Kinetic Analysis and Evaluation of Controlled Release of D Limonene Encapsulated in Spray Dried Cyclodextrin Powder under Linearly Ramped Humidity

Drying Technology An International Journal ISSN: 0737-3937 (Print) 1532-2300 (Online) Journal homepage: http://www.tandfonline.com/loi/ldrt20 Kinetic Analysis and Evaluation of Controlled Release of D-Limonene Encapsulated in SprayDried Cyclodextrin Powder under Linearly Ramped Humidity Chisho Yamamoto , Tze Loon Neoh , Hirokazu Honbou , Hidefumi Yoshii & Takeshi Furuta To cite this article: Chisho Yamamoto , Tze Loon Neoh , Hirokazu Honbou , Hidefumi Yoshii & Takeshi Furuta (2012) Kinetic Analysis and Evaluation of Controlled Release of D-Limonene Encapsulated in Spray-Dried Cyclodextrin Powder under Linearly Ramped Humidity, Drying Technology, 30:11-12, 1283-1291, DOI: 10.1080/07373937.2012.681089 To link to this article: https://doi.org/10.1080/07373937.2012.681089 Published online: 17 Aug 2012 Submit your article to this journal Article views: 172 View related articles Citing articles: View citing articles Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ldrt20 Drying Technology, 30: 1283–1291, 2012 Copyright # 2012 Taylor & Francis Group, LLC ISSN: 0737-3937 print=1532-2300 online DOI: 10.1080/07373937.2012.681089 Kinetic Analysis and Evaluation of Controlled Release of D-Limonene Encapsulated in Spray-Dried Cyclodextrin Powder under Linearly Ramped Humidity Chisho Yamamoto,1,2 Tze Loon Neoh,2 Hirokazu Honbou,2 Hidefumi Yoshii,2 and Takeshi Furuta3 Tottori Institute of Industrial Technology, Tottori, Japan Department of Applied Biological Science, Kagawa University, Kagawa, Japan Department of Chemistry and Biotechnology, Tottori University, Tottori, Japan A linearly ramped humidity system coupled with automatic sampling gas chromatography has been developed The apparatus was adopted to measure the dynamic release flux of D-limonene included in spray-dried b-cyclodextrin (b-CD) and the polymercoated counterparts under linearly ramped humidity (0.375%/min) at constant temperature (50
C) The release flux profiles of D-limonene were analyzed using a mathematical model based on an extended Arrhenius equation The activation energy of D-limonene release flux from b-CD was 278 (kJ/mol), which was the highest among the powders and around twice as high as our previous results obtained by the conventional static method Keywords Dynamic flavor release; Encapsulation by cyclodextrin; Humidity ramping method; Spray drying INTRODUCTION Cyclodextrins (CDs) are doughnut-shaped cyclic oligosaccharides with interior cavities capable of forming specific inclusion complexes with many organic compounds CDs are often used as encapsulants of hydrophobic flavors, a method called molecular encapsulation because the flavors are encapsulated in the molecular cavities of CDs After a century of continuous research and development, CDs have gained certain recognition in various fields.[1] Their applications are mainly intended for the entrapment of smaller molecules, catalysis through encapsulation, and as potential molecular transport devices In food-related applications, flavor compounds are being encapsulated into CDs for better retention and protection from various possible means of deterioration, as well as for controlled delivery.[1–4] In addition to food flavors, CDs are used for encapsulation of antibacterial compounds such as allyl isothiocyanate and hinokitiol Correspondence: Takeshi Furuta, Department of Chemistry and Biotechnology, Tottori University, 4-101, Koyama, Tottori 680-8552, Japan; E-mail: furuta@sun.ocn.ne.jp (b-thujapilicin) for potential applications in paper and cloth.[5–8] For the manufacturing of flavor powders, high flavor retention is an important quality factor but the controlled release characteristics of the encapsulated flavors from the powders are equally important in terms of storage stability and application A number of studies on flavor release have been conducted, and it has been reported that the flavor releases were closely related to the relative humidity (RH) of the storage environment.[1,9–13] In most of the studies on flavor release from powders, the rate of release was measured with a thin packed layer of the powders under constant temperature and humidity conditions (static method) The static method of characterizing flavor release is extremely time intensive, and it takes a few weeks to obtain the full release profiles of flavors from the powders.