Double Enapsulated Flavour

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968 JOURNAL OF FOOD SCIENCE Vol. 67, Nr. 3, 2002 2002 Institute of Food Technologists

JFS: Food Chemistry and Toxicology

Characteristics of Double-EncapsulatedFlavor Powder Prepared bySecondary Fat Coating Process Y.H. CHO AND J. P ARK

ABSTRACT: Double encapsulation of single-encapsulated powder containing flavor compounds was performed by a fat coating process using molten hydrogenated palm kernel oil (melting point = 47.3 C). Double-encapsulatedpowder showed a 47% increase in mean particle size and a 33% reduction in moisture uptake. Single-encapsulatedpowder exhibited rapid limonene oxidation throughout the storage time, while double-encapsulated powder wasconsistently stable. SEM images of the double-encapsulated powder showed singular or aggregated particles covered with a continuous fat matrix. Thermally controlled release from the double-encapsulated powder was observed.Flavor release from the double-encapsulated powder ranged from 36.6% to 57.8% at 37 C, with an increase to 81.3to 95.0% at 60 C.

Keywords: double encapsulation, fat coating, flavor, controlled release

Introduction

ENCAPSULATION HAS BEEN USED : (1) TO PROTECT FLAVOR FROMoxidation caused by heat, light, humidity, and other sub-stances over a long shelf life; (2) to prevent evaporation of vola-tile components; and (3) to convert flavor in liquid form to solidform (Kenyon and Anderson 1988; Shahidi and Han 1993). Hy-drocolloids, such as starch, dextrin, maltodextrin, gum arabic,and gelatin are commonly used as wall materials. Products of thistype used in encapsulation retain a good flavor profile and are

easy to handle. However, they are water-soluble, suffer from fla-vor loss under long-term storage, and may release flavor too rap-idly in some applications (Sparks and others 1995). To solvethese problems, it has been customary to coat spray-dried pow-der, or some other solid form of the flavor, with fat or wax. The fatcoating is commonly performed using a fluidized bed coating orspray chilling. When spray-dried powder is used as the core ma-terial, the process is called double encapsulation (Tan 1991). Thecoating must be applied as a film with a uniform thickness suffi-cient to provide a barrier against degradative factors such asmoisture, pH change, temperature change, and reactive chemi-cals (Churukuri 1990).

In some cases, melting of the coating material can be used asa release method. Thermally controlled release of flavor com-pounds is a characteristic property of secondary fat coated flavorpowder (Li and Reineccius 1995). Controlled release is a noveltechnology that can be used to increase the effectiveness of many ingredients and is defined as a method by which 1 or moreactive agents or ingredients are made available at a desired site,at a specific time, and at a specific rate. With the emergence of controlled-release technology, heat-, temperature-, or pH-sensi-tive additives can be conveniently used in food systems (Po-thakamury and Barbosa-Canovas 1995).

Many patents relating to the multiple encapsulation systemusing hydrogenated oil and waxes have been granted (Zibell1989; Cherukuri and others 1990, 1991; Tan and others 1991;King and others 1996). The major area of application for these

patents is sustained or controlled release of sweeteners and fla-

vors for chewing gum. Li and Reineccius (1995) described a sec-ondary fat coating process for use as an ingredient in microwavefrozen pancakes. However, no published research has referred tothe physical properties and structures of double-encapsulatedpowders. Onwulata and others (1998) investigated the character-istics of double-encapsulated powder containing anhydrousbutter oil, but lacking flavor compounds.

The objectives of this study were to investigate the physicalproperties and microstructure of double-encapsulated powder

containing flavor compounds, leading to a comparison with thesingle-encapsulated powder, and to observe the characteristicsof melting-activated flavor release from double-encapsulatedpowder.

Materials and Methods

Flavor model systemFive flavor compounds were selected based on boiling points

(90 to 200 C) and molecular weights (MW 100 to 140 Da). Thesecompounds were ethyl propionate, butyl acetate, 2-heptanone,limonene, and octanol-1. All were purchased from Sigma Co. (St.Louis, Mo., U.S.A.). These flavor components were mixed withrapeseed oil (1 part flavor: 4 parts oil).

