Influence of binder type and concentration on physical ...

Journal of Food, Agriculture & Environment, Vol.10 (3&4), July-October 2012 141

www.world-food.net Journal of Food, Agriculture & Environment Vol.10 (3&4): 141-150. 2012

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Received 10 June 2012, accepted 19 September 2012.

Influence of binder type and concentration on physical properties of agglomerated, spray-dried, and high oil loaded microcapsules

Plengsuree Thiengnoi 1, 2, Manop Suphantharika 1, 2* and Pravit Wongkongkatep 1 Department of Biotechnology, Faculty of Science, Mahidol University, Rama 6 Road, Bangkok 10400, Thailand. 2 Center of

Excellence on Agricultural Biotechnology: (AG-BIO/PERDO-CHE), Bangkok 10900, Thailand. *e-mail: [email protected]

Abstract This study aimed to investigate the effects of the type of binder and binder concentration on physical properties of agglomerated, spray-dried, and high oil loaded microcapsules. Spray drying was used to microencapsulate soybean oil (500 g kg -1 of dry matter) which served as a model core material in a wall system consisting of soy protein isolate (SPI) and maltodextrin (MD) (1:3 w/w ratio). Spray drying of the core-in-wall emulsions led to small particles (~20 µm) having poor handling and reconstitution properties. Fluidized bed agglomeration of the spray-dried microcapsules using MD with varying dextrose equivalent (DE) values (10-18) as an aqueous binder solution improved the handling and reconstitution properties of the powders. The system containing MD with the DE value of 14 (MD14) presented the highest dispersibility and was chosen to determine the effect of binder concentrations (0-200 g L-1 ). The optimum binder concentration was 150 g L-1 MD with a DE value of 14 which resulted in the largest particle size of the agglomerate (657 µm) having a very good flowability and low cohesiveness. The wettability (wetting time = 3 s) and dispersibility (98%) of this agglomerate were very good.

Key words: Soybean oil, microencapsulation, spray drying, agglomeration, fluidized bed.

Introduction Microencapsulation is a process in which liquid droplets or solid particles of sensitive ingredients (core materials) are entrapped within a matrix of a microencapsulating agent (wall material). The wall protects the core material against deterioration, limits losses of volatile materials and controls release of active materials 1. Microencapsulation is also used to transform liquids into dry, free-flowing powders which enhance handling properties. Although many microencapsulation techniques have been developed, spray drying is the most commonly used to microencapsulate food ingredients due to low cost and available equipment 2.

The wall material for microencapsulation by spray drying should exhibit high solubility, effective emulsification and film forming characteristics, efficient drying properties, and low viscosity at high concentrations 1. The surface properties of the wall material are also important factors to be considered during wall material selection 3-5. It is well recognized that gum arabic and proteinaceous materials such as sodium caseinate and whey protein are effective wall materials used alone or in combination with maltodextrin. Maltodextrin cannot be used as wall material in the absence of a surface-active wall constituent because they generally have no emulsification properties, however, incorporating maltodextrin into the wall systems has been shown to improve the drying properties of the wall matrix probably by enhancing the formation of a dry crust around the drying droplets 1. A series of studies has indicated that a combination of gum arabic and maltodextrin 6-8, sodium

caseinate and maltodextrin 9-11, and whey protein and maltodextrin 1 exhibit excellent microencapsulating properties and are suitable for microencapsulation of volatile and non-volatile core materials. However, there is no report on the evaluation of a combination of soy protein isolate and maltodextrin as wall material for microencapsulation of oil. Soy protein isolate was chosen as a microencapsulating agent in this research because of its useful functional properties for microencapsulation, such as emulsification, solubility, film-forming and water binding capacity. In addition, soy protein isolate is generally recognized as safe (GRAS). These properties make soy protein isolate a very attractive wall material for the microencapsulation of bioactive compounds 12, 13.

The spray-dried powders usually have a small particle size, typically in the range of 10-100 µm in diameter, regardless of the spray drying conditions used, especially those obtained from small-scale spray dryers 14. This small particle size may result in poor handling and reconstitution properties, product separation during shipping and handling, and dusting problems in manufacturing. To alleviate these problems, the spray-dried powders are often agglomerated.

Agglomeration is defined as the size enlargement process in which the starting material is fine particles join or bind with one another, resulting in an aggregate porous structure much larger in size than the original material, called agglomerates. The commonly used agglomeration processes can be divided into three types: (a) pressure agglomeration (e.g. tableting), (b) growth agglomeration

142 Journal of Food, Agriculture & Environment, Vol.10 (3&4), July-October 2012

(e.g. fluidized bed, jet agglomeration, pelletizing), and (c) agglomeration by drying (e.g., during spray-drying, drum drying). Depending on whether or not a binder liquid is involved in the process, types (a) and (b) can be subdivided into ‘wet’ and ‘dry’ agglomeration methods 15. Wet growth agglomeration is the most suitable method for microencapsulated spray-dried powders because the wall materials used in microencapsulation are usually water-soluble and form strong interparticle bridges on re-drying 14. In this process, the surface of particles is made sticky by wetting with water. Liquid bridges are formed when particles come into contact and consolidate during drying leading to solid bridges after water evaporation. However, when low-or non-water-soluble particles, e.g. the microcapsules with high levels of surface oil, have to be agglomerated, a binder must be used to form the solid bridge. Usually it is sprayed as an aqueous solution on the particle surface 16. Among the binder-related variables, the types of binder and the binder solution concentration have a major effect on such agglomerate properties as friability, density, porosity, bulk flow, and size distribution 17.

Fluidized bed agglomeration is one of the most suitable processes leading to agglomerates with high porosity and good mechanical resistance for handling and packaging 16. This process generally works by fluidizing the powder and then spraying water or a binder solution onto the bed of fluidized particles. Much of the published work on fluidized bed agglomeration has been conducted on the evaluation of processing factors, such as temperature and flow rate of the fluidizing air and the flow rate and droplet size of the atomized spray of water or a binder solution 17-19, and the properties of solid particles as well as binder solutions 3-5. These process-related variables and physicochemical properties have a direct influence on the growth kinetics and mechanism, the degree of agglomeration, the granule size distribution, and other end-use properties of the granules. In addition, the processing conditions developed are only specific to that product and must be redeveloped each time a new product is to be made.

There are some information available in the literature regarding the agglomeration of spray-dried microencapsulated powders 6, 8, 14. However, these works were carried out on the spray-dried microcapsules with low core loads (50-200 g kg-1) using gum arabic alone or in combination with maltodextrin as wall materials and mostly were agglomerated with water. In general, the highest possible core load that provides high oil retention is advantageous because the effect of wall materials on physicochemical properties of the product after reconstitution could be minimized 1. However, as the core load increases, the surface oil of the microcapsules becomes higher, regardless of the wall system. The powder tends to stick together and form lumps, which impede flow, resulting in poor flowability 20. The powder with higher levels of surface oil is also hydrophobic leading to poor wettability in water. The study on the effect of agglomeration on the properties of spray-dried microcapsules shows that the agglomeration does not change the properties of the spray-dried microcapsules but considerably improves their flowability and wettability 6, 8.

The objectives of this study were to investigate the effects of binder (maltodextrin) type and concentration on fluidized bed agglomeration of the spray-dried microcapsules with a high core load of 500 g kg-1 of soybean oil in the wall materials consisting of soy protein isolate and maltodextrin.

