Effect of homogenizing pressure and sterilizing condition on quality of canned high fat coconut milk Department of Food Engineering, King Mongkut s University of Technology, Thonburi, Tun
Trang 1Effect of homogenizing pressure and sterilizing condition on quality of canned high fat coconut milk
Department of Food Engineering, King Mongkut s University of Technology, Thonburi, Tungkru, Bangkok 10140, Thailand
Received 31 August 2004; accepted 6 January 2005
Available online 24 February
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 properties
1 Introduction
Coconut milk is a milky white oil-in-water
emulsion 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 unac- ceptably physical
defect of either fresh or processed coconut milk
Canning has been found to be a suitable process for
preservation of coconut milk The process starts
from extracting the milk from grated coconut meat
with or without added water The percentage 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: naphaporn.rat@kmutt.ac.th (N Chiewchan).
emulsifier and pass through the homogenizer Finally, it was filled in can and sterilized in the retort
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 reducing fat globule size are required prior to heat treatment 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 milk
0260-8774/$ - see front matter 2005 Elsevier Ltd All rights
reserved doi:10.1016/j.jfoodeng.2005.01.003
Trang 2than single-stage high pressure (5000 psi)
(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
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
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
which implied the decrease of the coconut milk
stability
From literature described above, homogenizing
pres-sure and temperature were significant parameters
affect-ing the stability of the emulsion This research
was
aimed to investigate the effect of homogenizing
pressure
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
obtained
from the study could be used as a guideline for
develop-ing of high fat coconut milk canndevelop-ing
process
2 Materials and methods
preparation
Fresh coconut milk without added water from a
local market was stored at room temperature and
passed through the cloth filter before experiments
The initial fat content of coconut milk (35–37%)
30% w/vby distilled water 0.6% (w/v) Montanox 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 115.6 C and (d) 121.1 C.
Trang 3sterilized using a horizontal still retort The thermal
measurement
The rheological measurements were carried out
using a rotational concentric cylinder viscometer
(HAAKE 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
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 microscope (Olympus Model CH30, Japan)
was used to determine the fat structure at a
magnification of 400· (before ther- mal process) or a
magnification of 100· (after thermal processing) and
photographs were taken from typical fields
2.4 Determination of fat globule size
distribution
The diffractometer (Malvern Instrument
Model
Mastersizer-S, UK) equipped with a 3 RF lens and
an
He–Ne laser (k = 633 nm) was used to determine size distribution of fat globules of coconut milk The steril- ized samples were diluted to approximately 1/1000 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 lm) The measurements were conducted three times for each samples
2.5 Color measurement Color of coconut milk was analyzed by
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 levels of homogenizing pressure (11/4, 14/4, 17/4, 20/4 and
23/4 MPa) and three levels of sterilizing temperature (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 sterilizing 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 Temperature Homogenization K (Pa s n ) n r 2
Temperature Homogenization Apparent viscosity
30 Non homogenization 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
Trang 4were reported as an average of three replicates.
and interac- tions were applied to the different sets of
data with a sig- nificant level of 0.05 (a = 0.05)
3 Results and discussion
properties
The plot of apparent viscosity against shear rate
of coconut milk homogenized at five pressure levels
rheograms obtained were similar for all
conditions Power law model was applied to
describe the rheological behavior of the samples
where s is the shear stress, c_ is the shear rate, K is
behavior index
The excellent fits were obtained with high
all samples 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 As coconut milk is a colloidal system containing fat globules dispersed
in water phase, the fat particles may rearrange them- selves 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 interaction
Fig 2 Micrographs (·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.
Trang 5which decreased viscosity (Charm, 1962).