Wall materialsThe carbohydrate wall system consisted of a mixture of malto-

dextrin (DE = 15, Sewon Co., Seoul, Korea), gum arabic (TICGums, Belcamp, Md., U.S.A.), N-Lok (National Starch and Chem-ical Co., Bridgewater, N.J.,U.S.A.), and gellan gum (Kelco, SANDIEGO, CALIF., U.S.A.) at a ratio of 30 : 26.4 : 39.6 : 4 (Cho andothers 1999). Hydrogenated palm kernel oil (melting point =47.3 C) was used as a coating fat.

Emulsion and microcapsule preparation Wall material was weighed and reconstituted in distilled water

at a 30% w/v concentration using a homomixer (Model 2.5 spec,

Tokushu Kikka, CITY?Japan). The coarse emulsion was prepared


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Characteristics of double-encapsulated flavor powder . . .

by blending the core/wall (1:4) mixture for 10 min at 10,000 rpm with a homomixer. The mixture was then homogenized at 20 MPausing a piston-type homogenizer (Rannie, APV, Albertslund,Denmark). This emulsion was spray-dried in a disk-type spray dryer (L-8, Ohkawara Kakohki, Yokohama, Japan) at an air inlettemperature of 180 C (outlet temperature = 100 C) and a nozzlespeed of 15,000 100 rpm. Double-encapsulated powder wasprepared from single-encapsulated powder by the secondary fat

coating process. The hydrogenated palm kernel oil was melted at50 C. Single-encapsulated powder prepared as above was putinto the coating chamber of a flow coater (Cheil Mechanical Co.,Seoul, Korea). Molten hydrogenated palm kernel oil was atom-ized through nozzles into the chamber, while single-encapsulat-ed powders were suspended in upward-moving stream of air.The double-encapsulated powder coated with hydrogenated oil was hardened by cool air.

Total oil determinationThe total oil content of the single-encapsulated powder was

determined using a Clevenger trap (Reineccius and others 1995).Single-encapsulated powder (30 g) was dispersed in 200 mL of distilled water in 500 mL flat-bottomed flask. The Clevenger trapand a water-cooled condenser were fitted into the top of the boil-ing flask and distilled for 2 h. The volume of oil collected in thetrap was directly read from oil collecting arm of the Clevenger ap-paratus and multiplied by a density factor of 0.9 g/mL to calcu-late the weight of oil recovered from the sample.

Surface oil determinationThe surface oil content of the single-encapsulated powder

was determined using a Soxhlet extraction apparatus according to the method of Reineccius and others (1995). A Hewlett Pack-ard 6890 gas chromatograph equipped with a flame ionizationdetector was used for detection. Separation was achieved on a 25m 0.32 mm I.D. 0.17 m Ultra II column (Hewlett-Packard,

Wilmington, Del. , U.S.A.). The oven temperature was held at35 C for 5 min, and then increased at 10 C/min to 180 C. Theinjection port and detector were maintained at 200 and 250 C,respectively. Hydrogen was used as a carrier gas at a column flow rate of 1 mL/min. Each flavor compound (0.2 mL) was mixed with

200 mL of pentane in a 500 mL flask and evaporated as above, foruse as an external standard.

Determination of the amount of coating fatThe extractable fat content of double-encapsulated powder

was determined according to the method of Li and Reineccius(1995). Double-encapsulated powder (2 g) was placed in an ex-traction thimble. The thimble containing powder was weighed.

Extraction was done in a Soxhlet extractor with petroleum ether(150 mL) for 3 h. The thimble was dried in an air-drying oven at80 C for 1 h. The thimble and its contents were weighed to calcu-late the fat content and the percent fat in the powder was calcu-lated.

Moisture contentThe AOAC (32.1.03., 1995) method for flour was used for mois-

ture determination. All samples were analyzed in duplicate.

Moisture uptakeEach powder was placed in a petri dish and weighed. The

moisture uptake of the powder was determined at 25 C and 80%relative humidity in an incubator (KCL-1000, Eyela, Tokyo, Ja-pan). Measurements were carried out in duplicate.

