Abstract Microencapsulation of supercritical CO2 ex-tracted caraway fruit oil was investigated. Encapsulationwas carried out by molecular inclusion with -cyclodex-trin, by spray-drying with maltodextrin and by spray-drying with a starch derivative. Carvone, one of the twomain constituents of caraway essential oil, was efficient-ly complexed with -cyclodextrin. Only half of the othermajor constituent, limonene, was complexed. The inclu-sion complex seemed to protect volatile substances moreefficiently during storage, whereas microcapsules withmodified starches as wall material were more heat toler-ant. During rapid heating, the -cyclodextrin microcap-sules protected the volatile substances from evaporationup to 100 C and HiCap microcapsules protected themup to 140 C, while the protection properties of the mal-todextrin microcapsules seemed to depend on the encap-sulated molecules (160 C for limonene and 120 C forcarvone).

Keywords Caraway Microencapsulation Cyclodextrin Starch derivatives

Introduction

Encapsulation of flavours can be used to protect volatilecompounds from evaporation as well as from off-flavourdevelopment during storage [1]. Encapsulation can eitherbe based on wall formation or on molecular inclusion bycomplexation with, e.g. cyclodextrins. Typical wall poly-

mers are hydrolysed starches with emulsifiers, and starchderivatives with hydrophobic substituents. Recently, -cyclodextrin was approved for use in food by the FDA[2], which has increased the interest in its food-relatedapplications.

As the mechanism of encapsulation is different in cy-clodextrins and in starch-based wall materials, it is ex-pected that protection and release of the encapsulatedcompounds would also differ. In complexation, the fla-vour load is limited by stoichiometry to around 10%,whereas spray-dried powders may contain more than20% flavour compounds [1]. -Cyclodextrin is reportedto be superior to starches in humid conditions and, also,to be more thermo-stable [2].

The encapsulation of limonene has been extensivelystudied. The stability of limonene has been used to esti-mate the level of protection against oxidation in thespray-drying of orange oil [3, 4, 5]. Yoshii et al. [6, 7, 8]and Furuta et al. [9, 10, 11, 12] have investigated com-plex formation between limonene and cyclodextrins bykneading at low water content. The other major com-pound of caraway essential oil, carvone, is a biologicallyactive sprout-inhibitor [13, 14]. Thus, caraway essentialoil is also used in addition to food ingredients in potatostores to retard sprouting.

The aim of this study was to protect volatile com-pounds of supercritical CO2 extracted caraway fruit oilfrom evaporation by microencapsulation. The propertiesof microcapsules achieved by different procedures andwall materials are compared and the role of molecularinclusion will be discussed.

Materials and methods

Materials. Caraway fruit oil (type 5737.090) extracted by super-critical CO2 was a mixture of essential oils and triacylglycerol(9:1) purchased from Flavex Naturextrakte GmbH (Rehlingen,Germany). Kleptose -cyclodextrin was purchased from Roquette(Lestrem, France). Limonene and carvone were obtained fromFluka Chemie AG (Buchs, Switzerland). Maltodextrin with dex-trose equivalent 18.5 was purchased from Cerestar (Neuilly-sur-

R. Partanen ( ) P. ForssellVTT Biotechnology, Tietotie2, P.O. Box 1500, FIN-02044 VTT, Espoo, Finlande-mail: Riitta.Partanen@vtt.fi

M. AhroDepartment of Applied Physics, FIN-20014 University of Turku, Finland

M. Hakala H. KallioDepartment of Biochemistry and Food Chemistry, FIN-20014 University of Turku, Finland

Eur Food Res Technol (2002) 214:242247DOI 10.1007/s00217-001-0446-1

O R I G I N A L PA P E R

Riitta Partanen Mikko Ahro Mari HakalaHeikki Kallio Pirkko Forssell

Microencapsulation of caraway extract in -cyclodextrin and modified starches

Received: 10 July 2001 Revised version: 12 October 2001 / Published online: 24 November 2001 Springer-Verlag 2001

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Seine, France). As an emulsifying starch, sodium octenyl succi-nate derivative HiCap 100 from National Starch & Chemical(Manchester, United Kingdom) was used. The dextrose equivalentof the emulsifying starch was between 32 and 37. Gum arabic(26,0770) was purchased from Aldrich (Milwaukee, USA) andother chemicals of analytical grade were obtained from varioussources.

