Optimizations of
Spray Drying Process Parameters for Liquorice (Glycyrrhiza glabra Linn.)
Extract
Sachinkumar D. Gunjal*, Satish
V. Shirolkar
Department of
Pharmaceutics, Dr. D.Y. Patil Institute of Pharmaceutical Sciences &Research,
Pimpri,
Pune – 411018,
India.
*Corresponding Author E-mail: sachin13802004@gmail.com
ABSTRACT:
The objective of
this work was to study the effect of spray drying process parameters on the
physicochemical properties of liquorice (Glycyrrhiza glabra) extract. The
stickiness and hygroscopicity are problems associated with spray drying
process. To overcome these problems drying agents are used. Dextrose equivalent
(DE12 and DE19) and maltodextrin are reported as drying agents in preparation
of liquorice extract by spray drying method1. In present work,
aerosil was used as spray drying agents. The inlet air temperatures, Feed flow
rate and aerosil concentrations were considered as independent variables.
Moisture content, % yield, bulk density, acidity and pH, hygroscopicity, time
required for solubilization were analyzed to determine the effects of spray
drying processing parameters. Increases in inlet air temperature were caused an
increase in yield, solubility and a decrease in moisture content, bulk density,
hygroscopicity. Increases in aerosil concentration caused an increase in yield
and a decrease in moisture content, bulk density, hygroscopicity, time required
for solubilization.
KEYWORDS: Optimization,
Spray drying, Liquorice extract, Glycyrrhiza glabra, Aerosil.
INTRODUCTION:
Liquorice is used traditionally as a soothing
remedy for the respiratory tract and to mask the bitter or acrid taste of other
drugs1. Liquorice (Glycyrrhiza glabra Linn.) plant belongs to
the family Leguminosae. The roots and rhizomes of this plant are reported for
demulcent, anti-inflammatory, anti stress, anti depressive and expectorant
property and also used for the treatment of peptic ulcer2. Liquorice
is also used as natural sweetener and it is 50–170 times sweeter than sucrose.
The chemical constituents of the roots include many bioactive compounds, such
as glycyrrhizin (~16%), different sugars (up to 18%) flavonoids, saponoids,
sterols, starches, amino acids, gums and essential oils.
Glycyrrhizin is a water-soluble pentacyclic
triterpenoid glycoside responsible for the sweetness of licorice and its
aglycone is responsible for various medicinal attributes and clinical
applications. The glycoside is present as calcium or potassium salt of
glycyrrhizic acid (GA) which is a weak acid containing three carboxyl and five
hydroxyl groups3. Liquorice extract is used on skin is mainly for
its antioxidant activity due to its potent antioxidants triterpene, saponins
and flavonoids. Skin whitening, skin depigmenting, antiaging, anti-erythemic,
emollient, anti-acne and photo-protection effects are produced using
Glycyrrhiza glabra extract4.
Liquorice is also used as one of ingredient in
herbal tea. Liquorice extract is used in certain types of chewing gum to impart
a flexible texture, certain chocolate candies to stabilize the fat dispersion,
in cigarettes, cigars, smoking mixtures, chewing tobacco to impart a sweet
taste and characteristic flavor and in beverage to increases the foaminess of
the beverage. Liquorice may also be used as a Brown coloring matter1.
Spray drying is
widely used for converting a wide range of liquid food products into powder
form. This process results in powders of good quality, low water activity and
makes it easy for transport and storage. The physicochemical properties of
powders produced by spray drying depend on some process variables, such as the
characteristics of the liquid feed (viscosity, flow rate) and of the drying air
(temperature). Therefore, it is important to optimize the drying process.
Powders obtained by spray drying may have problems like stickiness,
hygroscopicity. These powders can stick on the dryer chamber wall during
drying, leading to low product yield and also causes operational problems.
Stickiness depends on temperature and moisture content. If amorphous powders
are at temperatures and/or moisture contents higher than what is called the
powder sticky point then particles collide with each other and sticks with
another particle. Many researchers have correlated the sticky point temperature
of amorphous powders to the glass transition temperature, Tg1.
