APPLYING IRANIAN GUM TRAGACANTH TO IMPROVE TEXTURAL PROPERTIES OF MALTODEXTRIN MICROCAPSULES

APPLYING IRANIAN GUM TRAGACANTH TO IMPROVETEXTURAL PROPERTIES OF MALTODEXTRIN MICROCAPSULESMOHAMMAD MAHDI SAFFARI1, MINA FARZI1, ZAHRA EMAM-DJOMEH1,3, SOHRAB MOINI1 andMOHAMMAD AMIN MOHAMMADIFAR2

1Transfer Phenomena Laboratory (TPL), Department of Food Science, Technology and Engineering, University of Tehran, Karadj, Tehran 31587-11167, Iran2Department of Food Science and Technology, Faculty of Nutrition Sciences, Food Science and Technology/National Nutrition and Food TechnologyResearch Institute, Shahid Beheshti University of Medical Sciences, Tehran, Iran

KEYWORDSFlavor, gum tragacanth, maltodextrin,microencapsulation, wall material

3Corresponding author.TEL: +982612248804;FAX: +982612248804;EMAIL: [email protected]

Received for Publication July 2, 2011Accepted for Publication May 8, 2012

doi:10.1111/j.1745-4603.2012.00359.x

ABSTRACT

The effects of adding one of the species of Iranian gum tragacanth, Astragaluscompactus, to maltodextrin solutions used for microencapsulation of 2-methylbutylacetate (water-soluble flavoring compound of strawberry) were studied. Initialemulsions were evaluated regarding rheological behavior and particle size distribu-tion. The resulted microcapsules were also analyzed for particle size distributions,glass transition temperature Tg, the morphology of the capsules and the rate ofrelease from them. The results showed that addition of 0.5% w/w A. compactus gumto maltodextrin solutions (14.5% w/w) can increase the viscosity and Tg to anoptimum level and can prevent stickiness. Also this species of gum tragacanth hadan interesting effect in reducing physical defects of microcapsules and eliminatedruptures significantly. It was also showed that the rate of release of 2-methylbutylacetate decreased by incorporating gum tragacanth in the wall material.

PRACTICAL APPLICATIONS

Microencapsulation is of great interest in preservation of flavoring compounds.One of the most important wall materials is maltodextrin, which has several defectsto protect flavorings. This study proposes the use of a new material, Iranian gumtragacanth from Astragalus compactus, to overcome these defects. It was found thatnew microcapsules did not undergo rupture and could retain the flavoring well.

INTRODUCTION

Nowadays, the role of encapsulation technology in the pro-tection of active and susceptible compounds such as flavors,antioxidants, pigments, pharmaceutical, etc., resulted ingreat attentions toward this technology (Augustin et al. 2001;Heinzen 2002; Madene et al. 2006; Xie et al. 2007). One ofthe most important factors in encapsulation is the choice ofappropriate wall material for the production of the activecompounds (Imagi et al. 1992). Apart from gums (Beristainet al. 2001), whey proteins (Jimenez et al. 2006), sucrose(Kaushik and Roos 2007), natural and modified starches(O’Riordan et al. 2001) and maltodextrins (Righetto andNetto 2006) are some of the involved wall materials.

Krishnan et al. (2005) used maltodextrin besides gumArabic and modified starches for the encapsulation of carda-mom oleoresin and suggested a combination of these com-pounds (1/6, 4/6 and 1/6, respectively). In this study, it wasfound that walls composed of only maltodextrin did not showappropriate retention rate although they were smooth andspherical. Scanning electron microscope (SEM) pictures ofthese microcapsule showed that this phenomenon is due tothe rupture of capsules during spray-drying process. Thisresearch attributed the phenomenon to the disability of mal-todextrins in emulsion stabilization. The authors declaredthat modified starch acts even better than gum Arabic in theretention of mentioned flavor (Krishnan et al. 2005). Never-theless, chemically modified starches have some disadvan-

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Journal of Texture Studies ISSN 1745-4603

12 Journal of Texture Studies 44 (2013) 12–20 © 2012 Wiley Periodicals, Inc.

tages, which make them less suitable for using as a wallmaterial; they are not considered natural for labeling pur-poses, often have an undesirable off-taste and do not affordgood protection to oxidizable flavorings (Qi and Xu 1999).

