Depletion Flocculation of Beverage Emulsions by Gum Arabic and Modified Starch R

JFS: Food Engineering and Physical Properties

Depletion Flocculation of Beverage Emulsions by Gum Arabic and Modified Starch R. CHANAMAI AND D.J. MCCLEMENTS

ABSTRACT: The creaming velocity, apparent viscosity, and ultrasonic attenuation spectra (1 to 50 MHz) of 5 wt% n- hexadecane oil-in-water emulsions containing different droplet radii (r = 0.15 - 0.7 ␮m), biopolymer types (gum arabic or modified starch), and biopolymer concentrations (0 to 2.5 wt%) were measured. Depletion flocculation was observed in the emulsions when the nonabsorbed biopolymer concentration exceeded a critical concentration (CFC). The CFC increased with decreasing droplet radius for both biopolymers because the magnitude of the depletion attraction increases with droplet size. The CFC was lower for gum arabic than modified starch because it has a higher effective volume in solution. Depletion flocculation led to an increase in creaming instability and apparent viscosity of the emulsions. Flocculation could be nondestructively monitored by measuring the decrease in ultrasonic attenuation of the emulsions. These results show that depletion flocculation by gum arabic and modified starch can have an adverse effect on the stability of beverage emulsions. Key Words: gum arabic, modified starch, beverages, emulsions, flocculation

Introduction It consists primarily of amylopectin that has been chemically EVERAGE EMULSIONS ARE OIL-IN-WATER EMULSIONS THAT modified to contain nonpolar side-groups. These side- Bare normally prepared as a concentrate, that is, diluted groups anchor the molecule to the droplet surface, while the into finished products (Tan 1997, 1998). The emulsion in both hydrophilic starch chains protrude into the aqueous phase its concentrated and diluted form must have a high degree and protect droplets against aggregation through steric re- of stability. The oil phase usually consists of vegetable oil, fla- pulsion. Purity Gum is mildly anionic in aqueous solutions vor oil, and weighting agent, while the aqueous phase con- and has a surface activity that is almost as high as gum arabic sists of water, sugar, emulsifier, acids, and preservatives (Tan (Ray and others 1983; Tse 1990). 1997). Beverage emulsions are usually stabilized by am- Gum arabic and modified starch have relatively low sur- phiphilic polysaccharides, such as gum arabic or hydropho- face activities (compared to proteins or surfactants), and so bically modified starch (Ray and others 1995; Kim and others a large excess must be added to ensure that all the droplet 1996; McNamee and others 1998; Trubiano 1995; Garti 1999). surfaces are adequately coated (Phillips and Williams 1995).

