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DE LA FACULTAD DE INGENIERÍA
REVISTA TÉCNICAREVISTA TÉCNICA
Patrimonio del Estado Zulia e
interés Cultural desde 2001
Fecha de Construcción:
1954-1958
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VOL.42 ENERO - ABRIL 2019 No.1
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 1, 2019, Enero-Abril, pp. 03-47
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 1, 39-47, 2019
Composition and Thermogravimetric Characterization of
Components of Venezuelan Fermented and dry Trinitario
Cocoa Beans (Theobroma cacao L.): Whole Beans, Peeled
Beans and Shells
Aleida J. Sandoval1* , José A. Barreiro1 , Andrea De Sousa1 , Danny Valera1, Juan V.
López2 , and Alejandro, J. Müller2
1Dpto. de Tecnología de Procesos Biológicos y Bioquímicos, 2Dpto. Ciencia de los Materiales Universidad Simón
Bolívar, Aptdo. 89000, Caracas 1080-A, Venezuela. Tel-Fax: +58 212 9063953,
*autor contacto: asandova@usb.ve
https://doi.org/10.22209/rt.v42n1a06
Recepción: 02/05/2018 | Aceptación: 16/10/2018 | Publicación: 31/12/2018
Abstract
Some important chemical and thermal characteristics of components of fermented and dry Venezuelan Trinitario
cocoa beans (Theobroma cacao L.) were determined. Average bean shell weight (as percent of whole bean weight) was
15.5%, with an average thickness 0.310 mm. Its moisture content (d.b.: dry basis)
that of whole and peeled beans. In spite of the shell higher moisture content, its water activity (aw) was lower than that of
peeled and whole beans, evidencing higher water binding capacity. Crude fat content (d.b.) was higher in whole beans than
(d.b.) exhibited a decreasing order for
whole beans, peeled beans and shells. The ash content (d.b.)
beans. Cocoa bean constituents, exhibited similar thermal properties, as evidenced by their melting and pyrolysis behavior
obtained by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) techniques.
Keywords: cocoa beans; shells; water activity; DSC; TGA.
Composición y Caracterización Termogravimétrica de los
Componentes de Habas de Cacao Trinitario Venezolano
(Theobroma cacao L.) Fermentado y Seco: Habas Enteras,
Peladas y Cascarillas
Resumen
Se determinaron algunas características químicas y térmicas del cacao Trinitario venezolano (Theobroma cacao
L.). El peso promedio de la cascarilla del haba de cacao (como porcentaje del peso del haba entera) fue del 15.5%, con un
espesor promedio de 0.310 mm. Su contenido de humedad (b.s.: base seca)
de las habas enteras y sin cascarilla. A pesar de que la cascarilla tiene un mayor contenido de humedad, su actividad de
agua (aw) fue menor que la de las habas enteras y sin cascarilla, lo que demuestra una mayor capacidad de adsorción de
humedad. El contenido de grasa cruda (b.s.)
mayor que en las cascarillas. Se encontró que el contenido de proteína (b.s.) disminuyó en el siguiente orden: habas enteras,
habas sin cascarilla y cascarillas. El contenido de cenizas (b.s.)
enteras y sin cascarilla. Los constituyentes de las habas de cacao exhibieron propiedades térmicas similares, de acuerdo con
los datos de fusión y pirólisis obtenidos mediante calorimetría diferencial de barrido (DSC) y técnicas de análisis termo-
gravimétrico (TGA).
Palabras clave: habas de cacao; cascarillas; actividad de agua; DSC; TGA.
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 1, 2019, Enero-Abril, pp. 03-47
40 Sandoval y col.
Introduction
Trinitario fermented cocoa beans (a hybrid
of Criollo and Forastero types), represent an important
commodity in the international trade of cocoa in
cocoa products. It is usually well fermented; sun dried and
packaged in new jute bags.
Fowler [1] in a pioneer work, analyzed
the composition of cocoa bean shells (the thin skin
immediately surrounding the cocoa nib that is removed
after roasting the beans) of various origins, including
Venezuelan beans. Since the cocoa bean shell is essentially
waste material, some research works have proposed its
in different poly-lactic acid polymer matrices [2]. Besides
the work of Fowler [1] on cocoa bean shell composition,
no information about the composition and water activity
(aw) of peeled cocoa beans and shells was found in the
literature consulted. It has been established that a water
activity (aw) of less than 0.70 in cocoa beans is required
for microbiological stability [3, 4]. This water activity level
was associated with moisture content in whole beans of
7.10% to 7.34% (dry basis). Wood and Lass [5], suggested
a moisture content of 6-7% for long safe storage of whole
cocoa beans. Other authors indicated a moisture level of
less than 8% (wet basis) to guarantee microbiological
stability during storage [6, 7].