Complex formation of -cyclodextrin with limonene, carvone andcaraway fruit extract. -Cyclodextrin (10 wt%) was solubilised inwater at 65 C. Carvone, limonene or the caraway extract wereadded at the level of 12% volatile substances per dry weight. Thesolutions were allowed to cool at room temperature with magneticstirring and kept at +6 C overnight for complete precipitation.The solutions were filtered or centrifuged at 10 000 g for 10 minand the precipitate was air dried. Complexation efficiency was de-termined by measuring, by headspace GC, the contents of volatilesstored for one week at 70 C.

Emulsification of caraway extract. The maltodextrin emulsion wasmade by dissolving gum arabic (20 wt%) in water and homogeni-sing with maltodextrin solution (40 wt%) and caraway fruit extractwith a Heidolph DIAX 600 (Kelheim, Germany) homogeniser at24,000 rpm three times for a duration of 1 min each time. The Hi-Cap emulsion was made, using a similar procedure, from dis-solved HiCap (40 wt%) without any additional emulsifier. Theprocedure guaranteed the formation of an emulsion of caraway ex-tract that remained stable for the duration of the spray-drying. Thedry weight composition of the maltodextrin emulsion was 12%caraway extract, 5% gum arabic and 83% maltodextrin, and that ofthe HiCap emulsion was 12% caraway extract and 88% HiCap.

Spray-drying of caraway extract emulsions. Both maltodextrin andHiCap emulsions were spray-dried in a Niro (Soeborg, Denmark)Mobile Minor laboratory spray dryer with a rotating atomiser. Thetemperature of the inlet air was adjusted to 200 C and that of theoutlet air was kept at 802 C by controlling the flow rate. Theatomiser rotation speed was 25,000 rpm. Powder was collected inchamber and cyclone collection vessels, but only powder from thechamber collection vessel was used in the study.

Thermal analysis of complexes. Thermal analysis was carried outwith a Mettler (Dietikon, Switzerland) DSC820 differential scan-ning calorimeter equipped with a liquid nitrogen cooling system.A sample of 10 mg was weighed on an aluminium pan, which wassealed. Heating and cooling were performed at a rate of 10 C/minbetween 0 C and 200 C.

Sorption isotherms. Initial water contents were determined by KarlFischer titration. The residual water was extracted in methanol for2 h with continuous stirring. The amount of solvent injected intothe titrator was determined gravimetrically. Samples with initialmoisture content were weighed (100 mg) and placed in humiditychambers with different salt solutions: LiCl (RH 12%), MgCl2(RH 33%), Mg(NO3)2 (RH 54%), NaCl (RH 75%) and (NH4)2SO4(RH 81%). After one week of equilibration, the samples wereweighed again and the water sorption isotherms at room tempera-ture (232 C) were determined.

GC-analysis of carvone and limonene contents in the capsules. Allthe five microcapsule species were extracted overnight with meth-anol at room temperature. The samples were diluted in water, re-sidual methanol content being 5%. The gas phase of the sampleswas analysed by headspace-GC using n-butanol as an internalstandard. Equilibration was carried out at 60 C for 20 min. Limo-nene, carvone and n-butanol standard solutions in 5% methanolwere used for calibration. The gas chromatograph was a Perkin Elmer Autosystem XL, with a flame ionisation detector (FID)(Perkin Elmer Corporation, Norwalk, CT, USA) and the headspacesampler was a Perkin Elmer HS-40 (Perkin Elmer Corporation,Norwalk, CT, USA). Quantitation was done with PE Nelson Turbochrom software (version 4,1., Perkin Elmer Corporation,

Norwalk, CT, USA). The column used was PE-5 50 m, i.d.0.32 mm, df 1.0 m (Perkin Elmer Corporation, Norwalk, CT,USA). Helium was the carrier gas as well as the make-up gas. Thetemperature profile was as follows: 40 C, 1 min; 150 C, 20 min;200 C, 5 min. The heating rate was 12 C/min.

