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The cultivation of coffee embodies an agro-productive activity that contributes to invigorate the world economy (Ponce et al. 2016). According to the International Coffee Organization (OIC 2016), it is one of the most valuable primary products as a source of foreign exchange for developing countries.
In Ecuador, coffee cultivation has importance in the economic, social and environmental orders. In economic terms, it constitutes a source of income for the actors of coffee chains. Socially, these chains involve many ethnic groups and peoples in 23 out of the 24 provinces, and environmentally, they are basically cultivated in agroforestry systems, which contribute to environment conservation (Duicela 2016). This crop occupies an area of 199,215 ha, from which 68 % corresponds to Arabica species (Coffea arabica L.) and 32 % to the robusta (C. canephora Pierre ex Froehner). Loja province occupies the second place, with a surface of 29,552 ha and an annual production of 180,320 qq, which represents 13.5 % of the national total (COFENAC 2013).
The benefit of coffee is achieved by two methods. The first is the dry processing, which consists of drying and fermenting coffee under the sun, and the second is the humid benefit that implies the separation of the pulp and the mucilage by mechanical means and, then, ferment and wash the grains (Noriega et al. 2009 and FAO 2011). The pulp is the external part of the fruit, constituted by the epicarp (outer red layer) and the mesocarp (hyaline soft tissue layer) (Suárez de Castro 1983). It is the first residue obtained from the humid processing of coffee cherries and may represent between 40 and 43 % of the fresh weight of the whole fruit (Bressani et al. 1972, Ramírez 1999 and Montilla et al. 2008).
Several authors (Bressani et al. 1972, Ramírez 1999, Morgan 2003, Munguía 2015 and Pinto et al. 2017) agree that coffee pulp has an appreciable nutritional value that could be used in animal feed. Thus, these authors mention a dry matter content from 20 to 25 %, crude protein from 8 to 12%, crude fiber from 20 to 25 % and ash from 9 to 11 %. However, its chemical composition may vary depending on factors such as agroecological conditions, variety, crop management and processing method (Romero 1994). Therefore, it is necessary to deepen studies to evaluate how it behaves in the region. That is why the objective of this study was to determine the variability in the bromatological composition of fresh coffee pulp among cantons of Loja province.
Materials and Methods
Delimitation of the study area. From the 15 cantons that grow coffee, six were selected (Espíndola, Zosoranga, Puyango, Chaguarpamba, Quilanga and Loja), considering those with higher production and that are distributed in the four cardinal points. In each of these cantons, three pulping plants belonging to the coffee producer organizations were selected (figure 1).
Figure 1 Map with the selected cantons for the study of chemical characterization of coffee pulp in Loja province
Table 1 shows climate characteristics of the cantons selected for the study.
Characterization of production systems. To get a general overview of the coffee production systems in the selected cantons, 180 surveys were applied to producers of 18 coffee organizations, on aspects related to coffee variety, crop management and method of processing. The information collected allowed to relate the incidence of these factors in the bromatological composition of the pulp. In addition, to check the field information, the latest publications of institutions and organizations related to the sector were reviewed, such as Ministry of Agriculture, Livestock, Aquaculture and Fisheries (MAGAP), National Coffee Council (COFENAC), and some others.
Table 1 Climate characteristics of the cantons selected for the study
Source: INAMHI 2011
Creation: the author
Sample taking. In each selected plant, three samples (1 kg) were obtained, by stratified sampling, for a total of 54 samples, placed in properly identified polyethylene containers and taken to the bromatological laboratory of the National University of Loja for their analysis.
Laboratory analysis. Samples were dried in an oven at 65 ºC for 48 h, ground and sub-samples of 100 g were taken by the quartering method, for further bromatological analysis. The content of dry matter (DM), organic matter (OM), ash (A), ether extract (EE), crude protein (CP), crude fiber (CF) and nitrogen-free extract (NFE) was determined according to standard methodology of the AOAC (2005); while the neutral detergent fiber (NDF) and cellular content (CC) by the procedure of Van Soest et al. (1991).
