Mejorando La Estabilidad Aceite en Agua de Emulsiones de Coco

Enhancing the Stability of Oil-in-Water Emulsions Emulsified byCoconut Milk Protein with the Application of Acoustic CavitationVirangkumar N. Lad and Zagabathuni Venkata Panchakshari Murthy*

Department of Chemical Engineering, Sardar Vallabhbhai National Institute of Technology, Surat 395007, Gujarat, India

ABSTRACT: Coconut milk protein (CMP) is a naturally derived protein recovered from the kernel of fresh coconut(Cocos nucifera L.) having a high nutrient value. With increasing demand of naturally available efficient emulsifiers and stabilizers forthe production of food and health care emulsions with reasonable stability, many emulsifiers are being utilized for the commercialproduction of many products. Even though the CMP is reported as a poor emulsifier, we prepared very stable emulsions withCMP using sonication. The effects of ultrasound (250 W, 20 kHz and 120 W, 20 kHz) on the stability of sunflower oil-in-wateremulsions made by CMP are studied. It is found that though the acoustic energy is responsible for further reduction of dropletsize for CMP emulsions, energetic cavitations and high pressure shock waves, generated due to the collapsing bubble, are respon-sible for droplet breakup. The size of the dispersed droplets, in the case of sonication using an ultrasonic horn with all the con-centrations of CMP, was smaller than that created using an ultrasonic bath. Emulsions sonicated by the ultrasonic horn werefound to be very stable with variation of salt concentration.

1. INTRODUCTIONEmulsions are liquid−liquid dispersions in which droplets ofone of the liquid phases (known as the dispersed phase) aredispersed in the other immiscible liquid phase (known as thecontinuous phase). Depending on the type of dispersed phaseand continuous phase, emulsions are categorized as oil-in-water(O/W) or water-in-oil (W/O) emulsions. The O/W emulsionsconsist of droplets of organic oil phases dispersed in aqueousmedia. The W/O emulsions contain aqueous liquid phase dis-persed in immiscible organic oil phase. The process of emul-sification is entropically unfavorable; hence emulsions are ther-modynamically unstable systems. Emulsions find many applicationsin various industries such as the pharmaceutical, food, cosmetics,agriculture, paints, and polymeric chemicals. Surface active agents,having amphiphilic molecular structure, are capable of emulsi-fying and stabilizing such liquid dispersions.Proteins are a very important class of molecules involved

in the formation and stabilization of many food and cosmeticemulsions.1 Soy protein,2,3 whey protein,4−6 sodium casein-ate,2,7−9 casein,1,10 β-lactoglobulin,4,11−14 bovine serum albu-min,15 etc. are found to be suitable candidates as emulsifyingagents. However, high sensitivity to temperature, pH, and ionicstrength of protein stabilized emulsions have offered aconstraint to their use in many food products.16 Kong et al.17

studied the stability of emulsions prepared by protein and su-crose ester and discussed the micellar interaction in emulsioncontaining protein. Dunlap and Cote 18 found that increasingthe size of the polysaccharide conjugated with β-lactoglobulinresulted in more stable emulsions. Usages of protein hydro-lysates,10,19 mixtures of protein and hydrocolloids,20−22 andblending of other emulsifiers with proteins23,24 have been foundto be beneficial for protein stabilized emulsions against environ-mental stresses.Fresh coconut milk mainly contains water (about 54%), 35−

37% fat, 2−4% protein, 2−5% carbohydrates, and nonfat solidmatters.25−28 Tangsuphoom and Coupland29 have reported

improved stability of coconut milk emulsions homogenizedwith various surface active agents such as sodium caseinate,whey protein isolate (WPI), sodium dodecyl sulfate (SDS), andpolyoxyethylene sorbitan monolaurate. Consequently, they29

have found that the homogenized coconut milk preparedwithout additives destabilized by freeze−thaw cycles between−20 and −10 °C but not by chilling up to 5 °C. They alsofound that the emulsions prepared using WPI exhibited appre-ciable coalescence and phase separation after being heat treatedat 90 °C.30 Onsaard et al.31 have studied corn oil-in-water emul-sions prepared by coconut milk protein (CMP) using highpressure valve homogenization and found that CMP can beeffectively used for stabilizing fairly viscous emulsions such assauces, desserts, and salad dressings. The fair stability of emul-sions prepared using CMP for other less viscous food emul-sions still remains a challenge.Li and Fogler32 have explained the concept of acoustic emul-

sification, mentioning that the ultrasonic waves cause an inter-facial instability at oil−water interfaces. The transient cavitationbubbles produced during sonication collapse with generation ofhigh pressure shock waves. This phenomenon is almost adia-batic and generates very high local temperatures (3000 K tomore than 10 000 K) and pressures (more than 100 MPa)within bubbles for a short period of time.33−36 Cucheval andChow37 have demonstrated the emulsion formation by powerultrasound incorporated by high speed cavitation for a soybeanoil-in-water system using Tween-80 as a surfactant. Kentish etal.38 have successfully prepared flaxseed oil-in-water emulsionsusing Tween-40 surfactant with a mean droplet size as low as135 ± 5 nm using ultrasonic power at 20−24 kHz. Abismail etal.39 have prepared kerosene-in-water emulsions by sonication

