Elham Ansarifar; Fakhri Shahidi; Mohebbat Mohebbi; Arash Koocheki; Navid Ramazanian
Abstract
Introduction: Microencapsulation has become an important technique in the food industry. One of the methods of producing microcapsules is to use layer-by-layer adsorption, in which oppositely charged polyelectrolytes are adsorbed consecutively onto a colloidal template. Creating multilayer films based ...
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Introduction: Microencapsulation has become an important technique in the food industry. One of the methods of producing microcapsules is to use layer-by-layer adsorption, in which oppositely charged polyelectrolytes are adsorbed consecutively onto a colloidal template. Creating multilayer films based on electrostatic interactions between oppositely charged components was introduced in 1991 by Decher et al. Layer-by-layer (LbL) polyelectrolyte deposition has become a popular technique for preparing polyelectrolyte capsules because of its ability to create highly tailored capsule shells through a simple, inexpensive and easily controllable adsorption process. It has been applied to produce capsules of various sizes, ranging from the nanometer to micrometer scale, with well-defined barrier properties. In this technique, assembly is driven by the electrostatic attraction of oppositely charged materials to form polyelectrolyte shells. The structure of the polyion layered capsule shell is determined mainly by the electrostatic interactions between the polyions used. The mechanical strength and permeability of the capsules can be controlled by varying the number of layers or by changing the characteristics of the encapsulating materials. The purpose of this study was to produce microcapsules using supramolecular assemblies consisting of common food ingredients such as soy protein isolate (SPI) and high methoxyl (HM) pectin. Moreover, some features of the developed microcapsulation were studied.
Materials and methods: SPI fibrils were prepared based on the method developed by Akkermans et al., (2008) and its morphology was studied using transmission electron microscopy (TEM) and atomic force microscopy (AFM). 0.5% (w/w) SPI fibril and pectin solutions were prepared by mixing at pH 3.5 were left stirring overnight. The LbL process for the production of microcapsules with protein fibril-reinforced nanocomposite shells has been described in Humblet-Hua et al., 2012. It starts with the production of A 2% w/w emulsion of (0.05 gr diacetyl in 1.95gr sun flower oil) in fibril SPI solution is produced using a homogenizer with a rotor-stator dispersion tool using a setting of 13500 rpm for 90 S. Because the proteins are below their isoelectic point, the emulsion droplets have a positive charge. To avoid interactions between the nonadsorbed SPI and the biopolymer of the next layer, the droplets are separated from the serum by means of centrifugation. After the isolation, the droplets are dispersed into a solution of HMP. The HMP is negatively charged at the chosen pH of 3.5. The bilayered droplets can be isolated again and dispersed in a fibril solution to deposit a third layer of a positively charged mixture of SPI fibrils. Subsequently, additional layers of HMP and SPI fibrils can be deposited by repeating the same procedures. Some features of the microcapsulation, including size, zeta potential, and morphology and release kinetics were studied.
Results & discussion: TEM and AFM micrographs showed that SPI fibrils obtained had a contour length of a few hundred nanometers, thickness of between 1 and 10 nm and its structure is highly branched. One of the most common problems reported in previous studies using the LbL technique to produce multilayer particles, is the tendency for flocculation. In the present system, this problem was not observed. The size distribution of isolated emulsion droplets (templates) did not change significantly from 1-layer droplets to 5-layer droplets. In other words, the emulsion droplets were stable against flocculation after applying more layers of polyelectrolytes. The Sauter mean diameters D (3, 2) of these droplets fluctuated between 5 and 7 µm and slightly increased as the number of layers increased; noting that the emulsion droplets were poly-dispersed. Another possible problem that may occur using the LbL technique is the complex formation between non-adsorbed protein and the pectin molecules. These complexes with a typical diameter smaller than 1 mm were not detected here. Result showed that the zeta potential distribution of emulsion droplets reverses from about plus (+) 30 mV (odd number of layers with SPI fibrils as outer layers) to about negative (-) 20 mV (even number of layers with HMP as outer layers) confirming the layer-by-layer adsorption based on electrostatic attraction. Comparing SEM of microcapsules with various numbers of layers, an improvement in shell strength can be seen. Indentation is observed on 1-layer microcapsules showing that there are defects on the shell. They could be formed during the drying process or they are shell defects due to incomplete coverage of materials, meaning more layers are needed to fully cover the microcapsule shell. These defects are seen less on 5-layer microcapsules. These observations indicate that the more layers the more consistent the shells and the more resistant. It is against the physical drying process. Results showed that the time of the maximum in release shifts to higher values as the number of layers of the capsules increased. We clearly see that increasing the number of layers in the shell of the capsules leads to a delay of the release of diacetyl and maximum release time as a function of the number of layers is increasing steadily which show the release can be delayed even more by adding additional layers. These results prove that the release properties of the multilayer capsules can be tuned by controlling the number of layers in the shell of the capsules. The modeling results of four different kinetic models are indicated that the Rigter–Peppas was an appropriate model for diacetyl release prediction from multilayer microcapsulation. It could be attributed that the release mechanism is mostly governed by the Swelling–Fickian mechanism.