During spray drying
various techniques for producing a free-flowing powder have been proposed:
addition of dry ingredients (maltodextrin, glucose, soybean protein, aerosil,
sodium chloride, and skim milk powder), scrapping of dryer surfaces, cooling of
the drying chamber walls , and admission of atmospheric air near the chamber
bottom, allowing transport of the powder to a collector having a low humidity
atmosphere. High molecular weight drying aids have high glass transition
temperatures so it minimizes sticking. Besides reducing powder hygroscopicity,
such agents, normally used for microencapsulation, can protect sensitive food
components against unfavorable ambient conditions, mask or preserve flavors and
aromas and reduce the volatility and reactivity1.
Irem Karaaslan and
Ali Coskun Dalgic reported use of dextrose equivalent (DE12) and DE19
maltodextrin as drying agents in preparation of liquorice extract by spray
drying method1. Ashour, M.M.S. etal. used maltodextrin-Arabic
gum mix was used as drying agent for spray drying of liquorice extract3.
MATERIAL AND METHODS:
Collection of plant material,
Chemicals and reagents:
The liquorice roots used were
supplied from local markets (Maharashtra, India). All other chemicals and
reagents used were analytical grade.
Preparation of extract:
Roots were coarsely
powdered and extracted at 25 °C by using the 1: 3 as the ratio of liquorice:
water. The extract was then filtered using Filter Paper and transferred to a
bottle. Filtration was carried out to remove of fibers at room temperature. The
extracts obtained were stored at refrigerator at 4 °C for one day if required.
Spray drying of liquorice
extract:
Above extract was
subjected to spray drying using laboratory scale Labultima UV222 spray drier.
Experimental conditions followed for optimization as per Table 1.
Table 1.
Experimental conditions for spray drying of liquorice extract.
|
No. of Experiment |
Drying aid (%) |
Air inlet temperature (○C) |
Feed flow rate (mL/min) |
|
1 |
6 |
110 |
2 |
|
2 |
6 |
120 |
1 |
|
3 |
6 |
120 |
3 |
|
4 |
6 |
130 |
2 |
|
5 |
8 |
110 |
1 |
|
6 |
8 |
110 |
3 |
|
7 |
8 |
120 |
2 |
|
8 |
8 |
130 |
1 |
|
9 |
8 |
130 |
3 |
|
10 |
10 |
110 |
2 |
|
11 |
10 |
120 |
1 |
|
12 |
10 |
120 |
3 |
|
13 |
10 |
130 |
2 |
|
14 |
10 |
130 |
1 |
Evaluation
Parameter for Spray dried Powder:
Yield:
Yield of product
after spray drying is calculated as the ratio between the total mass of
recovered product and the mass of total solid initially fed into the system.
Process yield was calculated as the relationship between total solids content
in the resulting powder and total solids content in the feed mixture1.
Moisture content:
For determination
of moisture content, 1g of each powder was placed in an oven dryer at 80°C for
3 hrs. Samples were cooled in dessicators for 1 hr and then weighed. Moisture
content was determined as percentage mass loss1.
pH and Acidity:
The pH of
reconstituted powder was measured by a pH meter. 2gm of powder was added to 10
mL of distilled water. The titratable acidity was determined as glycyrrhizic
acid % (w/w) by titration with 0.1 N NaOH to a phenolphthalein end point at
room temperature. Duplicate samples were analyzed and the mean reading was
recorded1.
Time required for
solubilization:
A small sample of
dry powders of 0.6 g was added to 400 mL of water at 70 °C in a 500 mL beaker.
The mixture was stirred using a magnetic stirrer at 100 rpm. Solubility was
measured as the time in seconds to dissolve the dry powders completely5.
Bulk density:
Bulk density was
determined by adding 5 g of powder to a 10 mL graduated cylinder and holding
the cylinder on a vibrator for 1 min. The bulk density was calculated by
dividing mass of the powders by the volume occupied in the cylinder5.
Hygroscopicity:
Samples (1 g) of
each powder were placed in small glass covers, weighed and kept at relative
humidity of 75 % in stability chambers at 25 °C. After seven days, the samples
were weighed and the hygroscopicity is expressed as gm moisture/100 gm solids1.