Particle sizeSingle-encapsulated powder was dispersed in ethanol. The

particle distribution and mean particle size were analyzed using a particle size analyzer (Analysette 22, Fritsch, Idar Oberstein,Germany). Double-encapsulated powders were dispersed in dis-tilled water and analyzed as above. Measurements were made intriplicate.

Microstructural propertiesScanning electron microscopy (S-4200, Hitachi, Tokyo, Japan)

was used to investigate the microstructural properties of single-

and double-encapsulated powders. Microencapsulated speci-mens were loaded onto a specimen stub with two-sided adhesivetape. Specimens were subsequently coated with gold by ionsputter ( 1030, Hitachi). For study of internal particle structure,encapsulated powders were frozen at 20 C for 1 h, then broken

Figure 1Particle size distribution of encapsulated flavor powders. : single-encapsulated powder, : double-encap-

sulated powder.

Figure 2Moisture uptake of single- and double-encapsu-lated powders at 25 C, 80% RH. : single-encapsulated

flavor powder, : double-encapsulated flavor powder.


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with tweezers.

Oxidative stability Each microencapsulated powder was stored in an incubator

at 37 C. Every 7 d, 0.3 g of powder was withdrawn and dissolvedin 10 mL of HPLC grade water in a 50 mL centrifuge tube. Thecentrifuge tubes were sealed and shaken vigorously for 1 min us-ing a vortex mixer. The tubes were then stored at 60 C for 1 h.HPLC grade pentane (5 g) containing 1 mg of nonane as an inter-nal standard was added to each tube, then the tubes were shak-en as before. The tubes were transferred to a shaking incubatorand maintained at 40 C for 1 h, then centrifuged for 10 min at3000 g (Union 55R, Hanil Co., Inchon, Korea). The clear super-natant layer (1 L) was analyzed by GC for determination of thesurface oil. The formation of limonene 1,2-epoxide from L-limoneduring 37 C storage was measured as an indicator of oxidativestability in the single- and double-encapsulated powders.

Determination of flavor release from double-encapsulated powder

A manual solid phase microext raction (SPME) fiber holderand a 100 m polydimethylsiloxane coated fiber were used (Su-

pelco, Bellefonte, Pa., U.S.A. ). Sample (1.5 g) was weighed into a50-mL headspace vial and 28.5 mL of distilled water was added.The vial was sealed with a Teflon-coated septa and an aluminumcap. The samples incubated at 37 C for 1 h and 60 C for 1 h be-fore analysis. The vial was immersed in a 30 C water bath. AnSPME needle was inserted through the septum and the SPME fi-ber was allowed to equilibrate for 15 min with sonication. TheSPME fiber was exposed in the GC inlet (250 C) for 15 s during the desorption step.

Results and Discussion

Composition and properties of single- and double-encapsulated powders

The measured composition and properties of single- and dou-ble-encapsulated powders are shown in Table 1. The tota l oil re-tention and surface oil content of single-encapsulated powder were 61.3% and 5.12 mg/100 g, respectively. The amount of coat-ing fat of double-encapsulated powder was 31.5%. Moistureanalysis results showed that the percent moisture content in sin-gle-encapsulated powder remained approximately 1%. Double-encapsulated powder had higher moisture content, which may be due to the absorption of moisture from the environment dur-ing secondary fat coating process. Onwulata and others (1998)also observed higher moisture content in the double-encapsu-lated powder. The particle size distribution of double-encapsu-lated powder was measured and compared to the distribution of

single-encapsulated powder (Figure 1). There was a 47% increase

in the mean particle size in the double-encapsulated powder.The single-encapsulated powder had a narrower particle sizerange with a relatively uniform distribution, while the double-encapsulated powder showed a broader size range. These resultsagree with Onwulata and others (1998). The larger particle size of double-encapsulated powder is due to the aggregation of single-encapsulated powder grains within the fat matrix. Smaller parti-cles may be a fragment of fat.

The moisture uptake rate of encapsulated powders (Figure 2)increased rapidly, and then remained constant. Double-encap-sulated powder absorbed much less moisture than single-encap-sulated powder. Double-encapsulated powder is more efficientas a moisture barrier and for moisture sorption. This functional-ity enhances the benefits of encapsulation for storage stability against moisture and light.

