Effects of the emulsifier concentration on the microstructure...

Food Innovation Asia Conference 2010: Indigenous Food Research and Development to Global Market, June 17-18 2010, BITEC, Bangkok, THAILAND

Effects of the emulsifier concentration on the microstructure and end-use properties of spray dried coconut milk powders

Hamad, A.12*, and Suphantharika, M.1

(1Department of Biotechnology, Faculty of Science, Mahidol University, Rama 6 Road, Bangkok 10400 Thailand)

(2Department of Chemical Engineering, Faculty of Engineering, Muhammadiyah University of Purwokerto, Dukuh Waluh Road PO BOX 202 Purwokerto Indonesia)

*Email address: [email protected]

ABSTRACT

Properties of spray dried powder depended on the used process, feed composition and

operation condition during spray dry. Physical properties of the spray dry such as size, shape, porosity, and density influenced on the end-used properties i.e flowability, wettability and dispersibility of the spray dried powders. This study aimed to investigate the effects of the concentration of sodium caseinate used as an emulsifier on the characteristic and end-use properties of the spray dried coconut milk powders. The freshly prepared coconut milk was blended with various concentrations of sodium caseinate i.e. 0,1,2,3 and 5% w/v and 10% (w/v) maltodextrin. The emulsion was pasteurized at 70oC for 1 min, homogenized using the high pressure homogenizer at 200/20 bar for five passes and then spray dried by a spray dryer at 180oC for the input temperature. The oil droplet size of the homogenized coconut milks was found to be decreased with increasing concentration of sodium caseinate up to 3% and then increased there after. The stability of the coconut milk obtained after reconstitution at 40oC was highest at 3% and 5% sodium caseinate. These results indicate that the optimum concentration of sodium caseinate was 3%. However, all the spray dried coconut milk powder were very small and very cohesive leading to their poor flowability. The dispersibility of these powders was good but their wettability could be further improved. This study showed that emulsifier concentration would influence on microstructure and use-end properties of coconut milk powders. The resulted showed the fine particle and poor reconstitution Keywords: coconut milk, powder, emulsifier, spray dry, sodium caseinate

Introduction

Coconut milk is generally applied to the white, opaque protein oil water emulsion obtained by pressing grated or comminuted solid coconut endosperm, with or without addition of potable water or liquid endosperm (coconut water). The emulsion of known to be naturally stabilized by coconut proteins: globulins, albumin and phospholipids. Spray dry is the method of choice used in the commercial production of coconut milk powders. Such emulsifiers aid into the process and help to convert a high fat in coconut milk to flowable, but cohesive, powders through encapsulation of the fatty substance (Seow & Gwee, 1997). Major problem associated with drying of the fat rich liquid into powder are susceptibility to fat oxidation during drying and occurrence of high surface fat in dried powders. The process overcome by use encapsulation (Jena & Das, 2007).

Encapsulation is process in which liquid droplet or solid particles of sensitive ingredients or core materials are entrapped within a matrix of microencapsulating agent or wall material. The spray drying is the most commonly used to encapsulation food ingredient due to low cost and available cost (Gharsallaoui, Roudaust, Chambin, Voccillcccey, & Saurel,


2007). Since coconut milk is oil in water emulsion that is naturally unstable, obtaining a stable liquid emulsion is prerequisite for proper encapsulation in spray drying process (Jena & Das, 2007) The carriers required for encapsulation of fat must have high emulsifying property and be capable of dehydration. The milk product such as sodium caseinate had excellent emulsifier and dehydration properties while it had a relatively uniform composition.(Keogh & O'Kennedy, 1999). In addition to common emulsifier, protein can facilitate the stabilization of emulsion. Formation and stability of the emulsion are greatly affected by distribution of surface active ingredients in the bulk phase and the surface of the oil droplet. (Danviriyakul, McClements, Decker, Nawar, & Chinachoti, 2002) In coconut milk, proteins extracted from coconut cream are less surface active are not particularly effective at creating small droplets within the homogenization or preventing droplet aggregation during or after homogenization, thus after spray dried reconstitution has less stable emulsion (Onsaard, Vittayanont, Srigam, & McClements, 2005)., and investigation is needed to determine emulsifier concentration emulsifier in order to get stable emulsion and good re-use properties of powders.