Received: November 28, 2011Revised: February 11, 2012Accepted: February 19, 2012Published: February 21, 2012

Article

pubs.acs.org/IECR

© 2012 American Chemical Society 4222 dx.doi.org/10.1021/ie202764f | Ind. Eng. Chem. Res. 2012, 51, 4222−4229

pubs.acs.org/IECR

using polyethoxylated sorbitan monostearate as the surfactantand obtained droplet sizes much smaller than the emulsionsprepared by mechanical agitation. Though ultrasound has beenused for emulsification using a variety of surfactants for manydecades,39−41 the effects of sonication on coconut milk proteinare yet to be understood. Because coconut milk has highmedicinal and nutrient value, it is advantageous to explore thepossibility of replacing conventional emulsifiers and stabilizersfor emulsions used in cosmetics, pharmaceuticals, and foodemulsions with reasonable stability.The objective of the present work is to study the effects of

acoustic energy on the stability of emulsions made by coconutmilk protein. Also, the properties of sunflower oil-in-wateremulsions, prepared by acoustic energy using coconut milkprotein, have been evaluated.

2. EXPERIMENTAL PROCEDURES

2.1. Recovery of Coconut Milk Protein. Coconuts (Cocosnucifera L.) were purchased from a local market. Mature coco-nuts were dehisced and cracked to get the kernels. The freshkernels of mature coconuts were finely comminuted using adomestic electric grater. The coconut milk was obtained by pre-ssing the grated kernel in a triple-layer cloth filter. The creamand skim milk were obtained from the coconut by centrifugingthe coconut milk in a laboratory centrifuge at 4000g for 40 min.This coconut milk was refrigerated overnight at 6 ± 2 °C inorder to separate a soluble supernatant phase from an insolubleprecipitate phase. The pH of the supernatant phase wasadjusted to 3.9 using 0.1 M HCl, and it was centrifuged at5400g for 25 min twice with an interval of 3 min in between.Precipitates thus obtained were dispersed in Millipore water ofpH 5.9 ± 0.2 and conductivity 1.0 μS/cm (Millipore,Bangalore, India), and the pH was adjusted to 7.0 using 0.1M NaOH. It was then dried at room temperature to getpowdered material which was used as coconut milk protein.The drying by atmospheric air at room temperature was donefor approximately 15−16 h which avoided the exposure of CMPto elevated temperature and helped to prevent any possiblethermal denaturation of the CMP at higher temperature.In order to achieve the microbiological purity of the O/W

emulsion samples containing CMP, we used sodium benzoate(food grade) as an antimicrobial agent (a preservative) duringpreparation of protein solutions.The protein solubility was measured as per the method de-

scribed by Onsaard et al.42 in principle. The CMP was added toMillipore water containing 10, 100, 200, and 400 mM NaCl andadjusted to pH values ranging from 3 to 8. The solutions werestirred with a magnetic stirrer (Remi Motor, Mumbai, India) atroom temperature for 8 h and centrifuged thrice at 7500g for20 min with 3 min of idling the centrifuge in between. Thesolution was filtered using Whatman No. 1 filter paper, and thefiltered supernatant was analyzed for protein content usingthe Lowry method,43 with whey protein isolate as a standard.The protein solubility (% PS) was calculated using thefollowing expression:

= ·PP

% PS 100s

t (1)

where Ps is the protein concentration in the supernatant afterfiltration and Pt is the total protein concentration present in theoriginal solution.

2.2. Preparation of Emulsion Samples. Phosphate buffer(5 mM) was prepared and adjusted to pH 6.2 corresponding tothe pH of the aqueous phase of many coconut milk basedproducts.31,42 Protein solutions were prepared by dispersing therequired quantity of protein in buffer solution to have finalemulsion samples containing CMP concentration varying from0.2 to 2 wt %.Sunflower oil was used as the oil phase and was purchased

from a local supermarket. The O/W emulsions were preparedby dispersing sunflower oil in protein solutions of requiredamounts using a high speed Ultra Turrax homogenizer (T25Basic, IKA WERKE, Germany) for 4 min at 6500 rpm.

2.3. Application of Ultrasound to the EmulsionSamples. Homogenized emulsions were subjected to sonica-tion using an ultrasonic bath (Ultrasonic Cleaner, AquaScientific Instruments, Surat, India) or an ultrasonic horn(Sonicator, Aqua Scientific Instruments, Surat, India). Ultra-sound was provided by (i) the stainless steel ultrasonic bath op-erated at 120 W with a frequency of 20 kHz, (ii) the ultrasonicbath operated at 250 W with a frequency of 20 kHz, (iii) theultrasonic horn of stainless steel having 15 mm diameter op-erated at 120 W with a frequency of 20 kHz, or (iv) the ultra-sonic horn of stainless steel having 15 mm diameter operated at250 W with a frequency of 20 kHz as per the requirements. Inall the experiments, the ultrasound was applied in three stagesfor 4 min on mode (total 12 min) with 1 min intervals betweenthe successive stages of sonication.