[1,12] In addition, the method does not provide any additional observations triggered by the rapid structural evolution such as aggregation and surface solubilization of the powder particles, which is often reflected by abrupt changes in the release flux Dronen and Reineccius[14] and Mortenson and Reineccius[15,16] applied a proton transfer reaction mass spectrometer (PTR-MS) coupled to a dynamic vapor sorption (DVS) instrument as a rapid method of analysis to measure the release time course of flavors from spray-dried powders They obtained dynamic release profiles of flavors but did not report the establishment of the kinetics of the release reactions Mateus et al.[17] measured the release profiles of volatile organic compounds from roasted and ground coffee beans using PTR-MS and analyzed the release profiles with the empirical models of diffusion and Weibull’s equation.[12] Bohn et al.[18] also applied the method to an amorphous sucrose–based glassy matrix encapsulating cherry flavor and correlated the flavor release with the glass transition temperature of the matrix.[19] Although it is well known that the release of flavors 1283 1284 YAMAMOTO ET AL through the matrices of the solid state is closely related to environmental humidity, few studies have been conducted to develop a kinetic model of flavor release as a function of humidity Normand et al.[20] investigated the release profile of D-limonene from empty yeast cells by monitoring the weight change with DVS at various humidities They correlated the release flux with a modified Arrhenius equation Zhao et al.[21] and Li et al.[22] analyzed solid-state drug stabilities by applying an analogous Arrhenius equation by simultaneous varying temperature and humidity In addition to the DVS method, Neoh and coworkers[23,24] studied the release mechanism of organic compounds included in CDs using thermogravimetry However, the studies were not conducted under humid conditions Almost all of the studies on flavor release have been carried out under constant humidity conditions However, more informative data can be acquired quickly by applying variable humidity conditions In this study, a rapid evaluation of the release of D-limonene from spray-dried bCD=D-limonene complex powders was performed under linearly ramped humidity at constant temperature using a home-built DVS system Real-time release fluxes (release rates) of D-limonene were monitored by autosampling gas chromatography The release flux profiles under ramping humidity were modeled by applying an extended Arrhenius equation The kinetic parameters such as activation energy and frequency factor were estimated The impacts of polymer coating agents on the release mechanism were also investigated kinetically MATERIALS AND METHODS Materials Cavamax W7 (standard grade b-cyclodextrin, b-CD, Wacker Chemie AG, Stuttgart, Germany) was obtained from Cyclochem Co., Ltd (Kobe, Japan) Better Sol, supplied by Seishin Enterprise Co., Ltd (Tokyo, Japan), which is a soap-free colloidal emulsion made of polyethylene resin (PE) and various cross-linkers (solids content of 20%) was used as a coating agent Sumikaflex, a waterbased emulsion composed of ethylene-vinyl acetate (EVA) copolymer resins, which was also used as a coating agent, was purchased from Sumika Chemtex Co., Ltd (Tokyo, Japan) as a 50% emulsion solution The ethylene unit content of EVA was approximately 10% D-Limonene was purchased from Nacalai Tesque, Inc (Kyoto, Japan) Distilled water was used throughout the entire study Unless otherwise stated, all other chemicals used in this study were purchased from Wako Pure Chemical Industries, Ltd (Osaka, Japan) and were of analytical reagent grade Preparation of Complex Powders by Spray Drying D-Limonene was selected as a model flavor (guest compound) Three hundred grams of 33.9 wt% b-CD solution was prepared in a 500-mL laboratory bottle One and a half molar times of D-limonene relative to b-CD were added The total concentrations of b-CD and D-limonene were set constant at 40 wt% in all treatments The mixture solution was stirred with a magnetic stirrer for 24 h After complexation equilibrium, the polymer coating agent (Better Sol or Sumikaflex) was added to the mixture solution at to 12 wt% Because Better Sol and Sumikaflex contain polymer resins, they create a polymer coating after spray drying The feed liquid was homogenized with a Polytron homogenizer (model PT-6100, Kinematica Inc., Bohemia, NY) for at a rotor speed of 8,000 rpm The compositions of the feed liquids were