Materials and Methods Materials: Soybean oil was purchased from a local supermarket and used as a model core material. Soy protein isolate (SPI) containing 925 g kg-1 protein (Supro 670, The Solae Company, St. Louis, MO, USA) and maltodextrin (MD) with a dextrose equivalent (DE) value of 18 (MD18) (Siam Modified Starch Co., Ltd., Pathum Thani, Thailand) was used as a wall material for spray-dried microencapsulation of soybean oil. Maltodextrins with a DE value of 10 (MD10), 14 (MD14), and 18 (MD18) (Siam Modified Starch Co., Ltd., Pathum Thani, Thailand) were used as a binder for agglomeration of the spray-dried microcapsules.

Emulsion preparation: From our preliminary study, a wall solution containing 200 g kg-1 solids consisting of SPI/MD18 combination with a weight ratio of 1:3 was prepared in deionized water at room temperature (25°C) 21. Soybean oil was emulsified into the wall solutions at a proportion of 500 g kg-1. Emulsification was carried out by first preparing a coarse emulsion using an Ultra Turrax® T18 basic homogenizer (IKA® Werke GmbH & Co. KG, Staufen, Germany) operated at 22,000 rpm for 30 s followed by four successive homogenization steps using a high-pressure homogenizer (Type Panda, Niro-Soavi S.p.A., Parma, Italy) operated at 50 MPa at room temperature. The emulsion was characterized in terms of the oil droplet size distribution and the volume-weighted mean droplet diameter (d

4,3) using a laser diffraction particle size

analyzer (Mastersizer 2000, Malvern Instruments Ltd., Worcestershire, UK). The emulsion exhibited monomodal size distribution and a d

4,3 value of 1.04 ± 0.06 µm. It is well recognized that the emulsion

having the oil droplet sizes of ≤ 1 µm is stable and desired in oil microencapsulation by spray drying 6, 8, 22.

Spray drying: The emulsions were fed into a spray dryer (Mobile Minor Spray Dryer, Niro A/S, Soeborg, Denmark) by a peristaltic pump at a flow rate of 50 mL min-1, and atomized to small droplets by a centrifugal vaned atomizer wheel with a rotational speed of 23,000 rpm (0.4 MPa air pressure) in a co-current air flow system. In all cases, the inlet and outlet air temperatures were kept at 160 ± 5°C and 80 ± 5°C, respectively. All the powders were collected from the bottom of the dryer’s cyclone and were kept in glass jars in desiccators at 25°C.

Fluidized bed agglomeration: Agglomeration of the spray-dried soybean oil powders was performed in a commercial top-sprayed fluidized bed granulator and dryer (Strea-1, Fluid Bed Laboratory, Aeromatic-Fielder AG, Bubendorf, Switzerland) with 2 kg product capacity. The air distributor is a stainless steel perforated plate (0.16 m diameter) with a porosity of 8%. The atomizer is a downward-facing nozzle and was located 0.32 m above the air distributor. The spray-dried powder weighing 0.2 kg was placed in the product container, and fluidized by means of an upward flowing air stream. The temperature of the inlet fluidizing air entering the bed was set at 50°C. In this study, an aqueous solution of maltodextrin (100 g L-1) with a different DE value of 10, 14, and 18 was used as a binder to investigate their effect on agglomeration. To study the effect of binder concentration, the chosen maltodextrin solution was prepared at various concentrations, i.e. 0, 50, 100, 150 and 200 g L-1. The effect of viscosity of the binder (MD14) solutions could be negligible in this study due to the very low viscosity of the solutions in the concentration range


used. For the 200 g L-1 binder concentration, the viscosity of the solution was 3.1 mPa s at a shear rate of 132 s-1 and 25°C 23. The binder solution was fed by a peristaltic pump at a flow rate of 8 mL min-1 to a two-fluid spray nozzle where the liquid was sprayed onto the fluidized bed of the spray-dried soybean oil powders. The volume of each binder solution was kept constant at 200 mL, therefore the binder content of the resulting agglomerated powder was increased from 0 to 166.7 g kg-1 when the binder concentration was increased from 0 (water) to 200 g L-1. During agglomeration, it was necessary to regularly increase the fluidizing air flow to maintain a good fluidization of the growing agglomerates. When the binder solution was consumed, the product was dried for 10 min at a temperature of 50°C.

Methods of analysis: In order to obtain samples of the bulk powders from each experiment which are representative of the bulk in some particular property, the bulk powders were mixed to ensure homogeneity prior to sampling 24. For moisture analysis of the powder, the oven drying at 105°C until constant weight was used (AOAC Official Method 935.29) 25.

Determination of microencapsulation yield (MEY) and efficiency (MEE): The microencapsulation yield (MEY) was defined as the ratio (expressed as percentage) of microencapsulated oil load to the initial oil load in the emulsion 22. One gram of spray-dried powder or agglomerated powder was determined for the microencapsulated oil content using a modification of the Roese-Gottlieb method 26. In this study, the initial oil load in the emulsion was 500 g kg-1 of total dry matter. The MEY was calculated as follows:

(1)

Microencapsulation efficiency (MEE) parameter was defined as the percentage of oil that could not be extracted from the test sample by petroleum ether 22. One gram of spray-dried powder or agglomerated powder was weighed into a glass extraction flask and 25 ml of petroleum ether was added. The extraction flask was placed on a shaker and the extraction was carried out for 5 min at 25°C. The mixture was filtered, the solvent was evaporated over a water bath at 70°C for 9 min, and the solvent-free extract was dried under vacuum at 100°C and 6.7 kPa. The amount of extracted oil was then determined gravimetrically. The total amount of microencapsulated oil of the powder (1 g) was also determined using Roese-Gottlieb 26 method. The MEE was calculated as follows:

MEE (%) = 100 -

Particle-size measurement: For the spray-dried soybean oil powders, the particle size distribution and the volume-weighted mean diameter (d

4,3) were measured by the dry method in a laser

diffraction particle size analyzer (Mastersizer 2000, Malvern Instruments Ltd., Worcestershire, UK) fitted with a Scirocco 2000 dry powder feeder unit. The laser diffraction method used light scattering of the powders (50 g) as a dilute suspension in air. A particle-size distribution was fitted to the measured laser diffraction pattern. The particle diameter of a sphere with a volume equivalent

to the volume of the powder (d4,3

) was calculated by the instrument software 27.

For the agglomerated soybean oil powders, the mean particle size and particle size distribution were determined using sieve analysis. A vibratory sieve shaker (Model Octagon Digital 2000, Endecotts Ltd., London, UK) with a series of eight sieves having aperture sizes of 125, 180, 250, 355, 500, 710, 1000 and 1400 µm was used. The agglomerated soybean oil powder (50 g) was put on the sieve series and shaken at a vibration speed of 3000 min-1 with a displacement amplitude of approximately 3 mm for 15 min. Due to its high fat content, the agglomerated powders remained on the first sieve and aggregated into big balls. Addition of aluminium sodium silicate (Sigma-Aldrich Chemie GmbH, Germany) as a free flowing agent at a level of 1% w/w improved flowability of the sample through sieves 28-30. This agent covered the surface of powder particles, the adhesion among them was reduced and this reduced the possibility of wet bridges formation 31. The geometric mean particle size (i.e. the arithmetic mean of the logarithms) and the geometric standard deviation of the agglomerated powders were determined by graphical method using a log-probability plot 24. In order to compare particle size distributions of powders obtained from each treatment it is essentially to normalize the frequency distribution so that the area under the curve is 100%. The weight percentage of powders in each size class (dW) was divided by the width of the corresponding size class (dχ) and then plotted against the mean particle size (χ) of that particular size class 24.

