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Friday, 2015-Apr-10
The Science Behind a Cup of Coffee
1. Introduction
This lecture aims to present results obtained from different lines of research
developed at Federal University of Lavras to improve coffee quality.
Frequently people ask a number of questions like:
• Does coffee quality vary from one year to another?
• What causes differences in the speed of fruit ripening?
• Is it possible to correlate sweetness of the ripe fruit with cup profile?
• Does coffee quality vary according to exposure of the slope to sunlight?
• Why is natural coffee sweeter than fully washed?
• Do sugar molecules move from the mucilage to the seed during coffee
drying?
• What is the effect of temperature and processing on coffee quality?
• Do cells lose their integrity during drying?
Highlights of the interaction between environment and quality, and also the effect of
drying and processing on final coffee quality is discussed. General information about
the effect of genotype on quality is discussed as well using recent scientific evidence.
2. Environment, processing & Quality
Quality of commodity coffee varies from one year to the next. It depends mainly on
the environmental conditions and coffee processing technology. The occurrence of
defective beans is a result directly related to lack of technology, which leads to a
defective and low quality beverage.
Data collected from regional coffee cooperatives in five consecutive crop seasons
demonstrate a spatial distribution of the quality of the commercial crop.
Figure 1. Spatial distribution of the quality of commercial coffee samples.
Friday, 2015-Apr-10
All these changes in coffee quality are exactly what the market focuses on. But, what
are the reasons for these changes? Generally, the answer is variation in climatic
conditions and lack of technology and knowledge.
However, does the same thing happen to specialty coffees if only ripe fruits are
harvested and high technology is applied during the post-harvest ?
To answer this question and help us to improve our understanding of space and time
distribution of coffee quality, we have conducted an interesting project in the south of
Minas Gerais over the last eight years.
Samples of coffee (Coffea arabica L.) were collected over three harvest seasons
(2009/10, 2010/11 and 2011/12) from commercial farms located in Minas Gerais,
Brazil.
The area of coffee cultivation was stratified into three altitude classes and two slope
exposure groups, resulting in a combination of six environmental variables.
Altitude
Above 1200 m
Between 1000 m
and 1200 m
Bellow1000 m
Figure 2. Environmental stratification
For each environment, only ripe fruits were harvested from two genotypes: Yellow
Bourbon (yellow fruits) and Acaiá (red fruits).
Sensorial and chemical analyses were performed. To analyze the sensory data, two
different multivariate statistical models were used: logistic regression and
correspondence analysis. This result demonstrates that coffee quality depends on the
interaction of environment and genotype. However, we were able to describe the main
sensorial attributes that characterize the beverage of each genotype according to its
environment and processing.
The chemical analyses led us to describe different compounds that were able to
separate all samples according to the processing method. Chemical compounds like
L-valine, L-isoleucine, Pyroglutamic acid,fructose, L tyrosine and L-allo inositol were
more abundant in natural coffee than in parchment coffee.
Processing
L-valine
L-isoleucine
L-aspart ic acid
Pyroglut amic Acid
Mucic acid
Fruct ose
L-t yrosine
Galact inol
L-allo
inosit ol
Figure 3. Data from GC MS (Taveira, 2014)
3. Highlights of Coffee Ecophysiology and Quality
A comparative physiological pattern among coffee grown under different altitudes
was performed. We aimed to identify the behavior of growth and development of the
coffee tree through analysis of gas exchange, carbohydrate metabolism, lipid
peroxidation and quantification of the levels of hydrogen peroxide, as well as the
quantification of non-enzymatic antioxidant ascorbate. Coffee trees grown at high
altitude has lower photosynthetic, respiratory and photorespiratory rates than coffee at
low altitudes.
A s c o r b i c ac i d
ROS
1 ,2 0 0 m
Met ab o l i sm
Ph o t o s y n t h e si s
H O
2
2
L i p i d o x i d at i o n
ROS
Car b o h y d r at e
1 ,0 0 0 m
Figure 4. Comparative physiological pattern among coffee under different altitudes
(adapted from Silveira, 2014).
Friday, 2015-Apr-10
However, higher altitude coffee has more accumulation of carbohydrates combined
with a lower formation of reactive oxygen species and higher content of ascorbate.
4. Interference of drying and processing on coffee quality
In recent years, we have observed that more and more people, technicians and
producers have understood the importance of drying and processing for coffee
quality.
In this section, I present results from studies about the effect of drying and processing
on coffee quality.
The activity of fungi and enzymes such as polyphenol oxidase and peroxidase have
been associated with loss of integrity of the cell membrane, and are related to phenol
defective flavor. However, endosperm cells also lose their integrity during coffee
drying. To elucidate how and when cells lose their integrity, parchment coffee was
dried with heated air at 40, 50 and 60 °C. After drying, 10 seeds were selected at
random and analyzed using optical and electron microscopy.
Figure 5. Optical and electron microscopy of coffee seed dried at 40 and 60ºC
(Borem et al, 2008).
Coffee beans dried at 40ºC had the integrity of the plasma membrane preserved,
keeping the oil bodies uniformly distributed into the cell. However, drying at 60ºC
leads to coalescence of the vesicles and of the membranes. Although this is well
known, the question is when does cell rupture occur?