Water solubility
index (WSI) and water absorption index (WAI):
A small sample of
dry powders (2.5 g) was added to 30 mL of water at 30 °C in a 50 mL centrifuge
tube, stirred intermittently for 30 min, and then centrifuged for 10 min at
(5100rpm). The supernatant was carefully poured off into a Petri dish and
oven-dried overnight. The amount of solid in the dried supernatant as a
percentage of the total dry solids in original 2.5 g sample gave an indication
of the WSI. Wet solid remaining after centrifugation was dried in an oven overnight.
WAI was calculated as the weight of dry solid divided by the amount of dry
sample5.
RESULTS:
Interaction effects
of the process variables on the efficiency of the spray drying process:
Interactions among
the process parameters, i.e., air inlet temperature, feed flow rate and % of
drying aid are summarized in Figure 1-9. Powder characteristics such as
moisture content were examined in this study to evaluate the adequacy of the
spray drying operating conditions. The highest efficiency of spray drying (67
%) was achieved when the air inlet temperature was130°C. There were also
significant effects between air inlet temperature and feed flow rate on the
efficiency of spray drying. In order to keep the process stable and to minimize
disturbances, interactions between these variables need to be considered in
spray drying. The highest predicted efficiency of the spray drying 67 % was
found at air inlet temperature of130 °C together with feed flow rate at
1mL/min. Therefore, these all parameters must be taken into account for the
spray drying in order to avoid problems like stickiness and deposition on the
chamber wall. There was not enough heat to dry the solution when using low air
inlet temperature, and hence some moisture remained in the end product which caused
the powder to easily adhere to the drying chamber6.
Yield:
As temperature
increases % yield also increases. Highest yield is obtained at 130○C
inlet temperature and at 10% of aerosil as drying aid.
Moisture content:
Inlet air
temperature and drying aids reduced the moisture content, which is desirable
for the spray drying process. Generally, the greater the temperature
differences between the particles and air surrounding it, the greater the
evaporation rate. Moisture content also decreased with increasing concentration
of drying aid. Least moisture content was observed at 130○C
inlet temperature, 10% of aerosil as drying aid and 1mL/min feed flow rate.
pH and Acidity:
pH of powder was
maximum and % of acidic content was minimum for experiment no 13.
Table 2. Properties
of liquorice extract powder.
|
No. of Experiment |
Yield (%) |
Moisture Content (%) |
pH |
Acidity % |
Bulk Density gm/mL |
Time required for solublization (seconds) |
Hygroscopicity (gm/100gm) |
Water solubility index (WSI) % |
Water absorption index (WAI) % |
|
1 |
36 |
0.28 |
5.5 |
0.32 |
0.29 |
35 |
69 |
93 |
3.6 |
|
2 |
42 |
0.23 |
5.9 |
0.28 |
0.24 |
29 |
58 |
92 |
3.8 |
|
3 |
48 |
0.27 |
5.8 |
2.26 |
0.26 |
24 |
67 |
90 |
4.1 |
|
4 |
52 |
0.23 |
6.1 |
0.21 |
0.24 |
28 |
54 |
97 |
2.1 |
|
5 |
50 |
0.24 |
5.6 |
0.24 |
0.27 |
36 |
62 |
93 |
3.4 |
|
6 |
54 |
0.31 |
5.7 |
0.26 |
0.29 |
29 |
70 |
92 |
2.8 |
|
7 |
58 |
0.26 |
5.8 |
0.27 |
0.24 |
30 |
61 |
93 |
3.1 |
|
8 |
60 |
0.21 |
6.4 |
0.12 |
0.21 |
25 |
33 |
94 |
2.9 |
|
9 |
64 |
0.26 |
6.2 |
0.16 |
0.26 |
22 |
45 |
93 |
3.1 |
|
10 |
48 |
0.27 |
5.7 |
0.28 |
0.25 |
31 |
52 |
92 |
2.6 |
|
11 |
54 |
0.22 |
5.8 |
0.29 |
0.21 |
30 |
45 |
95 |
2.7 |
|
12 |
58 |
0.26 |
5.7 |
0.26 |
0.24 |
24 |
54 |
92 |
2.2 |
|
13 |
62 |
0.23 |
6.2 |
0.18 |
0.2 |
20 |
42 |
96 |
2.6 |
|
14 |
67 |
0.19 |
6.4 |
0.19 |
0.2 |
26 |
38 |
96 |
2.4 |
Bulk density:
The bulk density
decreased with increasing inlet air temperature. The bulk density of powders
was in the range 0.20 –0.29 gm/mL. At higher temperature of inlet air resulted
in a rapid formation of vapour-impermeable film of dried layer at the droplet
surface and the particle size was more at the higher temperatures. This effect
decreased bulk density of powder.