Morphological study: The microstructure of spray-dried microcapsules and agglomerated products was examined to observe the characteristics of the powders including appearance, size, and shape. The powder samples were mounted on aluminium stubs using a double-sided adhesive tape. The samples were then rendered conductive by coating with gold and examined by a scanning electron microscope (SEM S-2500, Hitachi Science Systems, Ibaraki, Japan) at an accelerating voltage of 15 kV. The samples were examined at a magnification of 1000× and 350× for the spray-dried and agglomerated powders, respectively, and the representative photomicrographs were obtained.

Determination of bulk and tapped densities: The bulk density (ρbulk

) of the spray-dried and agglomerated powders was calculated according to the relationship: mass/volume. The mass and volume of the powder samples were determined by gently loading the powder into a 100 mL tarred graduated cylinder to the 100 mL mark and the corresponding weight was noted. For the tapped density (ρ

tapped),

the content of the cylinder was tapped 1250 times, using a VanKel tap density tester (ASTM Version, Varian, Inc., Cary, NC) with a displacement amplitude of 3 ± 0.3 mm. The volume of the sample was then read and used in the calculation of tapped density, i.e. mass/tapped volume. Generally, the tapped density of most powders increases with the number of taps and attains its constant value at 1250 taps. This indicates powder bulk density tapped to the extreme 32, 33.

Determination of particle density: The particle density (ρparticle

) of the spray-dried and agglomerated powders was determined following the method of Sørensen et al. 34 with some modifications. One gram of the powder sample was transferred into a 10 mL measuring cylinder with a glass stopper. Petroleum ether (5 mL)

(g)emulsion in load oil initial

100(g) oil sulatedmicroencap (%) MEY

extracted oil (g) × 100 microencapsulated oil (g)

(2)


was added and the measuring cylinder was shaken until all the powder particles were completely suspended. Finally, a further 1 mL of petroleum ether (6 mL in total) was used to rinse down all the powder particles on the wall of the cylinder and the total volume of petroleum ether with suspended powder was read. The particle density was calculated as follows:

(3)

Determination of friability: Friability measurement of the agglomerated soybean oil powders was performed using the vibratory sieve shaker, which is the same as that used for particle size analysis, according to the procedure described in the literature 16, 35 with some modifications. The test samples (10 g) were hand- sieved with a 355-µm sieve, taking care that attrition did not occur during sieving, and the fine particles, which included any fragments already abraded, were removed. A 5 g fraction of the sieved sample was placed into 300-µm sieve with three glass balls having a diameter of 15 mm and weighing 5 g each. The sample was shaken at a vibration speed of 3000 min-1 for 5 min. The amount retained on the sieve was weighed and the friability percentage was calculated as follows:

(4)

Determination of flowability and cohesiveness: The spray-dried and agglomerated powders were evaluated for their flowability and cohesiveness in terms of Carr index (CI) 36 and Hausner ratio (HR) 37, respectively. Both CI and HR were calculated from the bulk (ρ

bulk) and tapped (ρ

tapped) densities of the powders as shown

below:

(5)

(6)

The flowability (CI) and cohesiveness (HR) of the powder were classified as follows: <15 (very good), 15-20 (good), 20-35 (fair), 35-45 (bad), and >45 (very bad) for CI and <1.2 (low), 1.2-1.4 (intermediate), and >1.4 (high) for HR, respectively. The CI is related to the HR by the formula CI = 100 x (1-1/HR), indicating that the CI increases with an increase in the HR values. This means that the higher the cohesiveness of the powders, the poorer their flowability.

Interfacial tension and contact angle measurements: Interfacial tension and contact angle of distilled water and binder solutions were measured in a contact angle meter (DropMaster, Model DM-CE1, Kyowa Interface Science Co., Ltd., Saitama, Japan) equipped with the interface measurement and analysis system (FAMAS) software. All measurements were performed at room temperature (25ºC) in ten replicates.

Interfacial tension at the air-liquid interface was determined by means of the pendant drop method. A drop (6 µL) was formed with a

0.5 mL microsyringe and suspended at the needle (0.413 mm diameter) tip which located in an optical glass cell. The drop shape was captured using a video camera connected to a microcomputer. The interfacial tension was obtained from the analysis of the image of the drop using the Laplace equation.

For the determination of solid-liquid contact angle, the powder compact method proposed by Lazghab et al. 38 was applied. The spray-dried powders or the agglomerates (0.3 g) were made into tablets (20 mm diameter and 1 mm thickness) by exerting an applied force of 3 tons using a hydraulic press (Model HP-20, K.V.S. Engineering Co., Ltd., Bangkok, Thailand). The contact angles of distilled water or binder solutions on the tablet surface were determined using the sessile drop method. A 2 µL liquid drop was placed on the horizontal surface of each tablet using a microsyringe. An image of each drop was captured immediately after the droplets were placed onto the surface by a camera. Contact angle determination was done using the instrument software.

Determination of wettability: Wettability is the ability, expressed as time in seconds, necessary for a given amount of powder to penetrate the quiet surface of water. In other words, wettability is the ability of a powder to absorb water on the surface and get wet. Due to lack of wettability, dried powder forms lumps after coming into contact with water 31. Hence, the desired powder must have a good wettability or short in wetting time. The recommended wettability value of dried milk products is less than 15 s 39, 40.

Wettability of the spray-dried or agglomerated powder was determined according to Sørensen et al. 39 with some modifications. An amount of distilled water (100 mL) at 25 ± 1°C was poured into a 250 mL beaker. A glass funnel held on a ring stand was set over the beaker with its tip 10 cm away from the water surface. A test tube was placed inside the funnel to block the lower opening of the funnel. The powder sample (1 g) was placed around the test tube and then the tube was lifted while the stop watch was started at the same time. The wetting time was recorded when all the powder particles penetrated the surface of water.

Determination of dispersibility: Dispersibility is the ability of a powder to separate into individual particles when dispersed in water with gentle mixing. Clearly, individual particles will disperse more readily than clumps of powder which may form a wet coat inhibiting both wetting and dispersion 39. The dispersibility of a powder is determined as the percentage of dry matter dispersed in water which can pass through a sieve 42. The sieve aperture size of 212 µm was used in this analysis due to it is large enough to filter the residue of powder in the dispersion. It is well established that the best particle size for rapid dispersion during reconstitution is 150-200 µm 31. The recommended dispersibility value of dried milk products is not less than 85% 43.

Dispersibility measurement of the spray-dried or agglomerated powder was performed according to the procedure described in Sørensen et al. 42 with some modifications. Distilled water (10 mL), at 25 ± 1°C, was poured into a 50 mL beaker. The powder (1 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 movements back and forth across the whole diameter of the beaker. The reconstituted solution was poured through a sieve (212 µm). The sieved solution (1 mL) was transferred to a weighed and dried aluminium pan and then weighed. The difference in weight

6(mL)powdersuspendedwithetherpetroleumofvolumetotal

(g)powderofweightparticle

100(g)powderof weighttotal

(g)sieve he through tpassingpowder ofweight(%)friability

100)(

CI

tapped

bulktapped

bulk

tappedHR


indicated amount of solution in g. The sample pan was dried for 4 h in a hot air oven at 105 ± 1°C. The dispersibility of the powder was calculated as follows:

(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 (w/ w) in the reconstituted solution after it has been passed through the sieve. Therefore,

(8)

Statistical analysis: For spray drying experiments, assays were performed on triplicate samples obtained from one batch of spray drying (n = 3), whereas in the case of agglomeration, assays were performed in triplicate for each sample obtained from duplicate experiments (n = 6). A one-way analysis of variance (ANOVA) and Student-Newman-Keuls (SNK) (p ≤ 0.05) were used to establish the significance of differences among the mean values of the physical, handling, and reconstitution properties of the agglomerated, spray-dried soybean oil microcapsules. The data were analyzed using SigmaStat version 3.1 Windows program (Systat Software, Inc., San Jose, CA) 44.