There are some studies regarding the thermal
characteristics of cocoa products mainly associated
to different types of chocolate and chocolate-related
products [8-10], rather than on the raw material used in
their production (i.e., cocoa beans). Du et al. [11] studied
the pyrolysis behavior of cocoa bean shells identifying the
different compounds evolving from thermal decomposition
of this materials under a temperature range of 25-1000°C,
using thermogravimetric analysis coupled with Fourier-
transform infrared spectroscopy. No information about
the thermal characterization of Venezuelan cocoa beans
has been found in the literature reviewed. These data
are needed to explore future application and uses of this
product, as an alternative energy source.
literature reviewed regarding the composition and
thermogravimetric properties of whole and peeled cocoa
beans, and cocoa bean shells, the aim of this research
work is to determine such properties particularly for
Venezuelan Trinitario type cocoa beans.
Experimental Section
Raw material and sample preparation
Fermented cocoa beans (Theobroma cacao L.)
variety Trinitario, were grown and harvested in 2014,
at Cúpira (Pedro Gual municipality), Miranda state,
Venezuela, and packed in new clean jute sacks. The cocoa
Fino
de Primera) by Cacao de Origen, Hacienda La Trinidad,
Caracas, Venezuela, according to the Venezuelan standard
for cocoa beans [12]. A composite sample of about 5 kg
of cocoa beans was provided by the same. Approximately
720 g of sample was selected at random for peeling to
obtain the cocoa bean shells and the peeled cocoa beans.
A similar amount was separated to be used as a whole
bean sample. Cocoa beans were carefully peeled by hand
in the laboratory to separate the cocoa bean shell. To carry
out the proximate analysis and thermal characterization
all samples were individually ground in a motorized mill
(Wiley N°4), using a 2-mm sieve.
Proximate analysis and water activity
Proximate analysis of whole beans, peeled
beans and cocoa bean shells were carried out according
to the procedures presented in AOAC [13]. Moisture
was determined by the atmospheric oven method (100-
102 °C for 16 h), until constant weight. Protein content
was determined by the micro-Kjeldahl method, using
a nitrogen conversion factor of 6.25. Crude fat was
determined using the Soxhlet method with hexane as
solvent
°C were also determined. All the analyses were done by
triplicate. Water activity (aw) was measured using a
Decagon CX-1 device, previously calibrated.
Relative weight of peeled beans and shells and shell
thickness
For this purpose, the following procedure was
followed [14,15]: Five 100-bean samples were formed
from beans selected at random. The cocoa beans were
peeled manually. The weight of whole cocoa beans, shells
and peeled beans was determined separately using an
analytical balance OhausTM model Adventurer (± 0.0001
g) and the percent shell calculated in relation with the
weight of whole un-peeled beans. The shell thickness was
determined by selecting at random 42 pieces of shells
and measuring their thickness in triplicate with a digital
micrometer (± 0.001 mm).
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 1, 2019, Enero-Abril, pp. 03-47
41Composition and thermal characteristics of components of Venezuelan Trinitario cocoa beans
Thermal Characteristics of whole cocoa beans, peeled
beans and shells
Thermal characteristics of whole cocoa beans,
peeled beans and cocoa bean shells, were determined
by means of differential scanning calorimetry (DSC) and
thermogravimetric analysis (TGA).
DSC analysis of ground whole cocoa beans,
peeled cocoa bean and cocoa bean shells was carried out
separately using a DSC 7 (Perkin Elmer™), previously
calibrated with Indium. An amount of approximately 10 ±
1 mg was weighed in hermetically sealed aluminum pans
and heated, under pure nitrogen ambient, from -20°C to
200°C at a rate of 5 ºC/min. An empty pan was used as a
reference.