2.4. Evaluation of Droplet Size. The droplet size distri-bution for the emulsion samples was found using the dynamiclight scattering (DLS) technique (Malvern Instruments, U.K.).It measures the Brownian motion of particles in the dispersionand relates it to the particle size. The DLS technique gives theharmonic intensity-weighted average hydrodynamic diameter orcumulative mean. The hydrodynamic diameter is calculated bythe well-known Stokes−Einstein equation:44,45

= κπη

dT

D3h(2)

where dh is the hydrodynamic diameter, κ is the Boltzmannconstant, T is the absolute temperature, η is the viscosity of thedispersion medium, and D is the translational diffusion coeffi-cient. Detailed discussions of the DLS principle are available inthe literature.44,46,47

The emulsion samples were diluted 100 times to preventmultiple scattering. The emulsion particle refractive index wastaken as 1.456 as reported in the literature,45 and that for thedispersion medium was 1.33. The relative refractive index of1.09 was used in the calculation of the droplet size distribution.It was then presented in terms of the volume-weighted meandiameter, also known as the De Brouker diameter. The volume-weighted mean diameter is calculated by the followingformula:48

=∑∑

dn d

n di i

i i4,3

4

3(3)

where ni is the number of droplets in the ith fraction and di isthe diameter of a droplet in the ith fraction.

2.5. Microscopy. Samples of emulsions were placed on amicroscope slide, gently covered with a coverslip and observedusing an optical microscope (Labovision, Ambala Cantt, India)equipped with a digital video camera. Micrographs were takenfrom four different fields on each slide and representative

Industrial & Engineering Chemistry Research Article

dx.doi.org/10.1021/ie202764f | Ind. Eng. Chem. Res. 2012, 51, 4222−42294223

micrographs were obtained. A few samples were also analyzedfor the droplet size measurement by image analysis using theimage analysis software Image J of NIH, USA.2.6. Stability to Creaming. The creaming index was cal-

culated by measuring the height of the lower aqueous layer HAand the initial height of the emulsion HE:

= ·HH

% creaming index 100A

E (4)

The creaming index provides indirect information of dropletaggregation in an emulsion;29 in general, the more aggregation,the faster the creaming.2.7. Analysis by Turbiscan. Turbiscan (Formulaction,

France) was used to study the stability of samples using back-scattering technique. The principle of Turbiscan can be foundelsewhere.49 All measurements were repeated once with freshlyprepared samples all the time.

3. RESULTS AND DISCUSSION3.1. Composition of Coconut Milk Protein. The compo-

sition of the protein recovered from coconut milk is presentedin Table 1 based on triplicate experimental runs. The amount of

protein found in the recovered material is comparable to that ofthe coconut skim milk protein isolate as reported by Onsaardet al.42 Detailed characterization of the protein recovered fromcoconut milk is out of the scope of the present paper. Kwonet al.50 have reported the characterization of coconut proteinand showed that albumins and globulins were the predominantcoconut protein fractions. They50 concluded that the coconutprotein had relatively high levels of glutamic acid, arginine, andaspartic acid. They50 also reported that the total protein,globulins, and glutelins were composed of polypeptides linkedvia disulfide bond(s).3.2. Solubility of Coconut Milk Protein. The effect of pH

on the CMP solubility is shown in Figure 1. The minimumCMP solubility occurred between 4 and 4.5, which is in thenear vicinity of the isoelectric point of protein as reported byvarious researchers.25,42,51,52 As shown in Figure 1, the solubil-ity of CMP increases with the pH as the sample set farther fromthat corresponding to the isoelectric point. The reason for thisbehavior can be explained by the fact that, at the isoelectricpoint, there is negligible electrostatic repulsion between proteinmolecules due to the presence of almost zero net charge ontheir surfaces. This electrostatic repulsion becomes strongerdue to the increase in net charge on the surfaces of molecules atpH values farther than that corresponding to the isoelectricpoint. The strong electrostatic repulsion prevents the aggrega-tion of molecules and results in increased solubility.42

3.3. Effects of Ultrasound and Concentration of CoconutMilk Protein on the Droplet Size of Dispersed Phase inthe Emulsions. Figure 2 shows the volume-weighted meandroplet size (d4,3) of the dispersed phase in 10% O/W emul-sions prepared with different concentrations of CMP. Thedroplet sizes were measured within 30 min after preparation ofemulsion samples, at the end of 7 days, and at the end of 14days after preparation of samples. The samples were stored at26−30 °C. The emulsions prepared with CMP concentrationless than 1%, without the application of sonication, exhibitedphase separation on the eighth or ninth day after preparation.The droplet size decreased for all the emulsions prepared with-out using ultrasound as well as for emulsions prepared using anultrasonic bath up to 1.2% CMP concentration. No significantreduction in the droplet size was observed beyond 1.2%concentration of CMP. This shows that the concentration of1.2% CMP was sufficient to produce almost stable emulsions inthe case of emulsions prepared without ultrasound as well as foremulsions prepared using the ultrasonic bath. The minimumamount of CMP was 1.6%, which resulted in the formation ofoil droplets of 3.2 μm in the case of emulsification with appli-cation of ultrasound at 120 W and 20 kHz using an ultrasonichorn. Further increase in the concentration of CMP did notalter the mean size of the droplets appreciably. This is due tothe fact that sonication using the ultrasonic horn created vigor-ous cavitations and ultimately led to the formation of smallerdroplets, resulting in more interfacial area. Hence, the mini-mum amount of CMP used to occupy this interfacial area wasincreased to 1.6%. Further, for all the range of CMP concen-tration, the smallest size of emulsion droplets was produced bythe use of the ultrasonic horn.It is clear from Figure 2 that the power ultrasound has re-

