International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 12 No: 01
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Coconut Milk’s Fat Breaking by Means of
Ultrasound
Siti J. Iswarin and Beni Permadi
Abstract—The effects of ultrasound on coconut milk
homogenization were studied. An ultrasonic generator was used
to homogenize 100 mL of coconut juice with certain energy levels
and exposure times. All samples were analyzed under microscope
at 1000× magnification to determine the diameters of fat
globules. It was found that ultrasonic treatment with high power
level has an important effect on coconut milk homogenization
and is an effective technique for the reduction of the fat globule
size. Effect of reduction represents the symptom of cavitations
phenomenon.
Index Terms—Coconut milk, fat globules, homogenization,
ultrasound.
I. INTRODUCTION
F
ATS is source of energy in food. A human may need 3,300
calories each day to have activities, which one-third of it is
originated from fat. Edible fats can be found in animals and
plants, such as cow’s milk, meat, coconut milk and seeds [1].
Unprocessed fats will easily deteriorate. Cow’s milk and
coconut milk at ambient room temperature of 25oC and
atmospheric pressure of 1 atm will coagulate and be broken
within 6 hours into cream, skim, and water components. In
this process the phospholipids, proteins, and fat will separate.
And homogenization is used to retard this process [2].
Homogenization of cow’s milk and coconut milk will
rearrange the density of milk constituents. Homogenization
reduces the diameter of fat droplets to relatively uniform size.
In addition, homogenization will increase the surface tension
of the fat membrane [3]. Food industries use ultrasound for
homogenization process [4-6].
An experiment by Januri [7] showed fat break down by
mean of a 40 kHz ultrasound. Ultrasound makes the solid part
of the milk to dissolve uniformly to form emulsion suspension
[8].
Researches on animal milk have long been conducted.
Those on coconut milk are yet to start. Ertugay et al. [9] used a
450-watt ultrasound generator to produce smaller fat droplets
compared to a high pressure (200 bars) conventional method.
Since coconut milk has comparable characteristics as food
Manuscript received December 12, 2011. This work was based on BP’s
undergraduate thesis.
S.J. Iswarin is with the Dept. of Physics, Brawijaya University, Malang
65145, Indonesia (phone: +62-341-575833; fax: +62-341-575834; e-mail:
[email protected]).
B. Permadi was an unduergraduate student of the Dept. of Physics,
Brawijaya University, Malang 65145, Indonesia.
with cow’s milk, coconut milk is economically feasible to
replace cow’s milk in countries like Indonesia where it is rare
[7,10].
In this paper we report our study on the homogenization
processes of coconut milk using ultrasound.
II. THEORETICAL BACKGROUND
A. Oils and Fats
Oils and fats are important to our body and are used to
supply energy. Edible fats are originated from plants (also
known as vegetable oils) and animals. The difference between
animal and vegetable fats is that animal fats contain
cholesterols while vegetable oils contain phytosterols. Another
difference is the lower unsaturated fatty acids content in
animal fats than those in vegetable oils.
Based on their sources, oils and fats can be classified as [1]:
1. Plant sources:
a) seeds: corn oils, soy oils, peanut oils, sesame seed
oils, etc.
b) annual fruit meat and skin: olive oils and palm oils.
c) annual plant seeds: coconut oils, cocoa butter,
cohune, etc.
2. Animal sources:
a) milk: milk fats.
b) meat: lards, cow’s fats and their derivatives, oleo oil
from oleo stock, swine tallow, and mutton tallow.
c) fish: sardine oils, cod oils, whale blubber, etc.
Chemically, oils and fats are composed of fatty acids and
glycerol called triglycerides. Fats may be either solid or liquid
at room temperature. The word “fats” is usually used to refer
to fats that are solids at normal room temperature, while “oils”
refers to fats that are liquids at normal room temperature.
B. Physicochemical Properties of Oils and Fats
Physical Characteristics
There are 13 physical characteristics that can be used to
classify oils and fats. They are: color, odor, flavor, solubility,
melting point and polymorism, boiling point, softening point,
slipping point, short melting point, density, refractive index,
fire point, and turbidity point. The most important
characteristics are the melting point, density, and the refractive
index.
