**2. Factors that influence coffee quality**

Coffee quality is influenced by factors such as the genetics, handling procedures, ecological conditions and agricultural practices. According to the International Organization for Standardization (ISO) quality is "the ability of a set of inherent characteristics of a product, system or process to fulfill requirement of customers and other interested parties" [21]. Depending on the actors in the value chain coffee quality could refer to, the variety, price of coffee, the consuming culture, tonnage or on bean physical characters and biochemical compounds in the green bean. It is the effect of cup quality that determine commercial coffee grade and not the bean size.

#### **2.1 Organoleptic cup quality**

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

130,000 metric tons in 1988 to about 45 metric tons, at present [4].

between sea-level till to an altitude that limits its vegetative growth.

**1.2 Coffee origin and diversity**

of the best quality Arabica coffees globally, but the production has declined from

Being a tropical crop, *Coffea* requires specific environmental conditions for commercial cultivation. The quality of developing bean from flowering to ripening is influenced by altitude, latitude, temperature, rainfall, soil, sunlight, wind and humidity [5–7]. Arabica coffee grows at altitude ranges of 1200–1800 meters above sea level (masl) rainfall amounts range between 400 and 600 mm per season though it is also cultivated at 400 m above sea level as long as there is no frost. Robusta coffee cultivation on the other hand is mostly grown at lower altitudes,

Compared to Arabica, Robusta coffee has smaller bean sizes, poor flavour and high bitterness content but is tolerant to coffee leaf rust disease, has resistance to white stem borer but is susceptible to drought stress [8, 9]. Due its poorer quality characteristics, Robusta coffee global market value is lower than that of *C. Arabica*.

The genus *Coffea* L has over 105 species, prevalently found in Africa and Madagascar [9, 10]. *Coff*ea belongs to the genus of the Rubiaceae family, is indigenous to Africa and is widely distributed in the tropics [11]. The centres of origin of Arabica coffee are the mountainous rain forests of Ethiopia, the western and eastern slopes of the Great Rift Valley and the Boma plateau of the Sudan. Wild species of *C. canephor* are found in Guinea, Uganda, Sudan, Northern Cameroon Southern Angola and in the Congo forests [11–13]. *Coffea liberica* Bull. Ex. Hiern, known for its resistance to diseases, insect pests, adaption to low elevation, is native to the tropical forests of Liberia and Cote de Ivoire [14] whereas *Coffea mascara* characterized by low levels absence of

caffeine is found in the forests of Madagascar Mauritius and Reunion [11–13]. The diverse existence of the genus *Coffea* in Uganda, with species such as *C. eugenioides* S. Moore, *C. excelsa* Chev and *C. spathicalyx* K. Schum., suggests that the country is the centre of origin [11, 13]. Whereas three of the genus *Coffea* species are economically important, coffee production and its industry depend on two species only; Arabica and Robusta coffee [15, 16]. The third important species of coffee, *Coffea liberica* is produced mainly in Liberia, Java, Malaysia and the Philippines but because of its low yield and poorer quality, it is used only for local consumption. With advanced breeding techniques, commercial interspecific hybrids such as Arabusta (*C. arabica* x *C. canephora*) have been developed. Blending coffees from the two species at varying ratios probably produces the preferred consumer flavours at lower costs [17]. With the exception of *C. arabica* that is tetraploid and self-fertile (2n = 4x = 44), all the other species in the genus *Coffea* are diploid (2n = 2x = 22), with gametophytic self incompatibility and therefore there exists gene flow between them and the cultivated *C. canephora* [18]. Given its allopolyploidy and self-pollinating nature, *C. arabica* is

characterized by low genetic diversity leading to a narrow genetic base [1].

Since the quality of coffee is the key determinant of prices in the world markets,

genetic improvement of Robusta coffee organoleptic cup characteristics, yield and caffeine is being undertaken by many researchers throughout the world in an attempt to match Arabica coffee characteristics in order to stabilize and sustain development in the coffee growing areas [17]. Promoting coffee liquor quality would add value, enhance income and increase the competitiveness of the world coffee prices. To sustain value, most coffee improvement programs are aiming to select and breed for cultivars with genetically superior organoleptic cup quality and