listed in Table 1a Spray drying was performed with an OhkawaraL8 spray dryer (Ohkawara Kakouki Co., Ltd., Yokohama, TABLE Composition of feed liquid, properties of spray-dried powder, and kinetic parameters of release Spray-dried powders (a) Feed liquid composition b-CD (%) D-Limonene (b) Properties of spray-dried powder (c) Kinetic parameters of release of D-limonene (%) Coating agent (%) Water (%) D-Limonene content (g=g-powder) D43 (mm) E (kJ=mol) B0 (K=%) C (1=%) ln A Uncoated PE1 PE2 EVA 33.9 6.1 60.0 0.087 6.85 278 90.0 303 0.780 33.9 6.1 6.0 54.0 0.091 21.6 238 77.2 272 0.728 33.9 6.1 12.0 48.0 0.088 65.5 214 57.5 240 0.532 33.9 6.1 4.8 55.2 0.079 40.2 183 39.2 199 0.472 Uncoated: spray-dried b-CD=D-limonene complex powder: PE1: PE (6%)-coated spray-dried complex powder: PE2: PE (12%)-coated spray-dried complex powder: EVA: EVA (4.8%)-coated spray-dried complex powder CONTROLLED RELEASE OF D-LIMONENE Japan) The size of the spray-drying tower has been described elsewhere.[25] The feed mixture was fed at 30 mL=min to the rotary disk atomizer and atomized at a speed of 10,000 rpm The drying medium (air) of 200
C was supplied at 110 kg=h with an outlet air temperature ranging between 145 and 150
C The spray-dried powders were collected in the cyclone and put in a hermetically sealed container and stored at 30
C until use The spraydried b-CD=D-limonene complex powder and the PE (6%)-coated, PE (12%)-coated, and EVA (4.8%)-coated spray-dried complex powders will be referred to throughout the remainder of this article as uncoated, PE1, PE2, and EVA, respectively Quantification of D-Limonene in Spray-Dried Powders Solvent extraction was employed for quantification of D-limonene in the spray-dried powders The spray-dried complex powder (0.1 g) was added with mL of water and mL of chloroform into a glass vial, which was tightly screw-capped, and vigorously vortexed for The chloroform contained cyclohexanone at a concentration of mL=mL chloroform, serving as an internal standard in gas chromatographic determination of D-limonene To extract the D-limonene into the organic solvent, the mixture was heated at 90
C for 30 with several periods of intermittent vortexing After cooling of the extracted samples to room temperature, a 10-min centrifugation at 3,000 rpm was performed The samples were extracted in triplicate for quantification by gas chromatography A 1-mL aliquot of the supernatant was injected in duplicate into a GC-14A gas chromatograph (Shimadzu Corp., Kyoto, Japan) Chromatographic separation was performed using a 20% PEG-20 M-packed (Shinwa Chemical Industries, Ltd., Kyoto, Japan) glass column (3.2 mm i.d  m-length) with nitrogen as the carrier gas (0.07 MPa) D-Limonene was quantified using a flame ionization detector (FID) The temperatures of the injection port, oven, and detector were set constant at 140, 130, and 230
C, respectively To obtain a calibration value for quantification of D-limonene, two bottles of standard solution of different D-limonene contents (1.6 and 3.2 mL=mL of D-limonene) containing mL=mL cyclohexanone in chloroform were prepared A 1-mL aliquot of each standard solution was injected into the gas chromatograph twice, and the average peak areas were used as a calibration value to calculate the amount of D-limonene Size and Structure of Spray-Dried Powder Particles The size distributions of spray-dried particles were measured with a laser scattering particle size analyzer (SALD-7100, Shimadzu Corp.) installed with a batch sample cell.[26] The powder (100 mg) was dispersed in mL of 2-methyl-1-propanol, in which the powder was not miscible nor did it agglomerate In addition, 2-methyl-1-propanol 1285 does not affect the particle size by shrinkage or expansion and has high dispersibility and wettability About 50 mL of each dispersion was introduced into the batch sample cell containing 6.5 mL of 2-methyl-1-propanol The volumeaveraged diameter, D43, was used as the mean diameter for all measurements Each sample was analyzed in duplicate A scanning electron microscope (SEM; JSM 6060, JEOL Co., Ltd., Tokyo, Japan) was used to observe the microstructure of the spray-dried particles The powder particles were mounted onto the SEM stubs using doublesided adhesive carbon tape (Nisshin EM Co., Ltd., Tokyo, Japan) In order to examine the inner structure, the microcapsules (attached to the stub) were fractured by adhering a second piece of adhesive tape on top of the samples and then quickly ripping them apart.