Time required for
solubilization:
Solubility was
measured as the time in seconds to dissolve the dry powders completely and it
was found in range of 20-36 seconds.
Hygroscopicity:
Hygroscopicity is
expressed as quantity of moisture in gm absorbed per 100 gm solids in 7 days
period. It is observed to be 33-70gm /100gm. Higher % of drying agent resulted
in least hygroscopic powder because evaporation
rates are faster and products dry to a more porous or fragmented structure,
there was a greater tendency for the particles to be hollow7.
Water solubility
index (WSI) and water absorption index (WAI):
The instant
properties of a powder involve the ability of a powder to dissolve in water.
The ideal powder would wet quickly and thoroughly, sink rather than float and
disperse/dissolve without lumps. Water solubility index increased with
increasing concentration of drying agent. Conversely, adding drying aids
reduced the water-holding capacity. The drying aids could form an outer layer
on the drops and alter the surface stickiness of particles due to the
transformation into a glassy state. The changes in surface stickiness reduce
the particle-particle cohesion resulting in less agglomeration, and therefore,
lower water-holding capacity of the powders5.
Water solubility
Index was observed in range of 90-97% and water absorption index was observed
in range of 2.1-4.1%/
Figure 1 Effect of various
spray drying parameters on % yield
Figure 2 Effect of various
spray drying parameters on moisture content
Figure 3 Effect of various
spray drying parameters on pH.
Figure 4 Effect of various
spray drying parameters on Acidity
Figure 5 Effect of various
spray drying parameters on bulk density.
Figure 6 Effect of various
spray drying parameters on time required for solubilization.
Figure 7 Effect of various
spray drying parameters on Hygroscopicity.
Figure 8 Effect of various
spray drying parameters on Water Solubility Index (WSI).
Figure 9 Effect of various
spray drying parameters on Water Absorption Index (WAI).
Optimization:
Numerical
optimization was carried out for the process parameters of spray drying to
obtain liquorice extract powder. Table 1 and 2 shows independent variables that
have a complex relationship with the responses may have more than one maximum
point. Analyzing the contour plots is the best way to evaluate the
relationships between responses and variables. The optimum drying conditions
can then be determined by superimposing the contour plots of relevant and
statistically significant responses. The following limits were proposed: yield
of not less than 50%, bulk density of not more than 0.25 gm/mL, moisture
content of at a range of 0.2 –0.25 %, hygroscopicity of not more than
50 gm /100 gm, time required for solubilization not more than
25 seconds1.
Figure 10 Superimposed contour plots showing powder properties affected
by % of drying agent and Air Inlet Temperature
Superimposed contour plots shows the ranges of variables which could be
considered as the optimum range for best product quality as shown in Figure 10.
The optimum ranges of variables obtained from the superimposed contours were
125–130 °C of inlet air temperature and 6–10 % of drying agent
(aerosil) concentration. These optimum conditions can be used to produce
liquorice extract powder with the estimated characteristics given above.
DISCUSSION:
The inlet air
temperatures and % of drying aids affected the quality of dried liquorice
powders. Aerosil as a drying aid increased the drying yield to 67 %. Moisture
content, bulk density, water adsorption index of liquorice powders decreased
with increasing inlet air temperature. Water solubility index increased with
increasing inlet air temperatures. Water solubility index and yield increased
with increasing drying aids concentration. The best quality liquorice powder
was achieved at 130°C inlet air temperature and 10 % aerosil as a drying aid.
ACKNOWLEDGEMENT:
The authors are grateful to
the authorities of Dr. D.Y. Patil Institute of Pharmaceutical Sciences &
Research, Pimpri, Pune for the facilities.
CONFLICT OF INTEREST:
The authors declare no conflict of interest.
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Received on 03.07.2018
Modified on 07.08.2018
Accepted on 16.09.2018
© RJPT All right reserved
Research J. Pharm. and Tech
2018; 11(11): 5105-5110.
DOI: 10.5958/0974-360X.2018.00932.0