Effects of coconut sugar and stabilizing agents on stability and apparent viscosity of high-fat coconut milk pdf

Available online at www.sciencedirect.comJournal of Food Engineering 87 2008 422–427 www.elsevier.com/locate/jfoodeng Effects of coconut sugar and stabilizing agents on stability and appa

Available online at www.sciencedirect.com

Journal of Food Engineering 87 (2008) 422–427

www.elsevier.com/locate/jfoodeng

Effects of coconut sugar and stabilizing agents on stability and apparent viscosity of high-fat coconut milk

Karunthapat Jirapeangtong, Suwit Siriwatanayothin, Naphaporn Chiewchan

* Department of Food Engineering, Faculty of Engineering, King Mongkut’s University of Technology Thonburi,

126 Pracha u-tid Road, Bangkok 10140, Thailand Received 27 September 2007; received in revised form 7 December 2007; accepted 1 January

2008 Available online 8 January 2008

Abstract

This study was aimed at determining the physical properties of sterilized high-fat coconut milk (30%) as affected by coconut sugar (10–

30%) and stabilizing agents, namely carboxymethyl cellulose (CMC, 0.6–1.0%) and Montanox 60 (0.6–1.0%) The emulsion stability

(ES) and rheological properties were determined after thermal processing at 121 C for 60 min At similar sugar content, increasing

concen-tration of CMC or Montanox 60 resulted in an increase in ES The concenconcen-trations of CMC and Montanox 60 in the range of 0.8–

1.0%

were found to give the ES in the range of 81.16–91.15% These conditions were selected to conduct the rheological measurements It

was found that all samples exhibited pseudoplastic behavior with the flow behavior index (n) between 0.63 and 0.84 The results

suggested that suitable ratio between coconut sugar and stabilizing agent contents should be specified in order to obtain a high quality of

processed sweetened coconut milk.

2008 Elsevier Ltd All rights reserved.

Keywords: Coconut milk; Emulsion stability; Rheological properties; Stabilizing agent; Sugar; Viscosity

1 Introduction

In Thailand, many traditional foods contain

coconut milk as a main ingredient The sweetened

coconut milk for desserts is typically prepared by

adding granulated cane sugar, coconut or palm sugars

to fresh or heated coconut milk and mixed

thoroughly The fruits or gelatinized formed flour

may also be added during heating

Coconut milk naturally contained about 54%

moisture,

35% fat and 11% solid non-fat (Simuang et al., 2004) and

is

categorized as oil in water emulsion The separation of

an

emulsion into creamy and water phases usually occur

after

standing for a while This leads to the physical defect

of

coconut milk

* Corresponding author Tel.: +66 2470 9243; fax: +66 2470 9240 E-mail address: naphaporn.rat@kmutt.ac.th (N Chiewchan).

of oil in water emulsion including processed coconut

milk, e.g fat content, type and amount of stabilizing

agents, homogenizing pressure and thermal process

conditions (Sringam, 1986; Seow and Gwee, 1997;

Sringam (1986) reported that type and quality of

emul- sifier and homogenization affected the stability of

coconut milk Klinkesorn et al (2004) reported that

addition of maltodextrin to corn oil in water

emulsion had a pro- nounced effect on the emulsion

canned coconut milk (14.5% fat) was found for the coconut milk with the addition of 0.5% emulsifier (Tween 60 and Span

80 (sorbitan monooleate) mixed to obtain a hydrophilic/ lipophilic balance, HLB, of 14.5) Srithunma

in combination with 0.6% Montanox 60 (polyoxyethylene sorbitan

0260-8774/$ - see front matter 2008 Elsevier Ltd All rights reserved

doi:10.1016/j.jfoodeng.2008.01.001

K Jirapeangtong et al / Journal of Food Engineering 87 (2008) 422–427 423 monostearate or Tween 60) provided good emulsion

for coconut milk containing 15–30% fat

CMC (0.2–1.0% w/v) and Montanox 60 (0.2–1.0% w/v)

on the quality of canned high-fat coconut milk (30%)

