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Achieving sustainable
cultivation of coffee
Breeding and quality traits
Edited by Dr Philippe Lashermes
Institut de Recherche pour le Développement (IRD), France
BURLEIGH DODDS SERIES IN AGRICULTURAL SCIENCE
E-CHAPTER FROM THIS BOOK
http://dx.doi.org/10.19103/AS.2017.0022.16
© Burleigh Dodds Science Publishing Limited, 2018. All rights reserved.
Chapter taken from: Lashermes, P. (ed.), Achieving sustainable cultivation of coffee, Burleigh Dodds Science Publishing,
Cambridge, UK, 2018 (ISBN: 978 1 78676 152 1; www.bdspublishing.com)
Harmful compounds in coffee
Noël Durand, CIRAD, France; and Angélique Fontana, University of Montpellier, France
1 Introduction
2 Pesticide residues
3 Ochratoxin A
4 Polycyclic aromatic hydrocarbons
5 Acrylamide
6 Conclusion
7 References
1 Introduction
Food safety is a major concern for consumers. However, chemicals that are often used
to preserve crops may be harmful to human health and can be present in food products.
Their presence may be linked to the methods of cultivation and processing of the product
(use of chemical inputs at the field and unsuitable techniques for the production of the
end products) or ‘fortuitous’ in the case of contamination resulting from external pollution.
The regulations on maximum levels of toxic substances (MRL, maximum residue limit)
and the control of the presence of these substances remain the only guarantees for the
consumption of healthy products from agriculture.
Coffee is one of the most widely consumed beverages in the world and the world
coffee production reached 151.6 million bags, or about 9.1 million tons (60 kg/bag)
in 2016 (ICO, 2017). As well as many other food and baby-food products, coffee is
also subject to regulations setting the maximum residue content of non-specific
products, such as pesticides used worldwide in agriculture and mycotoxins from fungal
contaminants, and more specific products related to its mode of preparation, such
as polycyclic aromatic hydrocarbons (PAHs) or acrylamide that can appear during the
drying or roasting steps.
Harmful compounds in coffee
2
© Burleigh Dodds Science Publishing Limited, 2018. All rights reserved.
2 Pesticide residues
When speaking about ‘pesticides’, many chemical substances are involved such as
insecticides, fungicides and herbicides. In coffee, the pesticides can be used at the field,
during storage or at the export step and then can be found in coffee beans.
The coffee tree is subject to attacks by diseases and pests whose severity is accentuated
by the tropical climatic conditions of the places where it grow. It results in a yield loss
and a breakdown in quality. The main diseases (Wintgens, 2009) for coffee tree are of
cryptogamic origin (orange rust, anthracnose) and are more frequent on Coffea arabica
than on C. canephora. Insects are the main pests and they can target the different organs
like leaves (Zonocerus variegatus), fruits (Hypothenemus hampei or coffee berry borer),
trunk (Termitidae) or roots (Planococcus fungicola).
About 70% of the world coffee production comes from small producers and most of
them are in developing countries. Because of the high cost of pesticides, these coffee
farmers use few chemical inputs. Consequently, most of the coffee produced in these
small farms can be considered to be obtained using organic farming. Moreover, the coffee
processing, and particularly hulling, promotes the elimination of pesticide residues since
chemicals are concentrated on the outer layers of the coffee bean.
Pesticides, like endosulfan against the coffee berry borer or aldrin against Termidae, are
rather used at the field in large farms in order to preserve yields and thus profitability of the
crop. A study has been carried out in Romania on commercial green and roasted coffee
(Stanciu et al., 2008) for the determination of nine organochlorine pesticides. The use of these
pesticides has been prohibited in most countries but they are still ubiquitous and persistent
pollutants. The residual levels ranged from 0.001 to 0.007 mg/kg. Only hexachlorobenzene
(HCB), lindane and aldrin were detected and the maximum value was obtained for aldrin.
