Edible Liquid Marbles and Capsules Covered with Lipid Crystals

Journal of Oleo Science Copyright ©2012 by Japan Oil Chemists’ Society J. Oleo Sci. 61, (9) 477-482 (2012) Edible Liquid Marbles and Capsules Covered with Lipid Crystals Yuki Kawamura1, Hiroyuki Mayama2 and Yoshimune Nonomura1＊ 1 Department of Biochemical Engineering, Graduate School of Science and Engineering, Yamagata University ( 4-3-16 Jonan, Yonezawa 992- 8510, JAPAN) 2 Research Institute for Electronic Science, Hokkaido University ( N21W10, Sapporo 001-0021, JAPAN) Abstract: Liquid marbles are water droplets covered with solid particles. Here we show a method for the preparation of edible liquid marbles and capsules covered with fatty acid crystals and triacylglycerol crystals. We prepared liquid marbles using a simple method; namely, a water droplet was rolled on lipid crystals in petri dishes. The resulting marbles were converted to capsules covered with a lipid shell by heating. These marbles were stable not only on glass surfaces but also on water surfaces because they had rigid hydrophobic exteriors. The lifetime of the liquid marbles on water depended on the alkyl chain length of the lipid molecules and the pH of the water. These findings are useful for applying liquid marbles to food, cosmetic, and medical products. Key words: Liquid marble, Hydrophobic material, Fatty acid, Triacylglycerol 1 INTRODUCTION oral formulations becomes possible. Liquid marbles and dry water are water droplets covered Here, we propose a method for the preparation of liquid with solid particles such as hydrophobic silica and fluorine marbles covered with fatty acid crystals and triacylglycerol resin particles; here, liquid marbles are macroscopic single crystals because these lipid crystals are suitable stabilizing water droplets, while dry water is a white powder contain- agents for edible liquid marbles. The advantages of such ing water droplets surrounded by solid particles1－7）. They crystals are as follows: first, they can be adsorbed on air- have received the attention of material scientists because liquid interfaces and form stable liquid marbles because of certain useful applications; for example, dry water have they are hydrophobic particles, i.e., the contact angles of been applied to some cosmetic products8, 9）. Capsules con- water droplets on these lipid crystals are 90°－150°19）. taining drug compounds and stimulus-responsive liquid Second, the toxicity of these lipids is low enough to allow marbles were prepared by covering marbles with a solid their use in food products or oral formulations, e.g., 50％ particles based on a copper substrate or polystyrene of the lethal dose was 4640 and 22 mg kg－1 when stearic latex10, 11）. Wang et al. reported a gas storage system in acid was given to rats by oral or intravenous administra- which methane molecules were absorbed in the water of tion, respectively20－22）. In the present study, we prepared the marbles12, 13）. Bormashenko et al. showed that liquid liquid marbles covered with fatty acid crystals and triacylg- marbles could be used effectively for the detection of water lycerol crystals and checked their stability on glass and pollution from oils and petroleum14）. However, there have water surfaces. Furthermore, we evaluated the effect of been few examples of food products or oral formulations aqueous pH on their stability because the ionization state consisting of liquid marbles because of the toxicity of these and solubility of fatty acids vary with the pH. hydrophobic particles; the thermal degradation products and fine particles of polytetrafluoroethylene are toxic and cause acute inflammatory responses in the lung15, 16）. Al- though amorphous silica has low toxicity, its use is limited 2 EXPERIMENTAL PROCEDURES in many countries17, 18）. If liquid marbles are stabilized with 2.1 Materials edible solid particles having low toxicity, a facile encapsula- Five kinds of fatty acids［lauric acid（CH（3 CH2）10COOH, tion technology for the preparation of food products and LUNAC L-98, length of alkyl chain＝C12, melting point＝＊Correspondence to: Yoshimune Nonomura, Department of Biochemical Engineering, Graduate School of Science and Engineering, Yamagata University, 4-3-16 Jonan, Yonezawa 992-8510, JAPAN E-mail: [email protected] Accepted March 28, 2012 (received for review January 31, 2012) Journal of Oleo Science ISSN 1345-8957 print / ISSN 1347-3352 online http://www.jstage.jst.go.jp/browse/jos/ http://mc.manusriptcentral.com/jjocs 477 Y. Kawamura, H. Mayama and Y. Nonomura 321-324 K）, myristic acid（CH（3 CH2）12COOH, LUNAC we estimated the lifetimes of the liquid marbles on water MY-98, C14, 330-332 K）, palmitic acid（CH（3 CH2）14COOH, surfaces when the marbles were placed onto 5 g of aqueous LUNAC P-95, C16, 339-340.5 K）, stearic acid（CH（3 CH2）16 solutions of hydrochloric acid or sodium hydroxide with pH COOH, LUNAC S-98, C18, 346-349 K）, behenic acid（CH3 2－12. We measured the contact angle using a DM-501 （CH2）20COOH, LUNAC BA, C22, 359-360 K）］were obtained contact angle meter（Kyowa Interface Science, Tokyo, from Kao Corporation. Three kinds of triacylglycerols Japan）following the application of 2 μL of a water droplet ［trilaurin（（CH（3 CH2）10COO）（3 CH2CHCH2）, 324.5 K）, tri- on the liquid marble surface. myristin（（CH（3 CH2）12COO）（3 CH2CHCH2）, 334-335 K）and tripalmitin（（CH（3 CH2）14COO）（3 CH2CHCH2）, 343.5 K）］ were purchased from Tokyo Chemical Industry Co., Ltd. Tristearin（（CH（3 CH2）16COO）（3 CH2CHCH2）, 351.5 K）was 3 RESULTS purchased from Wako Pure Chemical Industries Co., Ltd. 3.1 Preparation of liquid marbles and capsules covered with lipid crystals. 