sulted in significant reduction in droplet size. For instance, with1% CMP, the mean size of dispersed droplets in emulsionssonicated by the ultrasonic bath was 18.1 μm and that sonicatedby the ultrasonic horn was 5.9 μm, whereas the mean size ofdroplets in the absence of ultrasound was 22.3 μm. A similarreduction in mean droplet size has also been reported byCucheval and Chow37 for a soybean oil-in-water emulsion withTween-80 where they obtained a droplet size of 0.7 μm usingpower ultrasound. The reduction of the mean droplet size dueto the application of ultrasonic power has also been reported byJuang and Lin53 for water-in-oil emulsions prepared using Span-80 as an emulsifier. Gaikwad and Pandit54 and Tal-Figiel55 also

Table 1. Composition of Coconut Milk Protein Recoveredfrom Fresh Coconuta

component % by weight

proteins (by nitrogen conversion factor 6.25) 62.1 ± 0.2fat 26.9 ± 0.1moisture 2.9 ± 0.2ash 4.8 ± 0.1carbohydrates (by difference) 3.3 ± 0.9

aDeviations indicate the variation of the corresponding value duringtriplicate experimental runs.

Figure 1. Variation of solubility of coconut milk protein with pH.



observed reduction in the droplet size of the dispersed phasedue to acoustic power.It is observed that an increase in the power of ultrasound

resulted in the formation of smaller droplets. This is shown inFigure 3a for a CMP concentration of 1.2% and in Figure 3b fora CMP concentration of 0.8%. This can be explained by the factthat at higher intensity the bubble collapse produces increas-ingly high pressure responsible for more droplet breakup andformation of smaller droplets. Further, as clear from Figures 2and 3, the ultrasonic horn is more efficient in the formation ofsmaller droplets than is the ultrasonic bath. This is due to thepresence of the predominant collapse of microbubbles in thecase of the ultrasonic horn where the cavitational bubble cloudis focused in a comparatively small zone in the near vicinityadjacent to the horn transducer.45 In the case of sonication withthe ultrasonic bath, there is a lack of such an intense collapse ofmicrobubbles but the local intensity and amount of microjetstreaming are the overall effect. Maximum local cavitationalactivity is more predominant in the case of the ultrasonic horncompared to that of the ultrasonic bath, because it depends onthe total power dissipation per unit volume of liquid which isgreater in the case of the horn.56 Different effects of sonicationdue to various types and geometries of ultrasonic probes arealso reported by Atobe et al.57 and Faid et al.58 As revealedfrom Figure 3, the increase in the ultrasonic intensity has re-sulted in smaller droplets, which has been also reported byDjenouhat et al.59 and Juang and Lin,53 where they producedW/O emulsion using Span-80 as an emulsifier.The formation of smaller sizes of droplets due to high inten-

sity ultrasound is attributed to the vigorous pressure wavestransmitted through the ultrasound, which propagated by thevibrational motion of molecules comprising the liquid phase.Hence, the protein molecules experienced compression andstretching of their molecular structures alternately. This causedunfolding of the protein chains, which is the most responsiblefactor for enhanced surface activity of acoustically treated

proteins. This has resulted in the smaller sizes of droplets asshown in Figures 2 and 3.

Figure 2. Effect of ultrasound (120 W, 20 kHz) and concentration of coconut milk protein on the volume mean diameter of dispersed droplets inO/W emulsions. Solid filled bars represent mean droplet size of dispersed droplets in emulsions measured within 30 min after their preparation. Barswith slanted strips and horizontal strips represent the droplet size measured at the end of the 7th day and the 14th day, respectively, after emulsionpreparation.

Figure 3. Effect of ultrasound on change in mean droplet size ofdispersed droplets of O/W emulsions stored at 26−30 °C: (a) for1.2% coconut milk protein emulsion; (b) for emulsion containing 0.8%coconut milk protein The error bars represent deviations for threerepetitions. Sonication was applied at 20 kHz.



The physicochemical phenomena resulting due to sonicationis very much sensitive to the mode of application of ultrasound.60,61

When ultrasound is supplied through a horn, this causes veryintense pressure waves capable of deforming the molecularstructure resulting in the formation of a cavity. This cavity inturn excites the droplet by this time-varying pressure, thus lead-ing to experiencing transient cavitation resulting in fragmenta-tion of smaller droplets.The reason for the larger mean droplet size of emulsions

sonicated by the sonication bath is that in this case there is anabsence of cavitation responsible for fragmentation of largerdroplets to smaller droplets. Stable cavitation occurred due tooscillation of droplets around their equilibrium position whichcaused the stretching and compression of the protein chains.The reorientation of protein chains helped in increased stabilityof the emulsion by offering higher stabilizing capability. Aspresented in Figure 3, the stability of emulsions was increasedremarkably by the application of ultrasound. The almostconstant size of dispersed droplets (produced by sonicationusing the ultrasonic horn) in Figures 2 and 3 reveal that theemulsions sonicated by the ultrasonic horn were very stableeven at the end of 14 days. Backscattering data presented inFigure 4 also confirm the increased stability of emulsions

prepared using an ultrasonic bath. Much more stable emulsionswere produced by applying ultrasound through an ultrasonichorn. Figure 5 shows representative micrographs of 10% sun-flower oil-in-water emulsions prepared using 1.2% CMP.