The aim of this study was to investigate the influence of the emulsifier concentration on the microstructure and end–used properties of the spray dried coconut milk powders. The end-used of the powders included the stabilization spray dried emulsion after reconstitution, handling properties of powders (flowability and cohesiveness) and the reconstitution properties (wettability and dispersibility) (Turchiuli, Eloualia, El Mansouri, & Dumoulin, 2005)

Material and Methods

Material Fresh coconut milk without added water was purchased from local market in

Bangkok, Thailand. Before experiments it was passed through the cloth filter and would do experiments in the same day (Chiewchan, Phungamngoen, & Siriwattanayothin, 2006). Maltodextrin (D-Perse3) was purchased from Siam Modified Starch Co. Ltd Pathum Thani Thailand with dextrose equivalent (DE) value 12 - 15. It was used as wall material in spray dry. Sodium caseinate containing 92 % protein (ECCO 2300 Sodium caseinate) was provided by Vicchi Enterprise SuanLuang Bangkok, Thailand.

Methods 1. Emulsion preparation The experiment was carried on by the investigation of sodium caseinate as emulsifier at the fix amount of maltodextrin as wall material. Coconut milk emulsion was investigated by varied emulsifier (0, 1, 2, 3 and 5% w/v) at 10% w/v of maltodextrin. Emulsification was carried out by blended sodium caseinate using an Ultra Turrax T18 blender (IKA Werke GmbH & Co. KG, Staufen, Germany) operated at 13.500 rpm for 30 s (Hogan, McNamee, O’Riordana, & O’Sullivana, 2001). And then was added a maltodextrin using a stirred by a mechanical overhead stirrer (IKA model 20 RW, Janke and Kunkel GmbH and Co. KG, Staufen, Germany) at 300 rpm for 30 min. The sample was held on a hot plate for 1 min once its temperature reached 70oC to inhibit lipase and microbial growth. The prepared sample passed through a two stage homogenizer (type Panda, Niro-Soavi S.p.A., Parma, Italy) operated at 200 bar for the first stage and followed by 20 bar for the second stage, it passed through for five passes (Chiewchan et al., 2006). 2. Spray Drying

Coconut milk emulsion were fed into a spray dryer (Mobile Minor Spray Dryer, Niro A/S, Soeborg, Denmark) by a peristaltic pump, and atomized to small droplets by a


centrifugal vaned atomizer wheel with a rotational speed of 23,000 rpm (4 bar air pressure) in a co-current air flow system. In all cases, the inlet and outlet air temperatures were kept at 180 ± 1°C and 85 ± 1°C, respectively (Jena & Das, 2007). All the powders were collected from the bottom of the dryer’s cyclone and were kept in glass jars in desiccators at 25°C. 3. Methods Analysis Moisture content

Moisture content of the spray dried coconut milk powders was determined using AOAC methods (AOAC, 2000) Particle size measurement

Particle size distribution, volume-weighted mean diameter (d4,3) and surface-weighted mean diameter (d3,2) of the oil droplets emulsion and spray dried coconut milk were investigated using a laser diffraction particle size analyzer (Mastersizer MS20, Malvern Instruments, Ltd., Worcestershire, UK). Measurements were carried out with a 2-mW He-Ne laser beam (633 nm) and a 45-mm focus lens. The surface-weighted (d3,2) and the volume-weighted (d4,3) mean diameter were calculated as follows:

∑

∑=

2

3

3,2ii

ii

dn

dnd (1)

∑

∑=

3

4

3,4

ii

ii

dn

dnd

(2) where ni is the number of particles with diameter di. Creaming behavior after reconstitution

Creaming behavior was an indicator of emulsion stability. It was measured according to method reported by Danviriyakul et al. (2007). The powder was reconstituted to 10 g solids per 100 g reconstituted emulsion by dissolving 10 g of powder in 90 g of 50oC distilled water (Danviriyakul et al., 2002). The emulsion were placed in glass vials and stored at 4oC. Phase would be separated into cream and serum and visually observed after 24 hours.

3.4 Morphology study The appearance, size and shape of the spray dried samples were investigated by

placing the powders on aluminum stubs using a double-sided adhesive tape. The samples were then coated with platinum/palladium and were examined with a scanning electron microscope (SEM S-2500, Hitachi Science Systems, Ibaraki, Japan) operating at 15 kV accelerating voltage

3.5 Bulk and tapped density Powder was gently loaded into a 100 ml cylinder to the 100 ml mark and weighed.

The volume read directly from the cylinder was then used to calculate the bulk density (ρbulk) according to the relationship: mass/volume. For the tapped density (ρtapped), the cylinder was tapped 1250 times, using a VanKel tap density tester (ASTM Version, Varian, Inc., Cary, NC) with displacement amplitude of 3 ± 0.3 mm. The volume of the sample was then read and used in the calculation. The results were calculated from three replicate measurements.

