Effect of homogenizing pressure and sterilizing condition on quality of canned high fat coconut milk pps

Journal
of Food
Engineering 73 (2006)

38–44
www.elsevier.com/locate/
jfoodeng
Effect
of
homogenizing pressure and sterilizing
condition on quality
of
canned high fat

coconut
milk
Naphaporn Chiewchan
*
, Chanthima Phungamngoen, Suwit Siriwattanayothin
Department
of
Food

Engineering, King Mongkut s University
of
Technology, Thonburi, Tungkru, Bangkok 10140,
Thailan
d
Received 31 August 2004; accepted 6 January 2005
Available online 24
Februar

y
2005
Abstract
The
effect
of
homogenizing pressure
(15–27
MPa) and
commercial sterilizing condition (109.3–121.1
C under
pressure
of
5–15 psi)
on
the quality
of
canned high fat (30%) coconut
milk
was investigated.
All
heat-treated
homogenized

samples
exhibited
pseudoplastic behavior with flow behavior index (n) between 0.719 and 0.971.
At
similar sterilizing condition,
a

decrease
in
n
value
and an increase
in
consistency
index (K)
were observed for samples passing higher homogenizing pressures.
A
reduction
in
apparent
viscosity was found
for
the homogenized samples undergoing higher sterilizing temperatures.
For
color determination,

Hunter
L/b
values
of
homogenized coconut milk were greater than that for
fresh sample and the values increased with increasing

pressures.
The
reduction
in

L/b values was observed when the homogenized samples were subjected
to
heat treatment. Sterilizing at

121.1
C
for
60 min could provide an acceptable color comparing
to
fresh coconut milk while heating at lower temperature but
for

longer
time
permitted more browning reaction and resulted
in
an increase
of
b value. Overall, the results suggested that quality
of

canned
high
fat
coconut
milk in
terms
of
rheological
and

optical properties was influenced
by both
homogenizing pressure

and
sterilizing
condition.

2005 Elsevier Ltd. All rights
reserved.
Keywords: Coconut milk; Color; Homogenizing
pressure; Sterilizing temperature;
Rheological
propertie
s
1.
Introduct
ion
Coconut
milk is a
milky white oil-in-water
emuls
ion
extracted from coconut flesh.
It
plays an
important
role in
many traditional foods
of

Asian
and Pacific
regions
.
Separation
of an
emulsion
into
an
aqueous phase and
cream phase commonly
occurs
and
leads
to an
una
c-
ceptably physical
defect
of either
fresh
or
pro
cessed
coconut milk.
Canning has been found
to
be
a
suit

able
process
for
preservation
of
coconut milk.
The
process
starts
from
extracting the
milk from
grated
cocon
ut
meat
with or without added
water.
The
pe
rcentag
e
of
fat is
adjusted before heating
at
pasteurization tem-
perature.
The milk is
then added

with a
stabilizer
or
*
Corresponding author.
Tel.: +66 2470 9243; fax: +66

2470 9240.
E-mail address:


(N.

Chiewchan
).
emulsifier
and
pass through the homogenizer.
Finally, it
was filled
in
can and sterilized
in
the
retor
t.
Previous research works have demonstrated that
fat
particle size, dispersion and temperature
had

significant
effects on a stability
of
foods
containing
high fat content such as milk, yogurt
and
cheese
(Shaker, Jumah,
& Jdayil,
2000;
Xu, Nikolov,
Wasan,
Gonsalves,
&
Borwankar, 1998).
For
typical
canned coconut
milk
process, the addition
of
suitable emulsifiers and homog- enization
for
redu
cing
fat globule
size are required
prior to
heat

treat
ment
to
retain the emulsion stability.
Sringam
(1986)
reported that type and quality
of
emulsifier
and
homogenization affected the
stability
of
coconut
milk.
Increasing homogenizing
pressure
from
1000
to
5000 psi resulted
in
increasing stability
of

coco-
nut milk and
two-stage homogenization at

1000

and
2000
psi
resulted
in
greater stability
of
coconut
mil
k
0260-8774/$ - see front
matter
2005 Elsevier
Ltd.
All

rights
reserved. doi:10.1016/j.jfoodeng.2005
.01.003
N.
Chiewchan et al.
/
Journal
of
Food Engineering 73 (2006) 38–44 39
than single-stage high pressure (5000
psi)
homo
geniza-
tion (Gonzalez, de Leon,