Mass changes during heating of ground whole
cocoa beans, peeled cocoa bean and cocoa bean shells
were measured using a Thermal Gravimetric Analyzer
(Perkin ElmerTM, STA 6000). An amount of approximately
10 mg (± 0.1 mg) was weighed in aluminum oxide crucibles
and heated under a pure nitrogen atmosphere from 30 to
900°C at a heating rate of 10°C/min.
Statistical Analyses
Measures of central tendency and dispersion and
Student t-tests were calculated using Microsoft ExcelTM
2016. In this work, the standard deviation is indicated
in the text by a ± sign, unless used to specify instrument
precision. Analysis of variance and Duncan’s multiple
range tests were conducted for multiple comparisons
between results averages for chemical analysis of whole
bean, peeled bean and cocoa bean shells [16].
Results and Discussion
Moisture content and water activity (aw) of cocoa
beans
Moisture content of cocoa beans was 6.51 ±
0.05% (wet basis) with a range from 6.48 to 6.59% (wet
basis). The water activity measured at 25-27°C, averaged
0.617 ± 0.010 with a range of 0.618-0.611.
Table 1. Results obtained for the percent of shell and shell thickness in whole fermented Trinitario cocoa beans with
6.51% average moisture content (wet basis).
Physical property Mean
value Range Standard
deviation
interval
Shell in whole beans (% w/w) 15.5 15.9-15.2 0.37 14.6-16.5
Shell thickness (mm) 0.310 0.499-0.177 0.076 0.297-0.323
Relative weight of peeled cocoa beans and shells, and
shell thickness
The results regarding the relative weight of
peeled cocoa beans and shells are presented in Table 1.
From the results above, the ratio of shells to
peeled beans was calculated as 0.1839. Alvarez et al. [17]
and Lares Amaíz et al. [18] reported weight shell values of
of 14.81% and 14.21% respectively. Cocoa bean shell of
Venezuelan Criollo fermented cocoa beans from Chuao
ranged from 14.29% to 15.50% [19].
Average shell thickness determined was
0.310 ± 0.076 mm with a range of 0.499-0.177 mm
Cocoa bean shells have little commercial value and
can be considered waste material. Its value as feed is
limited due to the elevated content of theobromine
and caffeine. However, its use in infusions has been
reported [20]. Hutagalung and Chang [21] reported
with palm kernel cake and therefore, it could be utilized
as an alternative protein source to substitute grain
protein in animal diets. Cocoa beans shells also have
relatively high potassium content and may be used
to manufacture fertilizers or composts [21]. When
used as mulch, the shell contains approximately 2.5%
nitrogen, 1% phosphate and 3% potash, as well as a
natural gum that is activated when watered, having
use for mulch and compost preparation [21]. Its fat
content makes it suitable for burning as fuel [1]. From
the commercial point of view, the shell percentage
should be as low as possible, usually between 10-14%.
Chemical Analyses of beans and shell
The results for the moisture content and water activity
of whole and peeled cocoa beans and shells are presented in
Table 2.
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 1, 2019, Enero-Abril, pp. 03-47
42 Sandoval y col.
Table 2. Moisture content (wet basis) and water activity (aw) of Trinitario cocoa beans grown in Venezuela.
Moisture content (% wet basis)
Cocoa bean and
constituents Average* Standard
deviation Range
interval
aw
(25-27°C)
Whole beans 6.75a0.29 7.09-6.54 6.42-7.08 0.657
Peeled beans 6.22a0.20 6.44-6.07 6.00-6.44 0.684
Shells 17.30b0.50 17.84-16.85 16.73-17.87 0.660
between the percent moisture content of the peeled beans
(6.75 %) and that of the whole beans (6.22%). However,
the moisture content of the cocoa bean shells (17.30%)
(p≤0.05) than those of the whole
and peeled beans.
A material balance carried out, for the moisture
present in the peeled cocoa beans and in cocoa bean shells
(dry basis), assuming the percent of shells in the whole
beans was that found experimentally presented in Table 1
(15.5%), indicated that the percentage of the total water
present in peeled cocoa beans was around 64% of the total
bean moisture, while the amount of water in cocoa bean shells
resulted in about 36% of the total cocoa bean water present.
This fact indicated that about one third of the total water in
cocoa beans was located in the shell, in spite of the fact that
the shell represents only about one sixth of the weight of the
whole bean, being only a small part of the linear dimensions
of the bean (2.6 to 4.9%, data not shown). Average thickness
of shells was about 0.31 mm. This fact evidenced the higher
water adsorption capacity of the cocoa bean shell as compared
with that of the peeled bean.
