# Introduction itherto, many kinds of microcapsules have been prepared and applied in the various fields such as cosmetics, food, drugs, paintings, adhesives, textile, electric materials and so on [1][2][3]. The main functions of microcapsules are to protect the core materials from environment for a long time, to optionally release the core materials according to stimuli, to modify the surface of core material [1]. The microcapsules with these functions can be prepared by selecting the core and the shell materials with the desired chemical and physicochemical properties and by developing the microencapsulation procedure. If a few core materials with the different chemical and physicochemical properties could be microencapsulated at the same time, the multiple functions may be given to the microcapsules. For an example, in the case of applying the microcapsules to the food, cosmetics, drugs and textile, the nontoxic materials have to be used as the shell material. Furthermore, if one of the core materials tried to microencapsulate at the same time is hydrophilic and the other hydrophobic, the newly devised microencapsulation procedure has to be developed by using the designated core and shell materials. It is well known that grape polyphenol is water soluble and has a few physiological effects such as antiaging effect and anti-oxidation effect, but has a few defects such as a bitter taste and reaction activity. Accordingly, if grape polyphenol could be microencapsulated with some edible shell materials, the application fields of grape polyphenol may be considerably extended [4]. On the other hand, ?-tocopherol (vitamin E) has a few physicological effects such as anti-aging effect and prevention effect of lifestyle related disease, but has a few defects such as light and heat destruction and easy oxidization [5][6][7]. Accordingly, if ?-tocopherol oil could be microencapsulated with some nontoxic materials, various application fields for ?-tocopherol may be expected. Furthermore, the microcapsules with the multiple functions can be prepared by microencapsulating these core materials at the same time. However, as ?-tocopherol is hydrophobic and grape polyphenol is water soluble, in order to prepare the microcapsules containing these core materials as much as possible, it is necessary to develop the preparation method by using the nontoxic shell materials. The spray methods such as spray drying, spray chilled and spray gelling for preparing the various kinds of microcapsules are well known to be the effective methods, because the selectivity for the core and the shell materials is extremely wide and the continuous production is capable [8,9]. Also, the diameters of microcapsules can be easily controlled by changing the volumetric flow velocity of feed and the spraying pressure [10][11][12]. Accordingly, the spray method may be suitable to the preparation of microcapsules containing the dual cores with the different chemical and physicochemical properties at the same time. The purposes of this study are to develop the preparation method of microcapsules containing the hydrophilic and the hydrophobic core materials, to characterize the microcapsules and to discuss the formation mechanism. # II. # Experimental a) Materials Materials used to prepare the microcapsules containing the dual core materials were as follows. Grape Polyphenol (GP) (Sunprite Ind. Co., Ltd, Tokyo, Japan) was used as the first core material and ?tocopherol (?-oil) (Wako Pure Chemical Ind. Co., Ltd, Tokyo, Japan) was used as the second core material. Sodium Alginate (Alg?Na) (Wako Pure Chemical Ind. Co., Ltd, Tokyo, Japan) was used as the shell material. Calcium chloride (Wako Pure Chemical Ind. Co., Ltd, Tokyo, Japan) was used as the gelling agent for sodium alginate. Poem PR-100, DAO-7S and Soy bean Lecithin (SL) (Riken Vitamin Ind. Co., Ltd, Tokyo, Japan) were used as the oil soluble surfactants. ML-750 (SY Glystar : Sakamoto Yakuhin Ind. Co., Ltd, Tokyo, Japan) was the water soluble surfactant. b) Verification of effect of oil soluble surfactant species on stability of (W/O) emulsion and (W/O)/W emulsion In order to increase the content of core materials as much as possible, it is necessary to stabilize the (W/O) emulsion and the (W/O)/W emulsion with the help of surfactant species. For this purpose, the effect of oil soluble surfactant species on the stability of (W/O) emulsion and the (W/O)/W emulsion was estimated as follows. The GP aqueous solution of a given volume was poured into the ?