Gum arabic is the most commonly used biopolymer emul- For example, as much as 20% gum arabic or 12% modified Food Engineering and Physical Properties sifier in flavor beverage emulsions (Tan 1997, 1998). It is de- starch may be required to produce a stable 12.5 wt% oil-in- rived from the natural exudate of Acacia senegal and consists water emulsion (Tse and Reineccius 1995). As a result, there is of at least 3 high molecular weight biopolymer fractions. The a large excess of nonabsorbed polysaccharide in the aqueous surface-active fraction is believed to consist of branched ara- phase of emulsions prepared from them (Tan 1998; Garti binogalactan blocks attached to a polypeptide backbone 1999). Under certain circumstances, nonabsorbed biopoly- (Anderson and others 1985; Randell and others 1988; Phillips mers are capable of promoting droplet flocculation through a and Williams 1995; Jayme and others 1999). The hydrophobic depletion mechanism (Jenkins and Snowden 1996; Lips and polypeptide chain is believed to anchor the molecules to the others 1991; McClements 1999). Flocculation causes a number droplet surface, while the hydrophilic arabinogalactan blocks of effects that are detrimental to emulsion quality: (1) en- extend into the solution, providing stability against droplet ag- hanced creaming due to the increase in particle size, (2) de- gregation through steric and electrostatic repulsion (Phillips creased cloudiness due to the increase in particle size, and (3) and Williams 1995; Islam and others 1997; Jayme and others enhanced coalescence because droplets are brought into 1999). Gum arabic is an effective emulsifier because of its high close proximity (Dickinson and Stainsby 1982; McClements water solubility, low solution viscosity, good surface activity, 1999). The purpose of this study was to investigate the ability and ability to form a protective film around emulsion droplets of gum arabic and modified starch to promote depletion floc- (Glicksman 1983; Dickinson and others 1989). culation in model beverage emulsions and to determine their Problems associated with obtaining a reliable source of effects on the creaming stability and rheology of emulsions. consistently high-quality gum arabic has led many food sci- entists to investigate alternative sources of biopolymer emul- Materials and Methods sifiers for use in flavor beverages (Kim and others 1996; Tan 1997, 1998; Garti 1999). Hydrophobically modified starches Materials have been identified as 1 of the most promising replace- Experimental procedures. Polyoxyethylene sorbitan ments for gum arabic (Trubiano 1995). The modified starch monolaurate (Tween 20), a non-ionic surfactant, and hexa- used in this study (Purity Gum; National Starch, Bridgewater, decane were purchased from the Sigma Chemical Co. (St. N.J., U.S.A.) is an octenyl succinate derivative of waxy-maize. Louis, Mo., U.S.A.). Modified starch (Purity Gum) was ob-

tained from the National Starch and Chemical Co. (Bridge- Coulter Corp., Miami, Fla., U.S.A.). This instrument measures water, N.J., U.S.A.). The average molecular weight of the Pu- the back-scattering of monochromatic light (␭ = 800 ␮m) as rity Gum was about 4 ϫ 105 daltons, with a fairly broad dis- a function of sample height. Emulsions were placed into flat- tribution. Gum arabic was obtained from Importers Service bottomed, cylindrical glass tubes (100 mm height, 16 mm in- Corp. (Jersey City, N.J., U.S.A.). The major fractions of gum ternal dia) and stored at room temperature. The back-scat- arabic have been reported to have molecular weights of tering of light from the emulsions with height was then mea- around 2.5 to 10 ϫ 105 daltons (Jayme and others 1999). Dis- sured. The extent of creaming was assessed by determining tilled and deionized water was used in the preparation of all the height (H) of the interface between the opaque, droplet- solutions. rich layer at the top of emulsion and the less opaque, droplet-depleted layer at the bottom as a function of time (t). The Emulsion Preparation results are reported either as the full creaming profiles or as An aqueous surfactant solution was prepared by dispers- the initial creaming rate: dH/dt. ing 2.5 wt% Tween 20 in water. A 5 wt% hexadecane oil-in- water emulsion was prepared by weighing 100 g of hexade- Rheology Measurements cane and 1900 g of surfactant solution into a 2000 cm3 plastic The rheological properties of emulsions were measured beaker and blending with a high-speed blender for 1 min using a dynamic shear rheometer with a concentric cylinder (High Shear Homogenizing Container; Waring Laboratory, measurement cell (Constant Stress Rheometer, CS-10; Bohlin New Hartford, Conn., U.S.A.). The size of the emulsion drop- Instruments, Cranbury, N.J., U.S.A.). The dia of the rotating lets was then reduced further using a high-pressure valve inner cylinder was 25 mm, and the dia of the static outer cyl- homogenizer (Rannie 8.30R, Wilmington, Mass., U.S.A.). inder was 27.5 mm. Samples were placed in the temperature- Emulsions containing droplets with different sizes were ob- controlled measurement vessel and allowed to equilibrate to tained by withdrawing samples at different stages during the the required temperature (25 ЊC) for 5 min prior to making preparation procedure. The influence of biopolymer con- the measurements. The shear rheology of the samples was centration on the measurements was investigated by prepar- determined by preshearing them at a constant shear rate of ing a series of emulsions with the same droplet size distribu- 30 s-1 for 30 s, allowing a recovery period of 3 min, and then