Results and Discussion Physical properties of spray-dried microcapsules: The high DE maltodextrin (MD18) was chosen to be used as a wall material in combination with SPI in this study. It has been reported that the high DE maltodextrins (DE ≥ 15) exhibited better film-forming properties leading to the absence of surface cracks and therefore better oxidative stability of the microcapsules than those with low DE maltodextrins (DE ≤ 10). Therefore, combination of SPI and MD18 is an effective wall system for microencapsulation of oil 1, 7, 9, 11.

From our preliminary study, increasing the oil load from 250 to 500 g kg-1 resulted in a significant decrease in MEY and MEE from 89% to 76% and 98% to 93%, respectively 21. Even though soybean oil is not a volatile material, some losses did occur during spray drying. As the oil load increased, the higher amounts of the oil droplets present at the surface of emulsion droplets leaving the atomizer or those that migrated to the surface were swept off the particle surface during spray drying resulting in a lower MEY 22. In addition, the amounts of oil remained on the surface of microcapsules could be higher at the higher oil load. This surface oil is available to the extracting solvent under the test conditions and therefore increasing the amounts of extractable oil, which resulted in a lower MEE.

Physical properties of the spray-dried microcapsules are presented in Table 1. Mean particle size of the microcapsules was very small (20 µm) and can be classified as very fine particles 45, which is a typical characteristic of the powders obtained from small-scale spray dryers 23.

In terms of handling properties, a large difference between the bulk (ρ

bulk) and tapped densities (ρ

tapped) of the microcapsules

resulted in a high Carr index (CI) and Hausner ratio (HR), indicating

its poor flowability and high cohesiveness, respectively. This poor flowability at small particle sizes is due to the large surface area per unit mass of powder. There is more contact surface area between powder particles available for cohesive forces, in particular, and frictional forces to resist flow 46, 47.

In terms of reconstitution properties, the spray-dried microcapsules exhibited very poor wettability with a wetting time of 147 s, which coincides with a high contact angle value of 79°, and a fairly good dispersibility of 93%. In general, it is known that water wets very fine powders poorly because of its high surface tension 48. A bed of powder remained on the surface of water, with a viscous layer stopping capillary flow in the interparticle porosity 49.

It can be concluded that the spray-dried microcapsules had poor handling and reconstitution properties which could be improved by further agglomeration.

Effect of binder type on the properties of agglomerated microcapsules: The MD10, MD14, and MD18 were chosen to be used as binders for agglomearation due to their main attributes as good dispersibility and solubility, low viscosity, low hygroscopicity, film formation, bland flavor and exhibiting virtually no sweetness 50, 51.

Physical characteristics of binder solutions and agglomerated microcapsules: Physical properties of the binder solutions and agglomerated spray-dried microcapsules as a function of binder types are presented in Table 2. The value of interfacial tension between distilled water and air did not differ from the standard value within the range of the experimental error and was 71.89 mN m-1. The data indicate that all types of the maltodextrin investigated were surface active, as demonstrated by their ability to lower the interfacial tension of water. The interfacial tension significantly increased with increasing DE values of the maltodextrin. The solid-liquid contact angle of the binder solutions also increased with the DE values of maltodextrin and were significantly higher than that of the distilled water.

After fluidized bed agglomeration, larger agglomerates were obtained with a geometric mean diameter ranged from 363 to 685 µm depending on the types of binder used. The particle size distributions of the agglomerates obtained with different types of binder are presented in Fig. 1. In all cases, the agglomerates exhibited a monomodal size distribution with negligible amounts (<5%) of the fine particles (<125 µm) retained on the pan. The agglomeration of the spray-dried powder also occurred by using pure water, indicating that a part of the powder dissolved during agglomeration which eventually acted as a binder.

100

100

TS%)(10(%)litydispersibi

ba

a

(g) used beingsolution

100(g) dryingafter matter dry %TS

Properties

Microencapsulation yield (%) 75.77 ± 2.33

Microencapsulation efficiency (%) 93.19 ± 0.36

Particle size, d4,3 (µm) 20.43 ± 0.34

bulk (g cm-3) 0.27 ± 0.01

tapped (g cm-3) 0.45 ± 0.00

particle (g cm-3) 1.11 ± 0.01

CI (%) 39.26 ± 2.57

HR 1.65 ± 0.07

Contact angleb ( ) 78.91 ± 0.85

Wetting time (s) 146.67 ± 19.09

Dispersibility (%) 93.12 ± 2.21

Table 1. Properties of soy protein isolate/maltodextrin-based, soybean oil-containing, spray-dried microcapsules a.

a Assays were performed on triplicate samples obtained from one batch of spray drying (n = 3), except for contact angle measurements which were performed in ten replicates (n = 10). b Contact angle of distilled water on the surface of spray-dried samples.


The bulk densities of the agglomerated powders were comparable to or higher than that of the spray-dried powder, whereas the tapped densities were significantly lower. The reason for the lower tapped density observed for the agglomerates with small percentage (<5%) of fine particles is simply that there are not enough fine particles to fill the voids in between the large particles. The fines percentage which gives maximum tapped density is in the range of 20-40% 23, 32. In most cases, the particle densities of the agglomerates were slightly lower than that of the spray-dried powder, indicating a more porous structure of the agglomerates.

The agglomerates prepared using water as a binder had the highest friability compared with those obtained using MD as a binder, indicating the strenghtening of solid bridge by MD during agglomeration process.

The microencapsulation yield (MEY) and microencapsulation efficiency (MEE) of all agglomerates prepared using different types of binder were not significantly different and were comparable to that of the spray-dried powder (Table 1), indicating that these parameters were not affected by the agglomeration process under the conditions used in this study.

The effect of physicochemical properties of the liquid binders, i.e. interfacial tension, contact angle, and viscosity, was not clearly observed from our experimental results possibly due to too small variation of these parameters, as compared with those reported in the literature 4, to have a significant effect on the physical properties of the agglomerates.

Handling and reconstitution properties of agglomerated microcapsules: The handling and reconstitution properties of the agglomerates obtained with different types of binder are presented in Table 3. In all cases, the Carr index (CI) and Hausner ratio (HR) of the agglomerates (Table 3) were significantly lower than those of the spray-dried powder (Table 1). This can be interpreted mainly as the effect of size enlargement. Size enlargement by agglomeration significantly improves flow characteristics of the powders. As particle size increased, surface area per unit mass of powder decreased. There is less contact surface area between powder particles available for cohesive forces, and frictional forces to resist flow 46, 47. Therefore, the cohesiveness of powder was expected to decrease due to their weaker interparticle forces 32. However, the types of binder had no significant effect on the CI and HR of the agglomerates.