-oil dissolving the oil soluble surfactant and homogenized to form the (W/O) emulsion. Then, the (W/O) emulsion was observed by visual confirmation at the constant time intervals. If the stability of (W/O) emulsion is lower, the (W/O) emulsion may be broken and the phase separation may be observed. Furthermore, the (W/O) emulsion thus prepared was poured into the Alg?Na aqueous solution and homogenized to form the (W/O)/W emulsion. The stability of (W/O)/W emulsion was observed similarily as stated just above. If the stability of the (W/O)/W emulsion is lower, the (W/O)/W emulsion may be broken and the phase separation may be observed. On the other hand, two kinds of the (S/O) dispersions, where GP powder was dispersed in the ?oil, were prepared as follows. First, the (S/O) dispersion was prepared by directly adding GP powder into the ?-oil and stirred. Second, the (S/O) dispersion was prepared by adding the GP aqueous solution into the ?-oil, forming the (W/O) emulsion and then, by removing water from the (W/O) emulsion as shown in Figure 3. In this operation, the time for removing water from the (W/O) emulsion was changed from 0 to 12h at 50? in order to change the diameter of inner water droplets, namely the diameter of GP powder. Furthermore polyethylene glycol (PEG 600) was dissolved in the inner water phase in order to try to investigate whether the content of GP could be increased or not. In this fundamental experiment, the spraying conditions such as the volumetric flow velocity of feed and the spraying pressure, the oil soluble surfactant species and the time for removing water from the (W/O) emulsion were changed stepwise. The experimental conditions are shown in Table 1. # Table 1 : Experimental conditions d) Characterization Mean diameter The diameters of inner water droplets and GP powder were measured by the instrument for measuring the particle size (Otsuka Denshi Co., Ltd, Tokyo, Japan: ELS-8000). The diameters of microcapsules were measured by the particle size analyzer (Shimazu Seisakusho Co., Ltd, Kyoto, Japan: SALD-3000) Here, the mean diameters (dp) were obtained as the mean Sauter diameters. # Microencapsulation efficiency The microcapsules of a given weight were added into distilled water of 100 cm3, broken by the homogenizer and then, irradiated supersonic for 10 min to perfectly dissolve GP in the water phase. The amount of GP dissolved in the sampled water was measured by the spectrophotometer. For this measurement, the calibration curve between absorption degree and the concentration of GP was obtained beforehand. The microencapsulation efficiency (Fc) was estimated by the following equation. # Observation of emulsion and microcapsules The (W/O)/W emulsion, the (S/O)/W emulsion and the microcapsules were observed by the optical microscope (OLXMPUS Co., Ltd, Tokyo, Japan: BHT-MV) and their photographs were taken by digital camera. From these photographs, the stability of the multiple emulsions and the formation of microcapsules were observed. # III. Results & Discussion a) Effect of oil surfactant species on stability of (W/O) emulsion and (W/O)/W emulsion Figure 4 shows the results investigating the effect of oil soluble surfactant species on the stability of the (W/O) emulsion (Figure 4a) and the (W/O)/W emulsion (Figure 4b). Here, the transient feature of each emulsion was measured to estimate the stability. From Figure 4a, the following valuable results were obtained. Just after preparing the (W/O) emulsion, in the case of PR-100 and SL, the (W/O) emulsion was brown color, but in the case of DAO-7S, the (W/O) emulsion was dark brown color. Here, the dark brown color means that the (W/O) emulsion is broken and the GP aqueous solution is separated. 6 shows the optical microscopic photographs of microcapsules prepared under the same conditions as in Figure 5. From these photographs, it was found that there were spherical and irregular microcapsules and many ?