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European Journal of Applied Sciences – Vol. 12, No. 3
Publication Date: June 25, 2024
DOI:10.14738/aivp.123.17053
Badila, J. M. M., Biassala, E. T., Ngounga, C. K., Gobet, D., & Silou, T. (2024). Kinetics of Oven Drying of Ocimum basilicum Leaves
Harvested at Different Ages of Maturity. European Journal of Applied Sciences, Vol - 12(3). 278-291.
Services for Science and Education – United Kingdom
Kinetics of Oven Drying of Ocimum basilicum Leaves Harvested at
Different Ages of Maturity
Jeantia Michaely Matoko Badila
Department of Food Chemistry and Technology,
Faculty of Science and Techniques, (UMNG), Congo
Eliane Thérèse Biassala
Department of Food Chemistry and Technology,
Faculty of Science and Techniques, (UMNG), Congo
Célestine Kiminou Ngounga
Process Engineering Laboratory,
UNESCO-ENSP Chair, UMNG. Congo
Danielle Gobet
Department of Food Chemistry and Technology,
Faculty of Science and Techniques, (UMNG), Congo
Thomas Silou
Department of Food Chemistry and Technology,
Faculty of Science and Techniques, (UMNG), Congo and
Higher School of Technology Les Cataractes BP: 389, Brazzaville, Congo
ABSTRACT
Drying is a unitary operation that involves the simultaneous transfer of heat and
humidity to reduce the water content of products to a safe level. This work
therefore aims to study the characteristics of drying in an oven through the effect
of temperature and drying time on Ocimum basilicum leaves harvested at different
stages of maturity and to adapt the drying data into ten mathematical models to
determine which one is best validated by experimental data. The leaves studied
were collected at well-defined time intervals corresponding to the level of growth
or maturity of the plants, i.e. one month, two months and three months. Drying
was carried out using a natural convection oven at temperatures of 70, 80 and 90
°C. The water content varied from 80 to 86% depending on the age of the leaves.
The drying speed was rapid at the beginning of the process and decreased after 60
min. The coefficient of determination and chi-square were used as statistical
parameters for comparing the accuracy of the models. The Wang and Sing and
Exponential models gave a better fit and better validated the experimental data
compared to the other models whatever the temperature and age of the leaves.
Keywords: Drying temperature, Drying kinetics, Modeling, Ocimum basilicum, water
content.
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Badila, J. M. M., Biassala, E. T., Ngounga, C. K., Gobet, D., & Silou, T. (2024). Kinetics of Oven Drying of Ocimum basilicum Leaves Harvested at
Different Ages of Maturity. European Journal of Applied Sciences, Vol - 12(3). 278-291.
URL: http://dx.doi.org/10.14738/aivp.123.17053
INTRODUCTION
In most sub-Saharan countries, particularly in Congo, the sustainability of agri-food activities
is not well assured; this can be justified by several reasons, including poor quality control and
poor conservation of processed products. These difficulties are attributable to the complexity
linked to the production process and a very restrictive environment.
The overall challenge is to promote, through the optimization of integrated processes and unit
operations, sustainable product stabilization and transformation systems.
The optimization of these processes is based on a prior analysis of the product functions and
the variables implemented within each of the identified unit operations. Improved processes
make it possible to make the most of local biodiversity and open up new markets both locally,
regionally and for export.
The optimization of the extraction of essential oils depends very largely on the knowledge of
fundamental physical phenomena, for example, the way in which the oil is released from the
plant matrix under the effect of heat but also on the control of the drying process subsequent
to the extraction process and the quality of which influences the profitability of the latter.
Drying is a unitary operation that involves simultaneous transfer of heat and humidity to
reduce the moisture content of products to a safe level (Mujumdar and Menon, 1995). In other
words, drying can be defined as the process of removing moisture due to heat and mass
transfer between the biological product and the drying air by evaporation, and generally
caused by temperature and air convection forces (Perea-Flores, 2012).
In order to model drying curves, several authors have developed numerous kinetic models.