Food Engineering and Physical Properties tion and concentration and then adding different amounts of acquiring the apparent viscosity as a function of shear stress biopolymer and/or water to the aqueous phase to keep the (0 to 3 Pa). overall droplet concentration the same in each emulsion. Ultrasonic measurements Particle Size Determination by Light Scattering Ultrasonic attenuation spectra of emulsions were mea- The particle size distribution of the emulsions was measured in the frequency range of 1 to 50 MHz using a custom- sured using a laser light scattering instrument (Horiba LA- built ultrasonic spectrometer. This spectrometer was based 900, Irvine, Calif., U.S.A.). This instrument measures the an- on the frequency scanning ultrasonic pulse echo reflectome- gular dependence of the intensity of light scattered from a ter described in detail elsewhere (McClements and Fairley dilute emulsion. It then finds the particle size distribution that gives the best fit between the experimental measurements and predictions made using light scattering theory. A refractive index ratio of 1.08 was used by the instrument to calculate the particle size distributions. Measurements are ⌺ 3 reported as the surface-volume mean radius: r32 = niri / ⌺ 2 niri , where ni is the number of droplets of radius ri. To prevent multiple scattering effects, the emulsions were diluted with distilled water prior to analysis so that the droplet concentration was less than about 0.02 wt%. Each sample was analyzed 3 times, and the data are presented as the average. The droplet size distribution did not change during the course of the experiments, which suggests that the emulsions were stable to coalescence and Ostwald ripening.

Optical Microscopy Photomicrographs of the emulsions were obtained using a Nomarski Differential Interference Contrast optical microscope (DIC, Nikon microscope Eclipse E600; Nikon Corp., Tokyo, Japan). The 5 wt% hexadecane oil-in-water emulsions were gently agitated in a glass test tube prior to analysis to ensure they were homogeneous. A drop of emulsion was then placed on a microscope slide, covered by a cover-slip, and observed at a magnification of 400ϫ. An image of the emulsion was acquired using digital image processing soft- ware (Spot Dianostic instruments Inc., Stering Heights, Mich., U.S.A.) and stored on a personal computer. Figure 1—Photomicrographs of 5 wt% n-hexadecane oil- in-water emulsions (r = 0.52 ␮m): (a) Nonflocculated emul- Creaming Stability Measurements sion (0% gum arabic), (b) Nonflocculated emulsion (0.2 % The creaming stability of the emulsions was determined gum arabic), (c) Flocculated emulsion (0.8% gum arabic), and (d) Flocculated emulsion (2% gum arabic) by a commercial optical scanning instrument (Quickscan;

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1991, 1992). Briefly, a broadband pulse of ultrasound was attractive van der Waals forces and therefore prevent the propagated through an emulsion, and the attenuation coeffi- droplets from flocculating. The addition of a nonadsorbing cient was calculated from the decrease in its amplitude (Mc- polymer to the continuous phase of an emulsion increases Clements and Fairley 1992). The frequency-dependence of the attraction between the droplets because of an osmotic the attenuation coefficient was determined by carrying out a effect associated with the exclusion of polymer molecules Fourier Transform Analysis of the ultrasonic pulse before from a narrow region surrounding the droplets (Jenkins and and after it had traveled through the emulsion. To cover the Snowden 1996). As the polymer concentration is increased, whole frequency range, 2 different measurement cells and 4 the attractive forces between the droplets increases. Above a different broadband ultrasonic transducers were used. The critical polymer concentration, the attractive forces domi- 1st measurement cell was used for low-frequency measure- nate the repulsive forces, and so the droplets flocculate. It is ments (1 to 7 MHz). It had a 5-mm Plexiglas buffer rod (that therefore possible to control the degree of droplet floccula- separated the transducer from the sample) and a 16-mm tion in an emulsion by varying the concentration of polymer sample path-length. The 2nd measurement cell was used for in the continuous phase. high-frequency measurements (10 B 50 MHz). It had a 3-cm The tendency for emulsions to flocculate upon the addi- quartz delay line and a 1.4-mm sample path-length. One tion of biopolymer was initially studied by optical microsco- transducer was used with the 1st measurement cell: 3.5 py. Photomicrographs of emulsions (r = 0.52 ␮m) containing MHz, 0.5-inch dia (V682; Panametrics, Waltham, Mass., different concentrations of biopolymer (gum arabic) in the U.S.A.). Three transducers were used with the 2nd measurement cell: (a) 20 MHz, 0.25 inch (V212BA; Panametrics); (b) 50 MHz, 0.25 inch (V214BA; Panametrics); and (c) 100 MHz, 0.125 inch (V2054; Panametrics).

