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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
Diseño: Arquitecto Carlos Raúl
Villanueva, con elementos
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Zuliano Victor Valera.
VOL.42 MAYO - AGOSTO 2019 No.2
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 2, 2019, Mayo-Agosto, pp. 47-97
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 2, 2019, 47-53
Determination of the physical properties of fermented and
dried Venezuelan Trinitrio cocoa beans (Theobroma cacao
L.)
Aleida J. Sandoval1 ,José A. Barreiro1* , Andrea De Sousa1 , Danny Valera1 and
Alejandro J. Müller2
1Dept. de Tecnología de Procesos Biológicos y Bioquímicos.
2Dept. Ciencia de los Materiales. Universidad Simón Bolívar, Aptdo. 89000, Caracas 1080-A, Venezuela. Tel-Fax:
+58 212 9063953, *e-mail: asandova@usb.ve
https://doi.org/10.22209/rt.v42n2a01
Recepción: 02/05/2018 | Aceptación: 16/10/2018 | Publicación: 01/05/2019
Abstract
Some important physical properties of Venezuelan Trinitario cocoa beans (Theobroma cacao L.) were determined,
such as average dimensions of beans (length, width and thickness), bean weight; weight of 1000-beans; sphericity; geometric
diameter; geometry index; surface area; bean volume; bulk density; particle density; and porosity. The shape of the beans
could be approximated to that of a scalene ellipsoid, characterized by three different orthogonal dimensions (length, width
different surfaces (nitrile rubber, plywood, galvanized steel, carbon steel, glass and stainless steel).
Keywords: cocoa bean, water activity, physical properties
Determinación de las Propiedades Físicas de Habas
Fermentadas y Secas de Cacao Trinitario Venezolano
(Theobroma cacao L.)
Resumen
cacao L.) fermentadas y secas, incluyendo sus dimensiones promedio (longitud, ancho y espesor), así como peso de un haba;
aparente; densidad de partícula; y porosidad. La forma de las habas puede aproximarse a la de un elipsoide escaleno,
inoxidable).
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 2, 2019, Mayo-Agosto, pp. 47-97
48 Sandoval y col.
Introduction
International trading of Trinitario cocoa beans
(a hybrid of Criollo and Forastero types), is an important
commodity export for Venezuelan along with the Criollo
mixed with other cocoa bean varieties in order to improve
This product is usually well fermented; sun dried and
packaged in new jute clean sacks. If well fermented and if it
complies with the required Venezuelan quality standards
Fino de
Primera”).
Physical properties of food products, including
cocoa beans, are required for proper engineering design
of processing, cleaning, grading, conveying, drying, and
transportation equipment. Also, they are important for
analyze the heat and mass transfer processes involved
in processing and preservation. Few research works
regarding the physical properties of cocoa beans have
been found in the literature. Bart-Plange and Baryeh [2]
determined different physical parameters for category
B cocoa beans from Ghana (i.e., beans having less than
100-beans in a 100 g sample). The authors studied a
that the moisture content did not have any remarkable
and W/T (width to thickness). The same phenomenon was
found for sphericity and surface area. As expected, higher
moisture resulted in an increase in the average individual
weight, 1000-bean weight, particle density, porosity,
effect in bulk density. Proximate analyses of whole cocoa
beans have been reported by different authors [3-6] for
both non-fermented and fermented whole cocoa beans
from Venezuela. Afoakwa et al. [7] studied the change in
composition of cocoa beans during pod pretreatment and
fermentation. Pod pretreatment consisted on storing the
pods at temperature of 25-28 °C and 85-100 % relative
humidity for periods from 3-10 days.
literature regarding the physical-chemical properties of
cocoa beans and particularly of the Trinitario type, grown
in Venezuela. The objective of this research work is to
determine important physical properties of Venezuelan
fermented and dried Trinitario cocoa beans.
Experimental Section
Raw material, sample preparation and
characterization
Fermented cocoa beans Trinitario type, were
grown and harvested in 2014, at Cúpira (Pedro Gual
municipality), Miranda state, Venezuela, and packed in
new clean jute sacks. The cocoa beans were graded as
Fino de Primera), by Cacao
de Origen, Hacienda La Trinidad, Caracas, Venezuela,
according to the Venezuelan standard for cocoa beans
[1]. A composite sample of about 5 kg of cocoa beans was
provided by the same.
The chemical characterization of the cocoa beans
used in this research was carried out and reported in a
previous work [8]. The values reported for the proximate
analysis were (g/100 g ± standard deviation): Moisture
= 6.51 ± 0.05; fat = 44.23 ± 0.30; protein = 12.65 ± 0.22;
ash = 3.34 ± 0.03. The water activity measured (25-27 °C)
averaged 0.617 ± 0.010.