Mathematical modeling of the drying process helps predict the moisture removal behavior of
materials, reduces drying time and costs, and helps in the invention of suitable drying
equipment (Keneni, 2019).
The mechanism of the extraction process as well as that of drying equivalent to the water
extraction process can be explained by different models in the literature.
A very wide variety of plant species has been studied: Lavanda officinalis (Stanojevic et al,
2011), Salvia officinalis (Velickovic et al., 2001), Thymus vulgaris (Golmakani and Rezael,
2008), Apium graveolens (Sowbhagya et al. 2007), Ocimum basilicum (Cassel et al., 2009),
Mentha piperita (Ammann et al., 1999), Eucalyptus grandis (Kabuba, 2013), Eucalyptus cinerea
(Babu et al., 2009), Cymbopogon winterianus (Cassel and Vergas , 2006; Farhana et al., 2019),
Cymbopogon spp (Koul et al., 2004; Amenaghawon et al., 2014), Cymbopogon citratus (Thanh
et al., 2017).
The drying process can be described using theoretical and empirical models available in the
literature. Different drying models are analyzed and the model best suited to the drying
kinetics of the product considered is selected (Mambou et al., 2023). However, there does not
appear to be any information available on the drying kinetics of Ocimum basilicum leaves. The
genus Ocimum includes at least 65 species distributed in tropical and subtropical areas of
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European Journal of Applied Sciences (EJAS) Vol. 12, Issue 3, June-2024
Asia, Africa and South America (Makri, 2007). Ocimum basilicum, commonly known as basil,
has considerable economic and cultural importance, particularly as a food spice. This work
therefore aims to study the characteristics of drying in an oven through the effect of
temperature and drying time on the leaves of Ocimum basilicum at different stages of maturity
and to adapt the drying data in ten mathematical models to determine which one is best
validated by experimental data.
MATERIALS AND METHODS
Plant Material
Cultivation of Ocimum basilicum:
Ocimum basilicum was grown in Brazzaville precisely at AgriCongo 2 in Tsamba (Mayanga) in
January 2023 on a bed 1.15 m wide and 20 m long with a height of 35 cm. The bed was
loosened, cleared of any debris and enriched with well-decomposed organic matter to
accelerate the growth of seeds and the development of young plants. After abundant watering
of the bed for five days, small basil plants (786 plants in total) were transplanted to a depth of
approximately 2 cm from the soil.
Harvesting Ocimum basilicum Leaves:
Leaf harvesting was carried out at well-defined time intervals corresponding to the level of
growth or maturity of the plants, i.e. one month (Figure 1a), two months (Figures 1b) and
three months (Figure 1c). The choice of samples to study was made by drawing lots.
a) One month b) Two months c) Three months
Figure 1: Growth level of the Ocimum basiculum plants studied
Methods
Drying Kinetics of Harvested Leaves
Oven Drying Kinetics:
Drying was carried out using a Memmert brand UN30 natural convection oven. 100 g of fresh
leaves of Ocimum basilicum are separately dried at 70, 80 and 90 o C in an oven, and every 30
minutes the mass is weighed; the drying kinetics stops when the mass value becomes
constant (total evaporation of water). The weighings were carried out using a CONSTANT
brand analytical balance with a resolution of d=0.01 g.
Air Drying Kinetics:
100 g of fresh leaves of Ocimum basilicum are dried at room temperature.
• 1st day of drying: The mass is weighed every hour (for seven hours)
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Badila, J. M. M., Biassala, E. T., Ngounga, C. K., Gobet, D., & Silou, T. (2024). Kinetics of Oven Drying of Ocimum basilicum Leaves Harvested at
Different Ages of Maturity. European Journal of Applied Sciences, Vol - 12(3). 278-291.
URL: http://dx.doi.org/10.14738/aivp.123.17053
• 2nd day of drying: the mass was weighed twice during the day, after 24 hours and 32
hours
• 3rd day of drying: the mass was weighed twice during the day, after 48 hours and 56
hours
The experimental curves are obtained by the evolution of the wet mass m of the leaves during
drying by successive weighing until product stability is reached.