Results and Discussion

Depletion Flocculation in Beverage Emulsion The degree of flocculation in an emulsion depends on the balance of attractive and repulsive interactions between the droplets, for example, van der Waals, electrostatic, steric, depletion, hydrophobic, and hydration (Hunter 1986, 1989; Is- raelachvili 1992). The emulsions used in this work are stabilized by a non-ionic surfactant (Tween 20), and so the 2 major types of repulsive interaction are steric and hydration forces. In the absence of gum arabic or modified starch, these repulsive forces are sufficiently large to overcome the Food Engineering and Physical Properties

Figure 3—Creaming profiles of 5 wt% n-hexadecane oil- in-water emulsions containing gum arabic: (a) Figure 2—Dependence of viscosity of gum-arabic and Nonflocculated (0.2 wt% gum arabic) and (b) Flocculated modified-starch solutions on biopolymer concentration (0.8 wt% gum arabic)

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aqueous phase are shown in Figure 1. When the biopolymer the biopolymer concentration exceeded the CFC, the droplets concentration was below a certain value, defined as the criti- formed flocs (Figure 1c), which became more extensive when cal flocculation concentration or CFC, the droplets appeared the biopolymer concentration was increased further (Figure isolated and were fairly evenly distributed throughout the 1d). It should be noted that when the emulsions were left on emulsion (Figure 1a and 1b). The CFC was found to be about the microscope slide, the floc size increased over time, which 0.4 wt% for gum arabic and about 1.7 wt% for modified was probably caused by droplet-droplet, droplet-floc, and starch, which was attributed to differences in their effective floc-floc collisions induced by Brownian motion. volumes in aqueous solutions. This is demonstrated by measurements of the concentration dependence of the viscosity Influence of Depletion Flocculation on Creaming of the 2 biopolymer solutions (Figure 2). The concentration Stability of Emulsions increment of viscosity for gum arabic (about 5.5 mPa s wt%- The creaming stability of nonflocculated and flocculated 1) was 2- to 3-fold greater than that for modified starch 5% n-hexadecane emulsions with the same droplet radius (r (about 2 mPa s wt%-1), which suggests that its effective vol- = 0.52 ␮m) was monitored by measuring the back-scatter- ume is about 2 to 3 times larger (McClements 2000). When ing of laser light as a function of height over 23 h (Figure 3). For both of the emulsions, the back-scattering of light was fairly constant along their entire height at the beginning of the experiment because there was an even distribution of droplets throughout the system. Over time the droplets moved upwards due to gravity, which caused a decrease in the back-scattering at the bottom of the emulsions (because the droplet concentration decreased) and an increase at the top (because the droplet concentration increased). The creaming behavior of nonflocculated and flocculated emulsions was clearly different (Figure 3a and 3b). Cream- ing was much more rapid in the flocculated emulsion than

Food Engineering and Physical Properties in the nonflocculated emulsion, as would be expected because of the increase in the size of the particles in the system (McClements 1999). The influence of hydrocolloid type, hydrocolloid concentration (c), and mean droplet size on the creaming rate of 5 wt% n-hexadecane oil-in-water emulsions was measured (Figure 4). Below a certain biopolymer concentration (the CFC), the creaming rate remained relatively constant, being close to that of a nonflocculated emulsion. Once the CFC was exceeded, there was a rapid increase in creaming rate