Statistical analysis. With the results obtained in each of the indicators, an analysis of variance was carried out with a random block design, considering the origin as treatment and the processing plants as replications. In the necessary cases, Duncan (1955) test was applied to determine the difference between means. Data processing was performed using the Insfostat statistical package (Di Rienzo et al. 2012).
Results and Discussion
Production and quality of coffee is the result of the combination of genetic and environmental factors, such as botanical variety, topographic situation, climatology, soil, crop management and benefit method (Cañas 2015). The existing studies have been oriented more to performance and organoleptic quality, than to bromatological composition. Therefore, it is difficult to relate the available scientific literature with the composition of the pulp based on these factors.
After the surveys were processed, it was stated that 100% of the producers cultivate Arabian coffee, 95 % of them use the typical variety, which is in accordance with the Ministry of Agriculture, Livestock, Aquaculture and Fisheries of Ecuador (MAGAP 2014), the National Coffee Council (COFENAC 2013) and Duicela et al. (2017). Likewise, several studies (CENICAFE 2011, Cañas 2015 and Duicela et al. 2017) pointed out that, among the varieties of Arabian coffee, there are no variations in their organoleptic quality, so it could be deduced that this factor does not affect the bromatological composition of pulp.
Jiménez and Massa (2015) stated that Coffea arabica and its varieties have a wide adaptability to different ecosystems with altitudes ranging from 1,000 to 2,000 mosl, temperature from 15 to 24 °C and precipitations of 1,000 to 2,000 mm. The study area is located in the area known as Coffee Belt and its climatological characteristics (Table 1) are among the ranges indicated, making it suitable for the cultivation of this species.
On the other hand, Enríquez and Chamorro (2014) affirm that latitude and altitude influence directly on climate characteristics like temperature, solar radiation, rainfall distribution, relative humidity, and some others. Within climate factors, temperature regulates directly all the biological and metabolic processes of the plant, such as photosynthesis, flowering, fructification, maturation, and others. Several authors (Soto et al. 2001, Arcila et al. 2007 and Cañas 2015) stated that a mean temperature of 25 °C is considered as optimal for most of the biological phenomena occurring in the coffee plant. The study area has temperatures close to this value.
Crop management is carried out traditionally in 100 % of the farms, with minimum maintenance tasks like annual cuttings, manual control of weeds, little or no chemical and/or organic fertilization and without irrigation, which is verified with reports of MAGAP (2014) and COFENAC (2013). In this regard, several authors (Vega 2013 and Enríquez and Chamorro 2014) affirm that cropping practices influence more on performance than on product quality.
Finally, the benefit method in all the studied plants is by the humid way, with mechanized equipment, which coincides with that indicated by the organisms mentioned above. These results eliminate the sources of variation related to variety, crop management and processing method.
Table 2 shows that no statistical difference was detected in the bromatological composition, among the studied cantons.
Dry matter values were similar to those reported by Fonseca (1991), Munguía (2015) and Noguera and Posada (2017), higher than 17.89 % indicated by Morgan (2003), but less than 23.3 % and 24.55 % reported by Bressani et al. (1972) and Pinto et al. (2017), respectively. The variation among authors could be due to the edaphoclimatic conditions of coffee systems under study and to the used processing methods. On the other hand, it is known that DM contains nutrients that the plant synthesizes from soil and environment. However, when the process of formation and maturation of fruits is slower, the concentration of substances is favored, and vice versa. This phenomenon is directly influenced by climatic factors.
Content of organic matter is an indicator of the nutritional value of a food. In this study, a mean value of 89.55 % was observed, similar to that reported by Pinto et al. (2017). Ashes, that largely define mineral content, in this study, was in the order of 10.45 %, similar to that informed by Bressani et al. (1972), Fonseca (1991), Morgan (2003); Figueroa and Mendoza (2010), Munguía (2015) and Yoplac et al. (2017). Like DM, the content of OM and ashes, the variability between the results of other authors also depend, to a large extent, on the previously mentioned factors.