Kanakdande et al. (2007) studied the encapsulation ofcumin oleoresin in the same wall materials and reported thesame results. Almost in all research it was found that malto-dextrin capsules were disrupted under spray drying and thisdisruption causes the reduction of encapsulation yield(Krishnan et al. 2005; Kanakdande et al. 2007).

With respect to mentioned results, it can be concluded thatmaltodextrin is not a good encapsulating material by itself.The combination of this compound with gum Arabic andmodified starch can result in better capsules, but there are stillsome problems concerning the usage of modified starch andlimited supply of gum Arabic (Krishnan et al. 2005).

For solving the problem of maltodextrin capsules, mainlyrupture, the reasons of this failure should be identified andan appropriate compound that can overcome this problemand that is also acceptable by the consumers should be sug-gested. It should be noted that the disability of maltodextrinsin emulsion stabilization is the only reason which is men-tioned until now (Buffo and Reineccius 2000; Krishnan et al.2005).

Gum tragacanth is a high-quality hydrocolloid on theGenerally Recognized as Safe list (Eastwood et al. 1984;Anderson and Bridgeman 1988; Anderson 1989). Several dif-ferent species exist, each one having a specific characteristic,making it possible to use gum tragacanth as a stabilizer,emulsifier, fat replacer, gelling agent or microencapsulatingagent (Weiping and Branwell 2000; Balaghi et al. 2010).

Gum tragacanth is a polymeric, heterogeneous anioniccarbohydrate with a molecular weight of about 840,000 Da.This highly branched polysaccharide is slightly acidic and isbound with small amounts of protein (Gralen and Karrholm1950; Anderson 1989). Gum tragacanth consists of twofractions: bassorin, which is the swellable part, and tragacan-thin, which is the soluble part (Weiping and Branwell 2000).These fractions differ considerably in their structures. Bas-sorin consists of d-xylose, L-fucose, d-galacturonic acid,d-galactose and a very small amount of L-rhamnose. Thiscomponent has a high molecular weight and a rod-likemolecular shape (Stephen and Churms 1995). Tragacanthinis highly branched in which L-arabinose is the predominantsugar. Tragacanthin has a spheroidal molecular shape. It isassumed that bassorin yields tragacanthin on demethoxyla-tion (Aspinall and Baillies 1963; Stephen and Churms 1995;Weiping and Branwell 2000). It is reported that these com-ponents differ significantly in various species causing differ-ent behaviors under processing conditions (Mohammadifaret al. 2006).

So the aims of this study were to investigate the reasons ofrupture in maltodextrin capsules containing one of the water-

soluble flavoring compounds of strawberry and to use one ofthe species of Iranian gum tragacanth, Astragalus compactus,in order to overcome the problem. It should be noted thatthis species is selected among three species, considering theviscosity and stabilizing effects (Farzi et al. 2011).

MATERIALS AND METHODS

Materials

Iranian gum tragacanth exuded from A. compactus was col-lected during June and July 2009. The raw gum was groundand sieved. Powdered gum with a mesh size between 100 and500 mm was used in this study. The gum contained 11.80%moisture and total ash of 2.5%. The ratio of soluble toinsoluble part of this species was 0.84 and it contained 1.65%protein (Balaghi et al. 2010). Maltodextrin with dextroseequivalent (DE) of 20 was purchased from ApplichemGmbH (Darmstadt, Germany). Commercial sunflower oilfrom the same lot was purchased from the local market. Theemulsifier, polyglycerol polyricinoleate (PGPR), was kindlysupplied by Sakamoto Yakuhin Kogyo Company from Japan.2-Methylbutyl acetate (99%), one of the water-soluble fla-voring compounds of strawberry, was purchased fromSigma-Aldrich Chemie GmbH (Saint Louis, MO).