Figure 4—Dependence of creaming rates of 5 wt% n- Figure 5—Dependence of critical flocculation concentra- hexadecane oil-in-water emulsions with different droplet tion (CFC) on droplet size for 5 wt% n-hexadecane oil-in- radii (0.17 and 0.52 ␮m) on biopolymer concentration: (a) water emulsions containing gum arabic and modified gum arabic and (b) modified starch. starch

460 JOURNAL OF FOOD SCIENCE—Vol. 66, No. 3, 2001 Depletion Flocculation of Beverage Emulsions . . . because of the increase in the size of the particles within the Depletion flocculation is therefore highly likely in beverage emulsion (McClements 2000). A further increase in biopoly- concentrates, which may promote droplet coalescence on mer concentration caused an appreciable decrease in prolonged storage because the droplets are brought into creaming rate (up to 60%) because the increase in aqueous close proximity. Beverage concentrates are normally diluted phase viscosity caused the upward movement of the flocs to extensively (typically 300 to 2000 times) prior to use (Tan be retarded. 1998). The susceptibility of the finished product to depletion As would be expected from Stoke’s law, the creaming rate flocculation depends on the final concentration of biopoly- of the nonflocculated emulsions (c Ͻ CFC) increased as the mer in the aqueous phase. Dilutions of 300 to 2000 times droplet radius increased (Figure 4). The CFC of the emul- would give gum arabic concentrations between about 0.01 to sions also depended on droplet size, decreasing as the drop- 0.07 wt% in the final product and modified starch concentra- let radius increased. This was seen most clearly in measure- tions between about 0.006 and 0.04 wt%. Diluted emulsions ments of the minimum amount of biopolymer required to stabilized by modified starch are therefore unlikely to under- cause extensive creaming after 24-h storage (Figure 5). The go depletion flocculation because the biopolymer concen- decrease in CFC with increasing droplet radius is because the tration is always below the CFC. On the other hand, diluted strength of the depletion attraction increases with droplet emulsions stabilized by gum arabic may be susceptible to de- size, therefore less biopolymer is required to induce floccu- pletion flocculation if the droplet size is fairly large because lation for larger droplets (Jenkins and Snowdon 1996). These then the CFC is relatively low (Figure 5). results indicate that decreasing the droplet size can reduce the susceptibility of an emulsion to depletion flocculation. Influence of Depletion Flocculation on Rheology of For emulsions with the same droplet size and biopoly- Beverage Emulsions mer concentration, the CFC was appreciably less for gum It is well known that the rheology of emulsions is strongly arabic than for modified starch. As mentioned earlier, this dependent on droplet flocculation (Hunter 1986, 1989). For is because gum arabic has a greater aqueous phase effec- this reason, we examined the influence of depletion floccula- tive volume than modified starch (Figure 2), either because tion on the rheology of the model beverage emulsions. The its molecular weight is higher or because its structure is dependence of the apparent viscosity of flocculated and more open (McClements 2000). This means that emulsions nonflocculated emulsions (r = 0.52 ␮m) with different containing gum arabic are more susceptible to depletion biopolymer (gum arabic) concentrations on shear stress was flocculation, especially when one considers that they are measured (Figure 6). Flocculated emulsions exhibited pro- normally used at considerably higher concentrations (Tse nounced shear-thinning behavior over the shear stresses and Reineccius 1995). studied, that is, their shear viscosity decreased with increas- The practical significance of the above results depends on ing shear stress. Shear-thinning is the result of progressive the biopolymer concentrations found in actual flavor beverages. The concentration of gum arabic in a beverage concentrate is typically around 20 wt%, whereas that of modified starch is typically around 12 wt% (Tse and Reineccius 1995). Food Engineering and Physical Properties