Therefore, the pesticide residues from pre-harvest treatments appear to be negligible
(Stanciu, 2008). A study was conducted in Japan between June 2006 and March 2008 on
pesticide residues from imported green coffee (Ishiwaki, 2008). The results showed that
only 0.3% of the 1866 samples from the major farmers in Latin America, Asia and Africa had
residues above the limit set by Japanese legislation (DDT and thiabendazole). However, in a
recent study, more than 10 000 samples of Brazilian green coffee were analysed to monitor
their flutriafol and pyraclostrobin residues and nonconformities reached 12% for flutriafol
while they were only 0.15% for pyraclostrobin (de Oliveira, 2016). Therefore, these results
show an increase of coffee contamination by pesticide residues over the years.
Different studies have demonstrated that the roasting process reduced drastically the
levels of pesticide residues in coffee (Ishiwaki, 2008; Sakamoto, 2012; Mekonen, 2015).
Endosulfan, HCB, DDT and atrazine were not detected after roasting while chlordane and
heptachlor levels were strongly reduced.
Another possible source of contamination is the use of pesticides during storage or
at the export. Indeed, fumigations (methyl bromide, Basamid®) are often carried out on
green coffee to avoid insect outbreaks during these two steps (Wintgens, 2009).
Besides, the use of jute bags for the packaging of green coffee contribute to the bean
contamination: concentrations of pesticides in the jute bags can reach up to 100 times
those in the green coffee contained in these bags.
Studies on the subject are scarce but it seems that the contamination of green coffee by
pesticides mainly occurs accidentally and randomly. In the 2015 European Union survey
on pesticide residues in food, no MRL exceedance was reported for coffee beans (at least
60 samples analysed) (EFSA, 2017).
© Burleigh Dodds Science Publishing Limited, 2018. All rights reserved.
Harmful compounds in coffee 3
3 Ochratoxin A
Ochratoxin A (OTA) is a mycotoxin produced by some filamentous fungi of the genera
Aspergillus and Penicillium (Pitt, 2000; Abrunhosa, 2001; O’Callaghan, 2003; Ostry,
2013; Alvindia, 2016). In tropical zones, OTA is mostly produced in coffee by Aspergillus
ochraceus, A. westerdijkiae and A. steynii (Taniwaki, 2003; Frisvad, 2004; Samson, 2006;
Bacha, 2009, Geremew, 2016).
Much attention has been paid to OTA due to its nephrotoxic, immunotoxic, teratogenic
and carcinogenic effects (Abarca, 1994; Pfohl-Leszkowicz, 2007) and the International
Agency for Research on Cancer has classified OTA as a possible carcinogen for humans
(group 2B) (IARC, 1993). In Europe, cereals, wine and coffee are the foodstuffs that contribute
most to human OTA intake, for 50, 13 and 10%, respectively. European legislation had
fixed a maximum limit for OTA in roasted coffee (5.0 µg/kg) and instant coffee (10.0 µg/
kg) (European Commission, 2006), but there is no limit yet for green coffee. According to
the FAO, this maximum limit for roasted coffee could lead to an average shipment refusal
rate of around 7%, rising to 18% in some cases.
OTA contamination of coffee can be caused by the cherry contamination at the field
with toxigenic fungi. The toxinogenesis then occurs before or after harvest, and in this
case during post-harvest treatments.
The coffee bean contamination by OTA has been shown to be related to the quality
of the cherries (health status) at the harvesting time. In particular, cherries with defects of
agronomic origin (Table 1) could be the main sources of OTA contamination (Duris, 2010).
In some coffee producing countries, cherries damaged by the berry anthracnose (coffee
berry disease – CBD) are undoubtedly responsible for the high levels found in lower-
quality batches. Beans damaged by insects (beetles, antestia, fruit fly) could also play a
role in coffee contamination. In these cases, sorting damaged beans (agronomic defects)
makes it possible to greatly reduce OTA contamination.