&
Sanchez,
1990). Adding so-
Table 1
Process time
for
sterilizing high fat canned coconut
milk
(1985) studied the effect
of
temperature (15–50
C)
and
total solids (36.9–51.6%) on
the flow properties
of
coco-
nut milk. It
was
found that
coconut
milk
exhibited
midly
pseudoplastic behavior. Simuang,
Chiewchan, and Tansakul
(2004) examined the effects
of
temperature (70–90
C)

and fat content (15–30%)
on
the rheological properties
of
coconut milk.
Their
finding was similar
to
the work
of Vitali
et al. (1985)
which
all
samples exhib- ited pseudoplastic
behavior
.
They stated that fat concen- tration resulted
in an
increase
in
consistency index
(
K
).
Furthermore, the
previous research work demonstrated
that more
aggregates
of fat
globule were clearly ob- served

at
higher heating temperatures (Simuang et
al.,
2004).
This
resulted
in
the reduction
of K
values
which
implied the decrease
of
the coconut
milk
stability.
From literature described above,
homogenizing
pres-
sure and temperature were
significant
parame
ters
affect-
ing
the
stability of
the emulsion.
This
research

was
aimed to investigate the effect
of homogenizing
pressur
e
in
the pressure range
of
15–27
MPa
(11/4–
23/4

MPa
)
and
commercial sterilizing condition,
(109.3–121.1
C
under pressure
of
5–15 psi)
on
the stability
of
canned
high fat coconut
milk
(30%).
The information

obtaine
d
from the study could be used as a guideline
for
de
velop-
ing
of
high fat coconut
milk
canning
process
.
2. Materials and methods
2.1. Coconut milk
prepar
ation
Fresh coconut milk without added water from a
local
market was stored
at room
temperature
and
pa
ssed
through the cloth filter before experiments.
The initial fat
content
of coconut milk
(35–37%)

was

determined
by
Rose–Gottlieb method
(
AO
AC,
1990
)

and then di- luted
to
the
fat
concentration
of
30
%

w/vby distilled water. 0.6% (w/v)
M
ontanox
60
(Polyoxyethylene (20)
sorbitan
monostearate)
and
0.6% (w/v)
CMC

were added while the sample was
heating and stirring contin-
uously on a hot plate
(Framo
Geratetechnik
Model
M21/1, Germany).
The
sample was held
on a
hot plate
for
1 min once
its
temperature reached 70
C to
inhibit lipase
and
microbial growth. The prepared sample was
passed
through
a
two-stage homogenizer
(GEA Model
NS200
6L,
Italy)
at
different pressure levels, i.e. 11,
14,

17, 20 and 23
MPa for
the first stage and followed
by
4
MPa for
the second stage.
The
homogenized
sample
was then filled
in a
can (can size 300
·
407, 15 oz.)
and
a
The
time
in
min
at
121.1
C
that
will
produce the

same degree
of

sterilization as the given process at
its
temperature
T
.
Fig.
1. The change
in
apparent viscosity
of
high
fat
coconut milk
after sterilization: (a) 30
C (non-heat
sample), (b) 109.3
C,
(c)
115.6
C
and (d) 121.1
C.
dium
caseinate
and
stearoyl
lactylate
(0.5–2.5%
of
Pressure

