International Food Research Journal 22(1): 393-397 (2015)

Journal homepage: http://www.ifrj.upm.edu.my

Drying behaviour of Andrographis paniculata in vacuum drying

Hee, Y.Y. and *Chong, G.H

.
Department of Food Technology, Faculty of Food Science and Technology, Universiti Putra Malaysia
43400 UPM, Serdang, Selangor, Malaysia

Article history Abstract

Received: 18 May 2014 Hempedu bumi (Andrographis paniculata, AP), also known as the king of bitters, is an herb
Received in revised form: commonly found in Asian communities for medicinal usage. The drying behaviour of AP at
30 July 2014
temperatures of 40, 50, and 60oC with vacuum pressures of 10 and 30 kPa was investigated
Accepted: 3 August 2014
in this study. The data were then fitted with semi-theoretical and theoretical thin-layer drying
Keywords models. The results reveal that the drying time is significantly (p<0.05) affected by temperature
and pressure. A two-term, thin-layer model was determined as the most suitable model to fit the
Vacuum drying drying behaviour of AP. The effective diffusivity and active energy for moisture diffusion were
Drying kinetics 10-13 m2/s and 33.4 kJ/mol, respectively.
Hempedu bumi © All Rights Reserved
Andrographis paniculata

Introduction Herbs have a moisture content as high as 80%.

Removal of the moisture from herbs is necessary to
Herbs are gaining popularity worldwide for their prevent microbial contamination and to allow for
medicinal use, as “going natural” is on an upward further processing. Drying is one of the most ancient,
trend. It is believed that herbs, which are natural but effective, preservative methods that can be used
substances, are safer than synthetic products. Hussin to extend an herb’s shelf life. Conventional drying
(2001) estimates that approximately 80% of the world methods, such as sun drying, have been used for many
population uses some form of herbal medicine. It has years, but the drying conditions are uncontrollable
been reported that Malaysians spent approximately and the process is time-consuming. Oven drying
RM2.0 billion on herbal products in 1997(Hussin, is also commonly used in the dehydration process;
2001). These data demonstrate that herbs are widely however, this method results in a loss of flavour,
accepted and have great market potential. colour, and nutrients due to the high temperature
Hempedu bumi (Andrographis paniculata (AP)) used (Sharma and Prasad, 2001). To prevent the loss
is an herb from the family of Acanthaceae, which of sensory and nutritive qualities of herbs, different
grows in India, China, and southeast Asia. It is well types of advanced drying techniques have been
known as the ‘king of bitters’. AP has shown beneficial developed. Freeze drying is able to maintain many
effects on hyperdipsia, burning sensations, wounds, of the bioactive components in herbs, but the drying
ulcers, chronic fever, malarial and intermittent fever, rate is slow (Krokida and Philippopoulos, 2006).
inflammations, diarrhoea, cough, and skin diseases Microwave drying can retain much of the quality
(Warrier et al., 1993); anti-angiogenic activity of the herbs and is efficient (Zhou et al., 2011).
(Sheeja et al., 2007); hepatoprotective activity and However, a disadvantage of microwave heating is
anti-platelet activity (Nagalekshmi et al., 2011); and non-uniformity within the drying cavity, which can
anti-diabetic potential (Reyes et al., 2006). Kumar lead to scorching of the drying material despite the
et al. (2004) suggested that AP contains anticancer presence of a turn-table (Mermelstein, 1998).
and immunostimulatory compounds. In Malaysia, AP Vacuum drying is a method of removing water
has been widely used for diabetes and hypertension. from moist materials at low pressures. The vacuum
Andrographolide is the major constituent extracted expands the air and water vapour in food products
from the plant and is responsible for the bitter taste and creates a frothy structure. This method offers
and functional properties of the plant (Parasher et advantages such as a higher drying rate, a lower
al., 2011). Andrographolide is a diterpene lactone drying temperature, an oxygen-deficient processing
and is insoluble in water. The maximum level of environment, and higher quality products compared
andrographolide is found in the leaves of the plant with those derived from conventional atmospheric
(Kurian et al., 2007). drying. Ah-Hen et al. (2013) report that vacuum

