The present study reports a physicochemical comparison of shade-grown and sun-grown coffee beans, under unripe, rip and roasted-ripe conditions, using electrical conductivity measurements, electron paramagnetic resonance (EPR), infrared spectroscopy (FTIR), and high performance liquid chromatography (HPLC). Moreover, the assessed physicochemical parameters were compared with organoleptic evaluations based on the Coffee Quality Institute protocol. The values found for electrical conductivity, leached potassium, and stable free radicals were respectively 29%, 31%, and 350% higher for shade-grown coffee beans, whereas polyphenol oxidase enzymatic activity was 23% lower. By contrast, FTIR and HPLC measurements identified higher chlorogenic acid and lipid contents in sun-grown coffee beans. Importantly, the sensorial grade attributed to roasted-ripe grains was 12% higher for sun-grown coffee. Our findings suggest that shade-grown coffee beans have undergone microorganismal activity and undesired fermentation during cultivation, which resulted in lower coffee quality. A correlation between a set of selected physicochemical properties and organoleptic properties was robustly established and could be used in the development of future coffee bean quality control protocols.
The genus Coffea (C) comprises at least 124 species, of which C. arabica and C. canephora (Robusta) are economically important [
Coffee quality and productivity vary according to shading density during cultivation [
In general, the occurrence of a pest such as CBB is favored under humid conditions because of shading and/or frequent rainfall [
In addition to economic effects, shading can have environmental advantages. Coffee is an important tropical commodity and is often grown in high-priority biological conservation areas. Buechley et al. (2015) studied bird communities in farms with shaded coffee plants and in moist evergreen Afromontane forest in Ethiopia [
Coffee bean quality can be ascertained by assessment of physicochemical and compositional characteristics, such as sugar content, carbohydrates, lipids, chlorogenic acid (CGA), and caffeine [
As stated above, there are conflicting results regarding the impact of sun and shade on coffee bean quality. Therefore, it is important to considering the dependence of coffee bean and beverage qualities in regard to specific environmental aspects of each production region. It is expected that environments with high pluviometric precipitation can favor the presence of microorganisms, affecting the quality of the beans submitted to different conditions of solar exposure. In the present study, coffee (C. canephora) was cultivated either with full sun exposure or under shading from rubber trees (Hevea brasiliensis); physicochemical parameter, in particular, stable free radical assessment, was compared in the two groups of plants. Sensorial investigations of the roasted coffee beans were also carried. The plants were grown during a period with frequent rainfall, coinciding with fruit maturation, in the northern region of Espírito Santo State, Brazil.
Coffee samples used in the present study were produced in a farm in the municipality of Jaguaré, Espírito Santo State, Brazil (18˚56'S, 39˚58'W, at 70 m altitude). The experiment consisted of a coffee crop grown under full sun (sun-grown coffee) with 3.0 × 1.1 m spacing (3030 plants/ha) and a coffee crop intercropped with rubber trees (shade-grown coffee) planted at 7.8 × 2.3 m (557 plants/ha). Both crops were aligned in an East/West direction; the coffee trees were planted in late 2006, while the rubber trees (H. brasiliensis) were planted in late 2007. Coffee berry harvesting was performed manually between May and July 2014, when approximately 80% of the berries were ripe. A description of the growing region microclimate is available in Araújo et al. (2016) [
The growing region has a flat topography and is subjected to a warm tropical climate [
For electrical conductivity (EC) and leached potassium (LK) analysis, two samples of 50 beans were weighed, with a resolution of 1 mg, and each sample was immersed in 75 mL distilled water. The resulting soaking liquid were taken to biochemical oxygen demand (BOD) with forced ventilation for 5 hours, at 25˚C; the EC measurements of the soaking water were obtained using a BEL W12D apparatus while the LK measurements were recorded using a Digimed NK-2002 photometer.