The study of physical characteristics of cocoa
beans was restricted to the practical moisture content
range required for proper cocoa bean preservation after
fermentation and drying (6-7% wet basis). For all the
experimental parameters determined, the statistical
measures of central tendency and dispersion were
calculated. The following measurements were done:
a) Average bean dimensions. A 100-bean sample was
randomly selected from a divided 1000-bean sample,
and the characteristic perpendicular dimensions of each
bean measured using a vernier caliper, SciencewareTM
type 6914 (± 0.1 mm) [2]. The characteristic dimensions
(mm): length (L), width (W) and thickness (T) are
shown in Figure 1.
Figure 1. Dimensions of cocoa beans (L: length, W: width,
T: thickness)
The following physical properties were
calculated with the average bean dimensions (L, W, T),
using the equations recommended by the references
indicated:
b) Geometric diameter Dg, [9]: (1)
c) Sphericity [2 ,9 , 10]:
d) Geometry index [11]:
(2)
(3)
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 2, 2019, Mayo-Agosto, pp. 47-97
49
Physical properties of Trinitario cocoa beans
e) Bean surface area S (mm2) [12]: by the volume of toluene displaced by them with the
following equation:
(4)
Where a, b and c are the semi-dimensions of the
scalene ellipsoid l/2, w/2 and t/2 respectively.
Bean surface area S (mm2) [13]: (5)
f) Individual bean weight and weight of 1000-beans.
Average individual bean weight was estimated weigh-
OhausTM analytical balance, model Adventurer (± 0.0001
g) and calculating in each case the average weight of one
bean. Weight of 1000-beans was calculated weighing
-
tronic MettlerTM balance model PM16-N (± 0.1 g).
g) Bulk density. Bulk density (b) was determined using
a test weight method at room temperature (21°C). The
-
drical container with known volume (469.5 mL), from a
height of 5 cm above the edge of the container. The top
was leveled with a ruler without compaction after tap-
ing a couple of times. The container was emptied and
the beans weighed using an electronic MettlerTM balance
model PM16-N (± 0.1 g). Bulk density was calculated
dividing the sample weight (Wbeans) by the container
volume (Vcnt). The experiment was done by sextuplicate.
h) Volume and particle density. Cocoa bean volume
(V) and density (p) were evaluated by triplicate, using
the pycnometric method with toluene described else-
where [9, 14]. In each experiment, the sample consisted
in three beans selected at random. Both, the sample
(Ws) and the pycnometers (Wp) were weighed using an
analytical balance (OhausTM, Adventurer ± 0.0001g). The
experiments were done at constant temperature using
a PolyScienceTM thermostatic bath at 20°C (± 0.01°C).
Toluene ACS reagent grade (>99.5%), Fluka Chemie AG,
was used. The following formula was used:
(6)
Being: Vs: total volume displaced by sample
(mL), Ws: sample weight (g), Wp: weight of the empty
with toluene (g), Wps: weight of the empty pycnometer
with sample and toluene (g), tol (20°C): toluene density at
20°C=0.8623 g/mL [15]. The average volume of one bean
V (mL) was the total sample volume displaced by sample
(Vs) divided by three. The particle (bean) density (p) was
calculated by dividing the weight of the sample of beans
In this case, the linear semi-dimensions of the
beans measured before: L/2, W/2 and T/2 were used for
the calculation.
i) It is the fraction of void space existing
in a bulk bean volume entraining air and not occupied
by the beans [17]. It can be calculated with the particle
density (p) and the bulk density (b) using the equation
(9) [2, 14]):
In order to compare the experimental volume
obtained with the volume of a scalene ellipsoid, the exact
mathematical formula can be used [12, 16]):
j) .
f) was determined by quin-
tuplicate using a hollow plastic cylinder open at both
ends with a diameter of 14 cm and height of 50 cm. The
beans. The cylinder was slowly lifted at a rate of about
2 cm/s until the entire cylinder was discharged and the
product accumulated over the glass support forming a
cone. The heap height (H) and diameter (D) of the cone
were measured using a metric tape (± 1 mm). The angle
of repose f (°) was calculated using the trigonometric
formula:
The emptying angle of repose (e) was
determined by quintuplicate using a method similar to
that presented by Koocheki et al. [14]. A wooden box of
approximately 20x20x20 cm open on top and with a
The angle was calculated from measurements done with
a metric tape (± 1 mm) of the height of the heap at two
points and the horizontal length between them, applying
the trigonometric equation:
Where e is the emptying angle of repose (°),
H0a, H0b are the heap height at two points (mm), and Z the
horizontal distance between points H0a and H0b (mm)
(s) of the beans
(7)
(8)
(9)
(10)
(11)
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 2, 2019, Mayo-Agosto, pp. 47-97