after com- mercially sterilizing process (121.1 C for 60

min to achieve F0 = 5 min) Their results showed

that using CMC or Montanox 60 alone could not

improve the quality of coconut milk in terms of

emulsion stability, curding and color The combination

of the stabilizing agents used, i.e CMC:Montanox 60

(0.6:0.6% w/v) could provide high sta- bility products (ES

> 80%), no curding and no significantly difference in

colors comparing to fresh coconut milk after heat

treatment

In addition, the ingredients added to the emulsion

also

affected the stability For example, sucrose had an

effect

on the thermal stability of protein-stabilized

emulsions

and consequently led to an increase in droplet

aggregation

(Kulmyrzaev et al., 2000; Kim et al., 2003) Onsaard et

al

and

creaming of corn oil in water emulsion when higher

salt

concentration was added to the system

In terms of rheological properties, coconut milk

has

been found to exhibit pseudoplastic behavior

(Vitali

et al., 1985; Simuang et al., 2004; Chiewchan et al.,

2006) The composition of the coconut milk, such as

stabi-lizing agent and fat content, has been reported to have

sig-nificant effect on the flow behavior of coconut

milk

Coupland,

2005; Chiewchan et al., 2006; Peamprasart and

Chiewchan,

2006)

Although the stable formulation for production

of

canned high-fat coconut milk (30%) has been

recom-mended (Phungamngoen et al., 2004), the

preliminary

study showed that the suggested condition could not

pro-vide a good emulsion for the coconut milk

containing

sugar The suitable formulation of emulsifiers is

required

to obtain the sweetened coconut milk with high

stability

Therefore, this research was aimed at determining

the

effects of coconut sugar (10–30% w/v) and

stabilizing

agents, i.e CMC and Montanox 60, in the range of

0.6–

1.0% w/v, on the physical properties of sweetened

high-fat coconut milk The physical characteristics were studied

in terms of emulsion stability and apparent viscosity The

information obtained would provide the understanding of

the function of sugar on the stability of coconut milk and

could be used as guidelines for production of sterilized

sweetened coconut milk

2 Materials and methods 2.1 Sample preparation Coconut milk without added water from a local market was used in the experiments The initial fat content of coco- nut milk (35–39%) was determined using Rose–Gottlieb method (AOAC, 1990) The fresh coconut milk ( 1.5 l

Purk, Nonthaburi, Thailand) was then added to adjust the con- centrations to 10–30% w/v, respectively Montanox 60 (Adinop, Thailand) and CMC (Thai Food and Chemical, Thailand) at the concentrations of 0.6– 0.8% w/v were added while the samples were heated and stirred continu- ously The sample was held on a hot plate for 1 min once its temperature reached 70 C

to inhibit lipase The pre- pared sample was passed through a two-stage homogenizer (GEA NS200 6L, Italy) at 11/4 MPa The homogenized sample was then filled into glass bottles and sterilized at

121 C for 1 h (Phungamngoen et al., 2004) using an auto- clave (Hirayama HA-300D, Japan)

2.2 Determination of emulsion stability

To evaluate the stability, the sterilized samples were kept at room temperature ( 30 C) for 3 days and determined the stability of emulsion following the method described by Phungamngoen et al (2004) The emulsion stability can be calculated by following formula:

ðESÞ

Height of emulsion phase 100%

¼

Height of whole coconut

milk 2.3 Rheological measurement

The measurements were carried out using a rotational, concentric cylinder viscometer (HAAKE VT500, Ger- many) with NV type measuring system The sample (9 ml) was filled into the cup and shear rate was increased from 0 to 300 s 1 in 2 min The temperature of the sample was maintained at 30 C during the measurements by means of thermostat bath for controlling the stability of the sample

2.4 Microscopic study

A few drops of paprika oleoresin with 100,000 Color Unit (Chr.-Hansen, Murcia, Spain) 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 sample were transferred to the slide and a cover slip was placed over the sample A standard light microscope (Olympus CH30, Japan) was used to determine the fat structure at a magnification of 100 and photographs were taken from typical fields 2.5 Experimental design and data analysis

A 3 3 factorial design was used in scheduling of the experiments The experiments were performed at three lev- els of CMC (0.6%, 0.8%, 1.0% w/v), three levels

of Monta- nox 60 (0.6%, 0.8%, 1.0% w/v) and three levels of coconut

424 K Jirapeangtong et al / Journal of Food Engineering 87 (2008) 422–427

sugar The data were reported as an average of two

repli- cates Analysis of variance (ANOVA) of the

three factors and interactions were applied to the

different sets of data with a significance level of 95% (a

= 0.05)

3 Results and discussion

3.1 Emulsion stability

The influence of coconut sugar and stabilizing agents

on the ES of coconut milk samples are given in Table

1 At each level of coconut sugar concentration, the ES

of

coco-nox 60 up to 1.0% and fixing either CMC or Montanox

60 to 0.6% could not provide good emulsion stability

The results suggested that at least 0.8% of CMC and

0.8% Montanox 60 were required to produce the high sta-bility of sweetened high-fat coconut milk