Determination of total sugar concentration was performed by Antrona’s method [
For assessment of polyphenol oxidase (PPO) activity, 5 g of ripe beans were powdered in liquid nitrogen and placed in 40 mL of potassium aqueous phosphate solution (0.1 M, pH 6). Subsequently, the sample was stirred for 5 min and then passed through a vacuum filter (Whatman no. 1). PPO activity was estimated by the method described by Ponting and Joslyng (1948) [
Free radicals in all samples were analyzed by electron paramagnetic resonance (EPR) using a Bruker spectrometer model Elexsys 500 equipped with an X-band
cylindrical cavity operating at 9.8 GHz (modulation amplitude/frequency set at 1 G/100 kHz and microwave power of 0.6 mW). Room-temperature EPR spectra were recorded in the field range from 344 to 360 mT, in an air atmosphere. In order to obtain an average sample spectrum, at least five beans were randomly selected from each crop. All spectra were normalized by sample mass and the resonance field, g-factor and free radical content were assessed by fitting each spectrum using a Lorentzian-type function [
CGA and caffeine content determinations were performed by high performance liquid chromatography (HPLC) using a Shimadzu chromatograph (Prominence) equipped with a Shimadzu VP-ODS Slim-pack C18 reverse phase column (250 mm long × 4.6 mm internal diameter). The hot extraction method was applied to 0.5 g of each ground coffee sample, in 100 mL of ultrapure water (Milli-Q), under constant stirring for 20 min, at 80˚C. HPLC operation conditions were 1 mL/min flux, mobile phase with methanol, water and acetic acid (20:80:1), column temperature set at 40˚C, and reading wavelength of 272 nm. Quantification was performed by the external standard method using a calibration line obtained from chromatogram peak areas at 272 nm from the CGA standard solution 5-caffeoylquinic (5-CQA) and caffeine (1,3,7-trimetilxantina) from Sigma-Aldrich [
Fourier transform infrared spectroscopy (FTIR) measurements were performed using an Agilent Cary 630 spectrometer operating in ATR (attenuated total reflectance) mode with a diamond crystal, 60 scans, and resolution of 2 cm−1. Ten measurements were recorded for each sample and the spectral average was subtracted from a seven point baseline before normalization.
Statistical analysis was performed using the GENES software package with a completely randomized design [
Sensory quality of the beverage (cup test/taste) was evaluated by a company specialized in Robusta cup tests using criteria established by the Coffee Quality Institute [
The estimates for the values of the various tested parameters from ripe beans are shown in
For shade-grown coffee samples, EC and LK values were 29% and 31% higher compared with sun-grown coffee samples. As reported by Bellé et al. (2014), LK values are related to the membrane damages; the increase in the EC is expected since the leached potassium (K+) promotes the increase of cations in the solute [
Growth conditions | |||
---|---|---|---|
Sun-coffee | Shade-coffee | CV (%) | |
TS (g/kg) | 63.2 ± 3.3a | 47.2 ± 2.5b | 5.28 |
EC (µS/cm´g) | 20.5 ± 3.4a | 26.3 ± 4.4b | 17.02 |
LK (g/kg) | 0.13 ± 0.03a | 0.17 ± 0.03b | 22.37 |
PPO (µmol/min/g) | 35.6 ± 1.4a | 27.3 ± 1.1b | 3.99 |
a,bAverages followed by different letters on the same row differ statistically by Tukey’s test (P < 0.05).
Intercropping of C. canephora with rubber trees provides dense shading and promotes changes in microclimate conditions that, in combination with frequent rainfall, reduce water evaporation while keeping more moisture in the fruit for a longer period of time [
Our findings suggest that the higher humidity environment experienced by shade-grown coffee promoted an increase in formation of stable free radicals. Yeretzian et al. (2012) reported that free radical content during storage could increase due to oxidative processes in the surface fraction exposed to air [
The highest content of free radicals was observed in unripe beans and reflects their metabolism and chemical composition, which are different from those of ripe beans. Montavón et al. (2003) reported that unripe beans are relatively more
Item/beans types | Intensity (a.u) | |
---|---|---|
Shade-grown | Sun-grown | |
Ripe | 0.64 ± 0.7 | ND |
Unripe | 5.0 ± 0.8 | 1.4 ± 0.3 |
Roasted-ripe | 1.4 ± 0.3 | 1.0 ± 0.2 |
ND: non-detected signal.