From the reconstitution properties data (Table 3), it can be inferred that the fluidized bed agglomeration markedly improved the wettability of the powders from the wetting time of 147 s for the spray-dried powder (Table 1) to a satisfactory level ranged from 4 to 5 s for the agglomerates obtained with different kinds of binder. The recommended wettability value of dried milk products is less than 15 s 39. It is known that size enlargement by agglomeration not only increases the rate of water penetration into the space between the agglomerates, but also the capillary-driven flow of water into the fine pores within the agglomerates and consequently shortens the wetting time 33, 48. Even though the wetting times were not significantly different among the agglomerates prepared using different types of binder, the wettability of these agglomerates assessed through their solid-liquid contact angle significantly increased, i.e. the contact angle significantly decreased, with increasing DE values of the maltodextrin. These results imply that the wettability assessment of the particles based on the determination of the contact angle was more accurate than those assessed by the wetting time. The contact angles of the agglomerates were markedly lower than that of the spray-dried powders (Table 1), indicating a much higher wettability of the agglomerates.

Kinds of binder Properties

Water MD10 MD14 MD18

Interfacial tensionb (mN m-1) 71.89 ± 0.53a 65.30 ± 0.56d 66.55 ± 0.43c 68.28 ± 0.40b

Contact anglec ( ) 78.91 ± 0.85d 80.30 ± 1.16c 85.07 ± 0.88b 90.74 ± 1.09a

Moisture content (%) 1.74 ± 2.00c 3.78 ± 1.80a 3.00 ± 1.10b 3.48 ± 1.30a

Microencapsulation yield (%) 74.50 ± 1.31a 74.77 ± 1.12a 74.06 ± 2.06a 73.46 ± 1.78a

Microencapsulation efficiency (%) 92.92 ± 0.24a 92.92 ± 0.24a 92.42 ± 1.03a 92.44 ± 0.92a

Mean particle size (µm) 362.59 ± 2.36 685.38 ± 1.65 508.76 ± 1.79 668.83 ± 1.59

bulk (g cm-3) 0.26 ± 0.01c 0.34 ± 0.01a 0.26 ± 0.00c 0.30 ± 0.00b

tapped (g cm-3) 0.33 ± 0.01c 0.40 ± 0.00a 0.31 ± 0.00d 0.36 ± 0.00b

particle (g cm-3) 0.83 ± 0.06c 0.98 ± 0.12bc 1.14 ± 0.06ab 0.99 ± 0.14bc

Friability (%) 49.58 ± 1.46a 28.76 ± 0.74d 44.18 ± 1.25b 31.56 ± 1.20c

Table 2. Physical properties of binder solutions and agglomerates produced from soy protein isolate/maltodextrin-based, soybean oil-containing, spray-dried microcapsules with different kinds of binder at a concentration of 100 g L-1 a.

a Assays were performed in triplicate for each sample obtained from duplicate experiments (n = 6), except for interfacial tension and contact angle measurements which were performed in five replicates for each sample (n = 10). Mean ± SD values in the same row with different letters are significantly different (p ≤ 0.05). b Interfacial tension at the air-liquid (i.e. distilled water or binder solutions) interface. c Contact angle of distilled water or binder solutions on the surface of spray-dried samples.

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.00 0 200 400 600 800 1000 1200 1400 1600 1800

water

MD10

MD14

MD18

dW/d

x (%

/ µµµµ µm

)

Particle size (χ) χ) χ) χ) χ) µm

Figure 1. Particle size distributions of the agglomerates produced from soy protein isolate/maltodextrin (MD18)-based, soybean oil-containing, spray-dried microcapsules using an aqueous solution of different types of maltodextrin (100 g L-1) as a binder.


From the point of view of dispersibility, the particle adhesion within the agglomerates should be strong enough to avoid abrasion during packaging and transportation, but should largely dissolve in an aqueous environment, preferably with minimum mechanical energy. In the reconstituted dispersion, the particles should neither float to the surface nor sediment to the bottom of the container within a certain time period 48. In this study, the resultant agglomerates containing MD14 as a binder presented the highest dispersibility and was considered to be very good. This can possibly be due to its highest friability compared with the other MD agglomerated powders (Table 2). These results show that an agglomerate that has strong bonds between the primary particles may have good wettability but poor dispersibility. The bonding material requires a longer time to dissolve and weaken. This is in good agreement with those previously reported in the literature 52. The recommended dispersibility value of dried milk products is not less than 85% 43.

Even though the mechanism behind this finding was not clear, it is generally recognized that the typical DE of maltodextrins used for agglomeration is 10 or 15. This is due to its less hygroscopic than higher DEs because it has a little longer chain length. It also has high glass transition temperature which provides good product stability 53. The MD14 has been used in our previous study to agglomerate the spray-dried soymilk powder 23. From these reasons, the system containing MD14 as a binder was chosen for subsequent experiments.

Effect of binder concentration on the properties of agglomerated microcapsules: Physical and morphological characteristics of agglomerated microcapsules: Physical properties of the binder solutions and agglomerated spray-dried microcapsules as a function of the binder concentration and therefore of the binder mass input are presented in Table 4. The interfacial tension of the maltodextrin binder solutions significantly decreased with increasing maltodextrin concentration, indicating an increase in concentration of maltodextrin at the liquid surface. These results are in good agreement with those reported in the literature 54, 55. The solid-liquid contact angle of the binder solutions significantly increased with the binder concentration, which agrees with the published results in the literature 5. It has already been suggested that for the solid particles which are insoluble in the binder solutions, the growth of agglomerates is favored when the interfacial tension increases and the contact angle decreases 4. However, for the solid particles which are soluble in the binder solutions the opposite trend has been suggested 5. In this study, the spray-dried microcapsules are partially soluble in the binder solutions which could be classified into the latter case. Our results showed the particle size of the agglomerates increased when the interfacial tension decreased and the contact angle increased up to a binder concentration of 150 g L-1 beyond which the particle size decreased. It has been also reported in the literature that the solid particles soluble in the liquid binder solutions also play a major role in the formation and strength of solid bridges inside the agglomerates 5.

Binder concentration (g L-1) Properties

0 50 100 150 200

Interfacial tensionb (mN m-1) 71.89 ± 0.53a 67.18 ± 0.34b 66.55 ± 0.43c 65.12 ± 0.34d 64.52 ± 0.34e

Contact anglec ( ) 78.91 ± 0.85e 82.37 ± 0.92d 85.07 ± 0.88c 90.69 ± 0.94b 94.51 ± 0.74a

Moisture content (%) 1.74 ± 2.00d 2.22 ± 0.50c 3.00 ± 1.10b 3.24 ± 0.20a 3.30 ± 0.70a

Microencapsulation yield (%) 74.50 ± 1.31a 73.02 ± 1.25a 74.06 ± 2.06a 73.52 ± 1.33a 74.95 ± 1.32a

Microencapsulation efficiency (%) 92.92 ± 0.24a 92.09 ± 0.86a 92.42 ± 1.03a 91.83 ± 1.33a 91.72 ± 1.05a

Mean particle size (µm) 362.59 ± 2.36 453.13 ± 1.94 508.76 ± 1.79 656.63 ± 1.60 425.38 ± 2.03

bulk (g cm-3) 0.26 ± 0.01c 0.26 ± 0.00c 0.26 ± 0.00c 0.31 ± 0.00a 0.28 ± 0.00b

tapped (g cm-3) 0.33 ± 0.01b 0.33 ± 0.00b 0.31 ± 0.00c 0.35 ± 0.00a 0.33 ± 0.00b

particle (g cm-3) 0.83 ± 0.06b 0.94 ± 0.05b 1.14 ± 0.06a 0.94 ± 0.06b 0.89 ± 0.05b

Friability (%) 49.58 ± 1.46b 42.00 ± 2.67c 44.18 ± 1.25c 32.58 ± 0.89d 53.86 ± 2.05a

Table 4. Physical properties of binder solutions and agglomerates produced from soy protein isolate/ maltodextrin-based, soybean oil-containing, spray-dried microcapsules with different binder (MD14) concentrations a.

a Assays were performed in triplicate for each sample obtained from duplicate experiments (n = 6), except for interfacial tension and contact angle measurements which were performed in five replicates for each sample (n = 10). Mean ± SD values in the same row with different letters are significantly different (p ≤ 0.05). b Interfacial tension at the air-liquid (i.e. distilled water or binder solutions) interface.c Contact angle of distilled water or binder solutions on the surface of spray-dried samples.