Evaporation of carvone and limonene from the capsules. Evapora-tion of carvone and limonene from all the produced microcapsuleswas studied by gas-phase FT-IR spectroscopy. Experimental de-sign was divided into two parts: a) the effect of storage at roomtemperature on limonene and carvone release, and b) the stabilityof the microcapsules against rapid heating. Around 2 g of capsuleswere smoothly spread on the bottom of a 100-ml beaker. A total of167 beakers representing 167 analyses and 5 sample sets weretransferred to a fume hood and stored at 20.80.5 C andRH

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sis on complexation has been performed by differentialscanning calorimetry (DSC) [18] which was also ap-plied in our study. No enthalpy changes were observedin dry -cyclodextrin below 210 C (Fig. 1) wheremelting of the crystals occurred [2]. The boiling pointof carvone is 230 C and that of limonene is 177 C.The DSC thermograms of the dry -cyclodextrin com-plexes of limonene and carvone are shown in Fig. 2.There was a clear endothermic peak in both thermo-grams, which was interpreted as degradation of thecomplex. Both complexes showed relatively high heat

stability; limonene was released above 130 C and car-vone above 170 C. Compared to the thermogramsmeasured by Chang and Reineccius [18], ours wereeasier to interpret due to the more stable baselines.Chang and Reineccius observed degradation of the li-monene complex at 130 C, which was in good agree-ment with our results. As for the carvone complex, theyobserved degradation as early as 140 C. The differ-ences in thermograms and temperature of carvone re-lease could be because of some residual moisture assuggested by the authors themselves.

Table 1 Amounts of limoneneand carvone in freshly preparedand stored -cyclodextrin com-plexes and reference mixtures

Limonene (%) Limonene (%) Carvone (%) Carvone (%)in complex in reference in complex in reference

Fresh sample 10.9 12.0 11.3 12.6One week at 70 C 5.5 0.1 11.2

=not detected

Fig. 1 DSC thermogram of dry-cyclodextrin

Fig. 2 DSC thermograms of li-monene and carvone complex-ed with -cyclodextrin

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Sorption isotherms of the capsule materials

Water vapour sorption isotherms were determined forpure -cyclodextrin and -cyclodextrin complexed withcarvone. Maltodextrin with DE 18.5 and chemicallymodified starch (HiCap 100) were also studied with re-gard to the environmental humidity. Sorption isothermsare shown in Fig. 3. Maltodextrin and HiCap sorbedmore water vapour at high humidity than -cyclodextrin.Sorption of water in -cyclodextrin was dependent oncomplexation, as the carvone guest was bound to possi-ble hydration sites. At higher relative humidities, bothmaltodextrin and HiCap started to dissolve.

Retention of caraway limonene and carvone in the microcapsules

Caraway fruit extract contained 90% essential oil, ofwhich 37% was limonene and 59% carvone. In order to

compare the efficiency of -cyclodextrin complexationwith the efficacy of encapsulation in maltodextrin andHiCap, caraway extract was used at the same level in allmicrocapsules. The reference sample for the -cyclodex-trin inclusion complex contained caraway extract mixedwith dry -cyclodextrin and had not undergone the com-plex formation procedure. Storage stability tests werecarried out at room temperature and at 70 C for 56 daysand carvone content was analysed by headspace GC(Figs. 4 and 5). There appeared to be essentially no car-vone loss from microcapsules during storage at either ofthe temperatures. Carvone was completely evaporatedfrom the reference sample in 28 days at room tempera-ture and in 14 days at the elevated temperature. Thus, allthe wall materials gave good protection against evapora-tion.

Effect of storage at room temperature on the vaporisablelimonene and carvone

The aim was to measure the amount of vaporisable limo-nene and carvone from microcapsules at a constant time,i.e. the leak. Therefore, a short evaporation time and asmall sample amount were selected. The results do notrepresent the total content of volatile substances in mi-crocapsules but rather evaporation of the free com-pounds. The storage experiment lasted 45 days for theHiCap and maltodextrin microcapsules and 26 days forthe -cyclodextrin microcapsules.

The FT-IR results are presented in Figs. 6 and 7. Itshould be noted that the sampling method applied wasnot an equilibrium headspace method. The results for -cyclodextrin were obtained from pure carvone and purelimonene microcapsules without the caraway oil matrix.