sensitive to oxidation and that oxidation defense mechanisms become more efficient as the beans mature [
Typical FTIR spectra of coffee beans, obtained for all the analyzed samples, are shown in Figures 3(a)-(c). Absorption bands in the 900 to 1450 cm−1 region are associated with C-H, C-O, C-N, and P-O vibrations [
An FTIR band peaking around 1745 cm−1 is characteristic of carbonyl (C=O) stretching; this chemical bond is found in acids, esters, and other classes of
organic compounds associated with lipids [
The FTIR technique allows qualitative evaluation of chemical compounds in the coffee beans samples. However, a quantitative evaluation of caffeine and 5-CQA contents, corresponding to 76% - 84% of the total CGA, was obtained using the HPLC technique [
Bean type | Compost (g/kg dry basis) | Shade-grown | Sun-grown |
---|---|---|---|
Ripe | 5-CQA* | 44.8 ± 3.3a | 49.3 ± 3.6b |
caffeine** | 19.3 ± 1.0a | 17.2 ± 0.9b | |
Unripe | 5-CQA | 37.3 ± 2.7a | 45.0 ± 3.3b |
caffeine | 21.3 ± 1.1a | 19.7 ± 1.0b | |
Roasted-ripe | 5-CQA | 6.9 ± 0.5a | 15.0 ± 1.1b |
caffeine | 19.8 ± 1.0a | 19.8 ± 1.0a | |
CV (%) | *7.32 | **5.42 |
a,bAverages followed by different letters on the same row differ statistically by Skott-Knott’s test (P < 0.05).
Both FTIR and HPLC results consistently showed that CGA/5-CQA contents were higher for sun-grown coffee. Importantly, the HPLC analysis showed that the caffeine content of sun-grown coffee was at most equal to that in shade-grown coffee. Therefore, the highest FTIR spectra intensity observed at 2850 cm−1 in sun-grown coffee might be attributable to lipids only. It is generally considered that a higher lipid content implies better quality beans [
Contradictory conclusions have been reached in previous studies of the correlation between sun exposure and CGA levels. In some cases, CGA was found to be favored by shading [
The average value of the grades attributed to the roasted-ripe beans was 77.90 and 87.27 for shade-grown coffee and sun-grown coffee, respectively. This result confirms the beverages made with sun-grown coffee beans had both the best flavor and smell.
The results of the present study show that sun-grown coffee (C. canephora) produced in the Jaguaré city region, Espírito Santo State, Brazil, was of better quality than shade-grown coffee intercropped with rubber trees under periods of rainfall. From comparisons with the literature, which show different results depending on the set of parameters studied, we conclude that this is a specific characteristic of the studied site. PPO activity and the values obtained for EC and LK suggest that shade-grown coffee samples suffered damage due to the action of insets and microorganisms, thus inducing undesirable fermentation processes. These events are also responsible for higher amounts of stable free radicals observed in shade-grown coffee. Furthermore, the superior quality of sun-grown coffee, as indicated by sensorial analysis, was associated with higher lipid, CGA, and total sugar contents. The present report succeeded in correlating different physicochemical data, recorded from a range of experimental techniques, while evaluating the organoleptic quality of coffee beans grown under different shade conditions and roast processes. We envisage that the data analysis provided in the present study will contribute to advancing the use of physicochemical data in establishing protocols for future coffee bean quality control.
The authors acknowledge financial support from CNPq and FAPES Brazilian Government Agencies and also the Laboratório de Ciências Físicas, from Universidade Estadual Norte Fluminense, Rio de Janeiro, Brazil.
There are no conflicts to declare.
Alves, A.L., Pessoa, M.S., de Souza, P.E.N., Partelli, F.L., Moscon, P.S., da Silva, E.C., Guimarães, A.O., Muniz, E.P., Pinheiro, P.F., Borém, F.M. and Morais, P.C. (2018) Influence of Environmental and Microclimate Factors on the Coffee Beans Quality (C. canephora): Correlation between Chemical Analysis and Stable Free Radicals. Agricultural Sciences, 9, 1173-1187. https://doi.org/10.4236/as.2018.99082