3.2 Rheological properties The plots of apparent viscosity against shear rate

of coconut milk are shown in Fig 1 The rheograms obtained

0.4 nut milks increased as the total amount of

stabilizing

agents increased Montanox 60, acted as an

emulsifier,

was adsorbed to the surface of fat droplets preventing

the

aggregation of the fat droplets while CMC caused

an

increase in viscosity of continuous phase therefore

retarded

the gravitational separation of the droplets

1999; Klinkesorn et al., 2004; Phungamngoen et al.,

2004)

The better stability of coconut milk was obtained in

the

systems containing higher coconut sugar contents

The

results implied that sugar plays a significant role on the

sta-bility of coconut milk Sugar may increase the

viscosity of

the continuous phase (Kim et al., 2003; McClements,

2004)

and this resulted in the retardation of the fat droplet

aggre-gation The results also showed that the ES of coconut

milk

samples increased as the coconut sugar content

increased

An increase in stability of oil in water emulsion as

affected

by sugar was also reported by Maskan and Go¨ g˘u} s

(2000)

The effect of stabilizing agents on the ES was

also

observed The results showed that both CMC and

Monta-nox 60 concentrations had marked effect on the ES

of

sweetened coconut milk A significant increase (P <

0.05)

in the emulsion stability was observed for the samples

con-tai ni ng hi gh er co nc en tr ati on of eit he

r C M

C or M o nt a n ox 60

Ph un ga m ng oe

n

et al

(2 00 4)

re po rte

d

that the addition

of 0.6% CMC and 0.6% Montanox 60 was applicable for

the production of canned high-fat coconut milk (30% fat)

and could provide the ES of higher than 80% However,

it was found in this present investigation that the

previ-ously suggested concentrations of stabilizing agents could

not be applied to the coconut milk samples containing

sugar Furthermore, increasing levels of CMC or

Monta-Table 1 The emulsion stability of coconut milk at each condition

Ap par ent vis co sit

y (P a.s )

Ap par ent vis co sit

y (P a.s )

0.3 0.25 0.2 0.15 0.1 0.05 0

0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0

0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0

0.4 0.35

0.25

Shear rate (1/s)

b

Shear rate (1/s)

c

Shear rate (1/s)

d

Suga

r

(%)

CMC

(%) Montanox 60 (%)

0.2 0.15

10 0.6 52.02 ± 0.57 a 52.77 ± 0.13 a 53.00 ± 0.21 a

0.8 54.77 ± 1.91 ab 56.33 ± 1.56 ab 65.07 ± 1.60 de

1.0 60.40 ± 0.08 bcd 81.16 ± 0.28 hi 85.14 ± 4.02 i

20 0.6 53.10 ± 0.54 a 55.39 ± 1.86 ab 62.49 ± 0.84 cd

0.8 57.79 ± 3.77 abc 64.52 ± 0.36 d 72.50 ± 0.86 fg

1.0 69.97 ± 1.31 ef 82.54 ± 1.65 hi 86.09 ± 0.59 ij

0.1 0.05 0

Shear rate (1/s)

30 0.6 53.92 ± 2.50 ab 72.53 ± 1.54 fg 73.55 ± 0.01 fg

0.8 65.14 ± 0.64 f 73.00 ± 1.61 fg 85.09 ± 4.21 i

1.0 77.44 ± 0.71 gh 84.08 ± 0.92 i 91.15 ± 0.59 j

Fig 1 The change in apparent viscosity of coconut milk samples

containing 10% (e), 20% (j) and 30% (M) coconut sugar with varying stabilizing agents: (a) CMC 0.8% and Montanox 60 0.8% (b) CMC 0.8% and Montanox 60 1.0% (c) CMC 1.0% and Montanox 60 0.8% and (d) Values followed by the same letter are not significantly different (P <

0.05).

CMC 1.0% and Montanox 60 1.0%.