**1.3 Objectives in coffee improvement programs**

**50**

Coffee bean physical appearance is an integral indicator of cup quality, but it is the assessment by consumers through their human sensory organs and consumption habits that determine the final quality [17]. The most important attributes are; fragrance, aroma, flavour, bitterness, sweetness, saltness, acidity, mouth feel, aftertaste and cup balance. Fragrance originates from the smell of roasted or ground beans whereas aroma emanates during brewing with boiled water. Aroma helps evaluate flavour and coffee liquor brightness [22]. Flavour is described as an individual person feeling of appreciation during the tasting of the coffee brew taste, which does also include aroma. Fat stabilizes flavour compounds formed during roasting [18, 22, 23]. The undesirable coffee bitter taste in the mouth is positively correlated with the total dissolved coffee solids. High levels of saltiness and undesirable aroma are associated with high levels of potassium in Robusta coffee. Coffee brew taste is less preferred by consumers when potassium and caffeine are at lower levels [24]. Coffee medium roast has less soluble solids, a higher acid content, and more stringent aroma compared to the dark roast [25]. Roasted beans that are less bitter but have a high sweet taste is rated high by many consumers.

Acidity is regarded as the sharp and pleasing sweet to fruity/citrus taste close to the dry taste experienced on the back sides of the tongue while drinking red wine. Perceived acidity in coffee does not necessarily correlate with coffee pH, but is a result of the acids such as aliphatic, chlorogenic, alicyclic carboxylic and phenolic acids that are developed during medium and dark roasted stages. Cup acidity is influenced by high concentrations of citric acid, malic acid, and acetic acid and low concentrations of phosphorus and potassium. Acidity is thought to be influenced by phosphoric acid levels,though it may not directly correlate with perceived acidity [26]. Mouth-feel or liquor body is determined by micro fine fiber and fat content. Liquor weight is caused by micro fine fiber particles whereas texture is derived from oils extracted from ground coffee suspended in the brew. Brew colloids are formed when oils coagulate around fibers suspended in the brew. Coffee weight and texture (slipperiness) in the tongue is compared to pure water and is determined by the micro fine fiber and fat content [27]. Viscosity is caused by proteins and fibers in the brew and is normally denser in medium roasted and dark coffees than in lighter roasted beans (http://www.coffeeresearch.org/science/news.htm) [24].

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. org/vocab.asp) [28].

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 acids especially the quinic acid moiety.

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 in Robusta coffee hybrids and in commercial clones.

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

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 a full spectrum of tastes.

#### **2.2 Biochemical compounds of coffee**

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

**53**

*Organoleptic, Sensory and Biochemical Traits of Arabica Coffee and Their Arabusta Hybrids*

aroma and taste within the coffee to the biochemical composition of the bean that affects the final cup quality. These biochemical compounds act as aroma precursors and the interaction between then is key to the coffee quality of specific cultivars.

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

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

Arabica coffee is more preferred by most consumers than Robusta because it is less bitterness and has good flavour [49, 50]. These characteristics are contributed by the carbohydrates that account for more than 50% of the coffee bean dry weight [8]. During roasting, sucrose is degraded to form the anhydro-sugars and glyypxal that determine flavour and aroma [29]. These compounds react with amino acids through the Maillard reaction to form aliphatic acids, hydroxymethylfurfural, pyrazine and other furans. Furan derivatives are the principal products of decomposition of monosaccharides and higher sugars [51]. The composite roasting is regarded as essential in contributing to the final coffee flavour either being volatile or non-volatile [52]. Sucrose levels in Arabica coffee range from 5.1% to 9.4% in the dry matter of coffee beans which is higher than that of Robusta that range between

Trigonelline, a nitrogenous compound is derived from the methylation of the nitrogen atom of nicotinic acid (niacin) and an alkaloid that has a chemical formula, of C7H7NO2 and molecular weight of 137.138 g/mol [55]. Trigonelline is a major source in discriminating between Arabica and Robusta coffees during roasting [56]. Arabica has trigonelline levels ranging from 0.88% to 1.77% dmb whereas *C. canephora* species levels range from 0.75% to 1.24% dmb [53]. Trigonelline is a vitamin B6 derivative with 100% solubility in water and contributes to bitterness

*DOI: http://dx.doi.org/10.5772/intechopen.95520*

point of 178°C with pH values ranging from 6 to 9 [40].

*2.2.1 Caffeine*

disorders [48].

4–7% [53, 54].

*2.2.3 Trigonelline*

*2.2.2 Carbohydrates*

aroma and taste within the coffee to the biochemical composition of the bean that affects the final cup quality. These biochemical compounds act as aroma precursors and the interaction between then is key to the coffee quality of specific cultivars.