Scanning electron micrographs were used to study cell contraction. While solar
drying and drying with heated air at 40ºC of washed coffee allows slow and gradual
cell contraction, drying with heated air at 60°C causes contraction and expansion of
the endosperm cells for both natural and washed coffee. The most relevant cell
expansion occurs between the moisture contents of 30 and 20 %.
Friday, 2015-Apr-10
Different chemical or biochemical events may occur after cell rupture, like oxidation
and enzymatic or non-enzymatic reactions.
Metabolomic analysis showed that the metabolite profile of coffee changes during
drying.
The major differentiation occurs at moisture content above 30%, and the final
metabolomic profile depends on the drying process and temperature.
For the natural process, drying at 60°C resulted in a metabolomic profile different
from sun drying and drying at 40°C.
Finally, I discuss what coffee is most sensitive to damage in drying.
Physiological and biochemical approaches were used to collect data to help us better
understand this phenomenon.
The lowest activity of Peroxidase and Polifenoloxidase were found in natural coffee,
indicating lower tolerance to the drying process than fully washed coffee.
In addition, the lower tolerance of natural coffee to dryingthan fully washed coffee
was revealed by the low physiological data of germination.
5. References
Borém, F. M. (Org.) . Handbook of coffee post-harvest technology. 1. ed. Norcross,
Georgia: Gin Press, 2014. v. 1. 282p
Barbosa, J. N. ; Borém, F. M. ; Alves, H. M. R. ; Cirillo, M. A. ; Sartoli, M. ; Ducatti,
C. . Discrimination of Production Environments of Specialty Coffees by Means of
Stable Isotopes and Discriminant Model. Journal of Agricultural Science, v. 6, p. 5564, 2014.
Barbosa, J. N. ; Borém, F. M. ; Alves, H. M. R. ; Volpato, M. M. L. ; Vieira, T. G. C.
; Souza, V. C. O. . Spatial distribution of coffees from Minas Gerais state and their
relation with quality. Coffee Science, v. 5, p. 237-250, 2010.
Barbosa, J. N. ; Borém, F. M. ; Cirillo, M. A. ; Malta, M. R. ; Alvarenga, A. A. ;
Alves, H. M. R. . Coffee quality and its interactions with envirnmental factors in
Minas Gerais, Brazil. Journal of Agricultural Science (Print), v. 4, p. 181-190, 2012.
Borém, F. M. ; Isquierdo, E. P. ; Oliveira, P. D. ; Ribeiro, F. C. ; Siqueira, V. C. ;
Taveira, J. H. S. . Effect of intermittent drying and storage on parchment coffee
quality. Bioscience Journal (UFU. Impresso), v. 30, p. 609-616, 2014.
Borém, F. M. ; Marques, E. R. ; Alves, E. . Ultrastructural analysis of drying
damagein in parchment Arabica coffee endosperm cells. Biosystems Engineering, v.
99, p. 62- doi:10.1016-66, 2008.
Friday, 2015-Apr-10
Figueiredo, Luisa P ; Borém, Flávio M ; Cirillo, Marcelo Â ; Ribeiro, Fabiana C ;
Giomo, Gerson S ; Salva, Terezinha De J G . The Potential for High Quality Bourbon
Coffees From Different Environments. Journal of Agricultural Science, v. 5, p. 87-98,
2013.
Isquierdo, E. P. ; Borém, F. M. ; Andrade, E. T. ; Corrêa, J. L. G. ; Oliveira, P. D. ;
Alves, G. E. . Drying Kinetics and quality of natural coffee. American Society of
Agricultural and Biological Engineers. Transactions, v. 56, p. 1003-1010, 2013.
Isquierdo, E. P. ; Borém, F. M. ; Oliveira, P. D. ; Siqueira, V. C. ; Alves, G. E. .
Quality of natural coffee subjected to different rest periods during the drying process.
Ciência e Agrotecnologia (UFLA), v. 36, p. 439-445, 2012.
Ribeiro, F. C. ; Borém, F. M. ; Giomo, G. S. ; Lima, R. R. ; Malta, M. R. ; Figueiredo,
L. P. . Storage of green coffee in hermetic packaging injected with CO2. Journal of
Stored Products Research, v. 47, p. 341-348, 2011.
Saath, R. ; Taveira, J. H. S. ; Broetto, F ; Biagioni, M.A.M. ; Borém, F. M. ; Rosa, S.
D. V. F. . Activity of some isoenzymatic systems in stored coffee grains. Ciência e
Agrotecnologia (UFLA), v. 38, p. 15-24, 2014.
Silveira, H. R. O.Variação sazonal de atributos ecofisiológicos e metabólicos decafé
arábica em três altitudes. (Tese de doutorado) Lavras : UFLA, 2014. 73p.
Taveira, J. H. S. Metabolite profile and sensory quality of arabica genotypes grown in
different altitudes and processed by different post-harvest methods. (PhD thesis).
Lavras: UFLA, 2014. 71p.
Taveira, J. H. S. ; Borém, Flávio Meira ; Figueiredo, Luísa Pereira ; Reis, Nádia ;
Franca, Adriana S. ; Harding, Scott A. ; Tsai, Chung-Jui . Potential markers of coffee
genotypes grown in different Brazilian regions: A metabolomics approach. Food
Research International, v. 61, p. 75-82, 2014.