suggested that caffeine protects the plant from pests and that t has an allelopathic effect on seeds affecting their germination [41]. Caffeine is an odorless, white powder with a molecular weight of 194.19 g, melting point of 236°C, sublimation point of 178°C with pH values ranging from 6 to 9 [40].

Robusta coffee has a higher content of caffeine than that of Arabica, with an average value of 2.2%, whereas Arabica has about 1.2% with a range of 0.6 to 1.9% [42, 43]. Liberica has the lowest caffeine content of 1.35% of caffeine whereas Arabusta hybrids follow closely at about 1.72% [44]. Genetic and environmental factors are the major causes of variations of caffeine content in the coffee beans. Different levels of caffeine content in the coffee bean cause various physiological and psychological effects in humans [45–47]. About 80% of administered caffeine (1,3,7-trimethylxanthine) is metabolized by demethylation to paraxanthine (1,7- dimethylxanthine) via liver *cytochrome* P-450 1A2, and about 16% is converted to theobromine and theophylline, (3,7- and 1,3-dimethylxanthine, respectively) [47]. Higher levels of caffeine consumption have been associated with improved performance in human reaction time, verbal memory, and visuospatial reasoning but may also cause heart disease, kidney malfunction, and asthma among other disorders [48].