3.6 Particle density Particle density (ρparticle) of the powder sample was analyzed according to A/S Niro

Atomizer (1978c) with some modifications. The powder sample (1 g) was transferred into a 10 ml measuring cylinder with a glass stopper. Then 5 ml of petroleum ether was added and the measuring cylinder was shaken until all the powder particles were suspended (Sorensen, Krag, Pisecky, & Westergaard, 1978). Finally, all the powder particles on the wall of the cylinder were rinsed down with a further 1 ml of petroleum ether (6 ml in total) and the total


volume of petroleum ether with suspended powder was read. The particle density was calculated as follows:

6(ml)powdersuspendedwithetherpetroleumofvolumetotal(g)powderofweight

particle −=ρ

(3) 3.7 Porosity

Porosity (ε) of the powder samples was determines by using the relationship between the tapped (ρtapped) and particle (ρparticle) densities of the powder as shown below (Jinapong, Suphantharika, & Jamnong, 2008):

100)(

particle

tappedparticle ×−

=ρ

ρρε (4)

3.8 Flowability and cohesiveness Flowability and cohesiveness of the powder were evaluated in terms of Carr index

(CI) (Carr, 1965) and Hausner ratio (HR) (Hausner, 1967) respectively. Both CI and HR were calculated from the bulk (ρbulk) and tapped (ρtapped) densities of the powder as shown below:

100)(

CItapped

bulktapped ×−

=ρ

ρρ (5)

bulk

tappedHRρ

ρ= (6)

Classification of the flowability and cohesiveness of the powder based on the CI and HR values are presented in Tables 1 and 2 respectively

Table 1. Classifications of powder flowability based on Carr Index (CI) CI % Flowability 45 Very bad

Table 2. Classification of powder cohesiveness based on Hausner ration ( HR) HR Cohesiveness 1.4 High

3.9 Wettability

Wettability of the powders sample was determined according to A/S Niro Atomizer (Sorensen et al., 1978). An amount of distilled water (100 ml) at 40 ± 1°C was poured into a 250 ml beaker. A glass funnel held on a ring stand was set over the beaker with the height between the bottom of the funnel and the water surface of 10 cm. A test tube was placed inside the funnel to block the lower opening of the funnel. The powder sample (10 g) was placed around the test tube and then the tube was lifted while the stop watch was started at the same time. Finally, the time was recorded for the powders to become completely wetted (visually assessed as when all the powder particles penetrated the surface of the water).

3.10 Dispersibility Dispersibility measurement was performed according to the procedure described in

A/S Niro Atomizer (Sorensen et al., 1978). Distilled water (100 ml), at 40 ± 1°C, was poured into a 250 ml beaker. The powder (10 g) was added into the beaker. The stop watch was started and the sample was stirred vigorously with a spoon for 15 s making 25 complete


0

1

2

3

4

5

6

0 1 2 3 4 5 6Sodium cas einate (%w/v)

Part

icle

siz

e (

µm

))

movements back and forth across the whole diameter of the beaker. The reconstituted solution was poured through a sieve (212 µm). The sieved solution (10 ml) was transferred to a weighed and dried aluminum pan and dried for 4 h in a hot air oven at 105 ± 1°C. The dispersibility of the powder was calculated as follows:

100

100..

%)100(%

bxa

TSxalityDispersibi

−+= (7)

Where a is the amount of powder (g) being used, b is the moisture content in the powder, and % TS is the dry matter in percentage in the reconstituted solution after it has been passed through the sieve. 4. Statistical analysis All measurements were made in triplicate for each sample at least. Results are expressed as mean ± standard deviations. A one-way analysis of variance (ANOVA) and Duncan’s test were used to establish the significance of differences among the mean values at the 0.05 significance level. The statistical analyses were performed using SPSS for Windows (2003) program version 17.0 (SPSS Inc., Chicago, IL).

