Microencapsulation has been widely used to protect materials encapsulated the adverse conditions of processing and storage food. It is technology consists in packaging of active substances using thin polymer coating that act as a protective film applied the liquid, solid or gaseous material (Anal & Singh, 2007; Shoji et al., 2013). In the food science this technology has been seen as a promising method to overcome limitations related to instability of several incorporated substances in food, such as micronutrients (Nesterenko, Alric, Silvestre, & Durrieu, 2014; H. Wang, Shi, Cheung, & Xin, 2011), enzymes (Anjani, Kailasapathy, & Phillips, 2007), flavor (J. Wang, Cao, Sun, & Wang, 2011), probiotics (Gebara et al., 2013; Maciel, Chaves, Grosso, & Gigante, 2014), antioxidants and antimicrobial agents (Betz & Kulozik, 2011; Betz et al., 2012) reducing their interaction with the product, in addition, increasing its bioavailability after ingestion. The choice wall material and encapsulation technique is important factors for ensure protective effect encapsulated substance during processing, storage and ingestion of food. The wall material should be capable of forming a cohesive layer with the encapsulating agent (food ingredient), as well as being compatible, but immiscible with encapsulated agent, and provide resistance, impermeability, flexibility and stability. For its application in the food industry, the carrier material must be food grade, such as alginate, chitosan, carboxymethyl cellulose, carrageenan, gelatin and pectin, and they must be able to maintain the bioavailability of the compounds. (Anal & Singh, 2007; Joye, Davidov-pardo, & Julian, 2014). Differents techniques can be applied, such as spray drying, spray cooling, spray chilling, extrusion, freezing drying, cocristalization, simple and complex coacervation, liposomes and others (Gouin, 2004; Iris Julie Joye & McClements, 2014). However, the choice is depending of the encapsulated substance, characteristics desired in the final product and release mechanism. Once, the incorporation of particle in product can not be negatively affected sensory properties (Betz et al., 2012; Iris J Joye et al., 2014). This topic will be discussed the preparation, characterization and application of the microparticles in the food industry.
Currently, there are lot of techniques for the production of microparticles. The encapsulation techniques are divide in physical, (spray drying, spray chilling, spray cooling, fluid bed coating, extrusion, freeze drying and cocristalization), chemical (interfacial polymerisation) and physicochemical (simple and complex coacervation, ionotropic gelation and liposomes) methods. However, before selection one them, industry should have taken into account, the following points: processing and storage conditions, type of microcapsule desired (size and shape), properties of the carrier material, triggers and mechanisms of release, cost and scale of production (Shahidi and Han, 1993; Nedovic et al., 2011; Martín et al., 2015). Among the above described points properties of the carrier materials or wall materials are parameter important to be set, since affect the microparticle stability and microencapsulation efficiency. Thus, the wall material for application in foods must be approved as generally recognized the safe (GRAS) for food uses (carbohydrates, cellulose, gums, lipids and proteins), provide good rheological properties at high concentrations and easy handling during encapsulation process, be easily dispersed in the solvent or other material used during the encapsulation process, does not react with the encapsulating material during processing and storage and to promote the protection of the active material against environmental conditions. In practice, often the wall materials are used in combination to meet the above listed properties and its choice made based on the encapsulation technique. Spray drying, spray cooling, spray chilling, extrusion, emulsion, freezing drying, simple and complex coacervation, liposomes are the same techniques described for encapsulation of food ingredients. Spray drying is one of the oldest of the encapsulation technique and commonly applied in the food industry that has great potential for being economical, flexible, using equipment that is readily available and produces morphologically homogeneous microparticles. In this technique, the drying involves the use of a solution in a hot air stream to evaporate the solvent, which in the case of applications in food is water, followed by separation of the dried particles (Gharsallaoui et al., 2007; Shewan and Stokes, 2013, Martín et al., 2015). The parameter selection such as types atomizers (single-fluid, high-pressure spray nozzle or spinning disc), concentration and viscosity of the feed and feed flow rate, can be used for control the particles size, which size ranging between 5 a 80 μm (Shahidi and Han, 1993; Gharsallaoui et al., 2007; Nazzaro et al., 2012; Shewan and Stokes, 2013). It is most widely used for encapsulation flavors (Krishnan et al., 2005; Fernandes et al., 2014), lipids (Aghbashlo et al., 2012), vitamins (Donhowe et al., 2014), bacteria (Maciel et al., 2014), phenolic compounds (Fang and Bhandari, 2012), aroma (Costa et al., 2015) and heat sensitive compounds due to the very short exposure of the particle to hot air. Other encapsulation technique similar spray drying are spray cooling and spray chilling that involving also the dispersion of encapsulating material in a liquid and sprayed coating material from a nozzle in a controlled environment, with produce of small droplets. The difference between these techniques and spray drying is the temperature drying of the wall material using cold air, which enables the solidification of the particle (Poshadri and Kuna, 2010; Shewan and Stokes, 2013; Martín et al., 2015). Lipids are commonly used as