[27] The specimen stub was subsequently coated with Pt-Pd using an MSP-1S magnetron sputter coater (Vacuum Device Inc., Tokyo, Japan) The sputter-coated sample was then analyzed using the SEM operated at 2.0 kV Measurement of Release Flux of D-Limonene from Inclusion Complex Powders A home-built DVS system coupled with an autosampling gas chromatograph was adopted to conduct the rapid evaluation of the release of D-limonene from spray-dried CD powders under linearly ramped humidity at constant temperature The release equipment consisted of two parts: the DVS system, which humidifies the nitrogen flow at the prescribed rate, and the quantification system of the release flux of D-limonene from the powders under varying RH Nitrogen was used as a carrier gas based on the preliminary finding that revealed that D-limonene vapor reacted immediately with oxygen in air, producing several gaseous oxide compounds Nitrogen was vapor-saturated by bubbling the nitrogen gas through distilled water in a 500-mL laboratory bottle as shown in Fig A waterproof heater was wound around the bubbling bottle and immersed in a water bath The temperatures of the water bath and the water in the bubbling bottle were controlled using a programmable temperature controller (DSSP93, Shimaden, Tokyo, Japan) through a thermocouple in the water bath The vapor-saturated nitrogen was passed through a mist trap before being flowed into an air bath through a stainless steel pipe wound with a guard heater The distilled water in the bubbling bottle was stirred with a magnetic stirrer to ensure thorough dispersion and sufficient residence time for vapor saturation in the bubbles The nitrogen flow rate was 100 mL=min In order to achieve an RH profile ramping linearly from 10 to 100% within a prescribed time, the water vapor pressure– temperature relation was divided and linearized into seven sections over the temperature range between 10 and 60
C, 1286 YAMAMOTO ET AL FIG Schematic diagram of the home-built DVS system coupled with an autosampling gas chromatograph and data sets of time and temperature pairs were input into the temperature controller The vapor-saturated nitrogen flowing into the air bath was equilibrated at the constant temperature (40, 50, or 60
C) of the bath by passing through a spiral copper tube (3.2 mm i.d  m length) at the inlet of the bath The RH of the nitrogen gas was estimated as p=ps, where p is the saturated water vapor pressure at the current temperature of the bubbling bottle and ps is the saturated water vapor pressure at the air bath temperature The humidity-conditioned nitrogen was flowed through the glass release vessel (16 mm i.d  80 mm height) at the bottom of which the aluminum pan (13 mm i.d  mm depth) packed with the sample powder was set, as shown in Fig The D-limonene released from the sample powder was carried away by the nitrogen stream into the gas chromatograph for quantification The real-time release flux of D-limonene per unit mass of the sample powder (release flux), F (mg=s  cm2  g-powder), was calculated by multiplying the concentration of D-limonene in the nitrogen stream Cg (mg=mL) by the nitrogen flow rate V (mL=s) and dividing by the mass of the powder, m (g) and the surface area, A (cm2), of the powder: F ¼ V  Cg =ðA  mÞ ð1Þ The concentration of D-limonene in the nitrogen stream, Cg, was measured in real time with a gas chromatograph (GC-14B, Shimadzu) Sampling of the nitrogen stream and injection were automated by a timer-operated switching valve (Valco A6-G6 W, Valco Instruments Co Inc., TX) In sampling mode, each port of the valve was connected as shown by the solid lines in Fig The effluent nitrogen from the release vessel was flowed through a 5.0-mL sampling loop and exhausted In injection mode, the valve was switched by compressed air and the connections between ports were changed to that shown by the dotted lines in Fig The carrier gas from the gas chromatograph swept out the sampled effluent nitrogen from the sampling loop into a PEG-20 M-packed glass column for separation and finally for quantification of current Cg in an FID Two standard solutions of different D-limonene contents in chloroform (1.0 and 2.0 mL=mL of D-limonene) were prepared An absolute calibration curve was made by injecting a 1-mL aliquot of each standard solution into the gas chromatograph twice and averaging the peak areas of D-limonene Cg was calculated with the calibration curve The switching valve alternated between a 4-min sampling mode and a 1-min injection mode for