Temperature
Come
up Process
F
0
a
coconut milk) coupled with two-stage
homogenization
(psi)
(
C)
time (min) time (min)
(min)
could enhance the
stability.
5
109.3
15
160
5
Processing temperature also has significant effect
on
10
115.6
15 110 5
the stability
of
coconut milk.
Vitali,
Soler,

and Rao
15
121.1
15 60 5
40
N.
Chiewchan et al.
/
Journal
of
Food Engineering 73 (2006) 38–44
sterilized using a horizontal still
retort. The thermal
pro-
cess conditions are shown
in
Table
1
.
2.2.
Rheological
measurement
The rheological measurements were carried out
using
a
rotational concentric cylinder viscometer
(HA
AKE
Model
VT500, Germany) with

NV
type
measuring sys-
tem. Shear
rate
was increased
from
0
to
300 s

1

in
2 min.
The
temperature
of
samples was maintained
at room
temperature
(about
30
C) during
the
measur
ement
s.
2.3. Microscopic
study

A
few drops
of
oleoresin dye were added
to
10 ml
of
coconut
milk
sample
and
subsequently stirred
for at
least 1 min
to
disperse the dye.
A
few drops
of
the sam-
ple
were transferred
to
the slide
and a
cover
slip
was
placed over the sample.
An

optical
standard
microsco
pe
(Olympus
Model
CH30, Japan)
was used
to
determ
ine the fat structure at a
magnification
of
400
·

(before ther-
mal process)
or a
magnification
of
100
·

(after
therm
al
processing)
and
photographs were taken

from
typic
al
fields.
2.4. Determination
of
fat globule size
distributi
on
The
diffractometer
(Malvern Instrument
Model
Mastersizer-S,
UK)
equipped with
a
3
RF
lens
an
d
a
n
He–N
e

laser (k = 633 nm) was used
to
determine

size
distribution
of fat
globules
of
coconut milk. The
ster
il-
ized samples were diluted
to
approximately
1/100
0

with deionized water before measuring.
Size
distribution his- tograms are presented
in
volume
of fat
particle (%) against droplet diameter (in the
range
of
0.05–900
l
m).
The measurements were
conducted
three times
for

each
sampl
es.
2.5.
Col
or

meas
urem
ent
Color of coconut milk
was analyzed by
measuring
the reflectance
using a
spectrocolorimeter
(Juki Model
JP7100, Japan). 2
North
skylight was used as

the light source.
The
instrument was
calibrated
against
a
stan-
dard
white

reference
tile
(
L

=

91.66, a = 0.12,
b = 1.37).
A
glass cell (30
mm
diameter) containing
the sample was placed above the

light source and
covered with the lid. Although, three

Hunter
parameters,
namely
‘‘L’’
(lightness),
‘‘a’’
(greenness
and
redness)
and
‘‘
b

’’
(blueness and yellowness) were recorded,
only L
and b
values were required
to
describe the change
in
color.
2.6. Experimental design and data
analysis
The
experiments were conducted
for five
level
s
of
homogenizing pressure (11/4, 14/4, 17/4,
20/4
and
23/4
MPa
)
and
three levels
of
sterilizing
tempe
ratur
e

(109.3, 115.6 and 121.1
C). A
2-factor
factorial
design was used
in
scheduling
of
the
experiments.
The results
Table 2
Effect of
homogenization pressure
and
sterilizin
g

temperature
on
consistency index (K) and flow behavior index
(
n
)
Table 3
Apparent viscosity
at
300 s

1

for
high
fat
coconut
milk at
different
homogenization pressures and sterilizing
temperatures
Temperatur
e
Homogen
ization
K
(Pa s
n
) n
r
2
Temperature
Homogenizatio
n
Apparent
viscosity
(
C)
pressure
(MPa)
(

C)

pressure
(MPa)
(
g
a
;