Chemical Characteristics
The important reactions of oils and fats are hydrolyses,
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International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 12 No: 01
oxidation, and hydrogenation. In hydrolyses, fats will
transform to free fatty acids and glycerol with water as by
product. The presence of water may cause changes in odor and
flavor. However, hydrolyses process is intentionally made in
industry for specific purposes.
The oxidation process will take place when fats are exposed
to oxygen. This process will also change the odor and flavor.
The hydrogenation of fat in industry is generally aimed to
saturate the double bonds of the carbon chain in the fats. The
hydrogenation allows hydrogen molecules (H2) to react with
the compounds of fats. For edible oils, the oils must be free
from free fatty acids and low phosphate (H3PO4) contents
before the reactions take place [1].
C. Fats as Food
The food value of fats is determined by three factors:
nutritional value, non-fat contents, and the effects of non-fat
content to body. Vitamins A, D, E, and K are among those
soluble materials in fat [2].
Nutritional Value
Fats are food constituent that play an important role to
human as a source of energy. The recommended daily intake
of an adult ranges between 1,600 to 2,400 calories for women
and between 2,000 to 3,000 calories for men depending on age
and physical activity level; and one-third of it originates from
fats.
The intake and absorption of fats by human body are
determined by their melting temperature and unsaturated fatty
acid content. The lower the melting point the easier the body
absorbs them; and the unsaturated fatty acids are easier to
absorb than the saturated fatty acids. In general, plant oils
contain oleic, linoleic, and linolenic acids which are
unsaturated fats and 94% absorbable by human body. Fats
with melting temperatures of 36-38oC has a high absorbance
value [1].
Non-Fat Content
Non-fat fractions that determined the value of the fats are th
free fatty acids, nickel, preservatives (e.g. salts, anti oxidants,
benzoate compounds). They may occur naturally in the fats as
well as by introduction.
D. Coconut Oil
Coconut fruits comprise of meat, juice, and husk. Coconut
oil can be produced from the dry or wet meat. It is the primary
source of fat in the diets of many people in tropical countries.
Coconut oil contains a large portion of lauric acid, a saturated
fat that elevates blood cholesterol levels by increasing the
amount of high-density lipoprotein cholesterol that is also
found in significant amounts in breast milk as well as cow’s
milk [11]. Nutritional comparison between coconut oil and
cow’s milk is presented in Table I.
The coconut milk is juice made by pressing grated coconut
meat. The quantity of milk produced depends of the maturity
and freshness of the fruits. The color and taste of the milk are
attributed to the oil content of the milk. The distinctive rich
taste of coconut is irreplaceable by any other substances of the
2
kind that makes the consumption of coconut milk steadily
high.
Production of coconut oil has topped 6.22 million metric
tons in 2010-2011 and is predicted to reach 6.24 million
metric tons in 2011-2012, which is 2.5% of world vegetable
oil production with India being the largest market.
TABLE I
Nutritional contents of coconut oil and cow’s milk [1].
Contents
Water
Solids
Fats
Carbohydrate
Egg white
Minerals
Coconut Milk (%)
Cow’s Milk (%)
86
14
5
5
4
1
88
12
4
5
5
3
Fatty acids composition in coconut oil is presented in Table
II. It can be seen that the saturated fatty acids make up 90% of
the fatty acid. Coconut oil is composed of 84% triglycerides
with three saturated fatty acids, 12% with two saturated fatty
acids, and 4% with one saturated fatty acid.
TABLE II
Some fatty acid found in coconut oil [1].