2.2 Preparation We succeeded in preparing liquid marbles using a simple The procedures for the preparation of liquid marbles and method; namely, a water droplet was rolled on lipid crystals capsules are shown in Fig. 1. Initially, the lipid crystals in petri dishes. An image of the liquid marble covered with were ground using an agate mortar and were separated behenic acid crystals is shown in Fig. 2a. The surface of into large particles（particle size＝355－500 μm）and small the water droplet（diameter ≈ 3 mm）w as covered with both particles（particle size＝less than 180 μm）using sifters. The the large and small particles of behenic acid. If the marble large particles（1.0 g）and small particles（1.0 g）with amor- was stabilized using only the large particles, it was unstable phous shape were mounted on petri dishes A and B（inside owing to the presence of vacant spaces between the parti- diameter＝3.3 cm）, respectively. A droplet of water（5 μL） cles. On the other hand, when the water droplets were containing 0.05 wt％ rhodamine 6G（reagent grade; Kanto covered with only the small particles, these marbles col- Chemical Co.）was dripped onto petri dish A from a micro- lapsed several tens of minutes after their preparation. The syringe and was rolled with a spatula for several seconds. film consisting of small fatty acid crystals was too fragile to Rhodamine 6G stained the water phase and facilitated the hold the marble state against mechanical stimuli or gravity identification of the mixed states. From the results of pre- force. In the simple rolling method, all lipid crystals that liminary studies, we had determined that rhodamine 6G were examined in the present work formed liquid marbles. did not affect the condition of the binary systems. Next the The resulting marbles were converted to capsules covered formed droplet was moved to petri dish B and was again with a lipid shell by heating（Fig. 2b）. Systematic tests pre- rolled with a spatula. To obtain capsules, the liquid marbles dicted that near spherical capsules could be obtained when were heated at about melting point of the lipid for 30－40 the marbles were preserved at 358 K for 30－40 min. De- min. In this process, the marbles were introduced into a formed capsules were obtained by heating at higher tem- sealed vehicle with water to maintain a high level of humid- peratures. At temperature extremely higher than the ity. melting point, for example at 368 K for behenic acid, al- though their capsule structure was maintained, the marbles 2.3 Measurements were deformed by their own weight because the lipid film We observed the liquid marbles with a microscope（Dino- was melted rapidly. At lower temperature, the evolution lite Digital Microscope, ANMO Electronics Co., Ltd, from marbles to capsules was not observed. Hsinchu, Taiwan）. We checked the stability of the marbles on glass when they were put in the sealed petri dishes with 3.2 Stability of the liquid marbles on glass. water under a high-humidity environment. Furthermore, Figure 3 shows the lifetimes of the liquid marbles on Fig. 1 Method for the preparation of liquid marbles and capsules covered with lipid crystals. 478 J. Oleo Sci. 61, (9) 477-482 (2012) Edible Liquid Marbles and Capsules 3.3 Hydro phobicity and stability on water surfaces. The hydrophobicity of the marbles depended on the types of lipids covering the water droplets. The marbles covered with lauric acid（C12）and myristic acid（C14）crystals absorbed a droplet of water immediately following the application of 2 μL of water to their surfaces. In contrast, the marbles covered with other lipids repelled water, which formed a droplet with a 120°－140° contact angle（θ）, as shown in Fig. 4a. Relation to their hydrophobicity, floating ability of these hydrophobic marbles and capsules were in- vestigated. First, it was found that the marbles showed stable floating on water with pH 7（Fig. 4b）, while the capsules obtained from the liquid marbles collapsed just after contact with the water. Such floating ability was observed for the liquid marbles covered with lipids whose alkyl chains were longer than C16, while the marbles covered with lauric（C12）or myristic（C14）acid collapsed just after contact with water.

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