The contamination levels of green coffee by OTA vary according to the geographic
origin of coffee (Table 2) (Romani, 2000). The differences are attributed to the climatic
conditions of each region and the post-harvest treatments used. Indeed, washed (wet)
coffees, especially those from Central and South America, usually have low OTA content.
Table 1 Green coffee OTA levels in relation to bean defects (from Duris, 2010)
Types of coffee
Pack out from wet process (about 15%
w/w per batch) Dry process
Types of beans
% w/w
per batch
OTA
(µg/kg)
% contribution of
each defect/total
contamination
% w/w
per batch
OTA
(µg/kg)
% contribution of
each defect/total
contamination
Black 1.8 2.4 0.4 7.6 1.6 1.1
Diseased 11.4 71.3 90.4 20.6 37.5 57.7
Foxy 0.6 5.0 0.3 1.7 291.6 38.0
Insect
damaged
0.5 46.2 7.5 1.2 9.0 0.9
Defects 14.4 5.2 98.6 31.2 9.8 97.9
Sound 85.6 0.2 1.4 68.8 0.4 2.1
Harmful compounds in coffee
4
© Burleigh Dodds Science Publishing Limited, 2018. All rights reserved.
Higher rates were observed for unwashed robusta and arabica (dry) coffee, generally from
countries in Africa and Asia. A French study on the OTA contamination rate of commercial
roasted coffee showed that 27% of the samples had an OTA content of less than 0.5 μg/
kg, 33% between 0.5 and 1 μg/kg, 37% between 1 and 3 μg/kg and only one sample was
above the European limit (Tozlovanu, 2010). However, Mounjouepou (2007) found up to
20 μg/kg in Cameroon green coffee beans and 12 μg/kg were detected in local Ethiopian
coffee beans (Geremew, 2016). In this last study, the average OTA level was 1.53 μg/kg
but significant differences were observed between the samples from different processing
methods (washed or dry processed), and different storage conditions.
The effects of the different treatments on OTA contamination in coffee have been widely
studied. OTA presence in coffee beans can be related to harvesting conditions (Paulino
de Moreas and Luchese, 2003) and post-harvest processing conditions (Bucheli, 2000;
Romani, 2000; Suarez-Quiroz, 2004a, 2005a; Durand, 2013; Geremew, 2016), especially for
dry processing (Bucheli, 2000; Urbano, 2001; Bucheli, 2002). OTA contamination of coffee
can also occur during transport and storage, if carried out under poor conditions (Bucheli,
1998). Moisture, temperature and substrate have an important role in the development
of OTA-producing strains and their toxinogenesis (Suarez-Quiroz, 2004b). During storage,
the main factors influencing the development of toxinogenic strains are activity of water
(Aw) and temperature. An Aw of 0.95 and a temperature of 30°C are the optimal values for
the development of ochratoxinogenic Aspergillus (Suarez-Quiroz, 2004b).
The roasting conditions have also been studied (Suarez-Quiroz, 2005b; Ferraz, 2010)
and reduction levels ranging from 0–12% to 90–100% have been shown (Amezqueta,
2009). The effect on OTA contamination of coffee of two roasting techniques at different
degrees of roasting was studied (Fig. 1) (Castellanos-Onorio, 2011). The OTA content was
reduced by 90% with a drum roasting process (indirect heating) and 63% with a fluidized-
bed roasting process (continuous direct heating in a hot air stream). This study provided
important informations on the thermal stability of OTA during post-harvest treatments
of coffee. Indeed, European-type roasting (medium to dark) provide an OTA decrease
between 60 and 90% for drum roasting and between 25 and 63% for fluidized-bed
roasting. However, the OTA thermal degradation can lead up to newly formed products
whose toxicological identification and evaluation have to be studied.