Kinds of binder Properties

Water MD10 MD14 MD18

CI (%) 19.96 ± 2.04a 16.67 ± 1.44a 16.03 ± 1.86a 15.74 ± 1.60a

HR 1.25 ± 0.03a 1.20 ± 0.02a 1.19 ± 0.03a 1.19 ± 0.02a

Contact angleb ( ) 51.47 ± 0.93a 49.98 ± 0.83b 48.25 ± 0.76c 46.66 ± 0.76d

Wetting time (s) 4.83 ± 0.75a 4.67 ± 0.58a 3.50 ± 0.55a 4.00 ± 0.00a

Dispersibility (%) 95.13 ± 0.67b 92.52 ± 1.24b 97.95 ± 2.06a 93.21 ± 1.06b

Table 3. Flow characteristics (Carr index, CI, and Hausner ratio, HR) and reconstitution properties (wettability and dispersibility) of agglomerates produced from soy protein isolate/maltodextrin-based, soybean oil- containing, spray-dried microcapsules with different kinds of binder at a concentration of 100 g L-1 a.

a Assays were performed in triplicate for each sample obtained from duplicate experiments (n = 6), except for contact angle measurements which were performed in five replicates for each sample (n = 10). Mean ± SD values in the same row with different letters are significantly different (p ≤ 0.05).b Contact angle of distilled water on the surface of agglomerated samples.


All the physical properties of the agglomerates, except for the MEY and MEE which were not significantly affected by the agglomeration process, were significantly affected by the binder concentration. Fluidized bed agglomeration of the spray-dried powder resulted in larger and more irregular agglomerates with a geometric mean diameter ranged from 363 to 657 µm depending on the binder concentration used. The particle size distributions of the agglomerates obtained with different binder concentrations are presented in Fig. 2. All agglomerates showed a monomodal distribution with different geometric standard deviations (Table 4) and negligible amounts (<6%) of the fine particles (<125 µm). This result indicates that the binder concentration affected both the mean particle sizes and particle size distributions of the resultant agglomerated powders which in turn influenced their physical and reconstitution properties.

The results show that the agglomerate size increased, whereas the friability decreased as the concentration of binder solutions was increased from 0 up to 150 g L-1. However, a further increase in the binder concentrations up to 200 g L-1 resulted in smaller and more friable agglomerates. Therefore, it is possible to conclude that optimum binder concentration is reached at the 150 g L-1 level, which can be in correlation with the largest particle size of agglomerates (657 µm) and its lowest friability (33%). Therefore, when the amount of binder added to the powders was increased beyond the optimum level, the friability of the agglomerates became higher. Also, at the equilibrium agglomeration state, the weight of the agglomerates exceeded the strength of the interparticle bond. The gravitational force due to the weight of agglomerates along with forces of shearing among the particles and between particles and fluidizing chamber, induced by the fluidizing air, caused the agglomerates to break apart, consequently, reduced the particle size 16, 23, 56. These results could be interpreted by the fact that at lower binder concentrations, the particles were coated with only a small proportion of binder which bonded the powder particles together, while at higher binder concentrations exceeding the optimum level, the binder started to spread over the particles in several layers and the cohesion of binder molecules to each other was such that the powder particles were not bound to each other by a binder bridge 23, 56-58.

The bulk densities of the agglomerated powders were comparable to that of the spray-dried powder, whereas the tapped densities were significantly lower due to a lack of fine particles to fill the voids in between the large particles as discussed earlier. In most cases, the particle densities of the agglomerates were lower than that of the spray-dried powder, indicating a more porous structure of the agglomerates. SEM observations revealed that the spray-dried microcapsules showed a spherical structure without visible cracks or pore and exhibited a few wrinkles on the surface (Fig. 3a). These powder particles appeared as discrete particles and some small particles were deposited on the larger particles. These results reveal only a slight apparent degree of agglomeration among the individual spray-dried microcapsules. All the agglomerates produced with the different binder concentrations were much larger in size than the spray-dried microcapsules and exhibited a loose, porous structure and an irregular shape (Fig. 3b-f).

Handling and reconstitution properties of agglomerated microcapsules: The handling and reconstitution properties of the agglomerates obtained using different binder concentrations are presented in Table 5. In all cases, the Carr index (CI) and Hausner ratio (HR) of the agglomerates were significantly higher than those of the spray-dried powders (Table 1) due to the effect of size enlargement as discussed earlier. These results also show that the CI and HR values of agglomerates significantly decreased with increasing the binder concentrations up to 150 g L-1 and then increased with further increments up to 200 g L-1. This means that agglomerates having the largest particle size and narrowest size distribution obtained with 150 g L-1 binder concentration (Table 4) exhibited a very

Figure 3. Scanning electron micrographs of the soy protein isolate/ maltodextrin (MD18)-based, soybean oil-containing, spray-dried microcapsules (a) and the agglomerated products obtained by using an aqueous solution of maltodextrin (MD14) with different concentrations as a binder: (b) 0, (c) 50, (d) 100, (e) 150, and (f) 200 g L-1.

0.35

0.30

0.25

0.20

0.15

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0.00

dW/d

x (%

/ µµµµ µm

)

0 200 400 600 800 1000 1200 1400 1600 1800

0 g L-1

Particle size (χ) χ) χ) χ) χ) µm

50 g L-1

100 g L-1

150 g L-1

200 g L-1

Figure 2. Particle size distributions of the agglomerates produced from soy protein isolate/maltodextrin (MD18)-based, soybean oil-containing, spray-dried microcapsules using an aqueous solution of maltodextrin (MD14) with different concentrations as a binder.


good flowability and low cohesiveness as classified by its lowest CI (14%) and HR (1.16) values. It is well established that the mean particle size and particle size distribution had a major influence on powder flowability. The coarser powder in the absence of the fine particles flowed better, as expected. Fuchs et al. 6 and Turchiuli et al. 8 reported CI values of 44% for the spray-dried microencapsulated oil powder and 27-29% for the agglomerated spray-dried powder, indicating bad and fair flowability, respectively.

From the reconstitution properties data (Table 5), the wetting time as well as the solid-liquid contact angle of the agglomerates obtained using different binder concentrations significantly decreased with increasing binder concentrations up to 150 g L-1 and then leveled off afterward. The lowest wetting time of 3.0 s obtained at a binder concentration of ≥150 g L-1 is classified as a very good wettability. It is known that for a powder with good instant properties, it must be completely wetted within a few seconds 16. The dispersibility also increased from 93% for the spray-dried powder (Table 1) to 95-98% for the agglomerates. The agglomerates obtained using 150 g L-1 binder concentration exhibited the highest wettability (wetting time = 3.0 s) and dispersibility (98%) which are considered to be very good.