Results and Discussion

1. Physical properties of spray-dried coconut milk emulsion The effect emulsifier concentrations on the mean emulsion oil droplet are shown in fig 1. When emulsifiers were added to emulsion and the mixture subsequently homogenized, the effects would decrease the mean oil droplet. Formation of the smaller droplet during homogenization is due to their ability reduce the interfacial tension (Danviriyakul et al., 2002). Protein plays very important role in the stability of food emulsions by the formation of an adsorption layer on the surface of fat particles and micro-layering of protein sub-micelles around fat particles. It is found that by varying the concentration of the emulsifiers (Kralova & Sjoblom, 2009). Lower concentration of emulsifier reduced the magnitude of all of these effects as there was less material available to coat the new surface generated during homogenization. The minimal mean particle size showed at 3%. It indicated that emulsifiers were sufficient to stability fat globule and increasing amount of emulsifier higher than 3% would promote flocculated (Tangsuphoom & Coupland, 2009). Homogenized coconut milk emulsion showed bimodal particle size distributions. It was indicated that the larger droplet peak corresponding to the presence of residual flocs and the small droplet peak the fine droplet (fig 2). It can be conclude that 3% w/v of sodium caseinate is the optimum concentration of emulsifier in order to get stabilization of spray dried emulsion.


P a rtic le s ize (µm )

.1 1 1 0 10 0 10 0 0

volu

me

(%)

0

2

4

6

8

1 0

1 2

1 4

0 % S C1 % S C2 % S C3 % S C5 % S C

Fig.1. Effect of emulsifier concentration on the mean particle size of oil droplet spray dried emulsion

Fig 2. Particle size distributions of oil droplet emulsion coconut milk powders after homogenization on different concentration of sodium caseinate (SC)

Emulsion stability of the spray dried after reconstitution was monitored in term of creaming behavior after 24 hours (fig 3). The samples less than 3% w/v showed separated into cream and serum. The reason for the instability was that the emulsifier content and quality in coconut milk emulsion was not sufficient to stabilize the fat globule (McClements, 2005).

Fig 3. Creaming spray dried powder after reconstitution for 24 h at 4oC a).0 b).1 c).2 d).3 and e).5% w/v sodium caseinate

2. Physical and morphological characteristic of spray-dried coconut milk powders Physical properties of the different spray dried coconut milk sample are presented in Table 3. All physical properties of the coconut milk powders were compared to the control seemed affected by the emulsifier except the particle density and porosity. Without any emulsifier the powder showed the higher bulk and tapped density due to the powders were clump and solidity (Fig 5a). It had reason that without emulsifier unavailable protein that coat the new surface generated during drying, which resulting fat droplet was not covered in surface composition of the powder. Due to the higher surface oil present at the powder surface, the powder indicated solidity and stickiness (Millqvist-Fureby, 2003; Tangsuphoom

a) b) c) d) e)


P artic le s ize (µm )

.1 1 10 100 1000

Vol

ume

(%)

0

2

4

6

8

10

12

2% SC3% SC5% SC

& Coupland, 2008, 2009). The increasing concentration of the emulsifier was significantly unaffected to the physical properties of the spray-dried powder except mean particle size. The mean particle size and particle size distributions (Fig 4) could be responsible for very small change in the physical properties of the powders ((Jinapong et al., 2008). The particle sizes that ranged from 20 – 60 µm were classified as fine particle (Master, 1991).

Table 3.Physical properties of spray dried coconut milk powders of different concentrations of emulsifier

Emulsifier concentration

s A Moisture

(%) D4.3 (µm) D3.2 (µm)

ρ bulk (gr/ml)

ρ tapped (gr/ml)

ρ particle (gr/ml)

Porosity(%)

0B 2.06±0.19a

21.36±2.11d

3.68±1.24e 0.51±0.00

a 0.84±0.17

a 2.38±0.82

a 63.76±20.95

a

1 1.57±0.26b

42.68±0.81c

5.60±0.47d 0.32±0.01

c 0.46±0.02

b 1.70±0.38

a 74.56±3.55a

2 1.65±0.21a

b 62.69±2.29

a 29.27±0.20

a 0.31±0.17

c 0.43±0.01

b 1.91±1.06

a 73.09±11.58

a

3 1.93±0.04a

b 43.68±0.21

c 22.79±0.24

c 0.37±0.04

b 0.47±0.02

b 2.56±0.97

a 79.77±7.54a

5 1.82±0.35a

b 48.27±0.36

b 25.29±0.16

b 0.38±0.03

b 0.47±0.02

b 2.05±0.65

a 75.09±10.04

a Assays were performed in triplicate. Mean ± SD value in the same column with different superscripts are significantly different (p≤ 0.05) A Emulsifier concentration in expressed in term of % w/v sodium caseinate B Control in coconut milk powder without adding emulsifier.