Pa
s
)
30
Non
homogeni
zation
3.62
·
10

2
0.971
0.992
30
Non
1.54
·
10

2
15 (11/4)
5.81

·
10

2
0.858 0.968
15 (11/4)
2.71
·
10

2
18 (14/4)
6.62
·
10

2
0.806 0.979
18 (14/4)
2.80
·
10

2
21 (17/4)
9.34
·
10

2

0.759 0.964
21 (17/4)
3.10
·
10

2
24 (20/4)
10.42
·
10

2
0.740 0.977
24 (20/4)
3.55
·
10

2
27 (23/4)
14.56
·
10

2
0.719 0.954
27 (23/4)
4.55
·

10

2
109.3
15 (11/4)
3.95
·
10

2
0.926 0.981
109.3
15 (11/4)
1.85
·
10

2
18 (14/4)
4.97
·
10

2
0.904 0.981
18 (14/4)
2.27
·
10

2
21 (17/4)
5.64
·
10

2
0.883 0.987
21 (17/4)
2.38
·
10

2
24 (20/4)
7.15
·
10

2
0.852 0.983
24 (20/4)
2.70
·
10

2
27 (23/4)
8.45
·

10

2
0.810 0.982
27 (23/4)
2.94
·
10

2
115.6
15 (11/4)
2.32
·
10

2
0.949 0.984
115.6
15 (11/4)
1.32
·
10

2
18 (14/4)
3.46
·
10

2
0.911 0.982
18 (14/4)
2.05
·
10

2
21 (17/4)
3.61
·
10

2
0.892 0.984
21 (17/4)
2.27
·
10

2
24 (20/4)
4.18
·
10

2
0.863 0.985
24 (20/4)
2.47

·
10

2
27 (23/4)
4.58
·
10

2
0.822 0.958
27 (23/4)
2.66
·
10

2
121.1
15 (11/4)
2.02
·
10

2
0.959 0.988
121.1
15 (11/4)
1.20
·
10

2
18 (14/4)
2.56
·
10

2
0.913 0.984
18 (14/4)
1.43
·
10

2
21 (17/4)
2.82
·
10

2
0.894 0.975
21 (17/4)
1.58
·
10

2
24 (20/4)
2.78

·
10

2
0.869 0.977
24 (20/4)
1.78
·
10

2
27 (23/4)
3.13
·
10

2
0.823 0.981
27 (23/4)
1.96
·
10

2
N.
Chiewchan et al.
/
Journal
of
Food Engineering 73 (2006) 38–44 41

were reported as an average
of
three replicates.
Anal
ysis
of
variance
(ANOVA) of
the
two
factors
and
inter
ac-
tions were applied to the different sets
of
data with a sig-
nificant level
of
0.05
(
a

=
0.05)
.
3. Results and discussion
3.1.
Rheological
properties

The plot of
apparent viscosity against shear rate
of
coconut milk homogenized at five pressure levels
before and after sterilizing are shown
in Fig.
1. The
rheogram
s
obtained were
similar for all
conditions.
Power
law
model was applied
to
describe the rheological
beh
avior
of
the
sampl
es.
s ¼
K

c
_

n

ð
1
Þ
where
s is
the shear stress,
c
_

is
the shear rate,
K is
the
consistency
index
(Pa s
n
)
and
n
is
the
flow
be
havior
index.
The excellent fits were obtained with high
co
rrelatio
n

coefficients (r
2
= 0.954–0.992). The values
of K
and n

are shown
in
Table 2. It was revealed that
all
sampl
es

exhib- ited pseudoplastic behavior with the
flow
behavior index (n) between 0.719
and
0.971.
It
was
found that
the apparent viscosity decreased
with
increasing shear rate during the early period
of
measurement.
After a
sharp reduction, the
apparent
viscosity changed slightly and became

steady
at
higher shear rates.
A
s

coconut
milk is a
colloidal
system
containing fat
globules dispersed
in water
phase, the
fat
particles may rearrange
them-
selve
s
into
parallel direction
with
shear force
and fat
globule
aggregates may break into smaller
ones by shear
force. These particles
could flow
easily as

a
result
of
resistance
arising from
particle–particle
inter
action
Fig.
2.
Micrograph
s