Using the mass of product measured, the water content on a dry basis is calculated by the
following formula:
X =
m−MS
MS
(1)
With X: water content on a dry basis; m: mass of the product in grams; MS: mass of dry
matter.
Thus, the instantaneous drying speed as a function of time t is determined by the following
formula:
−
dX
dt =
−[X(t+∆t)−X(t)]
∆t
(2)
With dx/dt: drying speed; X: water content on a dry basis; t: time, ∆t: Time variation
The moisture ratio (TH) is calculated as follows:
TH =
mt−me
m0−me
(3)
With: mt: mass of the product at any t; me: mass of the product at equilibrium; m0: initial mass
of the product.
Modeling of Drying Kinetics
Modeling the drying kinetics of Ocimum basilicum leaves was carried out by the Origin Pro
2018 software while following the models chosen in Table 1. The data predicted by the
mathematical models were fitted to the drying curves of the experimental data to select the
models that best describe the drying process of the leaves studied.
Table 1: Mathematical models of drying kinetics used
Model name Model Reference
Newton TH = exp(-kt) Lewis, 1921
Henderson & Pabis TH=aexp(-kt) Zhang et al., 1991
Page TH=exp(-ktn
) Zanthopoulous et al., 2007
Page modifié TH=exp(-(kt)n
) Zarein, Samadi et al., 2015
Logarithmic TH=aexp(-kt)+c Corzo et al., 2011
Two exponential terms TH= a exp(-kt)+(1-a)exp(-kat)
Wang and Sing TH=1+at+bt2
Sharma et Prasad., 2004
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Thompson TH=exp(-a-(a2+4bt)1/2)/2b
Midilli TH=aexp(-ktn
)+bt Zarein, Samadi et al., 2015
Exponential TH=y0+Aexp(R0t)
Statistical Analysis
Chi-square (χ2) and coefficient of determination (R2) are statistical parameters used to
determine the degree of model fit. The highest R2 value, close to 1, represents the best fit of
the model (Mambou et al., 2023). However, the best-fitting model should have the lowest
values of χ2 (Mambou et al., 2023).
RESULTS AND DISCUSSION
Drying Characteristics
Drying curves were obtained by plotting leaf moisture content against drying time. These
drying curves were used to determine the effect of temperature on the drying process of
Ocimum basilicum leaves using the experimental drying data obtained by varying the
temperature (70, 80 and 90°C) during the drying time.
Figure 1 presents the results of the drying process and clearly shows that the drying kinetics
of Ocimum basilicum leaves mainly depends on the drying temperature and the age of the
leaves.
Figures 1a, 1b and 1c illustrate the variation in humidity level (reduced water content) as a
function of oven drying time respectively for leaves harvested 1, 2 and 3 months after
cultivation. As can be seen, the reduced water content decreases depending on the drying
temperatures but also the age of the plant. This clearly explains that increasing the drying
temperature leads to an increase in the moisture evaporation rate in Ocimum basilicum leaves.
This same phenomenon was observed by Akpinar (2006) during the drying of Ocimum
basilicum L. leaves at different temperatures. The same goes for the authors Kivaandra et al.,
(2021), Premi et al., (2012) who worked on the influence of drying temperatures on the
humidity level of Moringa oleifera leaves.
A moisture content value close to zero indicates the end of the drying process. This means
there is no change in moisture content.
Moisture content shows an exponential decrease over time at all temperatures and different
leaf ages. This moisture content behavior observed for drying Ocimum basilicum leaves is very
similar to that of other biological materials (Perea-Flores, 2012).
All these curves indicate a loss of the quantity of water contained in fresh leaves. The
humidity rate values all start from one (1) (i.e. 100 g of fresh material) and stabilize at values
close to zero as a function of time.
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Badila, J. M. M., Biassala, E. T., Ngounga, C. K., Gobet, D., & Silou, T. (2024). Kinetics of Oven Drying of Ocimum basilicum Leaves Harvested at
Different Ages of Maturity. European Journal of Applied Sciences, Vol - 12(3). 278-291.