3.4. Stability to Creaming. The stability of emulsionsagainst creaming is shown in Figure 6, which reflects poor

stability to creaming for emulsions due to the deprived surfaceactivity of CMP as reported by Tangsuphoom and Coupland.29

On the other hand, the emulsions prepared using sonicationwere comparatively more stable to creaming at pH >5. This isdue to prevention of flocculation and creaming of oil dropletsby sonication. Pongsawatmanit et al.12 have also reported thatsonication breaks the flocs and imparts stability to creamingand flocculation by providing sufficient repulsive interactionbetween individual oil droplets. The reduction in the creamingindex with application of ultrasound through the ultrasonichorn is due to the fact that the exaggerated cavitation resultingin the formation of smaller droplets caused the increase indepletion attraction between droplets.

3.5. Effect of Salt. The purpose of this series of experi-ments was to identify the effect of salt (which is most commonin many food emulsions) on sonicated emulsions. The presenceof NaCl resulted in increased protein solubility at all corre-sponding pH values as seen from Figure 1. This is due to thehigh interaction of ions with charged groups leading to moreprotein solvation as explained by Onsaard et al.42 Despite theincrease in the protein solubility with NaCl, the emulsion sam-ples prepared with NaCl concentration higher than 100 mMwere relatively unstable due to flocculation caused by the addi-tion of salt which was responsible for the reduction of the thick-ness of electrical double layer, which diminished the inter-droplet repulsion through electrostatic screening.1

Figure 4. Backscattering data for 10% sunflower oil-in-water emulsionsprepared using 1.2% coconut milk protein: (a) emulsion prepared withoutsonication; (b) emulsion prepared with sonication through an ultrasonicbath operated at 120 W and 20 kHz; (c) emulsion prepared withsonication through an ultrasonic horn operated at 120 W and 20 kHz.

Figure 5. Micrographs of 10% sunflower oil-in-water emulsions prepared using 1.2% coconut milk protein: (left) emulsion prepared withoutsonication; (middle) emulsion prepared with sonication through ultrasonic bath operated at 120 W and 20 kHz; (right) emulsion prepared withsonication through ultrasonic horn operated at 120 W and 20 kHz.

Figure 6. Effect of sonication on the creaming stability of O/W emul-sions containing 1.2% coconut milk protein. Stability was measuredafter the emulsions were stored for 7 days between 26 and 30 °C.



The mean droplet size of emulsion increased significantlywith increasing NaCl concentration for emulsion preparedwithout sonication (see Figure 7). The concentration of NaClhas not influenced the mean droplet size of dispersed oil phasesin the emulsions prepared using ultrasound through the ultra-sonic horn. The increase in the droplet size of emulsions pre-pared using the ultrasonic bath was limited until a plateauregion was reached, which is due to bridging flocculation ofdroplets.12 The droplet size of the dispersed phase increasedfrom 15.4 to 19.5 μm in the presence of 400 mM NaCl foremulsification with the ultrasonic bath operated at 120 W and20 kHz. This exhibited that the ultrasonicated emulsions wererelatively more stable to droplet aggregation and creaming forvarious concentrations of NaCl. For emulsion samples preparedwithout application of ultrasound, droplet aggregation was morepredominant with increasing salt concentration. This is explainedby the fact that the ef fective energy supplied during emulsificationby sonication has overcome the effect of electrostatic interactionsamong the dispersed droplets in the presence of ions (producedby ionization of NaCl in emulsions).

4. CONCLUSIONS

Sunflower oil-in-water emulsions with remarkably improvedstability were prepared with coconut milk protein by the appli-cation of acoustic energy for the first time. The mean dropletsize and stability of sunflower oil-in-water emulsions preparedusing CMP are found to be highly affected by the sonication.Further, the mode of application of ultrasound has a profoundeffect on the emulsification and stabilization of these emulsions.A 1.2% coconut milk protein concentration was found to besufficient for emulsification with ultrasound. Sonication resultedin reducing the mean droplet size of the dispersed oil phase andimparted better stability against pH.Sonication with the ultrasonic horn is found to be more ef-

fective in all the experiments for producing emulsions withsmaller droplet size and higher stability over the time period inturn. This is due to the exaggerated cavitation and collapse ofbubbles associated with high energetic interaction withemulsion droplets in the case of direct sonication using theultrasound horn. Moreover, the maximum local cavitationalactivity in the case of the ultrasonic horn is more predominant

due to the much higher power dissipation per unit of liquidvolume.The mean droplet size increased by the presence of NaCl up

to 200 mM, above which there was no appreciable change indroplet size for emulsions prepared using the the ultrasonicbath. By the presence of NaCl, the mean droplet size of emul-sions treated using the ultrasonic horn was not affected at all.Hence, it is concluded that the destabilization of emulsions withthe addition of salt can be controlled by power ultrasound.Coconut milk protein along with power ultrasound is found

to be capable of producing emulsions with smaller droplet sizeand better stability which can be effectively used for the pro-duction of many emulsions of high commercial value. Havingthe presence of beneficial nutrient ingredients and easy recov-ery from the natural material, coconut milk protein may offer asuitable alternative to many conventional emulsifiers and/orstabilizers used in a variety of cosmetics and food emulsions.