Fatty Acids
Chemical Structure
Portion (%)
Saturated:
Caproic
Caprilic
Capric
Lauric
Myristic
Palmitic
Stearic
Arachidic
C5H11COOH
C7H17COOH
C9H19COOH
C11H23COOH
C13H27COOH
C15H31COOH
C17H35COOH
C19H39COOH
0,0 - 0,8
5,5 - 9,5
4,5 -9,5
44,0 - 52,0
13,0 - 19,0
7,5 - 10,5
1,0 - 3,0
0,0 - 0,4
Unsaturated:
Palmitoleic
Oleic
Linoleic
C15H29COOH
C17H33COOH
C17H31COOH
0,0 - 1,3
5,0 - 8,0
1,5 - 2,5
Homogenization
Homogenization is a technique used to stabilize fat
emulsion in coconut milk (the milk is the medium) by
restricting the coagulation and keeping suspended materials
uniformly distributed. Homogenization is also employed to
equalize the component structures, to recombine and adjust the
density of the components in the milk. It also will increase the
milk viscosity [2].
Homogenization technique utilizes ultrasound of 20-30 kHz
frequency. The application of ultrasonic waves will break the
fat globules into smaller sizes with diameter ranges from 0.5 –
2.0 µm [12]. Uniform size and distribution increase milk
stability that in turn stopping emulsion to transform into cream
[3].
There are two types of emulsion known in food industry: oil
in water (O/W) and water in oil (W/O). Coconut milk is an
example of O/W emulsion and margarine is of W/O emulsion
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International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 12 No: 01
[10]. Coconut milk emulsion is stabilized by protiens that is
absorbed in the oil-water layers. The water acts as the
dispersant, the oil is in dispersed phase, and the protein is the
natural emulsfier [13].
Proteins in fats form lipoprotein compounds that act as the
envelope of the globules. The presence of the envelopes will
stabilize the droplets from coalescence (e.g. droplets to clump
together).
Fat Breaking
Fat is a reactive constituent in milk. It will react easily with
proteins and phosphor. Fresh milk contains fats that are
wrapped by proteins and phosphors (see Figure 1).
Other materials
Lemak
Phosphor
Proteins
Fig. 1 The structure of fat in fresh milk. The fat is wrapped by proteins and
phosphors (adopted from Ketaren, 1986 [1]).
To add other ingredients, such as vitamins, to the milk, the
globules must be broken to allow the fat to bind the introduced
ingredients. The breaking process usually is carried out in a
high pressure machinary. Prior to the process the water
content of the milk is reduced to upto 60%.
Membrane Recombination
Recombined membrane sstructures are different from the
orignal ones. Recombination process involves homogenization
that reduces the droplets diameter. Such could increase the
membrane surface tension upto 15 mN/M.
E. Ultrasonic Waves
Sound is a mechanical wave resulted from an oscillation of
pressure transmitted through a solid, liquid, or gas, composed
of a spectrum of frequencies. The portion of the spectrum that
can stimulate human organs of hearing is called the audible
sound that ranges from 20 Hz – 20 kHz. Sound with
frequencies below 20 Hz is infrasound, whereas sound with
frequencies above the upper human hearing threshold is
categorized as the ultrasound.
Ultrasonic waves are generated by means of piezoelectric
materials that convert electrical signals into mechanical
vibrations. The generated frequency depends on the frequency
of the supplied signals.
III. METHODS
A. Sample Preparation
The coconut milk used in the experiments was extracted
from matured coconut fruits. The coconut meats were first
removed from the endocarp upon the opening of the fruit to
obtain fresh meats. The meats were then grated and water was
3
added into the grated meat with a ratio of 1:2. The mixture
was squeezed to extract the milk. 2,600 mL of coconut milk
was required for the experiments.
B. Apparatuses
In the experiment we used an experiment type homogenizer
Samro SRH6-100 (Shanghai Samro Homogenizer Co. Ltd.)
that is capable of pumping a maximum pressure of 100 MPa
and delivering power up to 750 watts [14].
C. Ultrasonic Exposures
The coconut milk was divided into six groups, one group of
100 mL volume and five groups with 500 mL volume each.
One group of 100 mL was used as a control group. The other
groups were equally divided into volumes of 100mL each and
labeled as samples I.1, I.2, …, II.1, II.2, …, V.4, and V.5.