In recent years, attention has been paid on the effect of climate change on the OTA
contamination of coffee, studying the effects of factors like temperature or water activity
on ochratoxigenic strains (Gil-Serna, 2014, 2015; Paterson, 2014; Akbar, 2016).
Many factors contribute to the OTA contamination of coffee beans and thus prevention is
not easy to set up and maintain. However, the conditions for decrease OTA contamination
is now more or less known: protection against pests that damage the natural protection
of coffee (beetles, antestia and CBD), bean sorting, good practices for post-harvest
processes and storage (quick drying of coffee).
Table 2 Green coffee OTA contamination levels in relation to the origin of coffee (from Romani, 2000)
Zone
% contaminated
samples
% contaminated samples
≥3 µg/kg
Contamination range
(µg/kg)
Africa 90.0 58.3 48.0
Central and South America 32.0 3.3 0.1–7.7
Asia 61.0 11.1 0.2–4.9
© Burleigh Dodds Science Publishing Limited, 2018. All rights reserved.
Harmful compounds in coffee 5
4 Polycyclic aromatic hydrocarbons
PAHs are a broad class of organic compounds which are produced by incomplete
combustion or pyrolysis of organic materials at high temperatures as well as during some
industrial processes.
Some of these compounds, such as benzo[a]pyrene (BaP), are carcinogenic and
mutagenic and are thought to be involved in several cancers in humans. Therefore
regulations have been set to limit PAH levels in certain foodstuffs (European Commission
Regulations (EC) No 1881/2006). Currently, the maximum levels for BaP are 2 μg/kg and
5 μg/kg in oils and fats and in cocoa bean fats, respectively. Limits in roasted coffee are
not established yet but studies are underway in order to define it. Four PAHs (PAH4) are
now recognized by the European Food Safety Authority (EFSA) as suitable indicators
for PAH contamination of foodstuffs: benz[a]anthracene (BaA), chrysene (CHR), benzo[b]
fluoranthene (BbF) and BaP. Among these compounds, BaP is known to be the most toxic
and carcinogenic and the toxic potency (TEQ) of coffee samples is evaluated in terms of
BaP equivalent concentration using the toxic equivalent factors of each individual PAH
species relative to BaP carcinogenic potency (Houessou, 2008).
PAHs in coffee come from either an exogenous contamination (mainly during drying of
green coffee beans) or an endogenous one (formation in the bean during roasting).
Environmental pollution is one of the main causes of exogenous contamination of
coffee during the drying and storage stages (European Commission, 2002). For example,
when coffee beans are dried on roadsides, contamination mainly comes from car exhaust
emissions. The combustion drying systems are another important source of contamination
when artificial dryers are poorly regulated or maintained. However, the PAH contamination
of green coffee beans is rather low or even zero (Stanciu, 2008).
The PAHs endogenous contamination of coffee mainly occurs during roasting, although
several PAHs were found in both roasted and green coffee beans (Houessou, 2008). The
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
Light Mediu
mD
ark
Roasting degree
% Residual OTA
Rotating cylinder
Fluidized bed
Figure 1 Effect of roasting on OTA reduction in coffee beans using two types of roaster (from
Castellanos-Onorio, 2011).
Harmful compounds in coffee
6
© Burleigh Dodds Science Publishing Limited, 2018. All rights reserved.
concentration of PAH4 was found to range from 7 to 68 μg/kg in roasted coffee beans
(Sadowska-Rociek, 2015) while it reached a maximum of 0.4 μg/kg or 0.8 μg/kg in other
studies (Tfouni, 2012; Jimenez, 2014).
The contamination was reported to be closely linked to the roasting parameters,
especially the duration and the temperature (Houessou et al., 2007; Grover, 2013, Jimenez,
2014). Thus, the highest contamination levels are determined for longest and high
temperature roasting processes (Houessou, 2007; Orecchio, 2009). On roasted coffee,
studies have shown that BaP contamination is often less than 5 μg/kg for the medium
roasting which is by far the most common one (Houessou, 2007; Jimenez, 2014). In fact,
results are heterogeneous and the influence of many parameters, like coffee cultivars or
brewing procedures, has to be considered (Tfouni, 2013).