Oxidative stability Limonene was selected from among several flavor com-

pounds to use as an indicator of oxidative stability. Limonene is 1of the most abundant hydrocarbons found in essential oils, butits main drawback is a tendency to oxidize (Arctander 1969).

When orange peel o il is stored at elevated temperature the 2oxidation products of limonene, limonene-1, 2-epoxide and car-vone appear during storage. Since limonene-1, 2-epoxide andcarvone are the earliest compounds observed during oxidation,they were used as indicators of oil oxidation (Anandaraman andReineccius 1986). The results of limonene oxide formation forsingle- and double-encapsulated powders observed up to 20 wk at 37 C are shown in Figure 3. Single-encapsulated powder ex-hibited limonene-1, 2-epoxide formation after 7 wk. The forma-tion rate of limonene oxidation in single-encapsulated powder was much faster than for double-encapsulated powder. Similarresults were observed for the formation of carvone during stor-age, although with a lesser amount and a slower formation rate(data not shown). The rate of limonene oxidation is a function of

several factors, including water activity, availability of oxygen,

Table 1 Composition and properties of single- and double-encapsulated powders

Single- Double-

Total oil retention (%) 61.3 nmSurface oil content (mg/100g) 5.12 nmCoating amount (%) nm 31.5Moisture content (%) 1.20 1.80Particle size mean (m) 30.7 45.2Particle size range (m) 15.2 - 43.5 0.67 - 94.4nm: not measured.

Figure 3 Changes in concentration of limonene 1,2-ep-oxide formed from encapsulated flavor powders duringstorage at 37 C. : single-encapsulated flavor powder, :

double-encapsulated flavor powder.


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trace mineral composition, and the presence of antioxidants(Kim and Morr 1996). The coating of fat acts as a barrier so thatthe rate of limonene oxide formation in double-encapsulatedpowder is reduced.

Microstructural propertiesSEM images of single-encapsulated powder grains showed

relatively spherical and smooth particles (Figure 4A). Formationof particles with dented surfaces may be due to rapid shrinkageof the liquid droplets during the early stage of the drying process(Kim and Morr 1996. Double-encapsulated powder grains weretypically singular or aggregated particles (Figure 4B). A highermagnification micrograph of double-encapsulated powdergrains shows that a fat matrix was formed around the single-en-capsulated powder particles (Figure 5). According to Onwulataand others (1998), double-coated powder can be a simple orcompound powder with more than 1 particle encased within thefat matrix. This explains the wider particle size distribution fordouble-encapsulated powder.

The interior structure of the particle wall in single-encapsulat-

Figure 4 SEM micrograph of encapsulated flavor powder. A: single-encapsulated f lavor powder at 200 , B: double-encapsulated flavor powder at 100 .

Figure 5 A high magnification SEM micrograph of double-

encapsulated flavor powder grains at 2000 .

Figure 6 SEM micrograph of shattered particles. A: single-encapsulated flavor powder at 2,000 , B: double-encap-sulated flavor powder at 2,000 .


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ed powder shows a porous wall of < 6 m thickness (Figure 6A).Flavor compounds were dispersed in the capsule wall as smalldroplets of < 2 m dia. A large void was observed in the center of the capsule. This typical structure has been observed in spray-dried microcapsules by several investigators (Rosenberg andothers 1990; Sheu and Rosenberg 1995). Formation of the void isrelated to expansion associated with temperature increase with-in the capsule during the late stages of drying. Fractured parti-

cles of simple, double-encapsulated powders show a porous wallof thickness < 7.5 m covered by a coating of fat (Figure 6B).

Thermal release According to Sparks and others (1995), and in agreement with

our results, coated particles may be efficiently stored at temper-atures below the melting point of the coating material, and areprotected from release in water for a certain period of time during mixing and preparation. However, the flavor can be released dur-ing cooking. As shown in Figure 6, flavor release from double-en-capsulated powder ranged from 81.3% to 95.0% when the tem-perature exceeded the melting point of the coating fat. Flavorcompounds are quickly released when the coating fat melts at ahigh temperature and the double-encapsulated powder is dis-solved in water. However, since the incubation time is too short,flavor release from the dissolved powder does not reach 100%.Flavor release is retarded (36.6 to 58.8%) at an incubation tem-perature lower than the melting point. This result indicated thatthe coating was not complete, allowing some of double-encapsu-lated powder particles to dissolve in water. Consequently the fla-vor release at 37 C from double-encapsulated powder wasgreater than expected.