Each sample went through different treatments that varied
the ultrasound power and exposure times. The power used
were 2.5 W, 3.5 W, 4.5 W, 5.5 W, and 7.0 W; and the
durations of exposure were 5 minutes, 10 minutes, 15 minutes,
20 minutes, and 25 minutes. Therefore sample number I
received 2.5 watts of ultrasound power for a period of 5
minutes (sample I.1), 10 minutes (I.2), 15 minutes (I.3), 20
minutes (I.4), and 25 minutes (I.5). Similar treatments went to
samples number II, III, IV, and V.
After the treatments, the samples were brought under a
microscope to measure the droplets’ diameter. Later, the
samples were again divided into smaller volumes and were put
into five 20 mL-vials each. Further labeling was given to the
vials to be I.1.1, I.1.2, I.1.3, and so on to get 125 vials of
treated samples and five vials of the control sample. All
samples were then left in the room at a room temperature of
24.2oC ± 0.6 oC to observe the coagulation process. Time to
reach the coagulation was recorded.
IV. RESULTS AND DISCUSSION
The observed droplet diameters after treatment were
presented in Table III. Table IV shows the coagulation time.
TABLE III
Diameter of droplets (in µm) after treatments. The diameter of the control
group was 5.44 ± 0.15 µm.
Exposure
Time
(mins)
5
10
15
20
25
Power (watts)
2.5
5.44 ± 0.05
5.14 ± 0.09
4.88 ± 0.08
4.77 ± 0.08
4.72 ± 0.07
3.5
5.04 ± 0.09
4.90 ± 0.07
4.80 ± 0.10
4.74 ± 0.11
4.58 ± 0.08
4.5
5.00 ± 0.10
4.64 ± 0.05
4.52 ± 0.05
4.30 ± 0.07
4.14 ± 0.04
5.5
4.48 ± 0.05
4.46 ± 0.09
4.22 ± 0.08
4.04 ± 0.05
3.90 ± 0.07
7.0
4.56 ± 0.05
4.12 ± 0.08
3.88 ± 0.08
3.76 ± 0.11
3.64 ± 0.15
Table III shows a range of droplets diameter yielded after
the treatments. The largest diameter was 5.44 ± 0.05 µm from
the treatment of 2.5 watts and 5 minutes. This figure was just
similar to the initial droplets diameter of 5.44 ± 0.15 µm due
to the high binding energy of the droplets. The ultrasound
power was insufficient to break down the droplets. Subsequent
treatments gave an average of 10% decrease in diameter. The
smallest diameter obtained was 3.64 ± 0.15 µm. The numbers
are plotted in Figure 2.
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were consistent with results reported by Gordon and Pilosof
[5].
5.5
5.3
Droplet Diameter (μm)
5.1
4.9
4.7
5 mins
4.5
10 mins
4.3
15 mins
4.1
20 mins
3.9
25 mins
3.7
3.5
0
2
4
6
8
Ultrasound Power (watts)
Fig. 2 Relation of droplet diameter to the ultrasound power exposed to the
droplets. The curve colour indicates the ultrasonic exposure time. The graphs
reveal the expected decrease in the diameter upon the increase of the
ultrasonic power level.
Fig. 4 Wave propagation in the medum. The continuous disturbance will
cause turbulence flow in the medium that prevents coagulation.
Figure 3 depicts the curves of the droplets diameter as a
function of exposure time. The slopes of the curve are less
steep (correction factor of ± 0.1) compared to those in Figure
2. This indicates that the power level is more dominant in
breaking up the droplets than the duration of the exposure.
Ultrasonic
transmitter
5.5
5.3
Droplet Diameter (μm)
5.1
4.9
4.7
2.5 W
4.5
3.5 W
4.3
4.5 W
4.1
5.5 W
3.9
7W
Fig. 5 An illustration on how the turbulence flow in the medium will allow the
milk droplet to collide each other and hit the wall.