*Corresponding author.
Email: gunhean@upm.edu.my
394 Hee and Chong /IFRJ 22(1): 393-397

drying manages to shorten the drying time to 800 Table 1. Selected semi-theoretical and theoretical models
min rather than 1500 min at atmospheric drying. As for thin-layer drying
this method uses low temperatures, it is suitable for
heat-sensitive materials including fruits, vegetables,
and herbs. Studies of vacuum drying of eggplants,
carrots, apples, and pumpkins have been conducted
(Arevalo-Pinedo et al., 2004; Arévalo-Pinedo and
Murr, 2006; Wu et al., 2007). However, there is a
lack of reporting on the vacuum-drying kinetics of
AP. Therefore, the aim of this study was to fill this
gap in knowledge. This information is very useful for
designing a dryer and better understanding the drying
behaviour of AP.

Materials and Methods a, b,c= coefficient, k,ko= drying constant, L= half thickness of
slam (m), Deff= effective diffusivity (m2/s)
Materials and equipment
Fresh Andrographis paniculata was obtained and Ertekin, 2011; Mitra et al., 2011)because Me is
from MARDI, Serdang, and collected randomly to relatively smaller than Mt and Mo.
ensure that the sample was homogenised. The drying Several semi-theoretical and theoretical thin-
equipment used in this study consisted of a vacuum layer drying models (Table 1) were tested to select
oven (WTC Binder VDV53, Germany) and a double- the best model for describing the drying kinetics of
stage high-vacuum pump (Javac, Australia). AP under the vacuum conditions. By using SOLVER,
an optimisation tool in Microsoft Excel 2007, the
Drying experiment parameters of the different models were determined.
The experiments were conducted with 3 drying The lowest sum of the square error (SSE) difference
temperatures, 40, 50, and 60°C, at absolute pressure between the experimental and calculated moisture
of 10 and 30 kPa, with 3 replicates for each treatment. ratio was the criterion for choosing the best model
The vacuum-drying oven was preheated to the desired to describe the drying curve. In addition, the root
temperature. The leaves and stems of the herb were mean square error (RMSE) was used to determine
cut into small pieces of approximately 1 cm in length. the quality of the fit.
Then, 30 g of sample was spread in a single layer
on an aluminium tray and put in the drying chamber (3)
under the selected drying conditions. The vacuum
oven’s door was opened and the sample weight was where MRcal,i is the ith calculated moisture ratio and
recorded every 15 minutes during the initial drying MRexp,i is the ith experimental moisture ratio.
period. When a decrease in weight was not obvious, The effective diffusivity was related to
the drying period was extended to 30 minutes or 1 temperature by Arrhenius’ equation:
hour as necessary. The samples were dried until their
moisture content reached less than 0.11 kg water/ kg (4)
solid.
where D∞ is the pre-exponential factor of the
Mathematical modelling Arrhenius equation, Ea is the activation energy (kJ/
The moisture ratio (MR) and drying rate (DR) of mol), R is the universal gas constant (8.314 J/mol K),
AP during the thin-layer drying were determined as and T is the absolute temperature (K). The activation
energy was calculated by plotting the ln Deff versus
(1) 1/T.

(2) Moisture content determination

The moisture content of the samples was
where Mt is the moisture content of the sample at any determined using a moisture analyser (XM 120, Precisa
time, Me is the equilibrium moisture content, Mo is Instruments Ltd, Switzerland). For each moisture
the initial moisture content, and t is the drying time. content determination, a sample of approximately
However, the MR was simplified to Mt/Mo (Kayisoglu 1.0 g was placed in the sample pan of the apparatus.
This method was validated with the oven method by
 Hee and Chong/IFRJ 22(1): 393-397 395

