Microencapsulation of ascorbic acid by complex coacervation: Protection and controlled release
Introduction
Antioxidants are compounds that can either inhibit or reduce the lipid oxidation of fats, oils and fatty foods, as well as having functional mechanisms that have been widely studied (Mukai, Morimoto, Okauchi, & Nagaoka, 1993). Ascorbic acid (AA) is an important antioxidant found naturally in fruits and vegetables. It is used as an ingredient or additive in foods as well as to fortify foods due to its antioxidant function. It is, however, a very unstable compound and easily degraded.
AA degradation is strongly influenced by reactions catalyzed by transition metal ions, such as Cu2 + and Fe3 +, heat, light, pH (in alkaline media), high oxygen concentration and high water activity, all of which results in the increase of both the solubility of the ascorbic acid and the oxygen dissolution. AA degradation is also associated with a loss of color both in the presence and absence of amines (Buettner, 1988, Buettner, 1993, Fennema et al., 2010, Khan and Martell, 1967, Liao and Seib, 1987, Tannenbaum et al., 1985, Ukhun and Dibie, 1991). Microencapsulation could be used as an alternative to minimize the factors that interfere with the stability of AA, allow for controlled release and mask its acidic taste, which can be unappetizing.
According to Shahidi and Han (1993), microencapsulation can be defined as a process by which a membrane surrounds small particles of solids, liquids or gases with the objective of protecting the material from the adverse conditions of the environment, such as light, moisture, oxygen and interactions with other compounds. Microencapsulation can also stabilize the product, increase its shelf life and promote controlled release from the capsule under pre-established conditions. Coacervation is a chemical colloidal phenomenon that can be defined as “the partial immiscibility of two or more isotropic liquids, at least one being in the colloidal state” (Soper, 1995). This technique can be used to encapsulate lipophilic materials, and because AA is a hydrophilic compound, this study proposed an adaptation for applying this technique in practice. Thus, before coacervation, a primary W/O emulsion was prepared, followed by a double W/O/W emulsion.
The encapsulation of AA represents a promising alternative to overcome problems related to its application and its instability. There have been multiple studies in the literature that have addressed this topic, but they used different methods and encapsulating agents. For example, Trindade and Grosso (2000) encapsulated AA by spray drying using gum arabic and rice starch as the wall materials. Pierucci, Andrade, Baptista, Volpato, and Rocha-Leão (2006) also microencapsulated AA by spray drying using a concentrated pea protein as the wall material. Uddin, Hawlader, and Zhu (2001) compared the characteristics of AA microcapsules prepared by different techniques, including melt dispersion, solvent dispersion and spray drying, whereas Lee, Ahn, and Kwak (2004) microencapsulated AA by spray drying with polyacylglycerol monostearate for use in milk fortification. Farhang, Kakuda, and Corredig (2012) studied the stability of AA encapsulated in liposomes stored at 4 °C at two pH values (pH 3 and pH 7), and Rozman and Gasperlin (2007) encapsulated AA by W/O micro-emulsions. In general, all of these studies showed an effective increase in the stability of AA compared to the material in its free form in solution. Currently, however, there are no reports in the literature concerning the microencapsulation of AA using complex coacervation. Thus, the objective of this study was to microencapsulate AA by complex coacervation, structurally and physicochemically characterize the capsules obtained, and determine the stability of the encapsulated material.
Section snippets
Material
Pure ascorbic acid (AA) (Synth, Diadema/SP, Brazil) was used as the active material, and corn oil (Cargill, Brazil) was used to prepare the simple emulsion. Food grade gelatin (Gelita South America, Brazil) and gum arabic (Dinâmica Química Contemporânea Ltda., Brazil) were used as the wall materials for the preparation of the double emulsion, and polyglycerol polyricinoleate (PGPR 90) (Danisco, Denmark) was used as the emulsifier.
Preparation of microcapsules
The microcapsules were formed according to the method described
Morphological characterization of the microcapsules by optical and scanning electronic microscopy
Fig. 1A, B and C shows optical microscopy images of the production of both simple and double emulsions as well as of the coacervated microcapsules. An evaluation of the images obtained showed that the different concentrations of core and wall materials presented similar morphological characteristics and caused no modifications in the morphology of the microcapsules obtained.
The microcapsules were shown to be in the form of a reservoir in which the core was perfectly surrounded by the wall
Conclusions
According to the proposed objectives and the results obtained, this study showed that the use of the double emulsion technique prior to complex coacervation made it possible to obtain microcapsules with a hydrophilic core. The high values obtained for the encapsulation efficiency of AA proved the effectiveness of this technique for encapsulation.
The low hygroscopicity values obtained proved that the powder could be easily stored and handled. The spherical structure of the non-dehydrated
Acknowledgments
The authors thank FAPESP for the scholarship conceded (Process 2011/03882-9).
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