Conclusion: In this study, the microcapsules were produced using the LbL technique and food-grade SPI fibrils and HMP. The microcapsules had a poly-disperse size distribution. No flocculation of microcapsules during applying of additional layers was observed. It was found that increasing the number of layers, decreases the release rate of diacetyl. The diacetyl release data were kinetically evaluated by zero-order, first-order, Higuchi, and Rigter–Peppas models and the results showed that the release phenomena is mostly governed by the Fickian mechanism. Since the materials are food-grade, the applications of these microcapsules can include food products or pharmaceutical purposes.
Mohsen Zandi; Mohebbat Mohebbi; Mehdi Varidi; Navid Ramazanian
Abstract
.Introduction: Flavor release from food during consumption in the mouth plays an important role in flavor perception and influenced by the food matrix. Since, food matrix changes biochemically and physically during eating, therefore, food flavor microencapsulation results in controlled release at specific ...
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.Introduction: Flavor release from food during consumption in the mouth plays an important role in flavor perception and influenced by the food matrix. Since, food matrix changes biochemically and physically during eating, therefore, food flavor microencapsulation results in controlled release at specific situations. On the other hand, stability and availability of flavors are affected by food processing and storage. To control the flavor release at specific condition during consumption or stability and availability during food processing and storage; it is essential to encapsulate flavor components before use in food complex. Encapsulation is the term for a collection of technique that used as delivery of active and bioactive parts. This novel technology enables isolated of gases, liquid droplets, or solid particles in the core of microscopic vesicular system with porous or non porous semi permeable shell that release occurs in response to the specific situations. Controling release of active compound depends on microcapsule characteristics such as pore size, mechanical stability of the colloidal shell, shell thickness and shell permeability; molecular size and solubility of active parts in the shell and properties of the release media including shear force, temperature, pH, ionic strength, etc. This paper presents the formation and characterization of novel diacetyl encapsulated alginate-whey protein concentrate (AL-WPC) microcapsules. Diacetyl release was investigated at simulated mouth condition in different ratios of artificial saliva (0, 1:4 and 1:8) and three various oral shear rates (0, 50 and 100 s-1) and the diffusion coefficient was estimated using Fick’s law. The main aim of this work was to develop a prediction model to study the flavor release from microcapsules. Materials and Methodes: Aiming to show the applicability of our agent-based model platforms, the release of 2,3-butanedione (diacetyl) from alginate-whey protein concentrate (AL-WPC) microcapsules was used as a case study to validate our simulation model based on NetLogo platforms. For this purpose, our previous work on evaluation of diacetyl encapsulated alginate-whey protein microspheres release kinetics and mechanism at simulated mouth conditions was used (Zandi, M., Mohebbi, M., Varidi, M., Ramezanian, N., 2014). In previous our work, encapsulated diacetyl release was measured at three oral shear rates (0, 50 and100 s-1) and various ratios of saliva to microcapsule (0, 1:4 and 1:8) simulating mouth conditions. Then, experimental release data were fitted using different kinetic models. It was found that release from these microcapsules followed a classical Fickian diffusion. We use release data for calculating release rate. For model validating, diffusion equation was fitted to the experimental data, and diffusion coefficient was obtained for diacetyl release at various mouth conditions. To this purpose, the following model was obtained by solving unsteady diffusion equation in spherical coordinate:(M(t))/M_0 =100-exp(-(3×D×(R+b))/(R^2×b)×t) (1)where M (t) and M0 are the diacetyl release at time t and 0 respectively, R is a microcapsules radius (m), t is time, D is the diffusion coefficient and b is the shell thickness (m). We also use diffusion coefficient to calculate permeability for each specific condition by equation (2): P=(D×K)/b (2)Where P is the permeability coefficient, D is the diffusion coefficient and K is the partition coefficient.Finally, the model and experimental data were analyzed using Matlab software (R2007).Result and Discussion: In our study, AL-WPC microcapsule was fabricated by emulsification/internal gelation method, and diacetyl was loaded into microcapsule. Most of microspheres had a completely spherical shape with smooth surface, and range in size from 20-150 μm. The diacetyl encapsulated microsphere had a porous and smooth shell with some holes that caused the quicker diacetyl release initially. The mean hydrodynamic diameter 112.8 ± 0.9 μm (mean value ± SD for n= 2) was measured via particle size analyzer (DLS). the high efficiency of 79.34% was obtained for diacetyl encapsulated AL-WPC microcapsule. About 20% of diacetyl was loosed because of the solubility and volatility of the diacetyl molecule (diacetyl is a low molecular weight and water soluble component).. Conclusion: It was showed that the shear rate of release media had a significant (p