carrier material in these techniques for encapsulating hydrophilic ingredients, as well as water-soluble vitamins (Nesterenko et al., 2014), and some flavors (Sillick and Gregson, 2012). Extrusion technique is the most popular method for encapsulation probiotic bacteria, because particle production is simple, use relatively low temperature and does not need organic solvents. It involves preparation a hydrocolloid solution, adding food ingredient or probiotic, then the solution is dripped through a syringe needle or nozzle into a solution that promotes gelation. The size of particles is influenced by the diameter of the needle or nozzle, the flow rate and viscosity of the solution, and the properties of the gelling environment (Nazarro et al., 2012; Martíns et al., 2015). Another commonly used technique is the emulsion. It is the food ingredient (discontinuous phase) is added in an oil (continuous phase), then, the mixture is homogenized to form two combination of emulsion: water/oil or oil/water and water/oil/water. Once the emulsion formed, this, then broken by adding CaCl2 to form the particles within the oil phase (Heindebach et al., 2012; Nazzaro et al., 2012). The particles are collected by centrifugation or filtration. The size of particles can be vary between 25 μm and 2 mm, due the speed agitation which controlled the size of the beads (Martíns et al., 2015). Freeze drying method is the dehydration simple process based upon sublimation, where the whole dehydration process is completed under low temperature and low pressure. This technique has been used for encapsulation heat sensitive compounds, as well as phenolic compounds (Rutz et al., 2013), anthocyanins (Khazaei et al., 2014), flavor (Kaushik and Roos, 2007) and probiotics (Martin-Dejardin et al., 2013; Dianawati et al., 2013). The major disadvantages of method are the long processing time and poor protection due high-porous wall. Coacervation is a physicochemical method also called phase separation. This technique involves the fluid-fluid phase separation of an aqueous polymeric solution, where a changes in characteristics of the medium (temperature, ionic strength, pH and polarity), resulting in a precipitation of wall material and a continuous coating of wall polymer around the core droplets. There are two types of coacervation, simple and complex. Simple coacervation involve only one polymer and separation phase occurs by salt addition or pH and temperature changes. Complex coacervation involve two polymers and phase separation occurring due interation anion-cation. This encapsulation process is very efficient, relatively simple, low cost process and used for encapsulation of ingredients such as flavor (Jun-xia et al., 2011), lipids (Wang et al., 2014) and others. Liposome is encapsulation technique that has different methods of preparation. In general, the method of preparation involve the loading of the entrapped agents before or during the liposome producing. In manufacture procedure a mixing of the lipid / ingredient is dispersed in an organic solvent. Then, the organic solvent is removed by evaporation and the dry lipidic film deposited on the flask wall is redispersed in aqueous media under agitation at temperature above the lipid transition temperature. The classical methods reported in the literature for liposome preparation including thin-film hydration or the Bangham method, detergent dialysis solvent-injection techniques, and reversed phase evaporation. Novel technology have been employed for preparation of liposome, such as supercritical fluid technology, dual asymmetric centrifugation, membrane contactor technology, cross-flow filtration technology and freeze drying technology, aimed at industrial scale (Huang et al., 2014). Particle size is influenced by the method and may present a range of 30 nm to several micrometers. The major advantages of method in the food industry is that liposome can be formed from natural ingredients such egg, soy, dairy, or sunflower lecithin. Due to their composition variability and structural properties, liposomes are extremely versatile in food industrial for encapsulation of enzymes (Kheadr et al., 2003), carotenoids (Xia et al., 2015), micronutrients (Abbas and Azari, 2011), and other food ingredients.
The characteristics of the microparticles is determined by the wall material (biopolymer), and encapsulation technique. These factors influence the performance and stability of the microparticle in the food matrix and release of the ingredient in the gastrointestinal tract. Thus, a combination of analytical methods are required to characterize the composition, morphology, size, and electrical properties.
X-ray photoelectron spectroscopy, Raman spectroscopy, differential scanning calorimetric (DSC), infrared and X-ray diffraction are techniques that have been explored in determining of the chemical analysis of particle surface composition, interation between biopolymers in the microparticle, presence of encapsulated ingredients in microparticles and crystallinity of encapsulated ingredients or biopolymer matrices.
The morphology of the particles has been studied through analysis of microscopy optical, confocal, atomic force (AFM) and scanning electronics (SEM), which provide information about the microstructure, surface of the characteristics, such as composition and topology.
Microparticle size is typically measured by the dynamic light scattering, static light scattering laser diffration and microscopy methods, wich provide information about rate release ingredient and perception of the microparticles in food matrix.
Zeta potential (ζ-potential) analysis is often used to predict the stability of particles suspensions to aggregation and study the interaction between oppositely charged biopolymers wall of the microparticle, providing an indication of the electrostatic forces that act between the microparticles.