(
·
400

magnification)
of
high fat coconut milk samples passing different homogenization pressures:

(a)
non-homogenization,
(b)
11/4
MPa,
(c) 14/4
MPa,
(d) 17/4
MPa,

(e) 20/4
MPa
and (f) 23/4
MPa.
42
N.
Chiewchan et al.
/
Journal
of
Food Engineering 73 (2006) 38–44
which
decreased
viscosity
(Charm,
1962
).
Whe
n
the aggregates were completely
disrupt
ed,
further in- crease
in
shear rate
did
not affect the
apparent viscosity (Campanella, Dorward,
& Singh,
1995

).
At
the same temperature, a decrease
in n value and
a
n
increase
in K
value were obtained
for
the samples
pass-
ing higher homogenizing pressures. The increase
in pres- sure level permitted the size reduction.
Thi
s
meant
that higher
numbers
of
droplet were
presented
in
the

co
lloi-
dal
system
and

obstructed
the
flow.
Therefore,
an
increase
in
pressure caused an increase
in
apparent
vis-
cosity and the more pseudoplasticity.
Thermal
process-
ing also had significant
effect
on
the
viscosity of
coconut milk.
A
reduction
in apparent
viscosity
of
coco-
nut milk
was observed
with
increasing

sterilizing
tempe
ratur
e.
Tabl
e

3 shows the values
of
apparent viscosity (g)
at
maximum shear rate (300 s
1
).
It
was
found that
the
emulsions were more viscous after passing higher
pres-
sures.
From
the results,
coconut milk
exhibited
a
power-law pseudoplastic behavior, characterized
by
n
values less than 1 at

all homogenizing
pressures
and
ster-
ilizing
temperatures. Experimental results have
shown
that passing the coconut
milk
through
a
hom
ogenizer
100
90
80
70
60
50
40
30
20
10
0
0.1
(a)
1 10 100
1000
Particle diameter
(um)

100
90
80
70
60
50
40
30
20
10
0
0.1
100
80
60
40
20
0
0.1
(b)
1 10 100
1000
Particle diameter
(um)
(c)
1 10 100
1000
Particle diameter
(um)
Fig.

3.
Micrograph
s

(
·
100

magnification)
of coconut milk
samples
at
homogenization pressure
23/4
MPa

with different
sterilizing
tempera- tures: (a) 109.3
C,

(b)

115.6
C
and (c) 121.1
C.
Fig.
4. Effect
of

sterilizing temperatures: (a) 109.3
C,
(b)

115.6
C,
(c)
121.1

C on droplet
size
distribution at different
homogenizing
Vo
lu
me
of
par
ticl
e

(%
)
Vo
lu
me
of
par
ticl
e

(%
)
Vo
lu
me
of
par
ticl
e

(%
)
pressures: 11/4
MPa
(
s
),

14/4
MPa
(

), 17/4
MPa
(
n
),

20/4

MPa
(
j
)
and 23/4
MPa
(
·
).
N.
Chiewchan et al.
/
Journal
of
Food Engineering 73 (2006) 38–44 43
was accompanied
with an
increase
in
pseud
oplastici
ty
and
was shown by a decrease
in
values
of
flow
be
havior

index (n).
This observation was
consistent with the
work of Floury,
Desrumaux,
and
Legrand (2002). They re-
ported that the emulsion
obtained at low
homo
genizin
g
pressure show
Newtonian flow behavior with quite
low
viscosity
because there was
no
interaction between par-
ticles.
As homogenizing
pressure
increa
sed,

appa
rent
viscosity
of
the emulsion increased, with

a
strong
shift
of
the
fluid
from
a
Newtonian
to
pseudoplastic
behav- ior, indicative of resistance
arising

from
particle–particle interaction
in
the
emulsions
(Charm,
1962
).
The consistency index (K) is
an
indicator
of
the
vis-
cous nature
of

the system and was observed
to
be
in-
creased
with
the increase
in
homogenizing
pressur
e,
Furthermore,
a
decrease
in
consistency
index (K) was
observed with the increasing
temperature, indicating
a
decrease
in
apparent
viscosity at higher
tempe
ratur
es.
3.2. Effect on fat structure
of
coconut

milk
The effect
of
homogenizing pressure
on
fat
struc
ture
of
coconut
milk
were conducted using
optical
standar
d
microscope
(
Fig.