Taking the relatively high variation into account, itcan be concluded that the release of volatiles from mal-todextrin and HiCap microcapsules did not show a cleartrend in 45 days. Figures 6 and 7 indicate a rather con-

Fig. 3 Water vapour sorption isotherms of -cyclodextrin, the -cyclodextrin-carvone complex, HiCap and maltodextrin

Fig. 4 Changes in carvone content of caraway fruit extract micro-capsules and reference mixture with -cyclodextrin at room tem-perature

Fig. 5 Changes in carvone content of caraway fruit extract micro-capsules and reference mixture with -cyclodextrin at 70 C

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stant leak from the HiCap and maltodextrin capsules. Ifthe release observed had mostly been from the surface ofthe capsules, a decreasing trend would have been ob-served. Compared to the maltodextrin and HiCap micro-capsules, the evaporation of carvone and limonene from-cyclodextrin microcapsules decreased rapidly. The fastdecrease in the concentrations for -cyclodextrin indi-cates that the higher concentrations observed in the be-ginning were due to residues on the surface of the micro-capsules. When carvone and limonene had vanishedfrom the surface, no significant amounts were observed.Thus, vapour release and the shelf-life behaviour of -cyclodextrin is different from maltodextrin and HiCap.

Effect of heating on the capsule stability

Release of carvone and limonene from the microcapsulesas a function of temperature was analysed with gas phaseFT-IR, and the results are shown in Figs. 8 and 9. Mea-surements were made after residues of the volatiles fromthe surfaces of microcapsules had vanished. Temperaturewas increased step by step and intense rises of volatileswere noticed at product-specific temperature ranges. Re-lease of carvone from different capsules as a function oftemperature is shown in Fig. 8. Evaporation was releasedat higher temperatures from the caraway oil complexedin -cyclodextrin than from the pure carvone-cyclodex-trin inclusion complex. Analogous results of limonene of-cyclodextrin microcapsules containing pure limonenevs caraway extract are shown in Fig. 9.

Fig. 6 Changes in evaporated carvone from caraway fruit extract(HiCap, maltodextrin) and pure carvone (-cyclodextrin) micro-capsules during storage

Fig. 7 Changes in evaporated limonene from caraway fruit extract(HiCap, maltodextrin) and pure limonene (-cyclodextrin) micro-capsules during storage

Fig. 8 Volatile carvone concentration as a function of temperaturein -cyclodextrin, HiCap and maltodextrin microcapsules

Fig. 9 Volatile limonene concentration as a function of tempera-ture in -cyclodextrin, HiCap and maltodextrin microcapsules

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In the case of maltodextrin, carvone concentrationwas kept constant up to 120 C and increased slowly to200 C. Release of carvone from HiCap capsules, again,remained at almost zero level up to about 140 C, atwhich range of temperature the degradation of microcap-sules was already visible (the capsule material turnedbrown). For the caraway oil--cyclodextrin complex,evaporation of carvone started to increase at 120 C, af-ter which the increase was almost linear.

The maltodextrin capsules did not start to leak limo-nene significantly until quite high temperatures, above160 C, were reached (Fig. 9). For HiCap the corre-sponding temperature was about 20 C lower, at 140 C.For the caraway oil--cyclodextrin complexes the leak-age of limonene started to increase at a temperature of120 C. -Cyclodextrin complexes with pure carvoneand limonene started to release volatiles above 100 C(Figs. 8 and 9), which was at a considerably lower tem-perature than that at which the degradation of the com-plex was observed by DSC (Fig. 2). This could probablybe explained by the difference in conditions of the twomeasurements. The results indicate that despite someleak of carvone, maltodextrin is the most heat-stable ma-trix for encapsulated volatiles in dry conditions.

Conclusions

Carvone could be efficiently complexed with -cyclo-dextrin, whereas only half of the limonene was complex-ed. Equal amounts of caraway extract encapsulated inmaltodextrin, emulsifying starch and in -cyclodextrinwere relatively stable during storage. As the inclusioncomplex protected bound volatiles from evaporation in-cyclodextrin, some evaporation occurred from bothHiCap and maltodextrin capsules. As for thermal stabili-ty, modified starches gave better protection than -cyclo-dextrin, maltodextrin microcapsules being the most heatresistant. It can also be concluded that the FT-IR methodproved to be suitable for samples in powder form.

Acknowledgements The authors gratefully acknowledge finan-cial support from the National Technology Agency (Tekes, Fin-land) and Hannele Virtanen for the HS-GC analyses. Ms. TeijaJokila is acknowledged for her skilful technical assistance and Ms.Anja Pirinen for performing the FT-IR analyses. Aromtech Ltd isacknowledged for supporting the caraway extract.

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