the entire release experiment because the whole cycle of was necessitated by the limitation of the chromatographic separation The humidity of the nitrogen stream was continuously monitored with a humidity sensor (HMP233, Vaisala, Helsinki, Finland) connected to the effluent port of the valve RESULTS AND DISCUSSION Changes of RH in Nitrogen Stream under Linearly Ramping Program In this study, the RH of the nitrogen stream was changed in a linearly ramping manner For this purpose, the temperature of the bubbling bottle was regulated with the programmable temperature controller by segmenting the water vapor pressure–temperature relationship into seven linear sections Figure indicates the time course of RH under the ramping program from 10 to 100% for h; the rate of increase (ramping rate) was 0.375%=min The humidity was monitored at the exit of the release apparatus as mentioned in the previous section The humidity of the nitrogen stream satisfactorily increased linearly with time, thus warranting the performance of the home-built DVS system The time course of the water CONTROLLED RELEASE OF D-LIMONENE 1287 FIG Linearly ramped relative humidity in N2 stream (.) at the corresponding temperatures of the bubbling water (
) The humidity ramping rate was set at 0.375% RH=min temperature in the bubbling bottle is also illustrated in Fig The temperature profile is not linear but curved upwards against time Content of D-Limonene and Morphologies of Spray-Dried Particles D-Limonene contents and particle sizes of the spray-dried powders are listed in Table 1b All four powders contained approximately 0.8 molar ratio of D-limonene with respect to b-CD regardless of the type of polymer coating agent in use In contrast, the powder particle size varied drastically with both the amount and type of coating agent The addition of the coating agents may have increased the viscosity of the feed liquids, which is one of the key factors determining the diameter of the spray droplet; the more viscous the feed liquid is, the larger the atomized droplet size is.[25] The external and internal morphologies of the spraydried particles are illustrated in Fig The uncoated complex powder (Fig 3a) was very fine crystal particles of several micrometers, and the coated complex powders ranged from a few to several tens of micrometers As seen in Figs 3b–3d, the coated particles were spherical in shape and their surfaces were composed of the fine complex particles bound by the coating agents of PE and EVA Many pores appeared between the fine complex particles on the powder particle surfaces The surface of the EVA-coated powder particles was rougher than that of the PE-coated ones This might be attributed to the lower hydrophobicity of EVA compared to that of PE The internal structures of the coated powder particles are shown in Figs 3e–3g Fine complex particles packed in a random manner on the inside of the coated complex powder particles, forming relatively rougher and more porous structures compared to the surfaces A clear boundary discerning the outer crust from the inner core (randomly packed fine complex particles) was vividly observable in the powder particles coated with PE (Figs 3e and 3f), whereas in EVA-coated particles, such FIG SEM micrographs of spray-dried particles illustrating the external and internal morphologies of the (a) uncoated complex powder and the complex powders coated with (b), (e) PE (6.0%, PE1); (c), (f) PE (12%, PE2); and (d), (g) EVA a well-defined boundary was not clearly noticeable (Fig 3g) These differences in particle surface structure may have crucial impacts on the release characteristics of D-limonene Release Characteristics of D-Limonene from Spray-Dried Powders The release flux of D-limonene from the spray-dried powders in the solid state was measured under the RH ramping rate of 0.375%=min at 40, 50, and 60
C with the DVS-GC system shown in Fig As shown in Fig 4, the release flux, F, for the uncoated spray-dried complex powder was nearly zero up to 70% RH and increased monotonously with a further increase in RH Particularly at 60
C, the release flux, F, grew exponentially with the increase in RH above 80% As for the PE-coated powders, the release flux, F, was markedly decreased compared to that of the uncoated complex powder Higher amounts of the coating agent inhibited the release of D-limonene to a more remarkable extent In the case of PE2-coated powder (Fig 4c), the release of D-limonene was almost negligible at RH < 90% 1288 YAMAMOTO ET AL FIG Release profile of D-limonene under linearly ramped humidity (0.375% RH=min) at 40