Table 2. Drying time required to achieve 0.11 kg water/

kg solid for various drying conditions

Different letters (a, b, c) within each row indicate significant

differences (p<0.05).
Different letters (x, y, z) within each column indicate
significant differences (p<0.05). Figure 1. Drying rate of Andrographis paniculata under
Table 3. Results of fitness of various thin-layer drying various drying conditions
models at 10 kPa kg solid. The drying times required for various
conditions are shown in Table 2. From Table 2, we
can see that the temperature significantly affects the
drying time, where a higher temperature corresponds
to a shorter drying time. This result may be because
a larger driving force is implied for heat transfer and
mass transfer during drying at higher temperatures,
resulting in a higher moisture diffusivity (Nor et al.,
2009). This finding was similar to those in studies
utilising eggplant (Wu et al., 2007), sweet cherry
(Doymaz and İsmail, 2011), coconut presscake (Jena
and Das, 2007), Asian white radish slices (Lee and
Kim, 2009), carrot (Arevalo-Pinedo et al., 2004), and
pumpkin (Arévalo-Pinedo and Murr, 2006).
In this study, pressure was also found to affect
the drying time significantly (Table 2). Generally,
a longer drying time was needed as the pressure
increased from 10 to 30 kPa. This behaviour can be
explained by the fact that a reduction of pressure
results in a lower boiling point of water. At a lower
temperature, the water more easily converts to its
vapour form, and the driving force for the outward
moisture diffusion process increases. More water
vapour diffuses across the air-moisture interface
the AOAC standard moisture determination method and is available at the surface of the drying product.
930.15 with a 1 to 2% deviation. Thus, the moisture molecules can escape from the
drying product more easily and more rapidly (Nor et
Statistical analysis al., 2009). Similar behaviour has been reported for
The results of the data analysis are presented as carrot(Arevalo-Pinedo et al., 2004) and pumpkin
the mean values with standard deviations. Values (Arévalo-Pinedo and Murr, 2006).
were considered at 95% significance (α<0.05), and a
statistical program, Minitab 14, was used to perform Drying rate
the calculations. From Figure 1, it can be seen that the drying
rate was higher in the initial period of drying and
Results and Discussion decreased as the drying time increased. The initial
drying rate was also relatively higher as temperature
Drying characteristics increased at low pressure.
Fresh Andrographis paniculata (AP), with an
initial moisture content in the range of 2.41 to 2.88 Drying model
kg water/ kg solid, was dried in a vacuum dryer until Because a pressure of 10 kPa significantly
it reached a moisture content below 0.11 kg water/ shortened the drying time, the drying kinetics at this
pressure were studied. The moisture content data
396 Hee and Chong /IFRJ 22(1): 393-397

Table 4. Estimated values of the drying constants and

coefficients for the two-term thin-layer drying model

Table 5. Effective diffusivity of AP at various

temperatures and an absolute pressure of 10 kPa

Figure 2. Experimental and two-term model drying curves

at various drying temperatures and an absolute pressure
of 10 kPa

were converted into moisture ratios (MRs) and fitted

with several selected thin-layer drying models, as
shown in Table 1. The best model was selected based
on the least SSE and RMSE, which represent the
difference between the individual experimental and
calculated data and the goodness of fit, respectively.
As observed in Table 3, the lowest value of SSE
and RMSE were found for the two-term model.
Therefore, this model was selected as the best-fit
model to represent the thin-layer drying behaviour of
AP at 10 kPa. Table 4 presents the estimated values
of the parameters in the two-term model for different Figure 3. Relationship between effective diffusivity and
drying temperatures. These estimated values were temperature based on Arrhenius’ model
used to fit the experimental determined MR and are The drying time was relatively shorter at high
plotted in Figure 2. As seen, the two-term model temperatures and low pressures. Based on a non-
provided conformity with the experimental data. linear regression, a two-term model was chosen to
The results were also fitted with Fick’s second describe the drying behaviour of AP. The value of the
law as a theoretical model with which to determine effective diffusivity was 10-13 m2/s, and this value
the effective diffusivity and activation energy. The increased as temperature increased. The activation
obtained diffusivity values are shown in Table 5. energy for moisture diffusion was determined to be
The effective diffusivity increased as the temperature 33.4 kJ/mol.
increased. These results are in agreement with the
reported findings for Asian white radish (Lee and Acknowledgements
Kim, 2009) and black tea (Panchariya et al., 2002).
Arrhenius’ model was then used to determine This study was supported by Univertisi Putra
the relationship between effective diffusivity and Malaysia through Research University Grant Scheme
temperature and is illustrated in Figure 3. The results (vot. 9300360). The authors wish to acknowledge all
show a linear relationship between ln Deff and 1/T. staff of Faculty of Food Science and Technology who
The activation energy was determined to be 33.4 kJ/ were involved in this study.
mol. This value is lower than the activation energy
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