Another breaking mechanism is due to the high frequency
disturbance to the droplets. The disturbance will induce the
droplets to shake in similar frequency of the ultrasounic wave,
which in turn break the droplets into smaller size.
3.7
3.5
0
5
10
15
20
V. CONCLUSION
25
Exposure Time (mins)
Fig. 3 Relation of droplet diameter to the ultrasound exposure time. The curve
colour indicates the ultrasonic power. The graphs reveal the expected decrease
in the diameter as a function of the exposure time.
From Figures 2 and 3 one could extract the information that
the power increment will reduce the diameter of the droplets
down to 4.48 µm in 5 minutes and down to 3.64 µm in 25
minutes. It is shown that the droplet diameter was reduced by
18%.
The mechanical process of the droplet breakage is by
continuous disturbance to the coconut milk that allows
turbulence flow (see Figure 4). The turbulence flow will
inhibit the coagulation of the milk. The milk droplets flow
following the turbulence and are forced to collide each other
and to hit the container wall (see Figure 5). This process will
in turn break down the droplets to smaller size. Our results
We found that ultrasonic wave can be used to prevent
coconut milk coagulation and to reduce the droplet diameter.
The Ultrasonic wave is also capable of homogenizing the
resulted droplet diameter size. The droplets diameter is
determined by the exposure time as well as the power of the
wave.
The future works would deal with the use of the ultrasound
in milk components separation processes.
ACKNOWLEDGMENT
The authors would like to thank Dr. Johan Noor for his
assistance in developing this manuscript.
REFERENCES
[1]
[2]
[3]
[4]
Ketaren, S., 1986, Minyak dan Lemak Pangan, Cetakan Pertama, UIPress, Jakarta (in Bahasa Indonesia).
Bernion, M., 1981, The Science of Food, John Wiley and Sons,
Singapore.
Charley, H., 1982, Food Science, 2nd edition, Macmillan, USA.
Ashokkumar, M., Bhaskaracharya, R., Kentish, S., Lee, J., Palmer, M.,
and Zisu, B., 2010, The ultrasonic processing of dairy products – An
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IJENS
International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 12 No: 01
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
5
overview, Dairy Sci. Technol., 90(2-3): 147-168, DOI:
10.1051/dst/2009044.
Gordon L. and Pilosof, A.M.R., 2010, Application of High-Intensity
Ultrasounds to Control the Size of Whey Proteins Particles, Food
Biophysics, 5(3): 203-210, DOI: 10.1007/s11483-010-9161-4.
Chemat, F., e-Huma, Z., Khan, M.K., 2011, Applications of ultrasound
in food technology: Processing, preservation and extraction, Ultrasonics
Sonochemistry, 18(4): 813–835.
Januri, A., 2005, Analisis Serapan Susu Sapi terhadap Gelombang
Ultrasonik, Sarjana Thesis, Dept. of Physics, Brawijaya University,
Malang (in Bahasa Indonesia).
Winarno, F.G., 1992, Kimia Pangan dan Gizi, PT Gramedia Pustaka
Utama, Jakarta (in Bahasa Indonesia).
Ertugay, M.F., Sengul, M. and Sengul M, 2004, Treatment on Milk
Homogenization and Particle Size Distribution on Fat, Turk. J. Vet.
Anim. Sci., 28: 303-308.
Ranken and Kill, 1993, Food Industry’s Manual, Scabo Pub, US.
Hegde, B.M., 2006, Coconut Oil – Ideal Fat next only to Mother’s Milk
(Scanning Coconut’s Horoscope), JIACM, 7(1): 16-19.
Fellows, PJ, 1990, Food Processing Technology Principles and Practice,
Ellis Horworth, West Sussex, England.
Cancel, L.E., 1970, Coconut Food Products and Based, pp: 162-179. In
J.G. Woodroof: Production, Processing, Product, 2nd ed, AVI Publishing
Co. Inc., Wetsport Connecticut, USA.
China-Samro, High Pressure Homogenizer Operating Instructions,
SHR6-100, Shanghai Samro Homogenizer Co. Ltd., Shanghai, China.
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