■ AUTHOR INFORMATION

Corresponding Author*E-mail: [email protected] or [email protected].: +91 261 2201641 or +91 261 2201642. Fax: +91 2612227334.

NotesThe authors declare no competing financial interest.

■ REFERENCES(1) Dickinson, E. Flocculation of Protein-Stabilized Oil-in-WaterEmulsions. Colloids Surf., B 2010, 81, 130.(2) Jang, W.; Nikolov, A.; Wasan, D. T.; Chen, K.; Campbell, B.Effect of Protein on the Texture of Food Emulsions Under SteadyFlow. Ind. Eng. Chem. Res. 2005, 44, 4855.(3) Tang, C. H.; Chen, L.; Foegeding, E. A. Mechanical and Water-Holding Properties and Microstructures of Soy Protein IsolateEmulsion Gels Induced by CaCl2, Glucono-δ-Lactone (GDL), andTransglutaminase: Influence of Thermal Treatments Before and/orAfter Emulsification. J. Agric. Food Chem. 2011, 59, 4071.(4) Ma, H.; Forssell, P.; Partanen, R.; Buchert, J.; Boer, H. ImprovingLaccase Catalyzed Cross-Linking of Whey Protein Isolate and TheirApplication as Emulsifiers. J. Agric. Food Chem. 2011, 59, 1406.(5) Damodaran, S.; Anand, K. Sulfhydryl−disulfide Interchange-Induced Interparticle Protein Polymerization in Whey Protein-Stabilized Emulsions and Its Relation to Emulsion Stability. J. Agric.Food Chem. 1997, 45, 3813.(6) Viljanen, K.; Kylli, P.; Hubbermann, E. M.; Schwarz, K.;Heinonen, M. Anthocyanin Antioxidant Activity and PartitionBehavior in Whey Protein Emulsion. J. Agric. Food Chem. 2005, 53,2022.(7) Dickinson, E.; Evison, J.; Owusu, R. K. Preparation of FineProtein-Stabilized Water-in-Oil-in-Water Emulsions. Food Hydro-colloids 1991, 5, 481.(8) Hu, M.; Li, Y.; Decker, E. A.; Xiao, H.; McClements, D. J. Impactof Layer Structure on Physical Stability and Lipase Digestibility ofLipid Droplets Coated by Biopolymer Nanolaminated Coatings. FoodBiophys. 2011, 6, 37.(9) Kellerby, S. S.; Gu, Y. S.; McClements, D. J.; Decker, E. A. LipidOxidation in a Menhaden Oil-in-Water Emulsion Stabilized by SodiumCaseinate Cross-Linked with Transglutaminase. J. Agric. Food Chem.2006, 54, 10222.(10) van der Ven, C.; Gruppen, H.; de Bont, D. B. A.; Voragen, A. G.J. Emulsion Properties of Casein and Whey Protein Hydrolysates andthe Relation with Other Hydrolysate Characteristics. J. Agric. FoodChem. 2001, 49, 5005.(11) Das, K. P.; Kinsella, J. E. pH Dependent Emulsifying Propertiesof β-Lactoglobulin. J. Dispersion Sci. Technol. 1989, 10, 77.

Figure 7. Influence of NaCl and ultrasound on mean droplet size ofdispersed phase in O/W emulsions containing 1.2% coconut milkprotein. Droplet sizes were measured at the end of 30 min afterpreparation of emulsions.



mailto:[email protected]

mailto:[email protected]