Figure 6—Shear-stress dependence of the apparent vis- Figure 7—Dependence of normalized apparent viscosity cosity of 5 wt% n-hexadecane oil-in-water emulsions (at 0.1 Pa) of 5 wt% n-hexadecane oil-in-water emulsions containing different gum-arabic concentrations (shown with different droplet radii (0.17 and 0.52 ␮m) on biopoly- in text box) mer concentration: (a) gum arabic and (b) modified starch

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deformation and disruption of flocs in the shear field as the efficient of 5 wt% n-hexadecane oil-in-water emulsions (r = shear stress is increased (McClements 1999). The nonfloccu- 0.52 ␮m) containing nonflocculated and flocculated droplets lated emulsions exhibited Newtonian behavior, that is, their was measured (Figure 8). In the nonflocculated emulsion, viscosity was independent of shear stress. there was a slight maximum in the ␣/f spectra when the fre- The influence of biopolymer concentration on the appar- quency was increased from about 2 to 10 MHz and a steep ent viscosity (at 0.1 Pa) of emulsions was also measured (Fig- rise in ␣/f at higher frequencies. The maximum in ␣/f at low- ure 7). The apparent viscosity of the emulsions (␩) was divid- er frequencies is primarily due to thermal losses, while the ed by the apparent viscosity of an aqueous solution with the steep increase at higher frequencies is due to intrinsic ab- ␩ same biopolymer concentration ( 1) to obtain a normalized sorption losses associated with the oil and aqueous phases, ␩ ␩ ␩ viscosity ( N = / 1) that highlights changes resulting from as well as some scattering of the ultrasound by the droplets alterations in droplet characteristics. The normalized viscosi- (McClements 1996). When the emulsions became flocculated, ty was relatively constant when the biopolymer concentra- there was a decrease in the attenuation coefficient at low fre- tion was below the CFC but increased significantly when the quencies and an increase at high frequencies. The reason for CFC was exceeded. This increase in viscosity is because of the decrease at low frequencies is the fact that the flocculat- the increase in the effective volume fraction of the particles ed droplets are closer together, and therefore their thermal in the emulsion when flocculation occurs (McClements waves overlap with each other (McClements 1994; Hemar 2000). These changes are much more obvious for the gum- and others 1997). The increased attenuation at high frequen- arabic emulsions because flocculation occurs at appreciably cies is due to increased scattering by the relatively large flocs lower biopolymer concentrations. (McClements and others 1998). The critical flocculation concentration can be determined Influence of Depletion Flocculation on Ultrasonic by measuring the attenuation coefficient of emulsions con- Properties of Emulsions taining different biopolymer concentrations. The depen- The creaming and viscosity measurements indicate that dence of the attenuation coefficient (at 2 MHz) on biopoly- depletion flocculation has a pronounced influence on the mer concentration for 5 wt% n-hexadecane emulsions (r = physiochemical properties of beverage emulsions. It would 0.52 ␮m) is shown in Figure 9. The attenuation coefficient is

Food Engineering and Physical Properties therefore be useful to have an analytical technique that fairly constant up to the CFC of the emulsions (about 0.4 could rapidly and nondestructively determine whether the wt% for gum arabic and about 1.7 wt% for modified starch), droplets in an emulsion were flocculated or not. Light scat- indicating that the droplets are not aggregated. Above this tering or electrical pulse counting techniques cannot be used biopolymer concentration, the attenuation coefficient falls to study depletion flocculation because emulsion dilution rapidly, indicating that the droplets come into close proximi- usually causes disruption of the flocs. Optical microscopy is ty, that is, they are flocculated. Above a gum-arabic concen- time consuming and laborious and cannot be used to quanti- tration of about 1 wt%, the attenuation coefficient remained fy flocculation in emulsions containing small droplets. In this fairly constant, which suggested that the structure of the section, we show that ultrasonic spectroscopy provides a flocs did not change much as the biopolymer concentration convenient method of measuring droplet flocculation in situ. was increased further. These results show that ultrasonic The frequency dependence of the ultrasonic attenuation co- spectroscopy can give useful information about the degree