C (4), 50
C (
), and 60
C (&) from the (a) uncoated complex powder and the complex powders coated with (b) PE1, (c) PE2, and (d) EVA for all of the temperatures used Because PE is a hydrophobic compound, the water vapor in the nitrogen stream would be prevented from adsorbing into the particles by the PE film covering the particle surface Consequently, D-limonene included in b-CD could hardly be released from the molecular cavity In contrast, D-limonene began to release from the EVA-coated particles at an earlier stage before 70% RH The flux, F, increased exponentially with increasing RH and exhibited higher values at the same RH compared to other particles, particularly at 40 and 50
C This may be directly ascribable to the hydrophilicity FIG of EVA EVA increasingly adsorbed moisture at higher RH and might contribute to triggering the massive release of D-limonene At 60
C, however, the release flux ceased to increase further at RH higher than 80% but assumed a release profile similar to that of 50
C This phenomenon may possibly be caused by the collapse of the surface structure of the particles resulting from the melting of the fine complex particles at higher RH Figure shows the surfaces of particles coated with PE1 and EVA that had been exposed to the nitrogen stream of 80% RH for 120 For the particles coated with PE, the fine complex particles Changes of the surface structures of PE1- and EVA-coated complex powder particles exposed at 80% RH for h 1289 CONTROLLED RELEASE OF D-LIMONENE at the powder particle surface agglomerated to a lesser extent after humidification in comparison to the EVAcoated particles in which the surfaces were visually dissolved, causing structural collapse and filling up the pores The reduction of the ascent rate of F at 60
C and RH > 80% observed in Fig 4d may be due to the inhibition of diffusion of D-limonene from the inside of the complex powder particle to its surface Kinetic Analysis of Release Flux of D-Limonene at Various Humidity and Temperatures On the basis of an extended Arrhenius equation proposed by Normand et al.,[20] in which the release of D-limonene was assumed to be a function of both temperature and RH, a kinetic analysis of the release flux was conducted to estimate the activation energies and frequency factors of the release reactions The extended Arrhenius equation is an empirical equation expressed as:   E F ¼ A  exp   expðB  uÞ RT ð2Þ where T, u, E, and R are the temperature, relative humidity, activation energy, and gas constant, respectively A is a constant, but B is a function of T as explained below Equation (2) has also been applied by Zhao et al.[21] and Li et al.[22] to analyze the solid-state drug stabilities Taking the natural logarithm of both sides of Eq (2), one can obtain the following equation: ln F ẳ ln A  E ỵBu RT ð3Þ Equation (3) describes that at a constant temperature, ln F is linearly proportional to the relative humidity, u To examine the validity of Eq (3), a semi-logarithmic plot of F against u (ln F vs u) was constructed as shown in Fig 6, using the release data in Fig 4a At constant temperature, ln F can be clearly expressed by a linear equation of u in a higher range of u, and B can be obtained from the slopes of the plots However, the slopes vary at different temperatures, implying that B in Eq (2) is not constant but a function of temperature and is assumed to be B¼ B0 ỵC T FIG Correlation of F as a function of relative humidity, u, at 40
C (4), 50
C (
), and 60
C (&) for the uncoated spray-dried complex powder The humidity ramping rate was 0.375% RH=min The activation energy of the release flux, E, could be calculated from the slope of the plot of ln F0 against 1=T Figure illustrates both plots for ln F0 and B against the inverse of T Although there were a few variations, ln F0 and B still correlated well with 1=T The estimates of the four parameters, E, A, B0 , and C, are listed in Table 1c The activation energy of release flux for the uncoated complex powder was the highest among the powders Because there are few reported studies concerning the release of molecularly encapsulated flavors from CDs in the solidstate condition, appropriate comparison of the results was difficult Furuta et al.[1] investigated the release of D-limonene from b-CD at 50% RH by the static method and estimated the activation energy to be 123 kJ=mol Although the value seems much lower than the present results, it may be reasonable because the activation energy was obtained at a lower RH (50% RH) Because E in Eq (2) can be regarded as the activation energy of the release flux at zero relative humidity, the activation energies in Table 1c may be rational because much energy would be ð4Þ where B0 and C are constants If the y-intercept of the line in Fig were denoted as ln F0, the following equation could be derived from Eq (3) at temperature T: E RT ð5Þ FIG Arrhenius plots of ln F0 and B for the uncoated complex powder (