The PAH contamination of roasted coffee appear to be rather limited, particularly
concerning the BaP (Houessou et al., 2007; Orecchio, 2009; Lee, 2010). Moreover, the
contamination is even lower in coffee drinks, because of the PAH low solubility in water.
The PAH transfer to the coffee infusion is thus moderate (Maier, 1991; Houessou, 2005,
2007; Duedahl-Olesen, 2015). However, a more recent study has shown that Danish tea
infusions and coffee drinks contributed for about 29% of the total exposure of Danish
consumers to PAH4 (Duedahl-Olesen, 2015). In parallel, fats, bread and dried bread
products, but not coffee, were pointed out to be the main contributors to PAH exposure
for adults in France (Veyrand, 2013).
5 Acrylamide
Acrylamide (2-propenamide) is recognized by the International Agency for Research on
Cancer (IARC, 1994) as probably carcinogenic to humans (Group 2A). In 2002, the Swedish
National Food Administration and the University of Stockholm published results on the
presence of acrylamide in several foodstuffs like fried potatoes, bread, cookies, potato
and cereal-based snacks, coffee and other foodstuffs. Thus, coffee contributes to 39%
of the total acrylamide exposure of Swedish consumers and the acrylamide from coffee
corresponds to one-third of the daily acrylamide intake in Switzerland (Swiss Federal
Office of Public Health, 2002). Ever since, many research projects and the European coffee
industry have been interested in investigating the formation and presence of acrylamide
in roasted coffee and coffee products in order to understand the formation process of
acrylamide during roasting, storage and brewing of coffee.
The acrylamide results from the thermal treatment of foodstuffs via Maillard reaction.
It mainly comes from the reaction, at high roasting temperature, between the asparagine
amino acid and reducing sugars or reactive carbonyls (Guenther, 2007).
Different studies have established that the acrylamide contents varied from 35 to
540 µg/kg of roasted coffee (Roach, 2003; Andrzejewski, 2004; Delatour, 2004; Hoenick,
2005; Senyuva, 2005; Aguas, 2006; Lantz, 2006; Guenther, 2007; Summa, 2007), which
correspond to intake levels of 4–6 µg by day of acrylamide from coffee brew (Alves, 2010).
These values vary according to the composition of the arabica and robusta blend, roasting
degree, the mode of preparation of the beverage and the storage time of the roasted
coffee.
Acrylamide levels in foodstuffs have been monitored in EU from 2007 to 2009 under
Commission Recommendation 2007/331/EC. A total of 243 coffee samples (roasted and
instant) in 2007 and 321 in 2008, provided by 22 member states, were analysed. The
© Burleigh Dodds Science Publishing Limited, 2018. All rights reserved.
Harmful compounds in coffee 7
results showed that the acrylamide content was less than 400 µg/kg for 82% and 92% of
the roasted coffee samples in 2007 and 2008, respectively. Concerning the instant coffee
samples, 82% and 87% contained less than 800 µg/kg in 2007 and 2008, respectively.
Based on the EFSA monitoring data from 2007 to 2008 (EFSA, 2011), the commission
recommendation 2010/307/EU of 10/01/2011 had set indicative acrylamide values at
450 µg/kg for roasted coffee and 900 µg/kg for instant coffee. Some studies have shown
that higher amounts of acrylamide were produced during roasting of robusta coffee
compared to arabica coffee (Bagdonaite, 2004, 2008; Lantz, 2006). In the same time, the
concentrations of free asparagine in green coffee beans were found to be slightly higher
in robusta beans (Stadler, 2004; Lantz, 2006; Murkovic, 2006), and Lantz (2006) has shown
a positive correlation between the level of asparagine in green coffee and the acrylamide
content in roasted coffee. On the other hand, no clear correlation was established between
the glucose level in the green coffee and the acrylamide content in the roasted coffee.