Ap pa re

nt vis co sit

y (P

Ap par ent vis co sit

y (P a.s )

K Jirapeangtong et al / Journal of Food Engineering 87 (2008) 422–427 425 were similar for all conditions Power law model

was applied to describe the rheological behavior of the

s

1 ) of coconut milk at

where s is the shear stress, c is the shear rate, K is the

con- sistency index (Pa sn) and n is the flow behavior

index

It was found that high-fat coconut milk with

coconut

CMC (%)

Montanox 60 (%)

Coconut sugar (%)

2

d 6.78 10 2c 11.24 10 2a sugar possessed pseudoplastic or shear-thinning

behavior

Similar trends were observed for different sets of

with high correlation (R2 = 0.996–0.998) As the shear

rate increased, the particle–particle interaction was

deformed and finally disrupted which resulted in the

size reduction of the flocs and led to a decrease in

viscosity (McClements, 1999) The values of the

consistency index (K) and flow behavior index (n)

obtained from the curve fitting are given in Tables

2 and 3

It was considered that an increase in CMC content

had

more effect, comparing with Montanox 60, on an

increase

in K value and a decrease in n value CMC performed

as

a thickening agent that functioned to increase the

viscosity

of continuous phase (McClements, 1999) which

prevented

the droplet aggregation, while Montanox 60

performed

as a binding agent which could precipitate with the

excess

amount (McClements, 1999; Phungamngoen et al.,

2004)

In addition, at each level of CMC and Montanox 60,

it

was suggested that K value increased with an increase

in

sugar content

It seems that samples with lower % of CMC and

Monta-nox 60 contents tended to be closer to Newtonian flow

At

a fixed concentration of stabilizing agents, the

magnitude

of n values of coconut milk samples decreased with

an

increase in sugar content However, n value did not

change

significantly (P < 0.05) for coconut milk samples

with

contents

Table 2

The K (Pa s n ) of coconut milk

samples

CMC (%) Montanox 60 (%) Coconut sugar (%)

Values followed by the same letter are not significantly different (P < 0.05).

Table 3

T he n value of coconut milk samples

CMC (%) Montanox 60 (%) C oconut sugar (%)

0.8 0.8 2.90 10 2 k 4.79 10 2 i 5.72 10

1 2.99 10 2 e 5.01 10 2 c 6.64 10

2 b

1 0.8 3.86 10 2j 5.96 10 2g 8.36 10 2f

Table 4 shows the values of apparent viscosity at a

max- imum shear rate (300 s 1) There was a

statistically signifi- cant difference (P < 0.05) in the

apparent viscosity of the coconut milk samples

containing different concentrations of CMC, Montanox

60 and coconut sugar It was found that the emulsions

were more viscous when higher sugar contents were

added to the coconut milk samples The effects of

added ingredients on the rheological properties have

been reported previously Maskan and Go¨ g˘u} s

concentration increased the viscosity of sunflower oil

in water emulsions Tantayotai and Pongsawatmanit

coconut oil in water emulsions increased with

increasing concentration of NaCl

When sucrose was added to the coconut milk and

subse- quently heated, higher sucrose concentration

caused more aggregation of fat globules of coconut

milk The reason was that sucrose may alter the droplet–

droplet interaction Although the viscosity of the

observed by Kim et al (2003) They reported that

an increase in droplet particle size, which indicated

an increase of the droplet flocculation, was observed

in the oil in water emulsion containing NaCl

3.3 Microstructure of coconut milk

Fig 2 exemplifies the fat structure of fresh coconut milk and homogenized coconut milk before and after steriliza- tion In fresh coconut milk, the fat globules were of variable size and non-uniformly dispersed with some aggre- gates The presence of finer and more uniform fat globule size were exhibited after homogenization comparing with the fresh sample A good dispersion of fat globules in an aqueous phase was clearly seen for the sample with 10% sugar after homogenization However, it was observed that adding more concentration of coconut sugar resulted in the aggregation of fat globules Furthermore, the effect

of sugar concentration was more pronounced after steriliza- tion The fat globules tended to move closer and formed

Sim-Values followed by the same letter are not significantly different (P <

emulsion

nox 60 to 1.0% by fixing the concentration of

d

426 K Jirapeangtong et al / Journal of Food Engineering 87 (2008) 422–427

Fig 2 Micrographs (100 magnification) of fresh coconut milk (a) and coconut milk containing 10% (b, c), 20% (d, e) and 30% (f, g) coconut sugar and

1.0% CMC and 0.8% Montanox 60 before (b, d, f) and after (c, e, g) sterilization.

system containing NaCl (Onsaard et al., 2005)

aggregation and creaming increased with an increase in

NaCl concen- tration Moreover, heating may

conformational changes These con- formational

changes could increase the attractive forces between

fat droplets which led to the aggregation (Kim et al.,

2003)