) and the complex powders coated with PE1 (4), PE2 ( ), and EVA (&) ln F0 ¼ ln A  1290 YAMAMOTO ET AL needed to dissociate the complex molecules between the guest and host compounds under dry conditions.[1] Normand et al.[20] conducted release experiments for D-limonene enclosed in yeast cells under stepwise variation of humidity and reported the activation energy of the release flux to be 74 kJ=mol Zhao et al.[21] and Li et al.[22] suggested that the activation energies of degradation were 76 kJ=mol for penicillin potassium and 93.5 kJ=mol for aspirin under simultaneous variation of temperature and humidity However, all of these studies were carried out with physically encapsulated D-limonene or intact pharmaceuticals Because D-limonene inclusion complex is bonded in the molecular cavity of CD by Van der Waals forces and a hydrophobic interaction, it is reasonable to consider that more energy would be needed for the dissociation of the complexed ingredient Figure shows the plot of ln A as a function of E A satisfactory linear proportionality supported the establishment of a compensation effect for the apparent kinetic parameters Validation of the compensation effect may be indicative of the fact that the release of D-limonene in the four samples possibly occurred via mechanisms of a common nature As described earlier, because few studies have been conducted to measure the dynamic release of encapsulated flavors under varying humidity conditions and analyze it kinetically, the validity of the present results such as the activation energy of release could not be properly evaluated The flavor release rate from powders may be controlled mainly by molecular diffusion inside the powder particle, which is strongly influenced by the matrix structure of the particle The dynamic release measurements can respond sensitively to the structural changes such as collapses and melting caused by the adsorption of the moisture (Fig 4d) The subsequent interests of the study FIG Chemical compensation between ln A and E of for the uncoated complex powder (
) and the complex powders coated with PE1 (4), PE2 ( ), and EVA (&) lie in developing a mathematical model of the counterdiffusion of the flavor and moisture inside a particle, including the phase change of the matrix of the particle CONCLUSION Real-time release fluxes of D-limonene included in spray-dried b-CD powder and their polymer-coated counterparts were measured using the home-built DVS system coupled with an autosampling gas chromatograph The release of D-limonene from spray-dried b-CD and their corresponding coated powders was investigated under linearly ramped humidity at constant temperature The release fluxes were nearly zero below 70% RH and increased monotonously with an increase in RH Higher amounts of the coating agent inhibited the release to a more remarkable extent At constant temperature, the semi-logarithms of the release fluxes correlated linearly with the higher range of relative humidity An extended Arrhenius equation was applied and the kinetic parameters such as activation energy and frequency factor were estimated The activation energy of D-limonene release from the uncoated complex powder was highest and around twice as high as the previous results obtained by the static method REFERENCES Furuta, T.; 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Composition of feed liquid, properties of spray- dried powder, and kinetic parameters of release Spray- dried powders (a) Feed liquid composition b-CD (%) D- Limonene (b) Properties of spray- dried powder. .. Uncoated: spray- dried b-CD =D- limonene complex powder: PE1: PE (6%)-coated spray- dried complex powder: PE2: PE (12%)-coated spray- dried complex powder: EVA: EVA (4.8%)-coated spray- dried complex powder. .. of Controlled Release of D- Limonene Encapsulated in Spray- Dried Cyclodextrin Powder under Linearly Ramped Humidity Chisho Yamamoto,1,2 Tze Loon Neoh,2 Hirokazu Honbou,2 Hidefumi Yoshii,2 and Takeshi