Conclusions The study on microencapsulation of oil by spray drying in the wall system consisting of SPI and MD revealed that the spray-dried microcapsules were small particles having poor handling and reconstitution properties. Size enlargement by fluidized bed agglomeration rendered the agglomerated powders with an improved handling and reconstitution properties depending on the DE values and concentrations of maltodextrin used as a binder solution.

The results of this study suggest that the binder concentration and therefore the binder mass input contributed more effects on the physical, handling, and reconstitution properties of the agglomerated particles than the binder type. This research is ready to be applied in industry as a general guideline for selection of binder types or binder concentrations for agglomeration of food powders.

Acknowledgements Financial support from the scholarship under the Staff Development Project of the Commission on Higher Education, Ministry of Education, is acknowledged. This research is also partially supported by the Center of Excellence on Agricultural Biotechnology, Science and Technology Postgraduate Education and Research Development Office, Office of Higher Education Commission, Ministry of Education, (AG-BIO/PERDO-CHE).

Binder concentrations (g L-1) Properties

0 50 100 150 200

CI (%) 19.96 ± 2.04a 21.21 ± 0.00a 16.03 ± 1.86b 14.15 ± 0.23b 17.80 ± 2.72ab

HR 1.25 ± 0.03a 1.27 ± 0.00a 1.19 ± 0.03bc 1.16 ± 0.00c 1.22 ± 0.04ab

Contact angleb ( ) 51.47 ± 0.93a 50.28 ± 0.68b 48.25 ± 0.76c 46.93 ± 0.87d 46.47 ± 0.55d

Wetting time (s) 4.83 ± 0.75a 3.33 ± 0.58b 3.50 ± 0.55b 3.00 ± 0.00b 3.00 ± 0.00b

Dispersibility (%) 95.13 ± 0.67a 97.42 ± 1.08a 97.95 ± 2.06a 97.63 ± 1.97a 96.95 ± 1.00a

Table 5. Flow characteristics (Carr index, CI, and Hausner ratio, HR) and reconstitution properties (wettability and dispersibility) of agglomerates produced from soy protein isolate/ maltodextrin-based, soybean oil-containing, spray-dried microcapsules with different binder (MD14) concentrations a.

a Assays were performed in triplicate for each sample obtained from duplicate experiments (n = 6), except for contact angle measurements which were performed in five replicates for each sample (n = 10). Mean ± SD values in the same row with different letters are significantly different (p ≤ 0.05). b Contact angle of distilled water on the surface of agglomerated samples.

References 1Sheu, T. Y. and Rosenberg, M. 1995. Microencapsulation by spray

drying ethyl caprylate in whey protein and carbohydrate wall systems. J. Food Sci. 60:98-103.

2Gharsallaoui, A., Roudaut, G., Chambin, O., Voilley, A. and Saurel, R. 2007. Applications of spray-drying in microencapsulation of food ingredients: An overview. Food Res. Int. 40:1107-1121.

3Saleh, K. and Guigon, P. 2007. Coating and encapsulation processes in powder technology. In Salman, A. D. et al. (eds). Handbook of Powder Technology, Granulation. Elsevier, B. V., Amsterdam, 11:323-375.

4Hemati, M., Cherif, R., Saleh, K. and Pont, V. 2003. Fluidized bed coating and granulation: Influence of process-related variables and physicochemical properties on the growth kinetics. Powder Technol. 130:18-34.

5Rajniak, P., Mancinelli, C., Chern, R.T., Stepanek, F., Farber, L. and Hill, B. T. 2007. Experimental study of wet granulation in fluidized bed: Impact of the binder properties on the granule morphology. Int. J. Pharm. 334:92-102.

6Fuchs, M., Turchiuli, C., Bohin, M., Cuvelier, M. E., Ordonnaud, C., Peyrat-Maillard, M. N. and Dumoulin, E. 2006. Encapsulation of oil in powder using spray drying and fluidized bed agglomeration. J. Food Eng. 75:27-35.

7McNamee, B. F., O’Riordan, E. D. and O’Sullivan, M. 2001. Effect of partial replacement of gum arabic with carbohydrates on its microencapsulation properties. J. Agric. Food Chem. 49:3385-3388.

8Turchiuli, C., Fuchs, M., Bohin, M., Cuvelier, M. E., Ordonnaud, C., Peyrat-Maillard, M. N. and Dumoulin, E. 2005. Oil encapsulation by spray drying and fluidised bed agglomeration. Innov. Food Sci. Emerg. Technol. 6:29-35.

9Danviriyakul, S., McClements, D. J., Decker, E., Nawar, W. W. and Chinachoti, P. 2002. Physical stability of spray-dried milk fat emulsion as affected by emulsifiers and processing conditions. J. Food Sci. 67:2183-2189.

10Hogan, S. A., McNamee, B. F., O’Riordan, E. D. and O’Sullivan, M. 2001. Emulsification and microencapsulation properties of sodium caseinate/carbohydrate blends. Int. Dairy J. 11:137-144.

11Kagami, Y., Sugimura, S., Fujishima, N., Matsuda, K., Kometani, T. and Matsumura, Y. 2003. Oxidative stability, structure, and physical characteristics of microcapsules formed by spray drying of fish oil with protein and dextrin wall materials. J. Food Sci. 68:2248-2255.

12Boyacioglu, M. H. 2006. Soy ingredients in baking. In Riaz, M. N. (ed.). Soy Applications in Food. CRC Press, Boca Raton, FL, pp. 63- 81.

13Egbert, W. R. 2004. Isolated soy protein: technology, properties, and applications. In Liu, K. (ed.). Soybeans as Functional Foods and Ingredients. AOCS Press, Champaign, IL, pp. 134-162.

14Buffo, R. A., Probst, K., Zehentbauer, G., Luo, Z. and Reineccius, G. A. 2002. Effects of agglomeration on the properties of spray-dried encapsulated flavours. Flavour and Frag. J. 17:292-299.

15Schuchmann, H. 1995. Production of instant foods by jet agglomeration. Food Control 6:95-100.


16Turchiuli, C., Eloualia, Z., El Mansouri, N. and Dumoulin, E. 2005. Fluidized bed agglomeration: Agglomerates shape and end-use properties. Powder Technol. 157:168-175.

17Gore, A. Y. 1990. Fluidized bed granulation. In Kadam, K.L. (ed.). Granulation Technology for Bioproducts. CRC Press, Boca Raton. FL, pp. 29-70.

18Smith, P. G. and Nienow, A. W. 1983. Particle growth mechanisms in fluidised bed granulation. I: The effect of process variables. Chem. Eng. Sci. 38:1223-1231.

19Saleh, K., Cherif, R. and Hemati, M. 1999. An experimental study of fluidized-bed coating: Influence of operating conditions on growth rate and mechanism. Adv. Powder Technol. 10:255-277.

20Onwulata, C., Smith, P. W., Craig, J. C. and Holsinger, V. H. 1994. Physical properties of encapsulated spray-dried milk fat. J. Food Sci. 59:316-320.