50 Sandoval y col.
was determined by the method outlined by Kaliniewicz et
al
materials were used (plywood, galvanized steel, stainless
steel, carbon steel, glass and rubber). These are materials
frequently used for transportation, storage and handling
grains and seeds. The rugosity of each surface (Ra)
was measured using a Mitutoyo Surftest-211 surface
roughness tester. This device was previously calibrated
(Ser. 310179 / 2.95 µm). All tests were conducted at a
controlled temperature (20 ± 1°C). Ten measurements
were done for each surface tested. The test plate had an
adjustable angle of inclination graduated by means of
a hydraulic piston. Five beans were randomly selected
for each experiment. The orientation of the longitudinal
axis of beans on the friction plate in relation with the
direction of movement was set at different angles from
0, 45, 90, and 135° approximately. The experiments were
done by quintuplicate for each surface. The inclination
trigonometry:
Statistical analyses. Measures of central
tendency and dispersion and Student t-tests were
calculated using Microsoft ExcelTM 2016.
Results and Discussion
The results obtained for the evaluation of some
physical properties of cocoa beans are presented in Table
1.
The visual assessment of Trinitario cocoa
beans revealed an oblong-prolate shape, with three
perpendicular dimensions as presented in Figure 1: length
(L), width (W) and thickness (T). The results obtained for
these dimensions are presented in Table 1. These values
by Bart-Plange and Baryeh [2] for beans from Ghana
(Category B) with a moisture content of 8.6% (wet basis);
and similar to those presented by Alvarez et al. [5] for
commercial Venezuelan cocoa beans with 5.17% moisture
content. Average dimensionless ratios calculated from
dimensions measured in this work were: L/T=2.51 ±
0.31 and W/T=1.43 ± 0.22. These ratios were similar to
those presented by García-Alamilla et al. [10] for Mexican
fermented Criollo cacao with moisture content of around
8% (dry basis) of L/T =2.63 and W/T=1.54. According to
the triangular diagram for particle shape description [20],
based on the dimensionless ratios obtained: T/L=0.498;
W/L=0.699; (L-W)/(L-T)=0.725.
Where, H2 and H1 are the height over the
horizontal plane of the inclined friction plate at two
points separated a distance X along the plate, measured
angle of the friction plate at which the bean started to
move. In this case, a sliding movement was observed, in
s) was calculated
Table 1. Results obtained for some of the physical properties studied of Venezuelan fermented cocoa beans variety
Trinitario with 6.51% average moisture content (wet basis).
Physical property Mean value Range Standard
deviation 95% condence
interval
Length (mm) 23.8 26.8-20.6 1.8 23.5-24.2
Width (mm) 13.5 15.9-11.3 1.3 13.4-13.8
Thickness (mm) 9.6 11.4-7.6 1.0 9.4-9.8
Sphericity 0.61 0.74-0.51 0.04 0.60-0.62
Geometric diameter (mm) 15.9 16.1-13.7 0.53 15.8-16.0
Geometry index 0.51 0.66-0.38 0.07 0.50-0.52
Average bean volume (mL) 1.72 1.77-1.63 0.05 1.59-1.85
Surface area (mm2) 742.4 932.3-587.0 74.4 727.8-757.0
Bean weight (g) 1.44 1.46-1.41 0.02 1.41-1.47
1000-bean weight (g) 1421.3 1422.8-1418.6 1.66 1419.2-1423.4
Bulk density (g/mL) 0.552 0.561-0.542 0.008 0.544-0.560
Bean density (g/mL) 0.971 0.994-0.937 0.030 0.897-1.044
Porosity (void fraction) 0.432 0.438-0.422 0.009 0.410-0.454
(12)
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 2, 2019, Mayo-Agosto, pp. 47-97
51
Physical properties of Trinitario cocoa beans
The sphericity, geometric diameter and
geometry index were calculated with the bean dimensions
obtained for each cocoa bean measured. Mean values,
these parameters are presented in Table 1. The average
sphericity value obtained compares satisfactorily with that
reported by Bart-Plange and Baryeh [2] and with those
reported for fermented Mexican Criollo cocoa beans by
Garcia-Alamilla et al. [10]. The value agreed qualitatively
with that of an elongated solid, as commented before.
The average bean volume determined
experimentally using the pycnometric method was 1.72
mL (Table 1). A volume of 1.62 ± 0.45 mL was obtained
using the exact mathematical equation (8) to determine
the volume of a scalene ellipsoid. The statistical analysis
(p>0.05) in bean volume between the pycnometric
experimental value and the mean value obtained using
the mathematically exact equation for scalene ellipsoids,
evidencing that Trinitario cocoa beans studied in this
work could be safely approximated to this geometry.