(12) Pongsawatmanit, R.; Harnsilawat, T.; McClements, D. J.Influence of Alginate, pH and Ultrasound Treatment on Palm Oil-in-Water Emulsions Stabilized by β-Lactoglobulin. Colloids Surf., A2006, 287, 59.(13) Tcholakova, S.; Denkov, N. D.; Sidzhakova, D.; Campbell, B.Effect of Thermal Treatment, Ionic Strength, and pH on the Short-Term and Long-Term Coalescence Stability of β-LactoglobulinEmulsions. Langmuir 2006, 22, 6042.(14) Zhai, J.; Wooster, T. J.; Hoffmann, S. V.; Lee, T. H.; Augustin,M. A.; Aguilar, M. I. Structural Rearrangement of β-Lactoglobulin atDifferent Oil−Water Interfaces and Its Effect on Emulsion Stability.Langmuir 2011, 27, 9227.(15) Livney, Y. D. Milk Proteins as Vehicles for Bioactives. Curr.Opin. Colloid Interface Sci. 2010, 15, 73.(16) McClements, D. J. Food Emulsions: Principles, Practices, andTechniques, 2nd ed.; CRC Press: Boca Raton, FL, 2004.(17) Kong, Y.; Nikolov, A.; Wasan, D.; Ogawa, A. Emulsion Textureand Stability: Role of Surfactant Micellar Interactions in the Presenceof Proteins. Ind. Eng. Chem. Res. 2008, 47, 9108.(18) Dunlap, C. A.; Cote, G. L. β-Lactoglobulin−DextranConjugates: Effect of Polysaccharide Size on Emulsion Stability.J. Agric. Food Chem. 2005, 53, 419.(19) Dexter, A. F.; Middelberg, A. P. J. Peptides as FunctionalSurfactants. Ind. Eng. Chem. Res. 2008, 47, 6391.(20) Diftis, N.; Kiosseoglou, V. Improvement of EmulsifyingProperties of Soybean Protein Isolate by Conjugation withCarboxymethyl Cellulose. Food Chem. 2003, 81, 1.(21) Hattori, M.; Ogino, A.; Nakai, H.; Takahashi, K. FunctionalImprovement of β-Lactoglobulin by Conjugating with Alginate Lyase-Lysate. J. Agric. Food Chem. 1997, 45, 703.(22) Kim, H. J.; Choi, S. J.; Shin, W. S.; Moon, T. W. EmulsifyingProperties of Bovine Serum Albumin-Galactomannan Conjugates.J. Agric. Food Chem. 2003, 51, 1049.(23) Akoh, C. C. Emulsification Properties of Polyesters and SucroseEster Blends. 1. Carbohydrate Fatty-Acid Polyesters. J. Am. Oil Chem.Soc. 1992, 69, 9.(24) Riscardo, M. A.; Franco, J. M.; Gallegos, C. Influence ofComposition of Emulsifier Blends on the Rheological Properties ofSalad Dressing-Type Emulsions. Food Sci. Technol. Int. 2003, 9, 53.(25) Kwon, K. S.; Bae, D.; Park, K. H.; Rhee, K. C. AqueousExtraction and Membrane Techniques Improve Coconut ProteinConcentrate Functionality. J. Food Sci. 1996, 61, 753.(26) Peamprasart, T.; Chiewchan, N. Effect of Fat Content andPreheat Treatment on the Apparent Viscosity of Coconut Milk AfterHomogenization. J. Food Eng. 2006, 77, 653.(27) Raghavendra, S. N.; Raghavarao, K. S. M. S. Effect of DifferentTreatments for the Destabilization of Coconut Milk Emulsion. J. FoodEng. 2010, 97, 341.(28) Tasakul, A.; Chaisawang, P. Thermophysical Properties ofCoconut Milk. J. Food Eng. 2006, 73, 276.(29) Tangsuphoom, N.; Coupland, J. N. Effect of Surface-ActiveStabilizers on the Microstructure and Stability of Coconut MilkEmulsions. Food Hydrocolloids 2008, 22, 1233.(30) Tangsuphoom, N.; Coupland, J. N. Effect of ThermalTreatments on the Properties of Coconut Milk Emulsions Preparedwith Surface-Active Stabilizers. Food Hydrocolloids 2009, 23, 1792.(31) Onsaard, E.; Vittayanont, M.; Srigam, S.; McClements, D. J.Comparison of Properties of Oil-in-Water Emulsions Stabilized byCoconut Cream Proteins with Those Stabilized by Whey ProteinIsolate. Food Res. Int. 2006, 39, 78.(32) Li, M. K.; Fogler, H. S. Acoustic Emulsification. Part 2: Breakupof the Large Primary Oil Droplets in a Water Medium. J. Fluid Mech.1978, 88, 513.(33) Ashokkumar, M. The Characterization of Acoustic CavitationBubbles - An Overview. Ultrason. Sonochem. 2011, 18, 864.(34) Mason, T. J.; Lorimer, P. J. Sonochemistry: Theory, Applicationsand Uses of Ultrasound in Chemistry; Ellis Horwood: Chichester, U.K.,1988.