In spite of the fact that cocoa bean shells had
higher moisture content (17.30%) than the peeled cocoa bean
(6.22%), its water activity (aw) was similar but slightly lower
(0.660) than that of peeled beans (0.684). This evidenced
that a large fraction of the water present in the shells should
be bound water resulting in lower water activity. The
elevated water adsorption capacity of the shell could be
explained by the nature of the chemical species formed
during the fermentation process in the shell and inside
the bean. After beans are removed from the pod, they
have their surface covered by a mucilaginous pulp. This
pulp contains non-reducing sugars and other nutrients
that are utilized by microorganisms such as yeast, lactic
acid and acetic acid producing bacteria, and aerobic
mesophilic bacteria that proliferate over this pulp in the
surface of the beans. Non-reducing sugars are converted
by microorganisms to reducing sugars of lower molecular
weight, alcohols, lactic acid, acetic acid, and other
compounds. Also, protein is hydrolyzed to form peptides
by Afoakwa et al. [22] and Lagunes Galvez et al. [23], who
studied the change in biochemical composition of cocoa
beans during fermentation.
The results of other proximal analysis of
Trinitario cocoa beans are presented in Table 3 for the
whole and peeled beans and shells.
The results for the whole beans are similar to
those presented by other authors [3, 4, 17, 18].
pointed out that a smaller but substantial amount of fat
was present in the cocoa bean shell.
The statistical analysis showed that crude
this in turn, lower than in the whole bean (12.65%). The
lower protein content in the shell could be explained by
protein degradation and utilization by microorganisms
growing in the outer part of beans during fermentation.
and peeled beans (2.84%). Also, the ash content in peeled
beans was lower than in whole beans. It is known that
the shell is a good source of minerals, particularly various
phosphates and potash, allowing its use as a light fertilizer
[20].
Thermal analysis of cocoa
Thermal analysis of cocoa constituents was carried
out by means of DSC and TGA. Figure 1 shows DSC curves for
cocoa bean shell, peeled cocoa bean and whole cocoa bean.
events with peaks at 18.9/31.4°C and 18.4/30.4°C for
whole and peeled cocoa beans, respectively. On the other
hand, shells exhibit the bimodal peaks at 17.8 and 30.4°C.
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 1, 2019, Enero-Abril, pp. 03-47
43Composition and thermal characteristics of components of Venezuelan Trinitario cocoa beans
Table 3. Analyses of Venezuelan Trinitario cocoa beans: crude fat, protein, and ash (wet basis) of whole and peeled cocoa
beans and shells.
Crude fat content (% wet basis)
Cocoa bean and
constituents Average* Standard
deviation Range
Whole beans 44.23a0.30 44.52-43.93 43.89-44.57
Peeled beans 42.73b0.59 43.30-42.12 42.06-43.39
Shells 6.53c0.31 6.87-6.26 6.18-6.88
Crude protein content (% wet basis)
Cocoa bean and
constituents Average* Standard
deviation Range
Whole beans 12.65a0.22 12.86-12.43 12.41-12.90
Peeled beans 12.25b0.16 12.40-12.08 12.07-12.43
Shells 10.27c0.68 10.95-9.59 9.50-11.04
Ash content (% wet basis)
Cocoa bean and
constituents Average* Standard
deviation Range
Whole beans 3.34a0.03 3.31-3.37 3.31-3.37
Peeled beans 2.84b 0.04 2.88-2.80 2.79-2.88
Shells 6.10c0.07 6.14-6.05 6.05-6.15
These endothermic events correspond to the melting
of the different stable forms of cocoa butter. As known,
cocoa butter can crystallize in six different forms; i.e., it
is polymorphic, namely from the unstable form I to the
stable form VI, according to the nomenclature used in
chocolate industry. These different crystalline forms
melt in a relatively small temperature range varying
from 16-18°C for form I to 34-36°C for form VI, with the
intermediate temperatures values corresponding to the
melt of crystalline forms from II to V [24].
-10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60
31.4 °C
18.9 °C
30.4 °C
18.4 °C
30.4 °C
17.8 °C
CBS
PCB
CB
1 mW
Heat flow (mW) endo
Temperature (°C)
Figure 1. DSC heating scan for cocoa bean shell (CBS),
peeled cocoa bean (PCB), and whole cocoa bean (CB).