2).
It
was found
that the
non

hom
oge-
nized sample had larger fat
globule sizes than

homoge- nized ones. During the
homogenization, the

high shear forces acted
on
dispersed phase
to
redu
ce

droplet size
perature, some
heat labile proteins
were
destroy
ed (Seow
&
Gwee, 1997) and
fat
globules
tended
to form
aggregates. Therefore, the emulsion
syst
em

co
ntaine
d
less suspended single

fat
globules
to
resist

the flow.
The
micrographs supported the
results from

the rheo- logical studies that decreasing
in viscosity
of
heated trea-
ted
homogenized
coconut milk
was

caused
from
the change
in
microstructure.
The droplet size distribution and mean droplet
diam-
eter were also determined as shown in Fig. 4 and
Tabl
e

4
.
The patterns
of
the size distribution data
were changed
noticeably
at
higher heating
temperature. The effect
of
homogenizing
pressure
on
the droplet size
was

clear
ly
seen as the data from
different pressures were

discrete
from
each other.
Furthermore, new
large
droplets
in
the range

of
10–100
l
m

were
detected

which resulted
in
the
increase
of
the mean
droplet
diameter obtained
for
all
samples passing
higher
heating level. The results
suggested
that
the
stabili
ty
of
canned
coconut
milk

was influenced
by both
homogenizing
pressure and sterilizing
condition.
Table

4
Effect
of
homogenization pressure
on fat particle
diameter (D
m
)
of
canned high fat
coconut
milk
(
Floury

et
al.,
2002). Small
fat
globule sizes were
ob-
tained
at

higher homogenizing pressures.
Reduction
in
Temperature (
C)
Homogen
ization
pressure
(MPa)
Fat
particle
diamet
er
(
D
m
)

±
SD
(
l
m)
the
fat
particle diameters resulted
in an
increase
in
K

value and thus improved the product stability
(
Go
nzalez
et al., 1990; Srithunma,
2002
).
When the homogenized
coconut milk
sampl
es
were
subjected
to
heat treatments, small
fat
globules
formed irregular rearrangement
of
aggrega
tes.

Naturally, coco-
nut milk
composes
of
fat globules
surrounded
by
the aqueous protein

solution
(
Gonzal
ez

et al., 1990).
Addi- tion of
emulsifier
and
stabili
zer

helped
in
the stability
of
coconut milk by lowering
the interfacial tension
be- tween two phases,
therefore fat
globules could
disperse throughout the water
pha
se.

Fig. 3
exemplifies the effect
of
sterilizing
tempe

ratur
e

o
n

the
structure
of
fat globule. When the samples were
heated
at
high sterilizing tem-
109.3 15 (11/4) 3.57 ± 0.25
18 (14/4) 3.43 ± 0.24
21 (17/4) 3.26 ± 0.23
24 (20/4) 3.06 ± 0.21
27 (23/4) 2.81 ± 0.19
115.6 15 (11/4) 4.40 ± 0.35
18 (14/4) 4.31 ± 0.21
21 (17/4) 4.29 ± 0.31
24 (20/4) 4.12 ± 0.28
27 (23/4) 3.81 ± 0.26
121.1 15(11/4) 5.94 ± 0.34
18 (14/4) 5.49 ± 0.27
21 (17/4) 5.44 ± 0.38
24 (20/4) 5.42 ± 0.41
27 (23/4) 5.01 ± 0.24
Table 5
Effect

of
homogenizing pressure and sterilizing temperature
on
L/b values
of
high fat coconut
milk
Homogenizing
pressure
(MPa)
Temperatur
e
30