Conclusion

DOUBLE-ENCAPSULATED POWDERS HAVE A HIGHER RESISTANCE TOmoisture and oxygen than single-encapsulated powders, asparticles were encased within the fat matrix. It indicated that asecondary-fat coating could be used as an effective method forprotecting sensitive ingredients. Melting-activated release fromencapsulated powders was achieved by the secondary-fat coat-ing process. The melting-activated release system is applicablein the food industry since many foods such as microwave foodsand hot drinks are heated prior to consumption and thus, ingre-dients can be protected until their final use.

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fensbergskeEtablissement. p 1800.Cherukuri SR, Mansukhani G, inventors; Warner-Lambert Co., assignee. 1990.

Multiple encapsulated sweetener delivery system. U.S. patent 4,933,190.Cherukuri SR, Chau TL, Raman KP, Orama AM, inventors; Warner-Lambert Co.,

assignee. 1991.Multiple encapsulated flavor delivery system and method of preparation. U.S.

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King CK, Tan CT, Scharpf LG, O Chat DP, Schulman M, inventors; InternationalFlavors & Fragrances Inc., assignee. 1996. Fluidizing spray chilling system forproducing encapsulated materials. U.S. patent 5,525,367.

Kim YD, Morr CV. 1996. Microencapsulation properties of gum arabic and sever-al food proteins: Spray-dried orange oil emulsion particles. J Agric Food Chem44(5):1314-1320.

Li HC, Reineccius GA. 1995. Protection of artificial blueberry flavor in microwave frozen pancake s by spray drying and seco ndary fat coating processes.In: Risch SJ, Reineccius GA, editors. Encapsulation and controlled release of food ingredients . ACS symposium series 590. Illinois: American ChemicalSociety. p 181-186.

Onwulata CI, Konstance RP, Holsinger VH. 1998. Properties of single- and dou-ble-encapsulated butteroil powders. J Food Sci 63(1):100-103.

Pothakamury UR, Barbosa-Canovas GV. 1995. Fundamental aspects of controlledrelease. Trends in Food Sci Technol 6:397-406.

Reineccius GA, Ward FM, Whorton C, Andon SA. 1995. Developments in gumacacias for the encapsulation of flavors. In: Risch SJ, Reineccius GA, editors.Encapsulation and controlled release of food ingredients . ACS symposiumseries 590. Illinois: American Chemical Society. p 161-168.

Rosenberg M, Kopelman IJ, Talmon Y. 1990. Factors affecting retention in spray-drying microencapsulation of volatile materials. J Agric Food Chem 38:1288-1294.

Sparks RE, Jacobs IC, Mason NS. 1995. Centrifugal suspension-separation forcoating food ingredients. In: Risch SJ, Reineccius GA, editors. Encapsulationand controlled release of food ingredients . ACS symposium series 590. Illi-nois: American chemical society. p 87-95.

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Sheu TY, Rosenberg M. 1995. Microencapsulation by spray drying ethyl capry-late in whey protein and carbohydrate wall systems. J Food Sci 60(1):98-103.

Tan CT, Kang YC, Sudol MA, King CK, Schulman M, inventors; International Fla-vors & Fragrances Inc., assignee. 1991. Method of making controlled releaseflavors. U.S. patent 5,064,669.

Zibell SE, inventor; Wm Wrigley Jr Co., assignee. 1989. Method of making chew-ing gum with wax-coated delayed release ingredients. U.S. patent 4,885,175.

MS 20010160 Submitted 3/31/01, Revised 6/18/01, Accepted 6/19/01, Received1/28/02

Authors are with Dept. of Biotechnology, Yonsei Univ., Seoul 120-749, Korea.Direct inquiries to author Park (E-mail: [email protected]).Figure 7 Flavor release from double-encapsulated flavor powder incubated at 37 C ( ) and 60 C ( ).

Double Enapsulated Flavour

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