Ether extract of coffee pulp is relatively low. In this study, a mean value of 2.23 % was observed, similar to that reported by other authors (Bressani et al. 1972, Figueroa and Mendoza 2010, Munguía 2015 and Yoplac et al. 2017). This component could be related to the presence of lipid substances that are forming cell membranes and are the result of energy metabolism of the plant (Soto et al. 2001).
Several authors (Bressani et al. 1972, Ramírez 1999, Morgan 2003, Noriega et al. 2009, Munguía 2015 and Pinto et al. 2017) highlight the appreciable content of crude protein of coffee pulp, which may vary from 8 to 14 %. In this study, crude protein reached a mean value of 10.02 %, similar to results of Fonseca (1991), Bautista et al. (2005) and Figueroa and Mendoza (2010).
Most of the protein is found in the cellular content, product of the synthesis of amino acids from nitrogen compounds within soil. This way, it can be said that its content depends directly on nitrogen availability. Although the soils of the area are not periodically fertilized, because they are agroforestry systems that can accumulate large amounts of organic matter. In this regard, Enríquez and Chamorro (2014) point out that most coffee soils have good physical properties (texture, structure, depth, aeration, humidity retention, and some others) and chemical properties (pH between 5.5 and 6.5), good capacity of cation exchange, and, therefore, good nutrient availability.
It is known that about 60 % of total nitrogen of the pulp is found as true protein, to which is attributed largely its performance in animal feed. The remaining 40 % is non-protein nitrogen, which includes caffeine, trigonelline, niacin, purines, pyrimidines, and inorganic nitrogen (Bressani et al. 1978). According to Di Marco (2011), a food can be considered of good quality when it contains less than 50 % of NDF and more than 15% of CP, which allows to classify coffee pulp as a food of particular nutritional value.
Crude fiber values (from 18.5 to 19.7 %) agree with the results reported by Bressani et al. (1972), Morgan (2003) and Yoplac et al. (2017). However, they are inferior to the results obtained by Fonseca (1991) and Figueroa and Mendoza (2010), with 25.65 and 22.7 %, respectively. Cellular content and NDF coincide with that reported by Noguera and Posada (2017), but it differs from those obtained by Yoplac et al. (2017).
NFE content was 58.06 %, similar to that reported by Noriega et al. (2009) Figueroa and Mendoza (2010). However, Bressani et al. (1972), Fonseca (1991) obtained lower percentages (50.8 and 51.9 %), while Bautista et al. (2005) reported a content of 66.9 %. The variability found in the literature could be due to the fact that these values could be affected by the benefit method, which was not specified in these studies. In the case of the benefit by the humid way, variable amounts of water are used that can favor the dragging of these substances. At the moment the ecological benefit does not use water for the separation of the pulp, consequently a great part of sugars and mucilages are preserved.
Synthesis of carbohydrates and their accumulation in the different structures of the fruit occurs as a result of photosynthesis, a process that has a direct influence of environmental conditions, especially solar radiation, temperature, precipitation and nutrient availability (Soto et al. 2001 and Arcila et al. 2007). Fiber compounds are found forming the cell wall and it could be affirmed that their content in the pulp depends, to a great extent, on the climate conditions that regulate the energy metabolism of the plant (Cañas 2015). However, the low variability in the nutrient content could be explained because several producers concur with the same benefit center and, in the pulping process, residues (pulp) are mixed, which hides the incidence of agroecological factors in the final product.
Food composition is a determining aspect for its inclusion in the diet of any species and animal category. The values of CC, NDF and CP present in the coffee pulp suggest that it is a residue that could be used in animal feed, and it could even be of superior quality to others that are used in animal rations (Morgan 2003). However, for its inclusion in the formulations it would be necessary to evaluate other economic and logistical aspects.
It is concluded that fresh coffee pulp has no variation in its bromatological composition among the studied cantons and the values are within the ranges reported by the existing literature. Therefore, for purposes of selection and processing for the purpose of use in animal feed, economic and logistic criteria could be considered.