C
109.3


C
115.6


C
121.1


C
L
b
L/b

L
b
L/b
L
b
L/b
L
b
L/b
Non homogenization
77.92
4.85
16.07
–
–
–
–
–
–
–
–
–
15 (11/4)
79.35 4.30 18.44 74.58 8.54 8.73 73.54 6.42 11.49 77.90 4.83 16.13
18 (14/4)
79.52 4.29 18.51 72.44 8.14 8.90 71.55 6.18 11.58 77.89 4.79 16.24
21 (17/4)
79.96 4.25 18.78 73.26 8.09 9.06 70.87 6.07 11.68 78.55 4.75 16.53
24 (20/4)
80.47 4.26 18.88 73.69 7.90 9.32 72.02 6.05 11.90 78.49 4.72 16.61

27 (23/4)
80.49 4.26 18.96 72.91 7.80 9.34 71.88 6.01 11.95 78.79 4.69 16.77
44
N.
Chiewchan et al.
/
Journal
of
Food Engineering 73 (2006) 38–44
3.3. Effect on color
of
coconut
milk
The color
changes
of
coconut
milk
as affected
by
homogenizing pressure
and thermal
processing
were investigated and the color values
were presented
in
terms
of
Hunter L/b (Table 5).
It

was found that
L/b
values
of
homogenized coconut
milk
were great
er

than

that
for fresh coconut
milk and
increa
sed
with
increasing
homogenizing
pressure
(
P

< 0.05).

Smaller droplets
were produced when the
higher
homogenizing
pressures were

applied. The reflectance

increased
with increasing drop- let concentration
and
decreasing droplet size (Chantrap-
ornc
hai,
Clyd
esdale
,
&
McClements, 1999).
This
occurrence resulted
in
the higher lightness values
(
L
).
For
the effect
of
thermal processing, lightness
(
L
)
of
product at any sterilizing temperatures were not
signi

fi-
cantly different while b values decreased
with
ster
ilizing
temperature.
Therefore, L/b value
increased with increasing sterilizing
tempe
ratur
e.
In low acid food
such coconut
milk (pH about
6),
non-enzymatic browning reaction occurred when
high
heating temperatures (>100
C)
were applied
(Ames
&
Hofmann, 2001). In this research, three
levels
of
steriliz-
ing temperature, i.e. 109.3, 115.6 and
121.1
C
were

cho-
sen and the process time
to
approach
F
0
= 5
min
were
different (Table 1). The
higher b values were found
for
the sample passing
the thermal process
at
115.6
C

a
n
d
109.3
C,
respectively.
The
reason was that heating
at
lower temperature
had
taken longer

time to
achieve
F
0
= 5 min. Therefore, there was longer
period
of
tim
e
to
permit the browning reaction
to
occur. This
resul
ted
in
the significant reduction
in
L/b
value.
4. Conclusions
Following
the

power

law

model,

coc
onut

milk
sampl
es
passing through a 2-stage
homogenizer and
heating pro-
cess

(sterilization)
in

the

range

of
experimental
conditio
ns
exhibited pseudoplastic
behavior with the flow
be
havior
index (n) between
0.719 and 0.971. Increasing
hom
oge-

nizing

pressure
caused

a

decrease
o
f

fat

droplet

size

whi
ch
resulted
in
an
increase
of
apparent viscosity.
How
ever,
heat
treatment at higher temperature led to the
aggrega

t-
ing
of

fat particle and this phenomenon caused the
reduc-
tion of apparent viscosity. For optical
property
determination, Hunter L/b
values
of
homogenized coco-
nut milk were greater than that for
fresh sample and the
values increased with increasing
homogenizing
pressures. Comparing among
commercial
ster
ilizing