URL: http://dx.doi.org/10.14738/aivp.123.17053
a) Ocimum basilicum leaves at one
month
b) Ocimum basilicum leaves at two
months
c) Ocimum basilicum leaves at three
months
Figure 1: Leaf drying curves at temperatures of 70, 80 and 90°C.
Figure 1a represents the results of the drying kinetics of Ocimum basilicum leaves harvested
after one month. During these operations, the process stops when the humidity rate values
reach the value of zero, which corresponds for this study to the value of the dry mass
0
0.2
0.4
0.6
0.8
1
1.2
0 200 400 600
TH
Temps(min)
TH à70°C
TH à80°C
TH à 90°C
0
0.2
0.4
0.6
0.8
1
1.2
0 100 200 300 400 500
TH
Temps (min)
TH à 70°C
TH à 80°C
TH à 90°C
0
0.2
0.4
0.6
0.8
1
1.2
0 50 100 150 200
TH
Temps(min)
TH à 90°C
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stabilizing around 13 g at the 570th minute for the temperature of 70°C, 270th minutes for
the temperature of 80°C and 210th minutes for the temperature of 90°C, or 86.65% of water
evaporated (figure 2). Drying kinetics of Ocimum basilicum leaves harvested after two months
(figure 1b) show faster water evaporation compared to those of 1-month old leaves. The mass
values stabilize around 19 g (i.e. TH = 0) at the 360th minute for the temperature of 70°C,
240th minute for the temperature of 80°C and 210th minute for the temperature of 90°C, i.e.
80 .13% water evaporated (figure 2).
The drying kinetics of the three-month Ocimum basilicum leaves (figure 1c) was only achieved
at 90°C. the mass value quickly stabilized at 18 g (TH=0) at the 186th minute, i.e. a percentage
of water evacuated of 81.91% (figure 2).
Figure 2: Variation in the quantity of external water as a function of time at 90°C (of the three
harvests)
Examination of Figure 2 shows that after one month of cultivation, the leaves of Ocimum
basilicum are more humid with a water content of 86.65%; after two months the water
content is 80.13% and after three months the content is 81.91%. It is obvious to conclude that
the humidity level of basil leaves decreases as the plant ages and stabilizes after three months.
The variation in the quantity of external water is the quantity of water released during the
drying kinetics of the leaves of Ocimum basilicum. Figure 2 presents three curves (mext1,
mext2 and mext3) of variation in the quantity of external water as a function of time and
which correspond to the ages of the leaves studied.
For the three curves we see that:
• Before drying (t=0min) the leaves have not yet lost water;
• Throughout drying, the quantity of water present in the plant material gradually
increases, until it reaches a constant. The mass of water present in 100g of Ocimum
basilicum leaves is around 80g.
The curves in Figures 3a, 3b and 3c show us the evolution of the oven drying speed of Ocimum
basilicum leaves as a function of time.
0
10
20
30
40
50
60
70
80
90
100
0 50 100 150 200 250
meau(ext)
t(min)
meau(ext)1 meau(ext)2 meau(ext)2
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Badila, J. M. M., Biassala, E. T., Ngounga, C. K., Gobet, D., & Silou, T. (2024). Kinetics of Oven Drying of Ocimum basilicum Leaves Harvested at
Different Ages of Maturity. European Journal of Applied Sciences, Vol - 12(3). 278-291.
URL: http://dx.doi.org/10.14738/aivp.123.17053
a) Ocimum basilicum leaves at one
month
b) Ocimum basilicum leaves at two months
c) Ocimum basilicum leaves at three months
Figure 3: Variation in the drying speed of Ocimum basilicum L. leaves over time
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0 200 400 600
Vitesse (g.g
-1.min
-1
)
Temps (min)
vitesse à 70°C vitesse à 80°C
vitesse à90°C
0
0.01
0.02
0.03
0.04
0.05
0 200 400 600
vitesse (g.g
-1.min
-1
)
temps (min)
vitesse à70°C vitesse à 80°C
vitesse à 90°C
0
0.01
0.02
0.03
0.04
0.05
0 50 100 150 200
vitesse (g.g
-1.min
-1
)
temps (min)
vitesse