The acrylamide formation starts quickly from the beginning of the roasting. Taeymans
(2004) reported that more than 95% of the total acrylamide formed by the roasting process
is then degraded later in the process and thus the acrylamide content is strongly reduced
in the final product. These results were confirmed by Lantz (2006) who observed the
formation and then the reduction of acrylamide during the coffee roasting (Fig. 2). At the
beginning of roasting, the production of acrylamide reached maximum level of 950 µg/kg
and decreased to 220 µg/kg in the final product (medium roast).
These results explain the fact that there is less acrylamide in dark roasted coffee than in
light roasted coffee. This was confirmed with surveys on commercial samples of roasted
coffee: lower levels of acrylamide were measured in dark roasted coffees compared to
lighter roasted ones (Granby, 2004; Senyuva, 2005).
Acrylamide is highly soluble in water and, thus, easily transferred from the coffee
powder to the beverage (Andrzejewski, 2004). Several factors, like the coffee/water ratio
used or the type of coffee brewing (expresso, filtered, plunger pot, etc.) step in the coffee
beverage preparation and all this parameters have impact on the acrylamide content of
the brew. Lantz (2006) reported that the acrylamide content was lower in espresso coffee
Figure 2 Acrylamide levels of partially roasted coffees, by prematurely stopping the process of
roasting (Colombia coffee up to medium roast in 3 min) (from Lantz, 2006).
Harmful compounds in coffee
8
© Burleigh Dodds Science Publishing Limited, 2018. All rights reserved.
because of the short contact time with water which reduced the extraction of acrylamide
from the ground coffee.
Some studies have shown that acrylamide was not stable in roasted coffee, that is,
the concentration decreased over prolonged storage time (Andrzejewski, 2004; Hönicke,
2005; Lantz, 2006). Losses of 40–60% of acrylamide have been recorded in roasted and
ground coffees stored at room temperature over a period of 6–12 months (Delatour,
2004). The reaction mechanism responsible for the loss of acrylamide during storage has
not been elucidated yet.
There are few processes available to reduce the acrylamide level without affecting the
quality of the brew, especially in relation to its sensory properties. An option to reduce
the acrylamide intake of consumers from coffee is to select commercial blends with higher
arabica contents and darker degrees of roasting and, simultaneously, to prefer shorter
brews instead of long ones, but this will obviously depend on the consumer preferences.
There are few parameters to reduce the acrylamide level without affecting the quality of the
brew, especially in relation to its sensory properties. An option to reduce the acrylamide intake
of consumers from coffee is to select commercial blends with higher arabica contents and
median or dark degrees of roasting and, simultaneously, to prefer shorter brews (espresso-
type) instead of long ones, but this will obviously depend on the consumer preferences.
However, favouring dark roasting to limit acrylamide in coffee will lead to the formation
of other compounds with little organoleptic interest.
6 Conclusion
In recent years, the monitoring of harmful contaminants in food has become an important
topic for food safety authorities in the world in order to guarantee consumer health. Coffee,
which is one of the most widely consumed beverages in the world, is of course controlled,
particularly concerning pesticide residues, OTA, PAHs and acrylamide.
Although coffee is mainly produced in relatively uncontrolled agricultural conditions, it is
not a high-risk product for most of its production. Nevertheless, information and findings
have to be provided in the producing countries to avoid any drift. The effective control
of contaminants in coffee is often only based on the use of good agricultural practices
combined with high-quality post-harvest treatment. Roasting, which is the final step in
the treatment of coffee, plays an essential role in reducing contamination by OTA and
pesticides. Despite its role in the possible increase in PAH and acrylamide contaminations,
a ‘European’-type roasting seems to be a good compromise between formation and
reduction of coffee contaminants.
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