Preparation of Gum Dispersions

Gum dispersions (total solids: 15% w/w) were prepared byadding 0.5 g of gum tragacanth powder (100–500 mm) and14.5 g of maltodextrin to 85 g of distilled water that had beenheated up to 35C. This mixture was then stirred for 10 min at800 rpm. Sodium azide (100 mgl-1) was added to preventmicrobial growth. The solution was stored at 4C overnight toensure that the hydration of the gum was completed (Farziet al. 2011). The same procedure was followed for the mal-todextrin solutions with 15 g of maltodextrin added to 85 gof distilled water (15% w/w). All of the dispersions contained1.5% of microcrystalline cellulose (Merck, Darmstadt,Germany) as a filler to increase total solids in order to gainmore powder.

Preparation of w/o Emulsions

A solution with 1,000 ppm concentration of 2-methylbutylacetate was prepared. For preparation of primary emulsions,10% w/w of this solution was emulsified in 5% PGPR con-taining oil by ultraturax (IKA T25, Deutschland, Germany)at 24,000 rpm for 5 min. The emulsion was ice coated duringpreparation in order to avoid the increase of temperature.

Production of w/o/w Emulsions

Five percent (w/w) of primary w/o emulsions was homog-enized in gum dispersions for 5 min at 9,600 rpm by ultratu-

M.M. SAFFARI ET AL. APPLYING IRANIAN GUM TRAGACANTH FOR MICROCAPSULES

13Journal of Texture Studies 44 (2013) 12–20 © 2012 Wiley Periodicals, Inc.

rax. Ice coated w/o/w emulsions were sonicated for 45 s at60% power level by an ultrasonic homogenizer (UP200S,Hielscher Ultrasonics GmbH, Teltow, Germany) equippedwith a 13-mm-diameter sonotrode probe made of titaniumthat provided continuous, low frequency ultrasound(24 kHz) with a total nominal output power of 200 W.

Particle Size Analysis

The particle size distributions of emulsions were determinedat room temperature with a laser diffraction particle sizeanalyzer equipped with an accessory Hydro 2000S (MalvernMastersizer 2000 particle analyzer, Malvern InstrumentLimited, Worcestershire, U.K.). Obtained graphs are shownin Fig. 1. Size measurements are reported as the surfaceweighted mean diameter

D n d n di i i i[ , ]3 2 3 2= ∑ ∑ (1)

and volume weighted mean diameter

D n d n di i i i[ , ]4 3 4 3= ∑ ∑ (2)

where ni is the number of particles and di is the diameter.Particle size distributions of powder samples were analyzedby the dry accessory of the same equipment.

Rheological Properties of the Dispersion

Emulsions (25 mL) were subjected to controlled shear ratesbetween 2 and 50 s-1 through a Physica MCR 301 Rheometer(Anton Paar GmbH, Graz, Austria) equipped with a concen-tric cylinder measurement system. The temperature wasadjusted to 20C with a peltier system equipped with fluidcirculator. In order to ensure that each sample had identicalshear histories, the emulsions were presheared at a shear rateof 20 s-1 for 150 s and left standing for 60 s to allow structurerecovery and temperature equilibration. A power law modelwas used to describe the rheological properties of emulsions.

The flow behavior index (n) and consistency coefficient (m)values were obtained by fitting the shear rate versus apparentviscosity to the power law model:

Power law mappn- η γ=( )−� 1 (3)

in which happ is the apparent viscosity (Pa·s), m is theconsistency coefficient (Pa.), g is shear rate (s-1) and n is theflow behavior index (dimensionless).

Preparation of Microcapsules bySpray Drying

The resulting emulsions were spray dried in a Büchi-190model mini spray dryer (Büchi, Flawil, Switzerland) (insidechamber dimension: 100 cm height, 60 cm diameter)equipped with 0.5-mm-diameter nozzle. The pressure ofcompressed air for the flow of the spray was adjusted to5 bars. The inlet and outlet temperature was maintained at190 and 92C, respectively, and feed rate was 350 g/h. Themicrocapsules prepared were collected and filled in airtightsealable glass container and stored in a refrigerator untilfurther studies.