In view of this, the surface area was calculated using
Flammenkamp’s equation (4) for scalene ellipsoids. A
single bean average surface area of 742.4 ± 74.4 mm2 was
obtained, (Table 1). The surface area was also calculated
with equation (5) presented by McCabe et al. [13]. A
single bean average surface area of 794.1 ± 50.0 mm2
was obtained, with a range of 825.5-586.2 mm2 and 95%
2. The t-test
between the mean value predicted by Flammenkamp’s
equation (4) and the average surface area calculated using
equation (5), indicating that equation (5) is not adequate
to predict the bean volume.
Average weight obtained for a single cocoa
bean was 1.44 g ± 0.03 g (Table 1). Values reported in
the literature (1.19 to 1.26 g) [2, 5, 6] evidenced smaller
beans than in the present investigation. The weight of
1000-beans showed an average of 1421.3 g ± 1.2 g; which
by Bart-Plange and Baryeh [2] of 1124 g for Class B cocoa
beans from Ghana with 7.5% moisture in wet basis.
in the bulk density of cocoa beans (b = 0.552 ± 0.008
g/mL, Table 1) and the value reported by Bart-Plange
(p>0.05) was found between the average particle density
(p) determined by the pycnometric method in this work
(0.971 ± 0.030 g/mL, Table 1) and that reported by Bart-
Plange and Baryeh [2] of 0.935 g/mL for cocoa beans with
6.5% moisture (wet basis).
of bulk and particle density, showed an average value
of 0.432 ± 0.0
Plange and Baryeh [2] for cocoa beans from Ghana with a
moisture content of 8.6% (wet basis). However, there were
reported by Nganhou et al. [21] of 0.456 using drying data
of a bed of cocoa beans.
The results obtained for the frictional properties
studied in the different surfaces and their rugosity are
shown in Table 2.
Table 2. Frictional properties of Venezuelan Trininario cocoa beans with 6.51% average moisture content (wet basis) on
six different surfaces. Surface rugosity (Ra) (µm) is shown in cursive script in parenthesis
Frictional property Mean value Range Standard
deviation
95% condence
interval
Angle of repose (°) 19.6 21.2-17.1 1.8 18.1-21.0
Emptying angle of repose (°) 21.8 24.3-19.8 1.9 19.9-23.6
Static friction coefcient (µs) on:
Plywood (6.63)0.53 0.61-0.44 0.08 0.49-0.57
Steel-galvanized (0.66)0.49 0.53-0.41 0.04 0.47-0.51
Steel-carbon (1.15)0.47 0.49-0.35 0.09 0.42-9.52
Stainless steel-304 (0.48)0.28 0.39-0.25 0.06 0.24-0.32
Rubber-nitrile (1.56)0.62 0.71-0.36 0.11 0.55-0.69
Glass (0.05)0.42 0.58-0.30 0.11 0.36-0.48
average emptying angle of repose presented in Table
presented by Bart-Plange and Baryeh [2] of 23.74 and
25.5, respectively. This was probably due to the smaller
size of cocoa beans used by them that resulted in larger
Rev. Téc. Ing. Univ. Zulia. Vol. 42, No. 2, 2019, Mayo-Agosto, pp. 47-97
52 Sandoval y col.
angles of repose. The emptying angle of repose was larger
friction strongly depends on the normal load, material
properties, local interfacial strength and roughness
parameters [22]. The variability found regarding the
surface rugosity could originate in the differences in cocoa
beans weight, dimensions, bean surface irregularities,
roughness and angles at which they were placed on the test
surface. All those factors are known to affect the friction
direction perpendicular to the wood grain. There were
and galvanized steel in this work and those presented by
Bart-Plange and Baryeh [2] (0.54 and 0.46, respectively).
was highest for nitrile rubber, decreasing for plywood,
galvanized steel, carbon steel, glass and stainless steel.
A similar behavior was found by Gupta and Kumar [23]
galvanized iron, aluminum and stainless steel.
Conclusions
Important physical properties of well fermented
and dried Venezuelan Trinitario cocoa beans with 6.51%
(wet basis) moisture content were obtained in this
work, such as: bean dimensions; bean weight; weight of
1000-beans; sphericity; geometric diameter; geometry
index; surface area; bean volume; bulk density; particle
density; and porosity (void fraction). The shape of
Trinitario cocoa beans studied can be approximated
to a scalene ellipsoid, characterized by three different
orthogonal dimensions (length, width and thickness).
This fact could be established by taking into consideration
that the bean volume obtained experimentally did not
the volume for a scalene ellipsoid of the same dimensions
calculated using the mathematically exact equation for
of repose were determined, as well as the static friction
of engineering interest in the design of equipment for
processing, handling and storing this product.
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Esta revista fue editada en formato digital y publicada
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