-oil droplets were microencapsulated well with the gelled Alg?Na shell. Figure 7 shows the dependences of the mean diameters (dp) and their dispersion degree (?/dp) of microcapsules on the spraying pressure (P). Here, ? is the standard deviation of distribution of diameters. The mean diameters and the dispersion degrees decreased from 63 ?m to 25?m and from 3.2 to 1.7 with increasing the spraying pressure, respectively and almost become constant at P=0.3 [MPa]. From these results, it was found that the smaller and more uniform microcapsules could be prepared by increasing the spraying pressure. Figure 8 shows the dependence of the microencapsulation efficiency (?) on the spraying pressure. The microencapsulation efficiency was almost kept constant (?=30%) in spite of increasing the spraying pressure. This lower microencapsulation efficiency should be attributable to the unstable (W/O) emulsion. Figure 11 shows the transient water droplet diameters (dpW) with the time for removing the water phase. From this figure, it was found that the mean diameters of inner aqueous droplets were gradually decreasing with the removing time and become constant at the point of elapsing 6h and the (W/O) emulsion was changed to the (S/O) dispersion. Accordingly, the mean diameters become equal to the diameters of GP powder. Figure 12 shows the dependence of the mean diameter of inner water droplets on the concentration (CL) of SL (Figure 12(a)) and that of the mean diameters (dpS) of GP powder particles on the mean diameter of inner water droplets (Figure 12 (b)). The mean diameters of inner water droplets decreased with the surfactant concentration and the GP powder particle diameters was in proportion to the mean diameters of inner water droplets. It is well known that the content of core materials can be increased by decreasing the diameters of core materials [12][13]. Accordingly, the stability of the (S/O) dispersion could be increased by increasing the surfactant concentration. As a result, the microencapsulation efficiency could be increased. Figure 13 shows the dependence of the microenc-apsulation efficiency (?) on the mean diameters (dpW) of inner water droplets and the GP powder particle diameters (dpS), respectively. From Figure 13, it was found that the microencapsulation efficiency could be increased by decreasing the diameters of inner water droplets and GP powder particles and the microencapsulation efficiencies in the case of the (S/O) dispersion was larger than those in the case of the (W/O) emulsion. Furthermore, the addition of polyethylene glycol (PEG 600) in the inner water phase could considerably increase the microencapsulation efficiency. The effect of addition of PEG may be attributable to the fact that the adsorption layer of PEG on the surface of GP powder particles was formed as shown in Figure 11 (b) and the stability of GP powder in the ?-oil could be increased due to increase in affinity between GP powder and the ?-oil. In order to increase the content of core material, the formation of finer water droplets dissolving the hydrophilic core material, the formation of the (S/O) dispersion by removing water from the inner water and the formation of adsorption layer of stabilizer on the surface of powder particles were found to be considerably effective. IV. # Conclusion It was tried to prepare the microcapsules containing the dual cores, namely the (W/O) emulsion or the (S/O) dispersion by the spray-gelling method. The following results were obtained. The microcapsules with the mean diameters from 15?m to 70?m could be prepared. ![c) Preparation of microcapsulesThe flow chart and the schematic diagram of experimental apparatus for preparing the microcapsules are shown in Figure1and Figure2, respectively.](image-2.png "") 12![Figure 1 : Flow chart for preparing microcapsules](image-3.png "Figure 1 :Figure 2 :") 3![Figure 3 : Scheme for changing (W/O) emulsion to (S/O) dispersion Then, the (W/O) emulsion or the (S/O) dispersion thus prepared was poured into the Alg?Na aqueous solution dissolving the water soluble surfactant (ML-750) and stirred to form the (W/O)/W emulsion or the (S/O)/W emulsion by homogenizing. The (W/O)/W emulsion