Scanning Electron Microscopy

Morphology and structure of spray-dried microcapsuleswere evaluated with SEM (LEO 1455VP, Oxford, U.K.). Themicrocapsules were mounted on specimen stubs withdouble-sided adhesive carbon tapes. The specimen wascoated with gold-palladium and examined at 10 kV.

Differential Scanning Calorimetry

A differential scanning calorimeter (DSC, Perkin-ElmerPyris 6, The Perkin-Elmer Corporation, Norwalk, CT) wasused to determine the glass transition temperature of themicrocapsules (Tg). The temperature calibration was per-formed using the melting points of indium (156.6C) and

FIG. 1. PARTICLE SIZE DISTRIBUTIONS FOREMULSIONS CONTAINING MALTODEXTRIN(15%) AND MALTODEXTRIN (14.5%) + GUMTRAGACANTH (0.5%)

APPLYING IRANIAN GUM TRAGACANTH FOR MICROCAPSULES M.M. SAFFARI ET AL.


deionized water (0C). Sealed 20-mL aluminum pans wereused for measurements; an empty pan was used as the refer-ence. DSC pans were filled with powder in an environment ofnitrogen gas to prevent moisture adsorption prior to meas-urement. Heating rate of 10C/min was employed, startingfrom -20C, reaching 250C and retuning to 0–20C. Measure-ments were made in triplicate.

Gas Chromatography Headspace Analysis

Each sample was analyzed after 1 and 24 h using theheadspace solid-phase microextraction (HS-SPME) (staticHS-SPME) method, and the compounds were analyzed bygas chromatography (GC).

Divinylbenzene/polydimethylsiloxane (DVB/PDMS) fiber,50/30 mm film thickness bonded to a flexible fused silica core(Supelco, Bellefonte, PA), was selected for extractions. SPMEwas carried out with a commercially accessible fiber housed inits manual holder (Supelco).

One gram of powder was fitted with a self-sealing septum.SPME syringe (bearing a fiber) was introduced and main-tained in the HS. The samples were equilibrated for 30 min at25C. Then the fiber coating was exposed to the HS for 30 minat 50C. Finally, the fiber was inserted for 5 min into theinjection port of the GC (splitless mode) adjusted to 250C forvolatile-compound desorption. The absorbed volatile com-pounds were analyzed by an Agilent HP 6890N gas chroma-tograph (Agilent Technologies, Palo Alto, CA) equipped withan Agilent 5973N mass selective detector. The ionizationenergy was set at 70 eV. The detector was operated in theselected ion monitoring mode, scanning 43, 55, 70, 73 and130 m/z. Chromatographic data were recorded with HPChemstation software (Agilent Technologies, Inc. Life Sci-ences and Chemical Analysis Group, Santa Clara, CA) usingthe Wiley 275 mass spectral library. A DB-Wax capillarycolumn (30 m ¥ 0.25 mm internal diameter, 0.5 mm film

thickness) was used (Supelco). Helium (>99.999% pure) wasused as a carrier gas at a flow rate of 1.2 mL/min. The GC oventemperature program was as follows: initial temperature of45C for 1 min, then up to 260C with a heating rate of 10C/minand then was maintained 5 min at that temperature. Selectionof masses was performed by two methods: (1) injection ofcommercial reference compound produced by Sigma-AldrichChemie GmbH and (2) comparison of mass spectra withthose mentioned in the National Institute of Standards andTechnology and Wiley 275 mass spectral libraries.

Statistical Analysis

All the experiments were performed in triplicate and the datawere expressed as the mean values � standard deviation.