Figure 8—Ultrasonic attenuation spectra of 5 wt% n- Figure 9—Ultrasonic attenuation coefficient (at 2 MHz) of hexadecane oil-in-water emulsion (r = 0.52 _m) containing 5 wt% n-hexadecane oil-in-water emulsions containing dif- nonflocculated (0.2 % gum arabic) and flocculated (0.8% ferent gum-arabic and modified-starch concentrations gum arabic) droplets

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of flocculation in optically opaque emulsions. colloids. Cambridge: Royal Society of Chemistry. p 1-15. McClements DJ. 1999. Food emulsions: Principles, practice and techniques. Boca Raton: CRC Press. Conclusions McClements DJ. 2000. Comments on viscosity enhancement and depletion floc- HE CREAMING STABILITY AND RHEOLOGY OF MODEL BEVER- culation by polysaccharides. Food Hydrocoll (Forthcoming). McClements DJ, Herrmann N, Hemar Y. 1998. Influence of flocculation on the Tage emulsions was strongly influenced by the concentra- ultrasonic properties of emulsions: Theory. J Phys D 31, 2950-2955. tion of free biopolymer in the aqueous phase. When the McClements DJ. 1996. Principles of Ultrasonic Droplet Size Determination. Langmuir. 12, 3454-3461. biopolymer concentration exceeded a certain concentration McClements DJ. 1994. Yktrasibuc determination of depletion flocculation in oil- (CFC), the droplets became flocculated through a depletion in-water emulsions, Coll. Surf., 90, 25-35. mechanism. The CFC of gum arabic (about 0.4 wt% for r = McClements DJ and Fairley P. 1992. Frequency scanning ultrasonic pulse echo reflectometer. Ultrasonics, 30, 403-408. 0.52 ␮m) was significantly lower than that of modified starch McClements DJ and Fairley P. 1991. Ultrasonic pulse echo reflectometer, Ultra- (about 1.7 wt% for r = 0.52 ␮m). We also found that the CFC sonics, 29, 58-65. McNamee BF, O’Riordan ED, O’Sullivan M. 1998. Emulsification and microen- decreased with increasing droplet size because the strength capsulation properties of gum arabic. J Agric Food Chem 46, 4551-4555. of the depletion attraction increases with droplet size. Phillips GO, Williams PA. 1995. Interaction of hydrocolloids in food systems. In: Knowledge of the dependence of the CFC on droplet size Gaonkar AG, editor. Ingredient interactions: Effect on food quality. 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Beverage emulsions. In: Friberg SE, editor. Food emulsions. New stabilizing properties of gum arabic: Dilution and flocculation aspects. Food York: Marcel Dekker. p 491-524. Hydrocoll 3, 101-114. Tan CT. 1998. Beverage flavor emulsion B A form of emulsion liquid membrane Dickinson E, Stainsby G. 1982. Colloids in foods. London: Applied Science. encapsulation. In: Contis ET, Ho CT, Mussinan CJ, Parliament TH, Spanier AM, Garti N. 1999. Hydrocolloids as emulsifying agents for oil-in-water emulsions. editors. Food flavors: Formation, analysis and packaging influences. New York: J Disp Sci Tech 20, 327-355. Elsevier. p 29-42. Glicksman, M. Gum arabic. 1983. In: Glicksman M, editor. Food hydrocolloids. Trubiano PC. 1995. The role of specialty food starches in flavor emulsions. In: Ho Boca Raton, Fla.: CRC Press. p 7-30. CT, Tan CT, Tong CH, editors. Flavor technology: Physical chemistry, modifica- Hemar Y, Herrmann N, Lemarechal P, Hocquart R, and Lequeux F. 1997. Effect tion, and process. 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