(35) Sonawane, S. H.; Neppolian, B.; Teo, B.; Grieser, F.;Ashokkumar, M. Ultrasound Assisted Preparation of Semiconductor/Polymer Photoanodes and Their Photoelectrochemical Properties.J. Phys. Chem. C 2010, 114, 5148.(36) Young, F. R. Cavitation; McGraw-Hill: London, 1994.(37) Cucheval, A.; Chow, R. C. Y. A Study on the Emulsification ofOil by Power Ultrasound. Ultrason. Sonochem. 2008, 15, 916.(38) Kentish, S.; Wooster, T. J.; Ashokkumar, M.; Balachandran, S.;Mawson, R.; Simons, L. The Use of Ultrasonics for NanoemulsionPreparation. Innovative Food Sci. Emerging Technol. 2008, 9, 170.(39) Abismaïl, B.; Canselier, J. P.; Wilhelm, A. M.; Delmas, H;Gourdon, C. Emulsification by Ultrasound: Drop Size Distributionand Stability. Ultrason. Sonochem. 1999, 6, 75.(40) Behrend, O.; Schubert, H. Influence of Continuous PhaseViscosity on Emulsion by Ultrasound. Ultrason. Sonochem. 2000, 7, 77.(41) Li, M. K.; Fogler, H. S. Acoustic Emulsification―1. TheInstability of the Oil−Water Interface to Form the Initial Droplets.J. Fluid Mech. 1978, 88, 499.(42) Onsaard, E.; Vittayanont, M.; Sringam, S.; McClements, D. J.Properties and Stability of Oil-in-Water Emulsions Stabilized byCoconut Skim Milk Proteins. J. Agric. Food Chem. 2005, 53, 5747.(43) Lowry, O. H.; Rosebrough, N. J.; Farr, A. L.; Randall, R. J.Protein Measurement with Folin Phenol Reagent. J. Biol. Chem. 1951,193, 265.(44) Mori, Y.; Togashi, K.; Nakamura, K. Colloidal Properties ofSynthetic Hectorite Clay Dispersion Measured by Dynamic LightScattering and Small Angle X-Ray Scattering. Adv. Powder Technol.2001, 12, 45.(45) Leong, T. S. H.; Wooster, T. J.; Kentish, S. E.; Ashokkumar, M.Minimising Oil Droplet Size Using Ultrasonic Emulsification. Ultrason.Sonochem. 2009, 16, 721.(46) Wang, X. Z.; Liu, L.; Li., R. F.; Tweedie, R. J.; Primrose, K.;Corbett, J.; McNeil-Watson, F. K. Online Characterisation ofNanoparticle Suspensions Using Dynamic Light Scattering UltrasoundSpectroscopy and Process Tomography. Chem. Eng. Res. Des. 2009, 87,874.(47) Braun, A.; Couteau, O.; Franks, K.; Kestens, V.; Roebben, G.;Lamberty, A.; Linsinger, T. P. J. Validation of Dynamic LightScattering and Centrifugal Liquid Sedimentation Methods forNanoparticle Characterisation. Adv. Powder Technol. 2011, 22, 766.(48) Romero, A.; Cordobes, F.; Puppo, M. C.; Guerrero, A.;Bengoechea, C. Influence of pH on Linear Viscoelasticity and DropletSize Distribution of Highly Concentrated O/W Crayfish Flour-BasedEmulsions. Food Hydrocolloids 2008, 22, 1033.(49) Simon, S.; Pierrard, X.; Sjoblom, J.; Sorland, G. H. SeparationProfile of Model Water-in-Oil Emulsions Followed by NuclearMagnetic Resonance (NMR) Measurements: Application Range andComparison with a Multiple-Light Scattering Based Apparatus.J. Colloid Interface Sci. 2011, 356, 352.(50) Kwon, K.; Park, K. H.; Rhee, K. C. Fractionation and Character-ization of Proteins from Coconut (Cocos nucifera L.). J. Agric. FoodChem. 1996, 44, 1741.(51) Kwon, K. S.; Rhee, K. C. Emulsifying Capacity of CoconutProteins as a Function of Salt, Phosphate and Temperature. J. Am. OilChem. Soc. 1996, 73, 1669.(52) Samson, A. S.; Cater, C. M.; Mattil, K. F. Preparation andCharacterization of Coconut Protein Isolates. Cereal Chem. 1971, 48,182.(53) Juang, R. S.; Lin, K. H. Ultrasound-Assisted Production of W/OEmulsions in Liquid Surfactant Membrane Processes. Colloids Surf., A2004, 238, 43.(54) Gaikwad, S. G.; Pandit, A. B. Ultrasound Emulsification: Effectof Ultrasonic and Physicochemical Properties on Dispersed PhaseVolume and Droplet Size. Ultrason. Sonochem. 2008, 15, 554.(55) Tal-Figiel, B. The Formation of Stable W/O, O/W, W/O/WCosmetic Emulsions in an Ultrasonic Field. Chem. Eng. Res. Des. 2007,85, 730.



(56) Sutkar, V. S.; Gogate, P. R.; Csoka, L. Theoretical Prediction ofCavitational Activity Distribution in Sonochemical Reactors. Chem.Eng. J. 2010, 158, 290.(57) Atobe, M.; Fuchigami, T.; Nonaka, T. Ultrasonic Effects onElectroorganic Process. Part 23. Electroreduction of Dimethyl Maleatein Acoustic Fields Produced by Different Types of Ultrasonic Devices.J. Electroanal. Chem. 2002, 523, 106.(58) Faid, F.; Contamine, F.; Wilhelm, A. M.; Delmas, H.Comparison of Ultrasound Effects in Different Reactors at 20 kHz.Ultrason. Sonochem. 1998, 5, 119.(59) Djenouhat, M.; Hamdaoui, O.; Chiha, M.; Samar, M. H.Ultrasonication-Assisted Preparation of Water-in-Oil Emulsions andApplication to the Removal of Cationic Dyes from Water by EmulsionLiquid Membrane. Sep. Purif. Technol. 2008, 62, 636.(60) Ghows, N.; Entezari, M. H. Fast and Easy Synthesis of Core−Shell Nanocrystal (CdS/TiO2) at Low Temperature by Micro-Emulsion Under Ultrasound. Ultrason. Sonochem. 2011, 18, 629.(61) Velegraki, T.; Poulios, I.; Charalabaki, M.; Kalogerakis, N.;Samaras, P.; Mantzavinos, D. Photocatalytic and Sonolytic Oxidationof Acid Orange 7 in Aqueous Solution. Appl. Catal., B 2006, 62, 159.



Documents

Mejorando La Estabilidad Aceite en Agua de Emulsiones de Coco