RESULTS AND DISCUSSION

Emulsion Characteristics

Rheological tests showed that the emulsions containing mal-todextrin had Newtonian behavior and very low viscosity(Fig. 2), so it is not expected that maltodextrin couldproduce stable emulsion that can tolerate the shear forcesin spray dryer. By adding 0.5% w/w gum tragacanth to theaqueous phase of maltodextrin-containing emulsions, theviscosity increased significantly (from 3.3 to 120 mPa·s)(Table 1) and the flow behavior became shear thinning(Fig. 2). Thus, it is expected that by increasing the viscosity ofcontinuous phase, gum tragacanth can stabilize the emulsionagainst flocculation and also gravitational separation.

Studying the particle size of emulsions just after produc-tion, it was found that D3,2 and D4,3 in emulsions containinga mixture of maltodextrin and gum tragacanth were slightlyhigher than maltodextrin-containing emulsions (Table 1). Itis because of the higher molecular weight of gum tragacanth

FIG. 2. CHANGES IN SHEAR STRESS WITHSHEAR RATE IN EMULSIONS CONTAININGMALTODEXTRIN (15%) AND MALTODEXTRIN(14.5%) + GUM TRAGACANTH (0.5%)



and its capability to form a layer around the dispersedparticles in emulsion and so stabilizing the larger particlesas well.

Powder Characteristics

During spray drying of emulsions, it was notable that theproduction of powder from maltodextrin-containing emul-sions was accompanied by partial sticking to the spray dryerchamber and so the powder yield was low. Adding gum tra-gacanth to the emulsion resulted in decreasing this stickingand dripping and consequently increasing powder yield(Fig. 3).

Particle Size of Powder

Comparing the particle size of maltodextrin-containingpowders to those containing maltodextrin and gum traga-canth revealed that there was just a slight difference betweenthem. Powders containing only maltodextrin had slightlylarger particles because of sticking to each other during spraydrying (Table 1).

Glass Transition Temperature

Glass transition temperature (Tg) is a critical factor that playsan important role in stickiness of microcapsules (Roos andKarel 1990). Wall materials become rubbery at their Tg pointsand stick to other capsules or surfaces during the spray-drying process. This stickiness inhibits powder production.Apart from that, the resulted microcapsules tear due to adhe-sion and this can decrease the protective effect on core mate-rial. So Tg is one of the most important factors that should betaken into consideration during microencapsulation.

Our results showed that with addition of gum tragacanthto maltodextrin solutions, it will be possible to use high-DEmaltodextrins as gum tragacanth with Tg of 126.5 increasesthe Tg of maltodextrin capsules from 57 to 97.5 (Fig. 4),which indeed result in a powder with lower stickiness andrupture in comparison with maltodextrin capsules.

As Krishnan et al. (2005) mentioned for intact maltodex-trin capsules, the retention of flavor compound increaseswith the increase of DE of maltodextrin, but on the otherhand Tg decreases (Roos and Karel 1991), which meansimproper drying of compounds in the spray dryer. When theTg of maltodextrin is low, atomized particles in spray dryerstick to each other and to the spray dryer chamber and

TABLE 1. CHRACTERISTICS OF EMULSIONSAND MICROCAPSULES CONTAININGMALTODEXTRIN ANDMALTODEXTRIN + TRAGACANTH

Wall material

ParameterMaltodextrin(15% w/w)

Maltodextrin (14.5%w/w) + gum tragacanth(0.5% w/w)

D3,2 of emulsions (mm) 1.85 � 0.008 2.28 � 0.006D4,3 of emulsions (mm) 2.73 � 0.006 15.67 � 0.007m 0.003 � 0.0005 0.68 � 0.097n 0.99 � 0.0025 0.57 � 0.097h50 (mPa·s) 3.3 � 0.0024 120 � 0.098D3,2 of powders (mm) 4.6 � 0.019 4.4 � 0.014Tg point (C) 57.2 � 0.87 97.5 � 0.59

A

B

FIG. 3. SPRAY DRYING OF EMULSION CONTAINING(A) MALTODEXTRIN AND (B) MALTODEXTRIN + TRAGACANTHSticking can be seen obviously in maltodextrin-containing emulsions(A). Adding gum tragacanth could overcome this problem (B).