or the (S/O)/W emulsion was sprayed into the calcium chloride aqueous solution through the nozzle with the diameter of 1 mm to prepare the microcapsules containing the (W/O) emulsion or the (S/O) dispersion.](image-4.png "Figure 3 :") 45![Figure 4 : Effect of oil surfactant species on stability of (W/O) emulsion and (W/O)/W emulsion After 1 month and 2 months, the (W/O) emulsions prepared with PR-100 and SL were stable and brown color. Similarly, from Figure 4b, the following results were obtained. Just after preparing the (W/O)/W emulsion, in the case of SL, the (W/O)/W emulsion was stable and brown white color due to keeping the (W/O)/W emulsion, but in the case of PR-100 and DAO-7S, the (W/O)/W emulsions were quasi stable and brown color. After 24h, the (W/O)/W emulsions prepared with PR-100 and DA O-7S were broken and the GP aqueous solution was separated. However, the (W/O)/W emulsion prepared with SL was stable and brown white color. After 1 month, the (W/O) droplets was kept and floated on the Agl?Na aqueous solution, although a little GP aqueous solution dissolved in the Agl?Na aqueous solution. From these results, it was found that the (W/O) emulsion and the (W/O)/W emulsion prepared with SL were stable. Hereafter, SL as the oil soluble surfactant was used for preparing the (W/O) emulsion and the (W/O) /W emulsion. b) Observation of (W/O)/W emulsion and microcapsules Figure 5 shows the optical microscopic photograph of the (W/O)/W emulsion. The GP aqueous solution droplets are dark color and observed in the ?-oil droplets which are dispersing in the Alg?Na aqueous solution. The GP aqueous solution droplets were found to stably disperse in the ?-oil droplet.](image-5.png "Figure 4 :Figure 5") 5![Figure 5 : Optical microscopic photographs of (W/O)/W emulsion](image-6.png "Figure 5 :") ![Figure6shows the optical microscopic photographs of microcapsules prepared under the same conditions as in Figure5. From these](image-7.png "Figure") 6![Figure 6 : Optical microscopic photographs of microcapsules c) Effects of spraying pressure and volumetric flow velocity on mean diameters of microcapsules and microencapsulation efficiency](image-8.png "Figure 6 :") 7![Figure 7 : Depandences of mean diameter and dispersion degree on Spraying pressure](image-9.png "Figure 7 :") 8![Figure 8 : Depandences of microencapsulation effciency on spraying pressure Figure 9 shows the dependencies of the mean diameters and their dispersion degrees of microcapsules on the volumetric flow velocity (VR) of the (W/O)/W emulsion. With increasing the volumetric flow velocity of the (W/O)/W, the mean diameter increased from 15?m to 25?m and the dispersion degree decreased from 2.0 to 1.2. From these results, it was found that the larger and more uniform microcapsules could be prepared by increasing the volumetric flow velocity of the (W/O)/W emulsion.](image-10.png "Figure 8 :") 109![Figure 10 shows the dependence of the microencapsulation efficiency on the volumetric flow velocity of the (W/O)/W emulsion. The microenc-apsulation efficiency slightly increased from 28.0% to 32.0 %. However, the microencapsulation efficiency is very low because of the unstable (W/O) emulsion, too.](image-11.png "Figure 10 Figure 9 :") 11![Figure 11 : Transient inner water droplet diameters](image-12.png "Figure 11 :") 12![Figure 12 : Dependence of water droplet diameters on surfactant concentration and dependence of GP powder particle diameters on water droplet diameters](image-13.png "Figure 12 :") 1![The mean diameters decreased with the spaying pressure and increased with the volumetric flow velocity. 2. The microencapsulation efficiency in the case of the (W/O) emulsion as the core was about 30% at most.3. The microencapsulation efficiency was considerablyimproved by changing the (W/O) emulsion to the (S/O) dispersion and by dissolving poly ethylene glycol in the inner water phase.](image-14.png "1 .") * Key Point of Preparation of Nano/Microcapsules MTanaka 2008 Techno System Publishing Co. Ltd Tokyo * Saishin Maikurokapseruka Gijutsu (Microencapsulation Technique) TKondo 1967 TES, Tokyo * MKoishi KEto HHigure Preparation + Utilization) Microcapsules. 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