Although the area of unoccupied aqueous phase

and

more aggregation of fat globules were clearly seen, the

vis-cosity of the emulsion system containing sugar sugar may increase the viscosity of an aqueous phase, which hence resulted in an increase of the viscosity

of emulsion and higher stability

4 Conclusions This study has revealed that stabilizing agents, i.e CMC

and Montanox 60, and coconut sugar had significant effect

on both emulsion stability and rheological properties

stabilizing agents were required to sustain the colloidal

system con- taining sugar The 0.8–1.0% of CMC and

Montanox 60 were recommended for the production

of high stability sweetened coconut milk The quality

changes of sweetened coconut milk, such as emulsion

stability, viscosity, curding and color, during storage

should be determined to assure good quality of the

product A study of the combination effect of sugar

content and stabilizing agents with different fat

contents on emulsion stability and rheological

proper-ties is also interesting and is recommended for future

work

Acknowledgements

The authors wish to thank Adinop Company,

Thailand, for kindly providing Montanox 60

References

Association of Official Analytical Chemist (AOAC), 1990 Official

Method of Analysis, 15th ed The Association of Official

Agricultural Chemists, Virginia.

Chiewchan, N., Phungamngoen, C., Siriwattanayothin, S., 2006.

Effect of homogenizing pressure and sterilizing condition on

Engineering 73,

38–44.

Kim, H.J., Decker, E.A., McClements, D.J., 2003 Influence of sucrose

on

droplet flocculation in hexadecane oil-in-water emulsions stabilized

by

b-lactoglobulin Journal of Agricultural and Food Chemistry 51,

766–

772.

Klinkesorn, U., Sophanodora, P., Chinachoti, P., McClements,

D.J.,

2004 Stability and rheology of corn oil-in-water

emulsions

containing maltodextrin Food Research International 37,

851–

859.

Kulmyrzaev, A., Bryant, C., McClements, D.J., 2000 Influence of

sucrose

on the thermal denaturation, gelation, and emulsion stabilization

of

whey proteins Journal of Agricultural and Food Chemistry 48,

1593–

1597.

Maskan, M., Go¨ g˘u} s, F., 2000 Effect of sugar on the rheological properties of sunflower oil-water emulsions Journal of Food Engineering 43,

173–177.

McClements, D.J., 1999 Food Emulsions: Principles, Practice and Techniques CRC Press, Boca Raton, p 378.

McClements, D.J., 2004 Protein-stabilized emulsions Current Opinion

in Colloid and Interface Science 9, 305–313.

Onsaard, E., Vittayanont, M., Sringam, S., McClements, D.J.,

2005.

Properties and stability of oil-in-water emulsions stabilized by coconut

skim milk proteins Journal of Agricultural and Food Chemistry 53,

5747–5753.

Peamprasart, T., Chiewchan, N., 2006 Effect of fat content and

preheat treatment on the apparent viscosity of coconut milk after

homogeni-zation Journal of Food Engineering 77, 653–658.

Phungamngoen, C., Chiewchan, N., Siriwatanayothin, S., 2004 Effect

of some stabilizers on the quality of canned high fat coconut milk.

Journal of KMUTT’s Research and Development 27, 376–390 Seow, C.C., Gwee, C.N., 1997 Coconut milk: chemistry and technology International Journal of Food Science and Technology 32, 189–201 Simuang, J., Chiewchan, N., Tansakul, A., 2004 Effects of fat and temperature on the apparent viscosity of coconut milk Journal of

Food Engineering 64, 193–197.

Sringam, S., 1986 Preparation and stabilization of coconut milk.

Food Science and Technology Research Project Agro-Industry Faculty,

Kasetsart University, Bangkok p 25.

Srithunma, S., 2002 Effects of fat content and homogenization

pressure

on apparent viscosity of coconut milk Thesis for the Master’s Degree

of Food Engineering Faculty of Engineering, King Mongkut’s

University of Technology Thonburi, Thailand, p 42.

Tangsuphoom, N., Coupland, J.N., 2005 Effect of heating and homog-enization on the stability of coconut milk emulsions Journal of Food

Science 70, 466–470.

Tantayotai, T., Pongsawatmanit, R., 2004 Effect of homogenizer types

and sodium chloride concentration on the physical properties of coconut oil

in water emulsions Kasetsart Journal (Natural Science) 38, 1–7 Thungkao, P., 1988 Application of emulsifiers and gums for

the stabilization of canned coconut milk Thesis for the Master’s Degree

of Science Department of Food Science and Technology, Kasetsart

University, Thailand.

Vitali, A.A., Soler, M.P., Rao, M.A., 1985 Rheological behavior

of coconut milk In: Maguer, M.L., Jelen, P (Eds.), Food Engineering and Process Applications, vol 1 Elsevier Applied Science, London,

pp 33–38.