FIG. 4. THERMOGRAMS OF MICROCAPSULES CONTAINING (A) MALTODEXTRIN AND (B) MALTODEXTRIN + TRAGACANTH



disrupt and release the core material. This can result in theincrease of ruptured capsules and reduction of encapsulationyield. Although using low-DE maltodextrin decreases thenumber of ruptured capsules, the formed wall cannot retainthe core material as high-DE maltodextrins do.

Morphological Properties of Microcapsules

For the flavor retention ability of capsules, characteristicssuch as spherical shape and smooth surface are quite impor-tant. As a matter of fact, the ratio of surface area to volume insphere geometry is lower than for other geometric shapes,and the lower the surface area is, the better the flavor reten-tion in microcapsules is; thus, the best microcapsule is themost spherical one (Varavinit et al. 2001; Buffo et al. 2002).

SEM images from microcapsule powder showed thatmicrocapsules made using maltodextrin as wall materialwere completely spherical and their surfaces were smoothwithout any groove (Fig. 5a), but similar to what have beenreported by Varavinit et al. (2001), too many of these micro-capsules were disrupted during drying (Fig. 5b). These rup-

tures seem to be due to the low Tg of maltodextrin as wallmaterial and lack of emulsification ability of this wall mate-rial, which results in significant reduction in encapsulationefficiency and so significant release of core material duringdrying.

There were no changes in spherical shape and smoothsurface of microcapsules when tragacanth gum was addedto maltodextrin as the combined wall material (Fig. 5c).However, the number of ruptured microcapsules afterdrying was decreased significantly. In microscopic images, noruptured microcapsules could be observed (Fig. 5d).

It can be logically deduced that the obvious rupture reduc-tion is resulted from tragacanth gum in addition to malto-dextrin as combined wall material and this effect oftragacanth gum results from its role in emulsion stabilizationand increasing Tg of the combined wall material.

Flavor Release

Analyzing samples by HS GC/MS for the release of2-methylbutyl acetate from different microcapsules, it was

FIG. 5. SEM PICTURES OF MICROCAPSULES CONTAINING MALTODEXTRIN (A AND B) AND MALTODEXTRIN + TRAGACANTH (C AND D).PICTURES A AND C ¥5,000 AND PICTURES B AND D ¥1,000

Shows Ruptures in Microcapsules. EHT, extra high tension; SE1, secondary electrons 1; SEM, Scanning Electron Microscope; WD, wavelengthdispersive.



revealed that microcapsules containing gum tragacanthretain better the flavoring agent. As can be seen in Fig. 6, therates of release were slower after 1 and 24 h in the case ofmicrocapsules containing gum tragacanth. It could also indi-cate that with the addition of gum tragacanth to maltodex-trin microcapsules, it will be possible to gain better retentionof flavors as more microcapsules remain intact.

CONCLUSION

This study showed that reasons of rupture in maltodextrinmicrocapsules include its disability in emulsion stabilizationand low Tg and stickiness in spray dryer chamber, whichcauses too many ruptures in microcapsules. By the additionof 0.5% w/w A. compactus gum to maltodextrin solutions(14.5% w/w), the viscosity of double emulsion increasedsignificantly and the flow behavior became shear thinning.Thus, gum tragacanth could stabilize the emulsion duringspray drying. The resulted powders had smaller particle size.Also addition of gum tragacanth increased Tg to an optimumlevel, prevented stickiness and physical defects of microcap-sules and eliminated ruptures significantly. It was showedthat the rate of release of 2-methylbutyl acetate decreasedby incorporating gum tragacanth in the wall material. Allof these observations suggested the use of A. compactus gumfor improving encapsulation properties of maltodextrins.

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FIG. 6. FLAVOR RELEASE FROM MICROCAPSULES CONTAINING MALTODEXTRIN AND MALTODEXTRIN + TRAGACANTH AFTER 1 AND 24 H



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APPLYING IRANIAN GUM TRAGACANTH TO IMPROVE TEXTURAL PROPERTIES OF MALTODEXTRIN MICROCAPSULES