Fig 4.Particle size distributions of spray-dried coconut milk powders after homogenization on different concentration of sodium caseinate (SC)

b a c

d e

e

a


Fig 5. Scanning electron micrographs of spray dried of coconut milk powders of different concentration of

emulsifiers a) 0 b) 1, c) 2, d) 3, e) 5% w/v sodium caseinate at 1000 X magnifications The particle size distributions for the variation spray dried coconut milk powders

produced from different sodium caseinate concentration are shown in Fig 4. The powders showed smooth uni-modal size distribution curves of which their peaks shifted to larger particle.(Jinapong et al., 2008) The particle size distribution for samples at 0 and 1% w/v sodium caseinate was not available due to the powders indicated stickiness, thus could not be analyzed. The scanning electron micrographs of the spray dried coconut milk powders showed spherical structure with a few wrinkles on the surface. The larger powder particle was irregular shape and clump showed at 0% w/v sodium caseinate due to lack of emulsifier. 3. End-use properties of spray-dried coconut milk powders

The end use properties were determined by the handling and reconstitution properties of powders. In term of handling properties, the coconut milk powders had similar characteristics and were considered as cohesive powder by their Hausner ratio (HR) given in Table 4 as classified in Table 2. According to their high Carr index (CI) (table 4) which indicated that their flowability was very poor. This poor flowability at small particle size is due to the large surface area per unit mass of powder which resulting more contact area between powder particles available for cohesive force in particular and frictional force to resist flow (Fitzpatrick, 2005; Fitzpatrick, Iqbal, Delaney, Twomey, & Keogh, 2006). The high amount of fat content also caused the powder to have very poor flowability (Fitzpatrick, 2005). The noticeable change of the flowability if the particle size powder is difference by the order of magnitude, for example 10 vs 100 µm (Fitzpatrick, 2005).

Table 4.Flow characteristics (Carr index, CI, and Hausner ratio, HR) of spray dried coconut milk powders of different concentrations of emulsiofier

Emulsifier concentrations A CI (%) HR

0B 37.25±13.08a 1.63±0.34a

1 30.83±4.16ab 1.45±0.09ab

2 29.00±2.78abc 1.41±0.05ab

3 20.67±5.86bc 1.27±0.09b

5 18.17±3.51c 1.22±0.05b

Assays were performed in triplicate. Mean ± SD value in the same column with different superscripts are significantly different (p≤ 0.05) A Emulsifier concentration in expressed in term of % w/v sodium caseinate B Control in coconut milk powder without adding emulsifier. The reconstitution properties were determined by wettability and dispersibility (Table 5). All samples showed very poor in wettability due to the fine particle size (>900 second). It indicated that the powders were not instant. Without emulsifier powder showed smallest in dispersibility. Increasing of the concentration of the emulsifier seemed affected to dispersibility. It can be conclude that increasing of the emulsifier improved dispersibility.

Table 5. Reconstitution properties (wettability and dispersibility) of spray dried coconut milk of different concentrations of emulsifier

Emulsifier concentrations A Wetting time (s) Dispersibility (%)

0B > 900 79.08±11.86c

1 > 900 82.89±2.21c

2 >900 92.21±1.75ab

3 >900 96.14±1.69a


5 >900 96.35±3.27a

Assays were performed in triplicate. Mean ± SD value in the same column with different superscripts are significantly different (p< 0.05) A Emulsifier concentration in expressed in term of % w/v sodium caseinate B Control in coconut milk powder without adding emulsifier. In general, it is know that water wets very fine powders poorly because of its high surface tension (Schubert, 1993). The amount of emulsifier would be reduce surface tension (Ardhikari, Howes, Srentha, & Bhandhari, 2007), thus the stabilization of the emulsion of the spray-dried emulsion affected the dispersibility. .

Conclusion

The study on effect of emulsifier concentration on the microstructure and end-used properties revealed spray dried coconut milk powders led small particle having poor handling and reconstitution properties. The optimum emulsifier was at 3% w/v of sodium caseinate due to smallest oil droplet, thus had stabilization in creaming behavior. Despite the powder handling and reconstitution properties were not sufficiently improved, it should be improved by agglomeration.

Acknowledgements

This study was supported in part by the Thesis for Master’s degree students, Faculty of Graduate Studies, Mahidol University in academic 2010 and by the Higher Education Scholarship Project, Ministry of Education, Indonesia. The author would like to thank Siam Modified Starch Co. Ltd Pathuccccm Thani and Vicchi Enterprise SuanLuang Bangkok, Thailand for the samples in these experiments.

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