Figure 1 shows that the crystalline forms present
in cocoa constituents correspond to form I and form V, as
evidenced by the lower and higher temperature peaks in
the three DSC heating scans. The presence of these forms,
also named respectively g and b2, according to Greek letter
nomenclature, indicates the coexistence of the less stable
crystallites and the more desirable crystalline form in
2 form).
Thermal degradation behavior of cocoa
constituents was studied by TGA up to 900°C under
nitrogen atmosphere. The weight loss percentage due to
curve), are shown in Figure 2.
100 200 300 400 500 600 700 800 900
0
20
40
60
80
100
TG
DTG
Mass (%)
Temperature (°C)
(a)
-4
-3
-2
-1
0
First derivative (%/min)
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 1, 2019, Enero-Abril, pp. 03-47
44 Sandoval y col.
100 200 300 400 500 600 700 800 900
0
20
40
60
80
100
TG
DTG
Mass (%)
Temperature (°C)
(b)
-12
-10
-8
-6
-4
-2
0
First derivative (%/min)
Figure 2. TGA/DTA heating graphs for cocoa bean shell
(a), peeled cocoa bean (b), and whole cocoa bean (c)
temperature range of 25-160°C, with a peak at ca. 64°C.
Evaporation of moisture and water linked with the
structure has been associated to shell heating in this
temperature range [11]. The corresponding weight loss
at the end of this range was 10%. Figure 2a then shows
that pyrolysis starts with a shoulder at around 225°C,
followed by three peaks at 264, 324 and 464°C. The
shoulder has previously been related to the pyrolysis of
pectic polysaccharides in the shell [11]. The following two
peaks, on the other hand, have been linked to the thermal
degradation of high molecular weight macromolecules
such hemicellulose and cellulose [2, 11]. The high
temperature peak appearing at ca. 464°C and extending
to ca. 720°C indicates the thermal degradation of cocoa
butter and proteins [10, 11].
100 200 300 400 500 600 700 800 900
0
20
40
60
80
100
TG
DTG
Mass (%)
Temperature (°C)
(c)
-12
-10
-8
-6
-4
-2
0
First derivative (%/min)
The TGA graphs for peeled and whole cocoa
step in the same temperature range as that of the shell (25-
peeled and whole beans, respectively, is related to moisture
lost. The moisture content at the end of this temperature
range is around 4% for the peeled bean and 6% for the
230-350°C, related to the simultaneous pyrolysis of high
molecular weight polysaccharides which are also present
in these materials in smaller proportions. A marked peak
at ca. 400-415 °C are exhibited by both, peeled and whole
beans, evidencing thermal decomposition of fat. Finally a
wide mass step change between 500-700 °C is observed
in both TGA graphs, linked to protein decomposition
and further carbonization. Similar thermogravimetric
behavior has been reported for cocoa liquor, consisting of
cocoa butter and cocoa powder by Materazzi et al. [10].
Figures 2a through 2c also show that the
remaining mass at the end of the TGA tests were around
7%, 4%, and 5% of initial weight for shells, peeled and
whole beans, respectively. These percentages represent
the residues formed by carbonized sample (ashes). It is
grade samples in the same fashion as that shown in Table
3 for ashes content determined by standard methods.
Conclusions
The shell moisture was higher than that in the
whole and peeled beans. In spite of the fact that the shell
had higher moisture content than the peeled bean, its
water activity (aw) was lower, evidencing a higher water
binding capacity of the shell. This is probably due to the
formation during fermentation of compounds capable of
adsorbing water, such as reducing sugars, peptides, free
aminoacids, organic acids and minerals.
It was found that crude fat content was higher in
than that in shells. Crude protein content presented a
decreasing order for whole beans, peeled beans and shells.
in whole and peeled beans.
Thermal properties of cocoa constituents
showed bimodal endothermic events between 18-30°C,
indicating the coexistence of crystalline forms I (g) and V
(b2) in these materials. After water evaporation, occurring
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 1, 2019, Enero-Abril, pp. 03-47
45Composition and thermal characteristics of components of Venezuelan Trinitario cocoa beans
up to about 160°C, cocoa constituents decompose over a
residue of less than 10%.
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