conditions
of
study, heating at
121.1
C
for 60
min
provided an accept- able color
comparing to

fresh
coconut
milk.
Acknowledgments
Thi
s

work was supported by the National Center
for Genetic Engineering and
Biotechnology,
Thailand
(BIOTEC).
The authors wish to thank
Adinop
co
mpany
for
kindly providing the emulsifying
agents
(Mon
tanox
60 and Montane
80).
And
the National Metal and
M
ate-
rials Technology Center
(MTEC)
for allowing the use

of
the
Mastersizer-S.
Ref
erences
Ames,
J. M., &
Hofmann,
T. F.
(2001). Chemistry and

physiology
of
selected food colorants.
Washington, DC: ACS,
p. 227.
Association
of
Official Analytical Chemistry
(AOAC).
(1990).
Official method
of
analysis (15th ed.).
The
Association
of
Official Agricul- tural
Chemists, Virginia.
Campanella,

O. K.,
Dorward
&
Singh,
H.
(1995).
A

study
of
the
rhelogical properties
of concentrated food
emulsions. Journal
of
Food Engineering,
25
,

427–440
.
Chantrapornchai,
W.,
Clydesdale,
F., &
M
cClemen
ts,
D. J.
(1999).

Influence
of
droplet characteristics
on
the
optical
properties
of
colored oil-in-water emulsion. Colloids and
Surfaces A:
Physico-
chemical and Engineering Aspects, 155, 373–382.
Charm,
S.
E.
(1962).
The
nature
of role of fluid
consistency
in
food
engineering
application advance. Food
Research,
11
,
356–361.
Floury, J., Desrumaux,
A., &

Legrand,
J.
(2002). Effect
of
ultra-high
-
pressure homogenization
on
structure and
on
rheological
proper-
ties
of
soy protein-stabilized emulsions. Journal
of
Food
Science,
67(9), 3388–3395.
Gonzalez,
O. N.,
de Leon, S.
Y., &
Sanchez,
P. C.
(1990).

Coconut as
food. Philippines Coconut Research and Development

Foundation
Inc., pp. 13–40.
Seow,
C.
C.,
&
Gwee,
C. N.
(1997). Review,
coconut
milk:
Chemistry
and
technology. International Journal
of
Science and

Technology,
32, 189–201.
Shaker,
R. R.,
Jumah,
R. Y., &
Jdayil,
B. A.
(2000).
Rheological
properties
of
plain yogurt during coagulation process:

Impact
of
fat
content and preheat treatment
of
milk. Journal
of
Food

Engineer-
ing, 44, 175–180.
Simuang,
J.,
Chiewchan,
N., &
Tansakul,
A.
(2004).

Effect
of heat
treatment
and fat
content
on flow
properties
of
coconut
milk.

Journal
of
Food Engineering, 64, 193–197.
Sringam, S. (1986). Preparation and stabilization
of
coconut
milk
(p.
25).
Food
Science and Technology Research
Project,
Agro-
In
dus-
try
Faculty, Kasetsart University,
Bangkok.
Srithunma,
S. (2002).
Effects fat
content and

homoge
nization
pressure on apparent viscosity
of
coconut
milk
(p. 42).

Thesis
for
the Master

s Degree
of Food
Engineering,
Faculty

of

Engineer-
ing, King
Mongkut

s
University of
Technolo
gy,

Thonburi
,
Thailand.
Vitali, A.
A., Soler,
M.
P.,
&
Rao,

M. A.
(1985).

Rheological
behavior
of
coconut milk. In Food engineering and process

applications. In
M
.
L. Maguer &
P.
Jelen
(Eds.).
Transport
phenomena
(vol.
1).
Elsevier Applied
Science.
Xu,
W., Nikolov,
A.,
Wasan,
D.
T., Gonsalves,
A.,
&

Borwankar,
R.
P.
(1998).
Fat
particle structure and stability
of food
emulsions.
Journal
of
Food Science, 63(2),
183–188
.