21Thiengnoi, P. 2009. Microencapsulation of Soybean Oil by Spray Drying and Fluidized Bed Agglomeration with Soy Protein Isolate and Maltodextrin. Ph.D. thesis, Mahidol University,Bangkok, 142 p.

22Young, S. L. and Rosenberg, M. 1993. Microencapsulation properties of whey proteins. 1. Microencapsulation of anhydrous milk fat. J. Dairy Sci. 76:2868-2877.

23Jinapong, N., Suphantharika, M. and Jamnong, P. 2008. Production of instant soymilk powders by ultrafiltration, spray drying and fluidized bed agglomeration. J. Food Eng. 84:194-205.

24Allen, T. 1997. Particle Size Measurement. Vol. 1. Powder Sampling and Particle Size Measurement. 5th edn. Chapman & Hall, London.

25AOAC 1990. Official Methods of Analysis. Association of Official Analytical Chemists, AOAC International, Gaithersburg.

26Bradley, R. L., Arnold, E., Barbano, D. M., Semerad, R. G., Smith,D. E. and Vines, B. K. 1993. Chemical and physical methods. In Marshall, R. T. (ed.). Standard Methods for the Examination of Dairy Products. American Public Health Association, Washington D.C., pp. 433-531.

27Baldwin, A. and Pearce, D. 2005. Milk powder. In Onwulata, C. (ed.). Encapsulated and Powdered Foods. CRC Press, Boca Raton, FL, pp. 387-433.

28Early, R. 1992. Milk powders. In Early, R. (ed.). The Technology of Dairy Products. Blackie and Son Ltd, Glasgow, pp. 167-196.

29Hall, C. W. and Hedrick, T. I. 1975. Drying of Milk and Milk Products. AVI Publishing, Westport, CT.

30Pérez-Muñoz, F. and Flores, R. A. 1997. Particle size of spray-dried soymilk. Appl. Eng. Agric. 13:647-652.

31Carić, M. 2003. Milk powders: Types and manufacture and physical and functional properties of milk powders. In Roginski, H. et al. (eds). Encyclopedia of Dairy Sciences. Academic Press, New York, pp. 1869– 1880.

32Abdullah, E.C. and Geldart, D. 1999. The use of bulk density measurements as flowability indicators. Powder Technol. 102:151- 165.

33A/S Niro Atomizer 1978. Determination of powder bulk density. In Sørensen, I. H. et al. (eds). Analytical Methods for Dry Milk Products. De Forenede Trykkerier A/S, Copenhagen, pp. 18-19.

34A/S Niro Atomizer 1978. Determination of particle density. In Sørensen, I.H. et al. (eds.). Analytical Methods for Dry Milk Products. De Forenede Trykkerier A/S, Copenhagen, pp. 52-53.

35Utsumi, R., Hirano, T., Mori, H., Tsubaki, J. and Maeda, T. 2002. An attrition test with a sieve shaker for evaluating granule strength. Powder Technol. 122:199-204.

36Carr, R. L. 1965. Evaluating flow properties of solids. Chem. Eng. 72:163–168.

37Hausner, H. H. 1967. Friction conditions in a mass of metal powder. Int. J. Powder Metall. 3:7–13.

38Lazghab, M., Saleh, K., Pezron, I., Guigon, P. and Komunjer, L. 2005. Wettability assessment of finely divided solids. Powder Technol. 157:79-91.

39A/S Niro Atomizer 1978. Determination of wettability. In Sørensen, I. H. et al. (eds). Analytical Methods for Dry Milk Products. De Forenede

Trykkerier A/S, Copenhagen, pp. 26-27. 40Knipschildt, M. E. and Andersen, G. G. 1994. Drying of milk and milk

products. In Robinson, R. K. (ed.). Modern Dairy Technology . Vol.1: Advances in Milk Processing. Chapman & Hall, London, pp. 159- 254.

41Early, R. 1998. Milk concentrates and milk powders. In Early, R. (ed.). The Technology of Dairy Products. Blackie Academic & Professional, London, pp. 228-300.

42A/S Niro Atomizer 1978. Determination of dispersibility. In Sørensen, I. H. et al. (eds). Analytical Methods for Dry Milk Products. De Forenede Trykkerier A/S, Copenhagen, pp. 34–35.

43Barbosa-Cánovas, G. V., Ortega-Rivas, E., Juliano, P. and Yan, H. 2005. Food Powders: Physical Properties, Processing, and Functionality. Kluwer Academic/Plenum Publishers, New York.

44Sigmastat for Windows 2004. SigmaStat User’s Guide. Version 3.1. San Jose: Systat Software, Inc.

45Masters, K. 1991. Spray Drying Handbook. 5th edn. Longman Scientific & Technical, Essex.

46Fitzpatrick, J. J. 2005. Food powder flowability. In Onwulata, C. (ed.). Encapsulated and Powdered Foods. CRC Press, Boca Raton, FL, pp. 247-260.

47Fitzpatrick, J. J., Iqbal, T., Delaney, C., Twomey, T. and Keogh, M. K. 2004. Effect of powder properties and storage conditions on the flowability of milk powders with different fat contents. J. Food Eng. 64:435-444.

48Schubert, H. 1993. Instantization of powdered food products. Int. Chem. Eng. 33:28-45.

49Vu, T. O., Galet, L., Fages, J. and Oulahna, D. 2003. Improving the dispersion kinetics of a cocoa powder by size enlargement. Powder Technol. 130:400–406.

50BeMiller, J. N. 2007. Carbohydrate Chemistry for Food Scientists. AACC International Inc., St.Paul, MN, 389 p.

51Lloyd, N. E. and Nelson, W. J. 1984. Glucose- and fructose-containing sweeteners from starch. In Whistler, R. L. and Bemiller, J. N. (eds). Starch: Chemistry and Technology. Academic Press Inc., Orlando, FL, pp. 611-660.

52Takeiti, C. Y., Kieckbusch, T. G. and Collares-Queiroz, F. P. 2008. Optimization of the jet steam instantizing process of commercial maltodextrins powders. J. Food Eng. 86:444-452.

53Armstrong, T. 2010 [updated 2007 Jan 29; cited 2010 Dec 21]. Dextrose/ maltrodextrine/waxy maize starch [Internet]. Available from: http:// forum.dutchbodybuilding.com/f22/dextrose-maltrodextrine-waxy- maize-starch-97339/.

54Shogren, R. and Biresaw, G. 2007. Surface properties of water soluble maltodextrin, starch acetates and starch acetates/alkenylsuccinates. Colloid Surf. A: Physicochem. Eng. Asp. 298:170-176.

55Zheng, M., Jin, Z. and Zhang, Y. 2007. Effect of cross-linking and esterification on hygroscopicity and surface activity of cassava maltodextrins. Food Chem. 103:1375-1379.

56Rohera, B. D. and Zahir, A. 1993. Granulations in a fluidized-bed: Effect of binders and their concentrations on granule growth and modeling the relationship between granule size and binder concentration. Drug Dev. Ind. Pharm. 19:773-792.

57Planinsek, O., Pisek, R., Trojak, A. and Srćić, S. 2000. The utilization of surface free-energy parameters for the selection of a suitable binder in fluidized bed granulation. Int. J. Pharm. 207:77–88.

58Tüske, Z., Regdon, G., Erös, I., Srćić, S. and Pintye-Hódi, K. 2005. The role of the surface free energy in the selection of a suitable excipient in the course of a wet-granulation method. Powder Technol. 155:139–144.

Influence of binder type and concentration on physical ...

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