When the aggregates were completely disrupted,
further in- crease in shear rate did not affect the
1995)
At the same temperature, a decrease in n value and
an increase in K value were obtained for the samples
pass- ing higher homogenizing pressures The increase
in pres- sure level permitted the size reduction This
meant that higher numbers of droplet were
presented in the colloi- 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 temperature
Table 3 shows the values of apparent viscosity (g) at
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 homogenizer
100 90 80 70 60 50 40 30 20 10 0 0.1
(a)
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)
Particle diameter (um)
(c)
Particle diameter (um)
Fig 3 Micrographs (·100 magnification) of coconut milk sterilizing tempera- tures: (a) 109.3 C, (b) 115.6 C and (c) 121.1
Vo lu me
of par ticl
e (%
)
Vo lu me
of par ticl
e (%
)
Vo lu me
of par ticl
e (%
)
Trang 6(c) 121.1 C on droplet size distribution at different homogenizing
pressures: 11/4 MPa (s), 14/4 MPa ( ), 17/4 MPa (n), 20/4 MPa (j) and 23/4 MPa (·).
Trang 7was accompanied with an increase in
pseudoplasticity and was shown by a decrease in
values of flow behavior index (n) This observation was
Legrand (2002) They re- ported that the emulsion
obtained at low homogenizing pressure show
Newtonian flow behavior with quite low viscosity
because there was no interaction between par- ticles
As homogenizing pressure increased, apparent
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
pressure, Furthermore, a decrease in consistency
index (K) was observed with the increasing
temperature, indicating a decrease in apparent
viscosity at higher temperatures
3.2 Effect on fat structure of coconut
milk
The effect of homogenizing pressure on fat
structure of coconut milk were conducted using
that the non homoge- nized sample had larger fat
globule sizes than homoge- nized ones During the
homogenization, the high shear forces acted on
dispersed phase to reduce droplet size
perature, some heat labile proteins were
tended to form aggregates Therefore, the emulsion system contained 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
Table 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 clearly seen as the data from different pressures were discrete from each other Furthermore, new large droplets in the range of 10–100 lm 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 stability 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) Homogenization
pressure (MPa) Fat particle diameter
(D m ) ± SD (lm)
the fat particle diameters resulted in an increase in
K value and thus improved the product stability
(Gonzalez et al., 1990; Srithunma, 2002)
When the homogenized coconut milk samples
were subjected to heat treatments, small fat
globules formed irregular rearrangement of
aggregates Naturally, coco- nut milk composes of
fat globules surrounded by the aqueous protein
emulsifier and stabilizer helped in the stability of
coconut milk by lowering the interfacial tension
be- tween two phases, therefore fat globules could
exemplifies the effect of sterilizing temperature on 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) Temperature
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
Trang 83.3 Effect on color of coconut
milk
The color changes of coconut milk as affected
processing were investigated and the color values
was found that L/b values of homogenized coconut
milk were greater than that for fresh coconut
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
Clydesdale, & 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
signifi- cantly different while b values decreased with
sterilizing temperature Therefore, L/b value
increased with increasing sterilizing temperature
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
higher b values were found for the sample passing
the thermal process at 115.6 C and
109.3 C, respectively The reason was that heating
period of time to permit the browning reaction to
occur This resulted in the significant reduction in L/
b value
4 Conclusions
Following the power law model, coconut milk
samples passing through a 2-stage homogenizer and
heating pro- cess (sterilization) in the range of
experimental conditions exhibited pseudoplastic
behavior with the flow behavior index (n) between
0.719 and 0.971 Increasing homoge- nizing pressure
caused a decrease of fat droplet size which resulted in
an increase of apparent viscosity However, heat
treatment at higher temperature led to the
aggregat-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 sterilizing conditions of study, heating at
121.1 C for 60 min provided an accept- able color
comparing to fresh coconut milk
Acknowledgments This work was supported by the National Center for Genetic Engineering and Biotechnology, Thailand (BIOTEC) The authors wish to thank Adinop company for kindly providing the emulsifying agents (Montanox
60 and Montane 80) And the National Metal and
Mate-rials Technology Center (MTEC) for allowing the use of
the Mastersizer-S
References
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., & McClements, 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-
Indus-try Faculty, Kasetsart University, Bangkok.
Srithunma, S (2002) Effects fat content and homogenization
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 Technology, Thonburi,
Thailand.
Trang 9of 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.